Nitrogen-doped Fe(2)O(3)/NiTe(2) as an excellent bifunctional electrocatalyst for overall water splitting

NiTe2-GE composite as a promoter of Pt for efficient methanol electro-oxidation

Exploring oxophilic platinum (Pt) promoters is essential to address the significant challenges currently faced by direct methanol fuel cell technology. In this study, we developed a novel composite catalyst consisting of nickel telluride (NiTe2) and graphene (GE) supported platinum nanoparticles, which was applied to the methanol oxidation reaction (MOR) for the first time. Electrochemical tests demonstrated that the electrocatalytic performance of Pt for MOR can be markedly enhanced by using NiTe2-GE as a promoter. Specifically, the peak current density of Pt/NiTe2-GE reached 103.9 mA cm-2, significantly surpassing that of Pt/NiTe2 (27.1 mA cm-2) and Pt/GE (23.9 mA cm-2) catalysts, and it was also comparable to the commercial Pt/C catalyst (58.5 mA cm-2). Furthermore, Pt/NiTe2-GE exhibited superior catalytic stability, enhanced resistance to CO poisoning, and accelerated catalytic kinetics. This work reveals an effective strategy for the design of advanced anode catalysts for MOR.

Spindle-shaped medium-entropy metal telluride nanostructures as high-performance dual-catalytic electrocatalysts for overall water splitting

The development of low-cost and high-activity electrocatalysts is crucial for clean energy production and sustainable development. In particular, non-noble-metal-based medium-entropy materials (MEMs) have recently attracted considerable attention because of their excellent electrocatalytic performance and have become a new research hotspot in the field of electrocatalysis. Additionally, the fewer main elements allow MEMs to be easily recycled and synthesized, with potential industrial applications. Inspired by these advantages, spindle-shaped (Fe2CoNi)Te2 medium-entropy metal telluride (METe) nanostructures were prepared via in situ Te doping during thermal treatment of metal-organic frameworks (MOFs). The resulting spindle-shaped (Fe2CoNi)Te2 METe prepared with an optimal ratio of Fe2CoNi-MOF and the tellurium powder exhibits excellent electrocatalytic activity and stability for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), achieving low overpotentials of 155 and 263 mV at 10 mA cm-2 for the HER and OER, respectively, and outstanding stability in 60 h tests. Density functional theory calculations demonstrate that the enhanced performance of the medium-entropy (Fe2CoNi)Te2 METe nanostructures is attributed to a significant increase in the surface charge density, a substantial increase in the *H adsorption/desorption ability and a remarkable reduction in the Gibbs free energy of the rate-determining step due to the d-band center being closer to the Fermi level. This study provides a feasible strategy for achieving efficient and low-cost electrocatalysts.

Amorphous/crystalline nanostructured Co-FeOOH/CoCe-MOF/NF heterojunctions for efficient electrocatalytic overall water splitting

Hydrogen production by electrocatalytic water splitting is considered to be an effective and environmental method, and the design of an electrocatalyst with high efficiency, low cost, and multifunction is of great importance. Herein, we developed a amorphous Co-FeOOH/crystalline CoCe-MOF heterostructure (defined as Co-FeOOH/CoCe-MOF/NF) though a convenient cathodic electrodeposition strategy as a high-efficiency bifunctional electrocatalyst for water electrolysis. The Co-FeOOH/CoCe-MOF/NF nanocrystals provide remarkable electronic conductivity and plenty of active sites, and the crystalline/amorphous heterostructure with generates synergistic effects, providing plentiful active sites and efficient charge/mass transfer. Benefiting from this, the designed Co-FeOOH/CoCe-MOF/NF displays ultralow overpotentials of 226 and 74 mV to achieve 10 mA cm-2 for oxygen evolution reaction and hydrogen evolution reaction, and also shows the superior performance for overall water splitting with a low voltage of 1.55 V at 10 mA cm-2 in 1 M KOH. The work reveals a design of superior activity, cost-effective and multifunctional electrocatalysts for water splitting.

