Heterojunction catalyst in electrocatalytic water splitting

Recent advances on photocatalytic degradation of phthalate ester plasticizers using nanomaterial photocatalysts

Phthalate esters (PAEs) are a class of organic ester compounds containing benzene rings, which have been widely applied as additives in various fields, especially as plasticizers in plastic product to improve the flexibility. Due to the non-covalent bonding, PAEs inevitably leach out from the plastic polymers into environments. PAEs are endocrine disruptors, which possess seriously hazards to organisms, such as reproductive and genetic abnormalities. Now, PAEs pollution has become a serious environmental problem. Moreover, due to its difficulty in natural degradation, it has become a widespread concern to eliminate PAEs pollution with energy-saving technology. Among various degradation technologies for organic pollutant removal, photocatalytic degradation has attracted more attentions due to the merits of low energy consumption, high removal efficiency, abundant photocatalyst and low secondary pollution. In this article, the photocatalytic degradation using nanomaterial photocatalysts towards four kinds of typical PAEs were reviewed, including di(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), dimethyl phthalate (DMP), and diethyl phthalate (DEP). To improve the photocatalytic degradation efficiency, various semiconductor photocatalysts have been developed, and the optical and electrochemical properties, and the degradation mechanism and pathway have been also discussed. Finally, the challenges and perspectives of photocatalytic technology on PAEs elimination were presented.

Highly active FeNbO4/NiFeOOH heterojunction induced by coordination activation for efficient and stable industrial water oxidation

NiFe-oxyhydroxide (NiFeOOH) derived from in situ reconstruction is considered a genuinely active species in the alkaline oxygen evolution reaction (OER). However, the robustness of its durability remains a subject of debate and challenge. In this work, a pre-catalyst FeNbO4/NiFeC2O4, incorporating high valence metals, was first prepared through hydrothermal-low temperature calcination with oxalic acid as a ligand, and then reconstructed into FeNbO4/NiFeOOH under oxidative conditions. Performance tests revealed that FeNbO4/NiFeOOH required only 281 mV to achieve a current density of 500 mA cm-2, while demonstrating exceptional durability. Notably, when assembled into an anion exchange membrane (AEM) electrolytic cell, an ultrahigh current density of 1 A cm-2 was achieved at 1.88 V. Physical characterization showed that the coordination activation of oxalate not only induced the formation of the corrosion-resistant FeNbO4 phase, which enhances stability via partial pressure, but also triggered reconstruction through its oxidative dissolution. Density functional theory (DFT) calculations revealed that the reconstructed FeNbO4/NiFeOOH heterogeneous interface significantly improves the adsorption of oxygenated intermediates, resulting in a reduced energy barrier for the rate-determining step (RDS).

Optimization of Interfacial Electrons and Compressive-Tensile Strains at Lignin-Derived Carbon-Supported Multiphase Ni/Cu/MoO2 Interfaces for Boosting Large Current-Density HER

Developing efficient pH-universal hydrogen evolution electrocatalysts is critically needed yet challenged by pH-dependent. Here, a lignin-derived carbon-supported Ni/Cu/MoO2 heterostructure (Ni/Cu/MoO2@LC) through multiphase interfaces design is engineered, which displays excellent electrochemical activity, featuring low potentials of -14.4/-201.5 (acidic), -44.5/-615.7 (neutral), and -28.2/-242.3 mV (alkaline) at -10/-1000 mA cm-2. Theoretical and experimental analysis show that the Ni/Cu/MoO2@LC multiphase interfaces produce a synergistic coupling of compressive-tensile strains and interfacial electron transfer effect. This synergistic effect triggers electron redistribution, tailors the electronic configuration through d-band center optimization, and balances intermediate adsorption/desorption energetics. Additionally, lignin-derived carbon self-supported micro-nano-array structure enhances gas-liquid transport and corrosion resistance, allowing Ni/Cu/MoO2@LC to operate stably for at least 120 h, at -500 mA cm-2 in various pH solutions. Thus, this study provides a new idea for the design of cost-effective pH-universal HER electrocatalysts and a new approach for applying lignin-derived carbon in electrocatalysis.

Rational design of mixed-valence cobalt-based nanowires via simultaneous vanadium and iron modulations for enhanced alkaline electrochemical water splitting

Strategic modulation of the electronic structure and surface chemistry of electrocatalysts is crucial for achieving highly efficient and cost-effective bifunctional catalysts for water splitting. This study demonstrated the strategic incorporation of redox-active elements (vanadium (V) and iron (Fe)) to optimize the catalytic interface of mixed-valence cobalt-based nanowires (Co5.47N and CoP), which enhanced their hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalytic activity. Experimental and theoretical analyses revealed that the dual-cation doping increased the surface area and optimized the electronic structure of the nanowires, which promoted rapid water dissociation, favoured hydrogen adsorption kinetics, and stabilized the oxygen intermediates. Consequently, the V,Fe-Co5.47N and V,Fe-CoP nanowire electrocatalysts achieved low overpotentials of 55/251 and 63/265 mV for HER/OER at 10 mA cm-2 in 1 M KOH electrolyte, respectively, outperforming their pristine and single-cation-doped counterparts. The alkaline overall water-splitting devices assembled based on these bifunctional catalysts required an overall voltage of only 1.64 V and 1.66 V at 100 mA cm-2 and also demonstrated excellent durability. This work provides valuable insights into enhancing transition metal-based catalysts through the incorporation of redox-active elements for efficient water splitting.

Iron-doped XC-72 enhancing cobalt selenide for high-efficiency oxygen evolution reaction

As an emerging class of anodic catalyst material for water electrolysis and hydrogen production, transition metal selenides exhibit excellent electron transport properties and multiphase structures with varying conductivities. However, their widespread commercial application is hindered by sluggish reaction kinetics, a lack of exposed active sites, and significant volume expansion. Cobalt, a typical transition metal element abundantly found in the Earth's crust, offers sustainability and cost-effectiveness when used as an electrode material. In this work, a series of iron-modified carbon-supported cobalt selenides exhibit excellent catalytic performance in oxygen evolution reaction (OER) testing. Among them, CS/2XC-Fe@2 demonstrates outstanding activity for the oxygen evolution reaction in 1 M KOH, achieving a current density of 10 mA cm-2 at a low overpotential of 261.8 mV. Additionally, density functional theory (DFT) calculations further revealed that the Fe interface with catalytic sites enhances electron transfer capabilities, as evidenced by density of states and charge analysis, which facilitates the intermediate reactions during electrocatalysis by reducing the energy barrier by 0.25 eV. This study contributes to advancing theoretical calculations and structure-activity relationship research on transition metal selenides, potentially offering a pathway for the large-scale synthesis of non-noble metal electrocatalysts.

Unveiling heterointerface activation effects with different titanium dioxide crystal phases for electrocatalytic nitrate-to-ammonia reduction

Nitrate pollution poses severe risks to aquatic ecosystems and human health. The electrocatalytic nitrate reduction reaction (NITRR) offers a promising environmental and economic solution for nitrate pollution treatment and nitrogen source recovery; however, it continues to experience limited efficiency in neutral electrolytes. This study explores the heterointerface activation effects of TiO2/Cu2O heterogeneous catalysts with rutile (R-TiO2) and anatase (A-TiO2) phases and reveals that R-TiO2 is an active crystal phase with high nitrate reduction performance. The R-TiO2/Cu2O catalyst removed 99.8 % of nitrate in 180 min and achieved an ammonia yield of 0.23 mmol h-1 cm-2 with a Faraday efficiency of 85.7 % in a neutral electrolyte. In situ characterisation and theoretical calculations revealed that heterointerface reconstruction and oxygen vacancy (OV) formation overcome the poor electrical conductivity of R-TiO2, enhance electron transfer, and optimize the active sites. Furthermore, the Cu-O-Ti bond at the interface significantly weakens the adsorption energy of the critical intermediate *NO3, thereby facilitating NITRR. This study provides new insights into crystal phase modulation in catalyst design and offers innovative strategies for developing highly efficient NITRR electrocatalysts, paving the way for sustainable nitrate pollution treatment and nitrogen source recovery.