Facile synthesis of Co3Te4-Fe3C for efficient overall water-splitting in an alkaline medium

The large amounts of attention directed towards the commercialization of renewable energy systems have motivated extensive research to develop non-precious-metal-based catalysts for promoting the electrochemical production of H2 and O2 from water. Here, we report promising technology, i.e., electrochemical water splitting for OER and HER. This work used a simple hydrothermal method to synthesize a novel Co3Te4-Fe3C nanocomposite directly on a stainless-steel substrate. Various physical techniques like XRD, FESEM/EDX, and XPS have been used to characterize the good composite growth and confirm the correlation between the structural features. It has been shown that the composite's morphology consists of interconnected particles, each uniformly coated with a thin layer of carbon. This structure then forms a porous network with defects, which helps stabilize the material and improve its charge conductivity. XPS analysis shows that combining Fe3C with Co3Te4 adjusts the atomic structure of both metals. This interaction creates redox sites (Fe3+/Fe2+ and Co3+/Co2+) at the Co₃Te₄-Fe₃C interface, which are crucial for activating redox reactions and enhancing electrochemical performance. The results also confirm the presence of multiple synergistic active sites, which contribute to improved catalytic activity. The optimized chemical composition and conductive structure result in enhanced electrocatalytic activity of Co3Te4-Fe3C towards electron transportation between the material interface and medium. It is found that the Co3Te4-Fe3C catalyst exhibits robust OER/HER activity with reduced overpotential values of 235/210 mV@10 mA cm-2 and Tafel slopes of 62/45 mV dec-1 in an alkaline solution. For overall water-splitting, cell voltages of 1.44, 1.88, and 2.0 V at current densities of 10, 50, and 100 mA cm-2 were achieved with a stability of 102 h. The electrochemically active surface area of the composite is 1125 cm2, indicating that a large surface area offered numerous reactive sites for electron transfer in the promotion of the electrochemical activity. The enhancement in catalytic performance was also checked using chronoamperometry analysis, reflecting long-term stability. Our results provide a novel idea for designing a composite of carbide with chalcogenide with robust catalytic mechanisms, which is useful for various applications in environmental and energy conversion fields.

NiMOF-Derived MoSe2/NiSe Hollow Nanoflower Structures as Electrocatalysts for Hydrogen Evolution Reaction in Alkaline Medium

Metal-organic frameworks (MOFs) are crystalline porous materials for storage and energy conversion applications with three-dimensional pore structure, high porosity, and specific surface area, which are widely utilized in electrocatalysis. Herein, MoSe2/NiSe composites were synthesized by selenization reaction using NiMOF as the precursor. The composites were hollow nanoflower structures with a synergistic effect between MoSe2 and NiSe to promote rapid electron transfer, which exhibited good hydrogen evolution reaction performance in an alkaline medium. At a current density of 10 mA/cm2, the HER overpotential reaches 80 mV, the Tafel slope is 33.86 mV/dec, and the material has good stability, with polarization curves remaining essentially unchanged after 3000 cycles. These results indicate that the method has a promising application in the preparation of efficient and sustainable catalysts for hydrogen production in alkaline medium.

Regulation of electron density redistribution for efficient alkaline hydrogen evolution reaction and overall water splitting

The rational design of morphology and heterogeneous interfaces for non-precious metal electrocatalysts is crucial in electrochemical water decomposition. In this paper, a bifunctional electrocatalyst (Ni/NiFe LDH), which coupling nickel with nickel-iron layer double hydroxide (NiFe LDH), is synthesized on carbon cloth. At current density of 10 mA cm-2, the Ni/NiFe LDH exhibits a low hydrogen evolution reaction (HER) overpotential of only 36 mV due to the accelerated electrolyte penetration, which is caused by superhydrophilic interface. Moreover, an alkaline electrolyzer is formed and provide a current density of 10 mA cm-2 with a voltage of only 1.49 V. It is confirmed by the density functional theory (DFT) that electron from the Ni layer is transferred to NiFe LDH layer, redistributing the local electron density around the heterogeneous phase interface. Thus, the Gibbs free energy for hydrogen adsorption is optimized. This work provides a promising strategy for the rational regulation of electrons at heterogeneous interfaces and the synthesis of flexible electrocatalysts.