Progress in Signal Amplification and Microstructure Manufacturing for Photoelectrochemical Sensing

Photoelectrochemical (PEC) sensing based on chemical or biological recognition has received a tremendous amount of attention in recent years, providing analytical chemists a plethora of opportunities. However, emerging techniques and unknown processes in this field remain unexplored. We summarize the recently reported PEC sensing methods. First, we briefly describe the basic principles and technical characteristics of PEC sensing. Next, we highlight the application of various materials, nucleic acids, and other strategies for amplifying PEC signals. Finally, we discuss the current state of knowledge regarding the realization of miniaturized equipment during PEC sensor manufacturing. Summarizing the technological advances and research breakthroughs in PEC sensing over time can help increase the quality of follow-up research.

Homologous metal-organic complexes reconstructed oxy-hydroxide heterostructures as efficient oxygen evolution electrocatalysts

It is imperative to investigate more cost-effective, long-lasting, efficient, and reliable non-noble metal electrocatalysts for the oxygen evolution reaction (OER) in hydrogen production via water splitting. Metal-organic complexes have been extensively researched and utilized for this purpose, yet their transformation in this process remains intriguing and underexplored. To enable a comprehensive comparison, we synthesized three types of metal-organic complexes with varying morphologies using the same raw material. Specifically, monocrystalline and lamella Fe-Co metal-organic frameworks (MOFs), along with Fe-Co metal-organic gels (MOGs), were created using p-Phthalic acid (PTA) as a ligand to facilitate the oxygen evolution reaction in a 1 M KOH solution. The overpotential (η10) of MOF nanosheets (MOF-NSs) was 286 mV at 10 mA cm-2 under 1 M KOH, while that of MOGs was 297 mV, and MOF single crystals (MOF-SCs) exhibited an overpotential (η10) of 346 mV. Density-functional theory (DFT) calculations demonstrated that the formation of FeOOH/CoOOH heterostructures reduced adsorption energy barriers and accelerated the rate-determining step, thereby improving the overall catalytic performance of OER. Hence, the structural reconstruction approach can be leveraged to develop and fabricate high-performance OER electrocatalysts in energy and related applications.

Self-Powered Glucose Biosensor Based on Non-Enzymatic Biofuel Cells by Au Nanocluster/Pd Nanocube Heterostructure and Fe3C@C-Fe Single-Atom Catalyst

Self-powered biosensors (SPBs) based on biofuel cells (BFCs) use electrical output as a sensing signal without the need of external power supplies, providing a feasible approach to constructing miniaturized implantable or portable devices. In this work, a novel nanozyme of gold nanoclusters/palladium nanocubes (AuNCs/PdNCs) heterostructure is successfully fabricated to develop an innovatively self-powered and non-enzymatic glucose sensing system. The AuNCs/PdNCs with glucose oxidase (GOD)-like activity exhibits superior electrocatalytic and non-enzymatic sensing performance toward glucose. The non-enzymatic BFCs-based SPBs system, established on the AuNCs/PdNCs (anodic catalyst) and single atomic Fe sites coupled with carbon-encapsulated Fe3C crystals (Fe3C@C-Fe SACs as a cathodic catalyst) platform, exhibits an exceptional sensitivity to glucose with 0.151 µW cm-2 mm-1 (3.4 times higher than the PdNCs), outstanding selectivity and robust stability. The outstanding performance of the BFCs-based SPBs system can be attributed to the synergistic cooperation between the PdNCs and AuNCs.

Phosphorus and Cobalt Codoped Transition-Metal Oxides with Accelerated Surface Reconstruction for Efficient Alkaline Oxygen Evolution Reactions

Developing highly efficient nonprecious metal catalysts for oxygen evolution reactions (OERs) is crucial for the development of water electrolysis; however, these catalysts face challenges such as high overpotential and insufficient durability at high current densities. In this study, we successfully prepared ordered needlelike structured Co-Fe hydroxide with F-ion immersion (Fe/Co(OH)F) on the surface of nickel foam and explored the synergistic strengthening effects of Mo cation doping and P anion doping. The ordered needlelike structure of Fe/Co(OH)F was destroyed during the phosphating calcination process, while Mo doping transformed it into a rough surface platelike structure. By combining Mo doping with phosphating treatment, the obtained Fe/F-MoCo-POx catalyst presented a crystalline-amorphous heterostructure and platelike morphology with enhanced OER performance. At a high current density of 200 mA cm-2, the Fe/F-MoCo-POx catalyst exhibited an overpotential of 300 mV without i-R compensation and maintained a potential decay rate of only 0.16 mV h-1 after a 560 h durability test. Electrochemical testing combined with phase structure and composition analysis revealed that P doping induced the formation of an amorphous surface layer of hypophosphite Fe(PO3)3, which was found to undergo anion exchange with *OH during electrochemical testing. This surface reconstruction thus formed a rich -OH catalytic layer on the surface of Fe/F-MoCo-POx, which then exhibited a remarkably lowered overpotential and boosted OER kinetics, surpassing most state-of-the-art OER electrocatalysts. This finding underscores the synergistic effect of Mo and P doping in forming a crystalline-amorphous heterostructure, which boosts alkaline OER performance, aiding in cost reduction and improvement of the hydrogen production efficiency through water electrolysis at high current densities.

Electrochemical Hydrogen Evolution with Metal-Organic Framework-Derived Catalysts: Strategies for d-Band Modulation by Electronic Structure Modification

The effective use of metal-organic framework (MOF)-based materials in the electrocatalytic hydrogen evolution reaction (HER) relies on the understanding of their structural and electronic properties. While the structure and morphology of MOF-derived catalysts significantly impact HER activity, tuning the d-band structure through electronic structure modulation has emerged as a key factor in optimizing catalytic performance. Techniques such as composition tuning, heteroatom doping, surface modification, and interface engineering were found to be effective methods for manipulating the electronic configuration and, in turn, modulating the d-band. This review systematically explores the design strategies for MOF-derived catalysts by focusing on electronic structure modulation. It provides a detailed discussion of the various methods - used to modulate the electronic structure. Furthermore, the review establishes the relationship between d-band tuning, Gibbs free energy, and electronic structure modulation, supported by both spectroscopic and theoretical evidences.

Electronic Buffering Mechanism Enhances Stability and Water Oxidation Efficiency of CeO2@NiFe-LDH

Nickel-iron layered double hydroxide shows significant promise as an electrocatalyst in facilitating oxygen evolution reactions. But its development is hindered by low conductivity and insufficient cycling stability. Herein, the synthesis of a hierarchically structured heterostructure catalyst, CeO2@NiFe LDH, is reported through a straightforward two-step process involving hydrothermal treatment. The catalyst realizes a significant breakthrough in OER catalytic performance and stability. At a current density of 100 mA cm-2, the overpotentials amount to 255 mV in 1 M KOH, 263 mV in simulated seawater with alkaline conditions, and 346 mV in actual alkaline seawater. After 200 hours of continuous operation under high current density in simulated alkaline seawater, the morphology with no significant alterations observed, highlighting its high stability in complex seawater environments. Introducing CeO2 optimizes the binding energy of the OH intermediate, which facilitates the formation and dissociation of the OOH intermediate. In situ Raman analysis demonstrates the positive impact of CeO2 on the generation of active species. This research emphasizes the efficacy of CeO2 in improving the performance and durability of NiFe LDH for oxygen evolution reactions.

Interfacial creation of positively charged sites in LaPO4/Fe3(PO4)2 heterojunctions for high-current-density oxygen evolution

The creation of positively charged active sites is crucial for enhancing the adsorption of negatively charged hydroxide ions, thereby improving the sluggish oxygen evolution reaction (OER). We engineered LaPO4/Fe3(PO4)2 heterojunctions with a low flat-band potential, facilitating interfacial charge transfer and generation of positively charged holes, resulting in a highly active and stable OER catalyst at 500 mA cm-2.