Ultrasmall Ru nanoparticles-decorated nickel/nickel oxide three phase heterojunctions to boost alkaline hydrogen evolution

The rational design and optimization of heterogeneous interface for low loading noble metal HER eletrocatalysts to facilitate the upscaling of alkaline water/seawater electrolysis is highly challenging. Herein, we present a facile deep corrosion strategy induced by NaBH4 to precisely construct an ultrasmall Ru nanoparticle-decorated Ni/NiO hybrid (r-Ru-Ni/NiO) with highly dispersed triple-phase heterostructures. Remarkably, it exhibits superior activity with only 53 mV and 70 mV at 100 mA cm-2 for hydrogen evolution reaction (HER) in alkaline water and seawater, respectively, surpassing the performance of Pt/C (109.7 mV, 100 mA cm-2, 1 M KOH). It is attributed to collaborative optimization of electroactive interfaces between well-distributed ultrasmall Ru nanoparticles and Ni/NiO hybrid. Moreover, the assembled r-Ru-Ni/NiO system just require 2.03 V at 1000 mA cm-2 in anion exchange membrane (AEM) electrolyzer, outperforming a RuO2/NF || Pt/C system, while exhibiting outstanding stability at high current densities. This study offers a logical design for accurate construction of interfacial engineering, showing promise for large-scale hydrogen production via electrochemical water splitting.

Synthesis and Electrocatalytic Applications of Layer-Structured Metal Chalcogenides Composites

Featured with the attractive properties such as large surface area, unique atomic layer thickness, excellent electronic conductivity, and superior catalytic activity, layered metal chalcogenides (LMCs) have received considerable research attention in electrocatalytic applications. In this review, the approaches developed to synthesize LMCs-based electrocatalysts are summarized. Recent progress in LMCs-based composites for electrochemical energy conversion applications including oxygen reduction reaction, carbon dioxide reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, overall water splitting, and nitrogen reduction reaction is reviewed, and the potential opportunities and practical obstacles for the development of LMCs-based composites as high-performing active substances for electrocatalytic applications are also discussed. This review may provide an inspiring guidance for developing high-performance LMCs for electrochemical energy conversion applications.

Transforming electrochemical hydrogen Production: Tannic Acid-Boosted CoNi alloy integration with Multi-Walled carbon nanotubes for advanced bifunctional catalysis

The dimensions of alloy nanoparticles or nanosheets have emerged as a critical determinant for their prowess as outstanding electrocatalysts in water decomposition. Remarkably, the reduction in nanoparticle size results in an expanded active specific surface area, elevating reaction kinetics and showcasing groundbreaking potential. In a significant leap towards innovation, we introduced tannic acid (TA) to modify multi-walled carbon nanotubes (MWCNTs) and CoNi alloys. This ingenious strategy not only finely tuned the size of CoNi alloys but also securely anchored them to the MWCNTs substrate. The resulting synergistic "carbon transportation network" accelerated electron transfer during the reaction, markedly enhancing efficiency. Furthermore, the exceptional synergy of Co and Ni elements establishes Co0.84Ni1.69/MWCNTs as highly efficient electrocatalysts. Experimental findings unequivocally demonstrate that TA-Co0.84Ni1.69/MWCNTs require minimal overpotentials of 171 and 294 mV to achieve a current density of ± 10 mA cm-2. Serving as both anode and cathode for overall water splitting, TA-Co0.84Ni1.69/MWCNTs demand a low voltage of 1.66 V at 10 mA cm-2, maintaining structural integrity throughout extensive cyclic stability testing. These results propel TA-Co0.84Ni1.69/MWCNTs as promising candidates for future electrocatalytic advancements.