Co9S8/CoTe2 n-n Type Heterojunction: A Heterogenic Interfacial Integration of Co9S8 and CoTe2 Phases for Energy-Efficient Hydrazine Oxidation Assisted Hydrogen Production

Controlled and optimized heterogenic interfacial coupling is the key to enhance the electrochemical performance. Herein, for the first time, telluride-based Co9S8/CoTe2 heterostructure is reported as a bifunctional catalyst for energy-efficient H2 generation. Detailed investigations suggest that the heterogenic interfacial coupling leads to superior bifunctional electrochemical performance of the Co9S8/CoTe2 heterostructure. Furthermore, it displays excellent hydrazine oxidation reaction (HzOR) performance at industrial-level current density (500 mA cm-2 @ 338 mV) using an electrochemically neutral carbon paper substrate. The overall hydrazine electrooxidation-assisted water splitting (OHzWS) cell performance of the Co9S8/CoTe2 heterostructure couple is 10 mA cm-2 @ 0.22 V, which is 1.60 V less than the conventional overall water splitting. Band energy profiles of Co9S8/CoTe2 heterostructure reveal an n-n type heterojunction formation between Co9S8 and CoTe2 phases. The work function difference between the phases results in an impulsive electron flow from the CoTe2 to the Co9S8 phase and the creation of a built-in electric field. This prompts the electrochemical kinetics of HzOR and hydrogen evolution reaction (HER) by enabling faster charge transport at the interface. Furthermore, DFT supports the experimental findings, and Gibbs's free energy profile for HzOR studies indicate that the Co9S8/CoTe2 heterostructure interface is favorable for HzOR compared to Co9S8 and CoTe2.

d-Band Center Engineering of Nickel Nanoparticles Accelerates Water Dissociation for Hydrogen Evolution in Neutral NaCl Solution

While Pt is highly efficient for hydrogen evolution reaction (HER), its widespread use is limited by scarcity and high cost. Herein, a vertically aligned electrocatalyst is present comprising Ni3S2 nanotube arrays (NTAs) and Ni nanoparticles (NPs) (Ni3S2/Ni NTAs) for neutral HER. In a neutral 4 wt.% NaCl solution (pH = 7), the Ni3S2/Ni NTAs achieves a current density of 100 mA cm-2 at a low overpotential of 540 mV, outperforming both Ni3S2 NTAs and Ni NTAs and even the commercial Pt plate. The hollow tubular structure offers ample mass transfer channels, and strong electronic interaction between Ni3S2 and Ni is observed. Theoretical studies reveal that the lowered d-band center (ɛd) of Ni 3d orbital significantly reduces the activation energy for H2O dissociation and facilitates the movement of an H atom in H2O away from OH to form a transition state, consequently promoting H2 evolution. When Ni3S2/Ni NTAs is used as the cathode in a two-electrode diaphragm-free electrolyzer with a RuSnTi anode, efficient H2 production and energy-saving Cl2 evolution are achieved. This work highlights the potential of uniquely structured electrocatalysts for HER in neutral NaCl solutions.

Polarization: A Universal Driving Force for Energy, Environment, and Electronics

The sustainable future relies on the synergistic development of energy, environmental, and electronic systems, founded on the development of functional materials by exploring their quantum mechanisms. Effective control over the distribution and behavior of charges within these materials, a basic quantum attribute, is crucial in dictating their physical, chemical, and electronic properties. At the core of charge manipulation lies "polarization"-a ubiquitous phenomenon marked by separating positive and negative charges. This review thoroughly examines polarization techniques, spotlighting their transformative role in catalysis, energy storage, solar cells, and electronics. Starting with the foundational mechanisms underlying various forms of polarization, including piezoelectric, ferroelectric, and pyroelectric effects, the perspective is expanded to cover any asymmetric phenomena that generate internal fields, such as heterostructures and doping. Afterward, the critical role of polarization across various applications, including charge separation, surface chemistry modification, and energy band alignment, is highlighted. Special emphasis is placed on the synergy between polarization and material properties, demonstrating how this interplay is pivotal in overcoming existing technological limitations and unlocking new functionalities. Through a comprehensive analysis, a holistic roadmap is offered for harnessing polarization across the broad spectrum of applications, thus finding sustainable solutions for future energy, environment, and electronics.

A Review of Advances in Heterostructured Catalysts for Li-S Batteries: Structural Design and Mechanism Analysis

Lithium-sulfur (Li-S) batteries, acclaimed for their high energy density, cost-effectiveness, and environmental benefits, are widely considered as a leading candidate for the next-generation energy storage systems. However, their commercialization is impeded by critical challenges, such as the shuttle effect of lithium polysulfides and sluggish reaction kinetics. These issues can be effectively mitigated through the design of heterojunction catalysts. Despite the remarkable advancements in this field, a comprehensive elucidation of the underlying mechanisms and structure-performance relationships of heterojunction catalysts in sulfur electrocatalysis systems remains conspicuously absent. Here, it is expounded upon the mechanisms underlying heterostructure engineering in Li-S batteries and the latest advancements in heterostructure catalysts guided by these multifarious mechanisms are examined. Furthermore, it illuminates groundbreaking paradigms in heterostructure design, encompassing the realms of composition, structure, function, and application. Finally, the research trends and future development directions for the novel heterojunction materials are extensively deliberated. This study not only provides a comprehensive and profound understanding of heterostructure catalysts in Li-S batteries but also facilitates the exploration of new electrocatalyst systems.

Ultrafast Hole Trapping in Te-MoTe2-MoSe2/ZnO S-Scheme Heterojunctions for Photochemical and Photo-/Electrochemical Hydrogen Production

Te-MoTe2-MoSe2/ZnO S-scheme heterojunctions are engineered to ascertain the advanced redox ability in sustainable HER operations. Photo-physical studies have established the steady state transfer of photo-induced charge carriers whereas an improved transfer dynamics realized by state-of-art ultrafast transient absorption and irradiated-XPS analysis of optimized 5wt% Te-MoTe2-MoSe2/ZnO heterostructure. 2.5, 5, and 7.5wt% Te-MoTe2-MoSe2/ZnO photocatalysts (2.5MTMZ, 5MTMZ and 7.5MTMZ) exhibited 2.8, 3.3, and 3.1-fold higher HER performance than pristine ZnO with marvelous apparent quantum efficiency of 35.09%, 41.42% and 38.79% at HER rate of 4.45, 5.25, and 4.92 mmol/gcat/h, respectively. Electrochemical water splitting experiments manifest subdued 583 and 566 mV overpotential values of 2.5MTMZ and 5MTMZ heterostructures to achieve 10 mA cm-2 current density for HER, and 961 and 793 mV for OER, respectively. For optimized 5MTMZ photocatalyst, lifetime kinetic decay of interfacial charge transfer step is evaluated to be 138.67 ps as compared to 52.92 ps for bare ZnO.

In Situ Hydroxide Growth over Nickel-Iron Phosphide with Enhanced Overall Water Splitting Performances

In this work, three dimensional (3D) self-supported Ni-FeOH@Ni-FeP needle arrays with core-shell heterojunction structure are fabricated via in situ hydroxide growth over Ni-FeP surface. The as-prepared electrodes show an outstanding oxygen evolution reaction (OER) performance, only requiring the low overpotential of 232 mV to reach 200 mA cm-2 with the Tafel slop of 40 mV dec-1. For overall water splitting, an alkaline electrolyzer with these electrodes only requires a cell voltage of 2.14 V to reach 1 A cm-2. Mechanistic investigations for such excellent electrocatalytic performances are utilized by in situ Raman spectroscopy in conjunction with density functional theory (DFT) calculations. The computation results present that Ni-FeOH@Ni-FeP attains better intrinsic conductivity and the D-band center (close to that of the ideal catalyst), thus giving superior excellent catalytic performances. Likewise, the surface Ni-FeOH layer can improve the structural stability of Ni-FeP cores and attenuate the eventual formation of irreversible FeOOH products. More importantly, the appearance of FeOOH intermediates can effectively decrease the energy barrier of NiOOH intermediates, and then rapidly accelerate the sluggish reaction dynamics, as well as further enhance the electrocatalytic activities, reversibility and cycling stability.

Unveiling the Enhancement of Electrocatalytic Oxygen Evolution Activity in Ru-Fe2O3/CoS Heterojunction Catalysts

The development of highly efficient electrocatalysts for the sluggish anodic oxygen evolution reaction (OER) is crucial to meet the practical demand for water splitting. In this study, an effective approach is proposed that simultaneously enhances interfacial interaction and catalytic activity by modifying Fe2O3/CoS heterojunction using Ru doping strategy to construct an efficient electrocatalytic oxygen evolution catalyst. The unique morphology of Ru doped Fe2O3 (Ru-Fe2O3) nanoring decorated by CoS nanoparticles ensures a large active surface area and a high number of active sites. The designed Ru-Fe2O3/CoS catalyst achieves a low OER overpotential (264 mV) at 10 mA cm-2 and demonstrates exceptional stability even at high current density of 100 mA cm-2, maintaining its performance for an impressive duration of 90 h. The catalytic performance of this Ru-Fe2O3/CoS catalyst surpasses that of other iron-based oxide catalysts and even outperforms the state-of-the-art RuO2. Density functional theory (DFT) calculation as well as experimental in situ characterization confirm that the introduction of Ru atoms can enhance the interfacial electron interaction, accelerating the electron transfer, and serve as highly active sites reducing the energy barrier for rate determination step. This work provides an efficient strategy to reveal the enhancement of electrocatalytic oxygen evolution activity of heterojunction catalysts by doping engineering.