Hollow CoVOx/Ag nanoprism with tailored electronic structure for high efficiency oxygen evolution reaction

Developing high-active and inexpensive electrocatalysts for oxygen evolution reaction (OER) is very important in the field of water splitting. The catalytic performance of electrocatalysts can be significantly improved by optimizing the electronic structure and designing suitable nanostructure. In this work, we represent the synthesis of hollow CoVOx/Ag-5 for OER. Due to the interaction of CoVOx and Ag nanoparticles, the electronic structure is optimized to improve the intrinsic catalytic activity. Additionally, the extrinsic catalytic activity of CoVOx/Ag is enhanced by the abundant active sites from the hollow structure. As a result, the CoVOx/Ag-5 demonstrates significantly enhanced OER catalytic activity with a low overpotential of 247 mV at 10 mA cm-2. In addition, it also exhibits excellent durability, without obvious attenuation in performance after continuous operation for 60 h. Furthermore, the catalyst can enable full water splitting with appropriate 100 % Faraday efficiency, demonstrating its practical application.

High-performance bismuth vanadate photoanodes cocatalyzed with nitrogen, sulphur co-doped ferrocobalt-metal organic frameworks thin layer for photoelectrochemical water splitting

In this study, we prepare a highly efficient BiVO4 photoanode co-catalyzed with an ultrathin layer of N, S co-doped FeCo-Metal Organic Frameworks (MOFs) for photoelectrochemical water splitting. The introduction of N and S into FeCo-MOFs enhances electron and mass transfer, exposing more catalytic active sites and significantly improving the catalytic performance of N, S co-doped FeCo-based MOFs in water oxidation. The optimized BiVO4/NS-FeCo-MOFs photoanode exhibits impressive results, with a photocurrent density of 5.23 mA cm-2 at 1.23 V vs. Reversible Hydrogen Electrode (RHE) and an incident photon-to-charge conversion efficiency (IPCE) of 74.4 % at 450 nm in a 0.1 M phosphate buffered solution (pH = 7). These values are 4.84 times and 6.2 times higher than those of the original BiVO4 photoanode, respectively. Furthermore, the optimized BiVO4/NS-FeCo-MOFs photoanode demonstrates exceptional long-term stability, maintaining 96 % of the initial current after five hours.

In Situ Reconstruction of High-Entropy Heterostructure Catalysts for Stable Oxygen Evolution Electrocatalysis under Industrial Conditions

Despite of urgent needs for highly stable and efficient electrochemical water-splitting devices, it remains extremely challenging to acquire highly stable oxygen evolution reaction (OER) electrocatalysts under harsh industrial conditions. Here, a successful in situ synthesis of FeCoNiMnCr high-entropy alloy (HEA) and high-entropy oxide (HEO) heterocatalysts via a Cr-induced spontaneous reconstruction strategy is reported, and it is demonstrated that they deliver excellent ultrastable OER electrocatalytic performance with a low overpotential of 320 mV at 500 mA cm-2 and a negligible activity loss after maintaining at 100 mA cm-2 for 240 h. Remarkably, the heterocatalyst holds outstanding long-term stability under harsh industrial condition of 6 m KOH and 85 °C at a current density of as high as 500 mA cm-2 over 500 h. Density functional theory calculations reveal that the formation of the HEA-HEO heterostructure can provide electroactive sites possessing robust valence states to guarantee long-term stable OER process, leading to the enhancement of electroactivity. The findings of such highly stable OER heterocatalysts under industrial conditions offer a new perspective for designing and constructing efficient high-entropy electrocatalysts for practical industrial water splitting.

Highly Active and Stable Alkaline Hydrogen Evolution Electrocatalyst Based on Ir-Incorporated Partially Oxidized Ru Aerogel under Industrial-Level Current Density

The realization of large-scale industrial application of alkaline water electrolysis for hydrogen generation is severely hampered by the cost of electricity. Therefore, it is currently necessary to synthesize highly efficient electrocatalysts with excellent stability and low overpotential under an industrial-level current density. Herein, Ir-incorporated in partially oxidized Ru aerogel has been designed and synthesized via a simple in situ reduction strategy and subsequent oxidation process. The electrochemical measurements demonstrate that the optimized Ru98 Ir2 -350 electrocatalyst exhibits outstanding hydrogen evolution reaction (HER) performance in an alkaline environment (1 M KOH). Especially, at the large current density of 1000 mA cm-2 , the overpotential is as low as 121 mV, far exceeding the benchmark Pt/C catalyst. Moreover, the Ru98 Ir2 -350 catalyst also displays excellent stability over 1500 h at 1000 mA cm-2 , denoting its industrial applicability. This work provides an efficient route for developing highly active and ultra-stable electrocatalysts for hydrogen generation under industrial-level current density.