Cerium-Doped Nickel Sulfide Nanospheres as Efficient Catalysts for Overall Water Splitting

The development of non-precious metal electrocatalysts with excellent activity and durability for electrochemical water splitting has always been a goal. Transition metal sulfides are attractive electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this article, we designed and constructed efficient catalysts with multiple synergistic interactions and synthesized Ce-NiS2@NF nanosphere using a solvothermal method. Ce-NiS2@NF exhibits excellent HER performance, OER performance, and overall water splitting capability in alkaline electrolytes, demonstrating good stability. The addition of Ce influences the activity of the catalysts, attributed to the synergistic interactions creating more active sites and higher intrinsic activity through the introduction of Ce heteroatoms. Additionally, the self-supported conductive substrate promotes electron transfer, enhancing the intrinsic activity and active site density of the catalyst. This study provides an in-depth investigation into structural design and performance enhancement, offering ideas for designing efficient catalysts for overall water electrolysis. This work provides an in-depth study in terms of structural design performance enhancement and provides ideas for designing efficient alkaline bifunctional catalysts. Valuable insights have been provided in elucidating the intrinsic mechanism of the catalytic activity of cerium-doped nickel sulfide nanospheres, thus providing new guidance in the field of energy conversion technology.

Construction of a Three-Phase MnS2/Co4S3/Ni3S2 Heterostructure for Boosting Oxygen Evolution

The rational construction of highly efficient electrocatalysts for the oxygen evolution reaction (OER) plays a critical role in energy conversion systems. Designing heterostructures is a common and effective strategy to improve the performance of electrocatalysts. In this paper, an MnS2/Co4S3/Ni3S2 heterostructure was synthesized on Ni foam using a one-step vulcanization method. It provides a modified electronic structure and plentiful three-phase heterogeneous interfaces that can effectively enrich the active sites and accelerate electron transfer, thereby improving the OER activity. Thanks to the heterostructure, the MnS2/Co4S3/Ni3S2 exhibits a low overpotential of 265 and 304 mV for the OER to reach current densities of 50 and 100 mA/cm2, respectively. Furthermore, the surface reconstruction of MnS2/Co4S3/Ni3S2 has been investigated, which revealed the formation of metal hydr(oxy)oxides evolved during the OER process. This work provides a facile strategy for constructing three-phase heterostructures, shedding light on the development of high-performance, nonprecious metal-based OER electrocatalysts.

Interfacial Regulation of Rice-Grain-like Iron-Nickel Phosphide Nanorods on Phosphorus-Doped Graphene Architectures as Bifunctional Electrocatalysts for Water Splitting

The design of bimetallic metal-organic frameworks (MOFs) with a hierarchical structure is important to improve the electrocatalytic performance of catalysts due to their synergistic effect on different metal ions. In this work, the catalyst comprises bimetallic iron-nickel MOF-derived FeNi phosphides, intricately integrated with phosphorus-doped reduced graphene oxide architectures (FeNi2P-C/P-rGA) through the hydrothermal and phosphating treatments. The hierarchical architecture of the catalyst is beneficial for exposing active sites and facilitating electron transfer. The FeNi2P-C/P-rGA catalyst exhibits excellent performance in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline electrolytes. Notably, FeNi2P-C/P-rGA requires only the overpotential of 93 and 210 mV to achieve a current density of 10 mA cm-2 for the HER and OER with small values of Tafel slope and charge transfer resistance, respectively. Furthermore, the catalyst exhibits boosted activity for overall water splitting with a low potential of 1.56 V. This work can be considered to extend the design of multilevel catalysts in the application of water splitting.

Ultrathin and Conformal Depletion Layer of Core/Shell Heterojunction Enables Efficient and Stable Acidic Water Oxidation

Ru-based electrocatalysts hold great promise for developing affordable proton exchange membrane (PEM) electrolyzers. However, the harsh acidic oxidative environment of the acidic oxygen evolution reaction (OER) often causes undesirable overoxidation of Ru active sites and subsequent serious activity loss. Here, we present an ultrathin and conformal depletion layer attached to the Schottky heterojunction of core/shell RuCo/RuCoOx that not only maximizes the availability of active sites but also improves its durability and intrinsic activity for acidic OER. Operando synchrotron characterizations combined with theoretical calculations elucidate that the lattice strain and charge transfer induced by Schottky heterojunction substantially regulate the electronic structures of active sites, which modulates the OER pathway and suppresses the overoxidation of Ru species. Significantly, the closed core/shell architecture of the RuCo/RuCoOx ensures the structure integrity of the Schottky heterojunction under acidic OER conditions. As a result, the core/shell RuCo/RuCoOx Schottky heterojunction exhibits an unprecedented durability up to 250 0 h at 10 mA cm-2 with an ultralow overpotential of ∼170 mV at 10 mA cm-2 in 0.5 M H2SO4. The RuCo/RuCoOx catalyst also demonstrates superior durability in a proton exchange membrane (PEM) electrolyzer, showcasing the potential for practical applications.

Unlocking Efficiency: Minimizing Energy Loss in Electrocatalysts for Water Splitting

Catalysts play a crucial role in water electrolysis by reducing the energy barriers for hydrogen and oxygen evolution reactions (HER and OER). Research aims to enhance the intrinsic activities of potential catalysts through material selection, microstructure design, and various engineering techniques. However, the energy consumption of catalysts has often been overlooked due to the intricate interplay among catalyst microstructure, dimensionality, catalyst-electrolyte-gas dynamics, surface chemistry, electron transport within electrodes, and electron transfer among electrode components. Efficient catalyst development for high-current-density applications is essential to meet the increasing demand for green hydrogen. This involves transforming catalysts with high intrinsic activities into electrodes capable of sustaining high current densities. This review focuses on current improvement strategies of mass exchange, charge transfer, and reducing electrode resistance to decrease energy consumption. It aims to bridge the gap between laboratory-developed, highly efficient catalysts and industrial applications regarding catalyst structural design, surface chemistry, and catalyst-electrode interplay, outlining the development roadmap of hierarchically structured electrode-based water electrolysis for minimizing energy loss in electrocatalysts for water splitting.

Field-Effect Enhancement of Non-Faradaic Processes at Interfaces Governs Electrocatalytic Water Splitting Activity

Recognizing the essential factor governing interfacial hydrogen/oxygen evolution reactions (HER/OER) is central to electrocatalytic water-splitting. Traditional strategies aiming at enhancing electrocatalytic activities have mainly focused on manipulating active site valencies or coordination environments. Herein, the role of interfacial adsorption is probed and modulated by the topological construct of the electrocatalyst, a frequently underestimated non-Faradaic mechanism in the dynamics of electrocatalysis. The engineered Co0.75Fe0.25P nanorods, anchored with FeOx clusters, manifest a marked amplification of the surface electric field, thus delivering a substantially improved bifunctional electrocatalytic performance. In alkaline water splitting anion exchange membrane (AEM) electrolyzer, the current density of 1.0 A cm-2 can be achieved at a cell voltage of only 1.73 V for the FeOx@Co0.75Fe0.25P|| FeOx@Co0.75Fe0.25P pairs for 120 h of continuous operation at 1.0 A cm-2. Detailed investigations of electronic structures, combined with valence state and coordination geometry assessments, reveal that the enhancement of catalytic behavior in FeOx@Co0.75Fe0.25P is chiefly attributed to the strengthened adsorptive interactions prompted by the intensified electric field at the surface. The congruent effects observed in FeOx-cluster-decorated Co0.75Fe0.25P nanosheets underscore the ubiquity of this effect. The results put forth a compelling proposition for leveraging interfacial charge densification via deliberate cluster supplementation.

Identifying the Active Sites in MoSi2@MoO3 Heterojunctions for Enhanced Hydrogen Evolution

Developing Two-dimensional (2D) Mo-based heterogeneous nanomaterials is of great significance for energy conversion, especially in alkaline hydrogen evolution reaction (HER), however, it remains a challenge to identify the active sites at the interface due to the structure complexity. Herein, the real active sites are systematically explored during the HER process in varied Mo-based 2D materials by theoretical computational and magnetron sputtering approaches first to filtrate the candidates, then successfully combined the MoSi2 and MoO3 together through Oxygen doping to construct heterojunctions. Benefiting from the synergistic effects between the MoSi2 and MoO3, the obtained MoSi2@MoO3 exhibits an unprecedented overpotential of 72 mV at a current density of 10 mA cm-2. Density functional theory calculations uncover the different Gibbs free energy of hydrogen adsorption (ΔGH*) values achieved at the interfaces with different sites as adsorption sites. The results can facilitate the optimization of heterojunction electrocatalyst design principles for the Mo-based 2D materials.

Integrated MXene and metal oxide electrocatalysts for the oxygen evolution reaction: synthesis, mechanisms, and advances

Electrochemical water splitting is a promising approach to produce H2 through renewable electricity, but its energy efficiency is severely constrained by the kinetically slow anodic oxygen evolution reaction (OER), which uses about 90% of the electricity in the water-splitting process due to its multistep proton (H+)-coupled electron (e-) transfer process, high overpotential (η), and low energy efficiency. Therefore, the quest for efficient, sustainable, and cost-effective electrocatalysts for hydrogen production through water electrolysis has intensified, highlighting the potential of two-dimensional (2D) MXenes. MXenes have emerged as a promising class of materials characterized by excellent stability, hydrophilicity, and conductivity. However, challenges such as low oxidation resistance, facile stacking, and the absence of intrinsic catalytically active sites limit their performance. This review thoroughly explores various synthesis methods for MXenes and their integration with transition metal oxides (TMOs) to tackle the challenges and enhance catalytic activity. The review also delves into advanced strategies for structural tuning of MXenes and TMOs, such as termination engineering, heteroatom doping, defect engineering, and the formation of heterojunctions. The integration of MXenes with TMOs has addressed the current limitations of MXenes and significantly boosted OER activity. By considering these structural tuning parameters and limitation factors, researchers can gain insights into the design principles and optimization strategies for MXene- and TMO-integrated electrocatalysts. The review concludes with a summary of the key findings and an outlook on future research directions, emphasizing the unexplored potential and innovative approaches that could further advance the field of electrocatalytic water splitting.

Constructing a Self-Supported Bifunctional Multiphase Heterostructure for Electrocatalytic Overall Water Splitting

Developing well-performing and stable bifunctional electrocatalysts is of great importance for efficient green hydrogen production through water electrolysis. Herein, a three-dimensional self-supported CoMoS3.13/FeS2/Co3S4 on carbon paper (FeCoMoS/CP) heterostructure with interconnected nanosheets for overall water splitting was fabricated by a facile hydrothermal method followed by vulcanization treatment. The FeCoMoS/CP heterostructure with high structural integrity and more accessible active sites can effectively optimize the electronic structure through component regulation to achieve enhanced catalytic activity. Significantly, the FeCoMoS/CP required overpotentials of 257 mV at 50 mA cm-2 for OER and 280 mV at 20 mA cm-2 for HER. Importantly, the assembled FeCoMoS/CP||FeCoMoS/CP alkaline electrolyzer achieved a superior cell voltage of 1.48 V at 10 mA cm-2 with superb long-term stability, which implies a remarkable electrocatalytic performance of the FeCoMoS/CP heterostructure for overall water splitting. This work provides an applicable route for synthesizing high-performance bifunctional catalysts toward water electrolysis.

Sustainable photoelectrocatalytic oxidation of antibiotics using Ag-CoFe2O4@TiO2 heteronanostructures for eco-friendly wastewater remediation

Developing high-performance and durable catalysts presents a significant challenge for oxidizing toxic inorganic and pharmaceutical compounds in wastewater. Recently, there has been a surge in the development of new heterogeneous catalysts for degrading pharmaceutical compounds, driven by advancements in electrocatalysts and photoelectrocatalysts. In this study, a plasmonic Ag nanoparticles decorated CoFe2O4@TiO2 heteronanostructures have been successfully designed to fabricate a high-performing photoelectrode for the oxidation of pharmaceutical compounds. The developed Ag-CoFe2O4@TiO2 possessed a higher electrochemical stability and effectively harvested the UV to visible and NIR radiation in sunlight which generates the enormous photochemical reactive species that involved in the oxidation of ibuprofen in wastewater. Under direct sunlight irradiation, Ag-CoFe2O4@TiO2 achieved complete oxidation of ibuprofen in wastewater at 0.8 V vs RHE. This indicates that metallic Ag nanoparticles are involved in the charge separation and transport of charge carriers from the photoactive sites of CoFe2O4@TiO2, promoting the generation of abundant hydroxy, oxy, and superoxide radicals that actively break the bonds of ibuprofen. Additionally, oxidation agents such as urea and H2O2 were utilized to enhance the formation of superoxide ions and hydroxyl radicals, which rapidly participate in the oxidation of ibuprofen. Significantly, testing for recyclability confirmed the stability of the Ag-CoFe2O4@TiO2 photoanode, ensuring its suitability for prolonged use in photoelectrochemical advanced oxidation processes. Integrating Ag-CoFe2O4@TiO2 photoanodes into water purification systems could enhance economic feasibility, reduce energy consumption, and improve efficiency.

Simultaneous Interface Engineering and Phase Tuning of CeO2-Decorated Catalysts for Boosted Oxygen Evolution Reaction

Heterogeneous catalysts have attracted extensive attention among various emerging catalysts for their exceptional oxygen evolution reaction (OER) capabilities, outperforming their single-component counterparts. Nonetheless, the synthesis of heterogeneous materials with predictable, precise, and facile control remains a formidable challenge. Herein, a novel strategy involving the decoration of catalysts with CeO2 is introduced to concurrently engineer heterogeneous interfaces and adjust phase composition, thereby enhancing OER performance. Theoretical calculations suggest that the presence of ceria reduces the free energy barrier for the conversion of nitrides into metals. Supporting this, the experimental findings reveal that the incorporation of rare earth oxides enables the controlled phase transition from nitride into metal, with the proportion adjustable by varying the amount of added rare earth. Thanks to the role of CeO2 decoration in promoting the reaction kinetics and fostering the formation of the genuine active phase, the optimized Ni3FeN/Ni3Fe/CeO2-5% nanoparticles heterostructure catalyst exhibits outstanding OER activity, achieving an overpotential of just 249 mV at 10 mA cm-2. This approach offers fresh perspectives for the conception of highly efficient heterogeneous OER catalysts, contributing a strategic avenue for advanced catalytic design in the field of energy conversion.

Facile synthesis of CeO2-decorated W@Co-MOF heterostructures as a highly active and durable electrocatalyst for overall water splitting

Rational coupling of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts is extremely important for practical overall water splitting; however, it is still challenging to construct such bifunctional heterostructures. Herein, a CeO2/W@Co-MOF/NF bifunctional electrocatalyst was prepared via a two-step in situ growth method involving an electrodeposition process. The incorporation of the W element enhanced the electronic interaction and enlarged the electrochemical surface area. After the electrodeposition of CeO2, the obtained CeO2/W@Co-MOF/NF possessed abundant heterointerfaces with a modulated local distribution, which promoted water dissociation and rapid electrocatalytic kinetics. In particular, it required very low overpotentials of 239 mV and 87 mV to reach a current density of 10 mA cm-2 in OER and HER, respectively. A corresponding alkaline electrolysis cell afforded a cell voltage of 1.54 V at 10 mA cm-2 to boost overall water splitting. This work provides a feasible strategy to fabricate MOF-based complexes and explores their possible use as bifunctional catalysts toward overall water splitting.