Iron-doping-induced formation of Ni-Co-O nanotubes as efficient bifunctional electrodes

The rational design of earth-abundant and efficient electrocatalysts to replace precious metal-based materials is highly anticipated for overall water splitting. Herein, NiCo2O4 electrocatalysts with different Fe doping amounts (Fex-NCO, x = 1, 2, 3) were synthesized by a low-temperature chemical method. It was interesting to find that the doping of Fe induced the formation of NiCo2O4 nanotube arrays by modulating the Fe content. The Fe3-NCO electrode with a nanotube structure and rich oxygen vacancies exhibited exceptional electrocatalytic activities for the hydrogen evolution reaction (97 mV, 10 mA cm-2) and oxygen evolution reaction (188.4 mV, 10 mA cm-2). DFT calculations revealed that Fe promoted the modulation of the electronic structure, which played a crucial role in optimizing the reaction intermediates and altered the energy level of the d band center, and as a result, enhanced the water dissociation ability. Additionally, a low cell voltage of 1.56 V (10 mA cm-2) was realized for water splitting based on an as-fabricated Fe-doped NiCo2O4 nanotube array bifunctional electrode.

Two novel chiral AIEgens as coordination precursors: synthesis, structures and photophysical study

Two novel chiral molecules, (4S)-5,5-dimethyl-2-(4-oxo-4H-chromen-3-yl)thiazolidine-4-carboxylic acid (OCCA) and (4S)-5,5-dimethyl-2-(4-(1,2,2-triphenylvinyl)phenyl)thiazolidine-4-carboxylic acid (TPCA), were successfully synthesized by aldehyde amine condensation reaction, and their structures were characterized by 1H NMR and single crystal X-ray diffraction. The intensities of photoluminescence changed with the aggregation, exhibiting that OCCA and TPCA are aggregation-induced emission luminogens (AIEgens). After complete aggregation, OCCA emitted the purple-blue light at the peak of 388 nm and TPCA emitted the cyan light at the peak of 488 nm. The aggregation-induced emission (AIE) effects for OCCA and TPCA resulted from local state to twisted intermolecular charge transfer (TICT) and restriction of intramolecular motion (RIM), respectively. Other spectra including UV-vis, IR, and Raman spectra were also discussed in detail.

Triple roles of Ni(OH)2 promoting the electrocatalytic activity and stability of Ni3S4@Ni(OH)2 in anion exchange membrane water electrolyzers

Developing high performance and durable electrocatalysts is crucial for the practical application of large-scale water splitting under high current density. Here, we constructed a Mott-Schottky heterojunction bifunctional electrocatalyst coating of Ni3S4 with Ni(OH)2 thin film supported on Ni foam substrate (Ni3S4@Ni(OH)2) for anion exchange membrane water electrolyzers (AEMWEs). Remarkably, the η500 is as low as 274.6 mV toward the hydrogen evolution reaction and 423.8 mV toward the oxygen evolution reaction. AEMWEs deliver a stable performance that achieves current densities of 500 and 1000 mA cm-2 at a cell voltage of 1.84 and 1.95 V, respectively. In particular, the Ni3S4@Ni(OH)2 exhibits durable stability for 100 h at 500 mA cm-2 without significant degradation and uses 0.75 kW·h of electricity less than commercial Ni foam electrode to produce each standard cubic meter of hydrogen gas at 500 mA cm-2. The excellent performance is ascribed to the triple roles of Ni(OH)2, which prevent the inner Ni3S4 from decomposing during the reaction process, promoting the dissociation of water and formation of adsorbed hydrogen intermediate and accelerating electron transfer ability due to the Mott-Schottky heterojunction between Ni(OH)2 and Ni3S4. This work sheds light on the development of advanced bifunctional electrocatalysts based on non-precious transition metals for AEMWEs.