Construction of Heterojunction-Rich Metal Nitrides Porous Nanosheets Electrocatalyst for Alkaline Water/Seawater Splitting at Large Current Density

The exploiting electrocatalysts for water/seawater electrolysis with remarkable activity and outstanding durability at industrial grade current density remains a huge challenge. Herein, CoMoNx and Fe-doped CoMoNx nanosheet arrays are in-situ grown on Ni foam, which possess plentiful holes, multilevel heterostructure, and lavish Co5.47N/MoN@NF and Fe-Co5.47N/MoN@NF interfaces. They require low overpotentials of 213 and 296 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under alkaline media to achieve current density of 800 mA cm-2, respectively, and both possess low Tafel slopes (51.1 and 49.1 mV dec-1) and undiminished stability over 80 h. Moreover, the coupled Co5.47N/MoN@NF and Fe-Co5.47N/MoN@NF electrolyzer requires low voltages of 1.735 V to yield 500 mA cm-2 in alkaline water. Notably, they also exhibit exceptional electrocatalytic properties in alkaline seawater (1.833 V@500 mA cm-2). The experimental studies and theoretical calculations verify that Fe doping does reduce the energy barrier from OH* to O* intermediates during OER process after catalyst reconstruction, and the non-metallic N site from MoN exhibits the lowest theoretical overpotential. The splendid catalytic performance is attributed to the optimized local electron configuration and porous structure. This discovery provides a new design method toward low-cost and excellent catalysts for water/seawater splitting to produce hydrogen.

Hierarchical CoWO4/NixFeyS microspheres bearing crystalline-amorphous interface as a multifunctional platform for outperformed water splitting and sensitive hydrazine sensing

Highly efficient and multifunctional electrocatalysts are of high value in energy transformation and electrochemical sensing. Herein, hierarchically architectured cobalt tungstate/nickel iron sulfide (CoWO4/NixFeyS) microspheres with a crystalline-amorphous interface have been prepared on bimetallic substrate of nickel-iron foam (NIF) by a two-step hydrothermal method. Electrochemical characterization shows that CoWO4/NixFeyS microspheres can boost the electrocatalytic activity effectively through the synergistic effect on the crystalline-amorphous interface. When the CoWO4/NixFeyS is applied as the electrocatalysts for oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), the overpotentials at a high current density of 500 mA cm-2 are only 322.8 mV and 306.5 mV, respectively. The overall water splitting device composed of CoWO4/NixFeyS/NIF couple only needs a cell voltage of 1.80 V to reach a current density of 100 mA cm-2, and 2.19 V to reach 500 mA cm-2. The CoWO4/NixFeyS/NIF can be also utilized as an effective electrochemical platform for the sensing of toxic hydrazine in a wide range from 50 μM to 17.3 mM, with a detection limit of 46.4 μM. All these results display that the CoWO4/NixFeyS/NIF can be a high-performance multifunctional material for energy transformation and environmental pollutant monitoring.

Partial Exsolution Enables Superior Bifunctionality of Ir@SrIrO3 for Acidic Overall Water Splitting

The pursuit of efficient and durable bifunctional electrocatalysts for overall water splitting in acidic media is highly desirable, albeit challenging. SrIrO3 based perovskites are electrochemically active for oxygen evolution reaction (OER), however, their inert activities toward hydrogen evolution reaction (HER) severely restrict the practical implementation in overall water splitting. Herein, an Ir@SrIrO3 heterojunction is newly developed by a partial exsolution approach, ensuring strong metal-support interaction for OER and HER. Notably, the Ir@SrIrO3-175 electrocatalyst, prepared by annealing SrIrO3 in 5% H2 atmosphere at 175 °C, delivers ultralow overpotentials of 229 mV at 10 mA cm-2 for OER and 28 mV at 10 mA cm-2 for HER, surpassing most recently reported bifunctional electrocatalysts. Moreover, the water electrolyzer using the Ir@SrIrO3-175 bifunctional electrocatalyst demonstrates the potential application prospect with high electrochemical performance and excellent durability in acidic environment. Theoretical calculations unveil that constructing Ir@SrIrO3 heterojunction regulates interfacial electronic redistribution, ultimately enabling low energy barriers for both OER and HER.

In Situ Raman Study of Surface Reconstruction of FeOOH/Ni3S2 Oxygen Evolution Reaction Electrocatalysts

Construction of heterojunctions is an effective strategy to enhanced electrocatalytic oxygen evolution reaction (OER), but the structural evolution of the active phases and synergistic mechanism still lack in-depth understanding. Here, an FeOOH/Ni3S2 heterostructure supported on nickel foam (NF) through a two-step hydrothermal-chemical etching method is reported. In situ Raman spectroscopy study of the surface reconstruction behaviors of FeOOH/Ni3S2/NF indicates that Ni3S2 can be rapidly converted to NiOOH, accompanied by the phase transition from α-FeOOH to β-FeOOH during the OER process. Importantly, a deep analysis of Ni─O bond reveals that the phase transition of FeOOH can regulate the lattice disorder of NiOOH for improved catalytic activity. Density functional theory (DFT) calculations further confirm that NiOOH/FeOOH heterostructure possess strengthened adsorption for O-containing intermediates, as well as lower energy barrier toward the OER. As a result, FeOOH/Ni3S2/NF exhibits promising OER activity and stability in alkaline conditions, requiring an overpotential of 268 mV @ 100 mA cm-2 and long-term stability over 200 h at a current density of 200 mA cm-2. This work provides a new perspective for understanding the synergistic mechanism of heterogeneous electrocatalysts during the OER process.

Effect of multi-interface electron transfer on water splitting and an innovative electrolytic cell for synergistic hydrogen production and degradation

The cleaning and utilization of industry wastewater are still a big challenge. In this work, we mainly investigate the effect of electron transfer among multi-interfaces on water electrolysis reaction. Typically, the CoS2, Co3S4/CoS2 (designated as CS4-2) and Co3S4/Co9S8/CoS2 (designated as CS4-8-2) samples are prepared on a large scale by one-step molten salt method. It is found that because of the different work functions (designated as WF; WF(Co3S4) = 4.48eV, WF(CoS2) = 4.41eV, WF(Co9S8) = 4.18 eV), the effective heterojunctions at the multi-interfaces of CS4-8-2 sample, which obviously improve interface charge transfer. Thus, the CS4-8-2 sample shows an excellent oxygen evolution reaction (OER) activity (134 mV/10 mA cm-2, 40 mV dec-1). The larger double-layer capacitance (Cdl = 17.1 mF cm-2) of the CS4-8-2 sample indicates more electrochemical active sites, compared to the CoS2 and CS4-2 samples. Density functional theory (DFT) calculation proves that due to interface polarization under electric field, the multi-interfaces effectively promote electron transfer and regulate electron structure, thus promoting the adsorption of OH- and dissociation of H2O. Moreover, an innovative norfloxacin (NFX) electrolytic cell (EC) is developed through introducing NFX into the electrolyte, in which efficient NFX degradation and hydrogen production are synergistically achieved. To reach 50 mA cm-2, the required cell voltage of NFX-EC has decreased by 35.2%, compared to conventional KOH-EC. After 2h running at 1 V, 25.5% NFX was degraded in the NFX EC. This innovative NFX-EC is highly energy-efficient, which is promising for the synergistic cleaning and utilization of industry wastewater.

FeNiCo|MnGaOx Heterostructure Nanoparticles as Bifunctional Electrocatalyst for Zn-Air Batteries

Driven by the pressing demand for stable energy systems, zinc-air batteries (ZABs) have emerged as crucial energy storage solutions. However, the quest for cost-effective catalysts to enhance vital oxygen evolution and reduction reactions remains challenging. FeNiCo|MnGaOx heterostructure nanoparticles on carbon nanotubes (CNTs) are synthesized using liquid-phase reduction and H2 calcination approach. Compared to its component, such FeNiCo|MnGaOx/CNT shows a high synergistic effect, low impedance, and modulated electronic structure, leading to a superior bifunctional catalytic performance with an overpotential of 255 mV at 10 mA cm-2 and half-wave potential of 0.824 V (ω = 1600 rpm and 0.1 m KOH electrolyte). Moreover, ZABs based on FeNiCo|MnGaOx/CNT demonstrate notable features, including a peak power density of 136.1 mW cm-2, a high specific capacity of 808.3 mAh gZn -1, and outstanding stability throughout >158 h of uninterrupted charge-discharge cycling. Theoretical calculations reveal that the non-homogeneous interface can introduce more carriers and altered electronic structures to refine intermediate adsorption reactions, especially promoting O* formation, thereby enhancing electrocatalytic performance. This work demonstrates the importance of heterostructure interfacial modulation of electronic structure and enhancement of adsorption capacity in promoting the implementation of OER/ORR, ZABs, and related applications.

Platinum-Tellurium Heterojunction Nanosheet Assemblies for Efficient Direct Formic Acid Electrooxidation Catalysis

Two-dimensional (2D) heterojunction nanomaterials offer exceptional physicochemical and catalytic properties, thanks to their special spatial electronic structure. However, synthesizing morphologically uniform 2D platinum (Pt)-based metallic nanomaterials with diverse crystalline phases remains a formidable challenge. In this study, we have achieved the successful synthesis of advanced 2D platinum-tellurium heterojunction nanosheet assemblies (Ptx-PtTe2 HJNSAs, x = 0, 1, 2), seamlessly integrating both trigonal PtTe2 (t-PtTe2) and cubic Pt (c-Pt) phases. By enabling efficient electron transport and leveraging the specific electron density present at the heterojunction, the Pt2-PtTe2 HJNSAs/C demonstrated exceptional formic acid oxidation reaction (FAOR) activity and stability. Specifically, the specific and mass activities reached 8.4 mA cm-2 and 6.1 A mgPt-1, which are 46.7 and 50.8 times higher than those of commercial Pt/C, respectively. Impressively, aberration-corrected high-angle annular dark field scanning transmission electron microscopy (AC-HAADF-STEM) revealed a closely packed arrangement of atomic layers and a coherent intergrowth heterogeneous structure. Density functional theory (DFT) calculations further indicated that rearrangement of electronic structure occurred on the surface of Pt2-PtTe2 HJNSAs resulting in a more favorable dehydrogenation pathway and excellent CO tolerance, beneficial for performance improvement. This work inspires the targeted exploration of Pt-based nanomaterials through 2D heterostructure design, leading to an important impact on fuel cell catalysis and beyond.

Rational Design of FeCo-S/Ni2P/NF Heterojunction as a Robust Electrocatalyst for Water Splitting

The rational design of nonnoble-metal-based catalysts with high electroactivity and long-term stability, featuring controllable active sites, remains a significant challenge for achieving effective water electrolysis. Herein, a heterogeneous catalyst with a FeCo-S and Ni2P heterostructure (denoted FeCo-S/Ni2P/NF) grown on nickel foam (NF) was synthesized by a solvothermal method and low-temperature phosphorization. The FeCo-S/Ni2P/NF catalyst shows excellent electrocatalytic performance and stability in alkaline solution. The FeCo-S/Ni2P/NF catalyst demonstrates low overpotentials (η) for both the hydrogen evolution reaction (HER) (49 mV@10 mA cm-2) and the oxygen evolution reaction (OER) (279 mV@100 mA cm-2). Assembling the FeCo-S/Ni2P/NF catalyst as both cathode and anode in an electrolytic cell for overall water splitting (OWS) needs an ultralow cell voltage of 1.57 V to attain a current density (CD) of 300 mA cm-2. Furthermore, it demonstrates excellent durability, significantly outperforming the commercial Pt/C∥IrO2 system. The results of experiments indicate that the heterostructure and synergistic effect of FeCo-S and Ni2P can significantly enhance conductivity, facilitate mass/ion transport and gas evolution, and expose more active sites, thereby improving the catalytic activity of the electrocatalyst for the OWS. This study provides a rational approach for the development of commercially promising dual-functional electrocatalysts.

Ionic liquid-assisted synthesis of N, F, and B co-doped BiOBr/Bi2Se3 on Mo2CTx for enhanced performance in hydrogen evolution reaction and supercapacitors

Heteroatom doping and heterojunction formation are effective strategies to enhance electrochemical performance. In this study, we present a novel approach that utilizes an ionic liquid-assisted synthesis method to fabricate a BiOBr-based material, which is subsequently loaded onto Mo2CTx via a selenization treatment to create a BiOBr/Bi2Se3 heterostructure, denoted as NBF-BiOBr/Bi2Se3/Mo2CTx. The incorporation of heteroatoms improves its hydrophilicity and electronegativity, while the formation of heterojunctions adjusts the electronic structure at the interface, resulting in lower OH-/H+ adsorption energy. The specific surface area of NBF-BiOBr/Bi2Se3/Mo2CTx is 193.1 m2/g. In hydrogen evolution reaction (HER) tests, NBF-BiOBr/Bi2Se3/Mo2CTx exhibits exceptional catalytic performance in acidic media, requiring only an overpotential of 109 mV to achieve a current density of 10 mA cm-2. Furthermore, NBF-BiOBr/Bi2Se3/Mo2CTx demonstrates superior electrochemical performance in an asymmetric supercapacitor, with an energy density as high as 55.6 Wh kg-1 at a power density of 749.9 Wh kg-1. This work provides a novel approach for heteroatom doping and heterojunction synthesis, offering promising prospects for further advancements in the field.

Sodium chloride modulated construction of hollow Co/Co3O4 heterostructure with enhanced mesoscale diffusion towards overall water splitting

Fabricating an efficient electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) isthe most challenging task for overall water splitting. Herein, we utilized the confinement effect of molten sodium chloride (NaCl) to controllably prepare hollow Co/Co3O4 nanoparticles embedded into nitrogen-doped carbon (H-Co/Co3O4-NC). Experimental and theoretical investigations revealed that the interfacial interaction within Co/Co3O4 heterostructure played a pivotal role in modulating the electronic structure and facilitating the electron transfer. Meanwhile, the superiority of hollow nanostructure could promote the mesoscale mass diffusion. Remarkably, the as-prepared H-Co/Co3O4-NC catalyst achieved the low overpotentials of 316 mV and 252 mV towards OER and HER, respectively, which delivered overall water splitting with the potential of 1.76 V at a current density of 10 mA cm-2.

Engineering core-shell hollow-sphere Fe3O4@FeP@nitrogen-doped-carbon as an advanced bi-functional electrocatalyst for highly-efficient water splitting

Given the rapidly increasing energy demand and environmental pollution, to achieve energy conservation and emission reduction, hydrogen production has emerged as a promising alternative to traditional fossil fuels because of its high gravimetric energy density, and renewable and environmentally friendly characteristics. Herein, a core-shell hollow-sphere Fe3O4@FeP@nitrogen-doped-carbon (labeled as H-Fe3O4@FeP@NC) with a dual-interface, novel morphology, and superior conductivity is prepared as an advanced bi-functional electrocatalyst for electrochemical overall water splitting using a collaborative strategy comprising of facile self-assembly and phosphating. The prepared catalyst exhibits superior electrocatalytic activity compared to H-Fe3O4@NC and H-Fe3O4 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Additionally, the overpotential of H-Fe3O4@FeP@NC for OER/HER (258/165 mV at 10 mA/cm2) is significantly lower than those of H-Fe3O4@NC (274/209 mV) and H-Fe3O4 (287/213 mV) at 10 mA/cm2. Meanwhile, the as-synthesized H-Fe3O4@FeP@NC, as an electrode pair, displays a low cell voltage of 1.69 V at 10 mA/cm2 and excellent stability after 100 h, indicating its practical application for overall water splitting. This work presents a practical and economical strategy toward the fabrication of catalyst for efficient water splitting and fuel cell.

Strongly Coupled Heterostructured CoP/MoO2 as an Advanced Electrocatalyst for Urea-Assisted Water Electrolysis

Developing low-cost electrocatalysts with excellent activity and durability in urea-assisted water splitting is urgently needed in order to achieve sustainable hydrogen production. Herein, we in situ synthesized a robust coupled heterostructured electrocatalyst (CoP/MoO2) on a nickel foam (NF) substrate and explored its electrocatalytic performances in the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and urea oxidation reaction (UOR). The overpotential of CoP/MoO2/NF is found to be only 11 mV at 10 mA cm-2 during the HER process, which is significantly lower than that of commercial Pt/C. Meanwhile, the UOR catalytic performance of CoP/MoO2/NF indicates fast reaction kinetics, along with a considerable low driving potential (1.26 V) compared to that of the OER (1.51 V). In situ and ex situ techniques demonstrate that these excellent electrocatalytic properties are mainly ascribed to the effective synergistic coupled effect and strong electronic interactions between single-component CoP and MoO2, which can tune electronic states of Co and Mo, expose more active sites, enhance intrinsic catalytic activity, and accelerate charge transfer. Moreover, when used in electrochemical overall water splitting and urea-assisted water electrolysis, CoP/MoO2/NF can reach a current density of 10 mA cm-2 at only 1.46 and 1.32 V. This outperforms Pt/C||RuO2 and numerous nonprecious metal electrocatalysts and maintains a stable long-term electrolytic operation for 84 h. This work provides a promising pathway for the development of efficient catalysts during urea-assisted water electrolysis for hydrogen production.