Modulating Electronic Structures of Bimetallic Co-Fe Sulfide Ultrathin Nanosheet Supported on g-C3N4 Promoting Electrocatalytic Hydrogen Evolution Performance

Heteroatom doping is a possible way to regulate the catalytic capability of electrocatalysts for hydrogen evolution reaction (HER). This work focuses on the development of bimetallic Cobalt-Iron sulfide ultrathin nanosheets supported on the graphitic carbon nitride (g-C3N4) catalyst as efficient HER electrocatalysts (CoS2/FeS2/CN) with good stability at wide pH value. The ultrathin nanosheet exposes more active sites and enhances the catalyst activity. Electrochemical experiments demonstrate that adding g-C3N4 and Fe to CoS2 increases its catalytic activity and stability. Furthermore, g-C3N4 and Fe co-doped with CoS2 can modulate electronic structures on the interface. The CoS2/FeS2/CN exhibits outstanding HER performance, reaching a current density of 10 mA cm-2 with overpotentials of only 76.5 mV in an acidic solution and 175.6 mV in an alkaline solution. It also demonstrates exceptional durability, superior to commercial platinum/carbon catalysts. This work introduces a promising approach for designing low-cost, high-performance HER electrocatalysts with a wide pH range.

Engineering P-Fe2O3-CoP nanosheets for overall freshwater and seawater splitting

Tailoring surface composition and coordinative environment of catalysts in a nano-meter region often influence their chemical performance. It is reported that CoP exhibits a low dissociation ability of H-OH, originating from the poor desorption of intermediate species. Herein, we provide a feasible method to construct P-Fe2O3-CoP nanosheets through a gas-phase phosphorization process. P doping induces the formation of interfacial structure between Fe2O3 and CoP and the generation of defective structures. The resulting P-Fe2O3-CoP nanosheets afford high freshwater/seawater oxidation activity (250/270 mV@10 mA/cm2) in 1 mol/L (M) KOH, which is even lower than commercial RuO2. Compared with CoP||CoP, P-Fe2O3||P-Fe2O3, and Co3O4||Co3O4, the assembled P-Fe2O3-CoP||P-Fe2O3-CoP exhibits the superior water/seawater electrolysis performance with 1.61/1.65 V@10 mA/cm2. The synergistic effect of P doping, defective structure, and heterojunction leads to high water oxidation efficiency and water splitting efficiency.

In situ fabrication of sporoid-like flexible electrodes via Fe-regulated electron density for highly efficient and ultra-stable overall seawater splitting

Construction of ultra-stable, flexible, efficient and economical catalytic electrodes is of great significance for the seawater electrolysis for hydrogen production. This work is grounded in a one-step mild electroless plating method to construct industrial-grade super-stable overall water splitting (OWS) catalytic electrodes (Fe1-Ni1P@GF) by growing loose and porous spore-like Fe1-Ni1P conductive catalysts in situ on flexible glass fibre (GF) insulating substrates with precise elemental regulation. Cost-effective Fe regulation boosts the electronic conductivity and charge transfer ability to achieve the construction of high intrinsic activity and strong electron density electrodes. Fe1-Ni1P@GF exhibits remarkable catalytic performance in hydrogen and oxygen evolution reaction (HER and OER), providing current densities of 10 mA cm-2 for HER and 100 mA cm-2 for OER at overpotentials of 51 and 216 mV, respectively. Moreover, it achieves 10 mA cm-2 at 1.42 V for OWS, and exhibits stable operation for over 1440 h at 1000 mA cm-2 in quasi-industrial environment of 6.0 M KOH + 0.5 M NaCl, without any performance degradation. This strategy enables the preparation of universally applicable P-based electrodes (ternary, quaternary, etc.) and large-area flexible electrodes (paper or cotton), significantly expands the practicality of the electrodes and demonstrating promising potential for industrial applications.