Amorphous Nickel Hydroxide Shell on Ni8P3 Nanorods for Boosted Highly Stable Overall Water Splitting at High Current

Developing highly active, highly stable, and cheap electrocatalysts for water splitting is of great significance for hydrogen production. Herein, we report an amorphous Ni(OH)2-clothed transition Ni8P3 catalyst, in which the amorphous Ni(OH)2 shell provides catalytic active sites and serves as a proton conductive encapsulation layer to ensure efficient proton supply to the active Ni8P3 sites. As expected, the Ni8P3@Ni(OH)2 catalyst exhibits significant water decomposition performance at low and high current densities of 10, 100, and 1000 mA cm-2 at 1.45, 1.71, and 2.21 V, respectively, which is comparable to those of commercial electrocatalysts. In particular, the prepared Ni8P3@Ni(OH)2 electrodes possess exceptional long-term durability (200 h) at high current (over 1 A). The significantly improved water-splitting activity and durability in alkaline medium are expected to make them attractive catalyst materials to produce renewable chemical fuels.

Enhanced electrocatalytic efficiencies for water electrolysis and para-nitrophenol hydrogenation by self-supported nickel cobalt phosphide-nickel iron layered double hydroxide p-n junction

Charge redistribution across heterointerfaces is an important tactic to enhance the catalytic activities and bifunctionality of hybrid catalysts, especially for green hydrogen production from water electrolysis and harmless electrocatalytic valorization of organics. Herein, a self-supported p-n junction catalytic electrode was constructed by tandem electrodeposition of nickel cobalt phosphide (NiCoP) and nickel iron layered double hydroxide (NiFe LDH) onto Ni foam (NF) substrate, denoted as NiCoP@NiFe LDH/NF, to enhance the electrocatalytic capabilities for water electrolysis and hydrogenation of an organic, para-nitrophenol (4-NP). Benefitting from the charge redistribution across the p-n junction, high electrocatalytic efficiencies for oxygen evolution reaction (OER, overpotential of 388 mV at 100 mA cm-2) and hydrogen evolution reaction (HER, overpotential of 132 mV at 10 mA cm-2) could be achieved concurrently by the NiCoP@NiFe LDH/NF electrode, and both overpotentials were located within the mainstream levels in this domain. The bifunctional catalytic features enabled a full water electrolysis response of 10 mA cm-2 at 1.61 V. In addition, the p-n junction electrode catalyzed the hydrogenation of 4-NP at a conversion of 100%, para-aminophenol (4-AP) selectivity of 90% and faradaic efficiency (FE) of 88% at -0.18 V. The current work offers a feasible strategy for fulfilling electrochemical H2 production and hydrogenation valorization of 4-NP pollutant by constructing a self-supported p-n junction catalytic electrode.

Sulfur Vacancy-Engineered Co3S4/MoS2-Interfaced Nanosheet Array for Enhanced Alkaline Overall Water Splitting

Electrochemical water splitting, a crucial reaction for renewable energy storage, demands highly efficient and stable catalysts. Defect and interface engineering has been widely acknowledged to play a pivotal role in improving electrocatalytic performance. Herein, we demonstrate a facile strategy to construct sulfur vacancy (Sv)-engineered Co3S4/MoS2-interfaced nanosheet arrays to modulate the interface electronic structure in situ reduction with NaBH4. The abundant sulfur vacancies and well-arranged nanosheet arrays in Sv-Co3S4/MoS2 lead to pronounced electrocatalytic properties for hydrogen and oxygen evolution reactions (HER/OER) in an alkaline medium, with observed overpotentials of 156 and 209 mV at 10 mA cm-2, respectively. Additionally, as a bifunctional electrocatalyst, Sv-Co3S4/MoS2 requires a cell voltage of 1.67 V at 10 mA cm-2 for overall water splitting and exhibits long-term stability with activity sustained for more than 20 h. This study provides a novel approach to producing transition metal compound-interfaced electrocatalysts with rich vacancies under mild conditions, showcasing their potential for efficient water splitting applications.

Amorphous-crystalline heterostructures enable energy-level matching of cobalt sulfide/nickel iron layered double hydroxide for efficient oxygen evolution reaction

Interface engineering of heterostructures has emerged as a promising approach to enhance the catalytic activity of nonprecious electrocatalysts. Herein, a novel amorphous cobalt sulfide-crystalline nickel iron layered double hydroxide (a-CoS@NiFe-LDH) hybrid material is presented for application as an electrocatalyst for oxygen evolution reaction (OER). Benefitting from the well-matched energy level structures, the a-CoS@NiFe-LDH catalyst delivers a low overpotential of 221 ± 14 mV at an OER current density of 20 mA cm-2 and a small Tafel slope of 83.1 mV dec-1, showing good OER properties. First-principle computations reveal that the electronic interaction between amorphous cobalt sulfide (a-CoS) and crystalline nickel iron layered double hydroxide (NiFe-LDH) components within a-CoS@NiFe-LDH promotes the adsorbate evolution mechanism and reduces the adsorption energies for oxygen intermediates, thereby enhancing the activity and stability for OER. This work opens up a new avenue to enhance the OER catalytic efficiency via the construction of amorphous-crystalline heterostructures.

Design of polymetallic sulfide NiS2@Co4S3@FeS as bifunctional catalyst for high efficiency seawater splitting

The shortage of freshwater resources in the world today has limited the development of water splitting, and our eyes have turned to the abundant seawater. The development of relatively low-toxicity and high-efficiency catalysts is the most important area in seawater electrolysis. In this paper, the preparation of NiS2@Co4S3@FeS via a hydrothermal method on nickel foam has been studied for the first time. In the process of vulcanization, Fe will first generate FeS by virtue of its high affinity for vulcanization. Once Fe is vulcanized, the residual sulfur will be used to generate NiS2, while the vulcanization of Co requires a higher sulfur concentration and reaction temperature; thus, Co4S3 will be generated last. NiS2@Co4S3@FeS is confirmed to have excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalytic properties in alkaline seawater. Its unique structure allows it to expose more reaction centres, and the synergies between the multiple metals optimize the charge distribution of the material and accelerate the OER and HER kinetics. NiS2@Co4S3@FeS requires overpotentials of only 122 mV and 68 mV for the OER and HER when reaching 10 mA cm-2, which is superior to most catalysts reported to date for seawater electrolysis, and the material displays acceptable stability. In an electrolytic cell composed of both positive and negative electrodes, when the current density is 10 mA cm-2, the NiS2@Co4S3@FeS material displays a low overpotential of only 357 mV for seawater splitting. Density functional theory shows that the FeS electrode has the optimum Gibbs free energy of H to accelerate reaction kinetics, and the synergistic catalysis of the NiS2, Co4S3 and FeS materials promotes the hydrogen production activity of the NiS2@Co4S3@FeS electrode. This work proposes a novel idea for designing environmentally friendly seawater splitting catalysts.

Interface engineering on super-hydrophilic amorphous/crystalline NiFe-based hydroxide/selenide heterostructure nanoflowers for accelerated industrial overall water splitting at high current density

Designing heterojunction catalysts with energy effects at the interface, particularly combining the surface structure advantages of super-hydrophilic interfaces with the high activity advantages of bimetal synergistic optimisation, is the key to developing economical and efficient industrial electrocatalytic water-splitting catalysts. In this study, a coupled nanoflower-like NiFe(OH)x/(Ni, Fe)Se heterostructure catalyst supported on Ni foam (NF) (NFSe@NFOH/NF) was designed and successfully prepared using hydrothermal and electrodeposition strategies. Owing to the electron interaction at the heterogeneous amorphous (NFOH)/crystalline (NFSe) interface and the bimetallic synergistic effect of Ni and Fe, the prepared NFSe@NFOH/NF exhibited excellent and stable oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalytic properties, with low overpotentials of 214/276 mV at 100 mA⋅cm-2 and 262/340 mV at 500 mA⋅cm-2. The assembled water electrolyser comprising NFSe@NFOH/NF || NFSe@NFOH/NF needed only small voltages of 1.73 and 1.85 V to yield current densities of 100 and 500 mA⋅cm-2, respectively. This study offers an innovative design idea for the rational adoption of interface engineering and amorphous-crystalline engineering techniques to construct catalysts with excellent catalytic activity and stability for electrocatalytic overall water splitting (EOWS) at a high current density, which further facilitates the advancement of sustainable energy technology in the future.