N-doped carbon sheets supported P-Fe3O4-MoO2 for freshwater and seawater electrolysis

Electric-driven freshwater/seawater splitting is an attractive and sustainable route to realize the generation of H2 and O2. Molybdenum-based oxides exhibit poor activity toward freshwater/seawater electrolysis. Herein, we adjusted the electronic structure of MoO2 by constructing N-doped carbon sheets supported P-Fe3O4-MoO2 nanosheets (P-Fe3O4-MoO2/NC). P-Fe3O4-MoO2/N-doped carbon sheets were precisely prepared by pyrolysis of Schiff base Fe complex and MoO3 nanosheets through phosphorization. Benefiting from the unique structures of the samples, it required 119/145 mV to drive freshwater/seawater reduction reaction at 10 mA/cm2. P-Fe3O4-MoO2/NC catalysts exhibited superior freshwater/seawater oxidation reactivity with 180/189 mV at 10 mA/cm2 compared with commercial RuO2. The low cell voltages for P-Fe3O4-MoO2/NC were 1.47 and 1.59 V towards freshwater and seawater electrolysis, respectively. Our work might shed light on the structural modulation of Mo-based oxides for enhancing freshwater and seawater electrolysis activity.

Modulating metal-support interaction and inducing electron-rich environment of Ni2P NPs by B atoms incorporation for enhanced hydrogen evolution reaction performance

Modulation of the electronic interaction between the metal and support has been verified as a feasible strategy to improve the electrocatalytic performance of supported-type catalysts. Here, we have successfully synthesized an electrocatalyst of Ni2P nanoparticles (NPs) anchored on B, N co-doped graphite-like carbon nanosheets (Ni2P@B, N-GC), and elucidated the main mechanism by which B atoms doping enhances electrocatalytic hydrogen evolution reaction (HER) performance. The B atoms with electron-rich characteristic not only modulate the electronic structure on carbon skeleton, but also regulate the interfacial electronic interaction between Ni2P NPs and the carbon skeleton, which can lead to the increased available electron density of Ni sites. Such optimization is conducive to accelerating proton transfer and promoting reactive activity. As revealed, the Ni2P@B, N-GC catalyst with B atoms doping exhibits superior performance to the Ni2P@N-GC catalyst in acidic, neutral and alkaline medias. In addition, the assembled Ni(OH)2@B, N-GC||Ni2P@B, N-GC electrolyzer displays prominent overall water splitting performance in alkaline solution, which only demands 1.57 V to reach 10 mA/cm2, and in complicated natural seawater electrolyte, as low as 1.59 V. Hence, the B atoms doping strategy shows the significant enhancement for HER electrocatalysis.

Self-sacrifice-template epitaxial growth of hierarchical MnO2@NiCo2O4 heterojunction electrode for high-performance asymmetric supercapacitor

Constructing three-dimensional (3D) hierarchical bimetallic pseudocapacitive materials with abundant opening channel and heterojunction structures is rather promising but still challenging for high-performance supercapacitors. Herein, a self-sacrifice-template epitaxial growth strategy was proposed for the first time to construct 3D hierarchical bimetallic pseudocapacitive material. By using this strategy, NiCo2O4 nanowires (NiCo2O4NW) arrayed randomly to form a porous shell via in-situ epitaxial growth fully enclosing a MnO2 tube core, forming multiple transport channels and nano-heterojunctions between MnO2 and NiCo2O4NW, which facilitates electron transfer, i.e. exhibiting high electronic conductivity than any single component. As a result of the self-sacrifice-template epitaxial growth method, special hollow tectorum-like 3D hierarchical structure with considerable inter-nanowire space and hollow interior space enables easy access of electrolyte to NiCo2O4NW surface and MnO2 core, thereby resulting in highly exposed redox active sites of MnO2 core and NiCo2O4NW shell for energy storage. Comprehensive evaluations confirmed MnO2@NiCo2O4NW was a supercapacitor electrode candidate, delivering a superior energy density of 106.37 Wh kg-1. Such performance can be ascribed to the synergistic coupling effect of 3D hierarchical tube and nano-heterojunction structures. The proposed self-sacrifice-template epitaxial growth strategy provides important guidance for designing high-performance energy storage materials.

Fe2O3/Ni Nanocomposite Electrocatalyst on Cellulose for Hydrogen Evolution Reaction and Oxygen Evolution Reaction

A key challenge in the development of sustainable water-splitting (WS) systems is the formulation of electrodes by efficient combinations of electrocatalyst and binder materials. Cellulose, a biopolymer, can be considered an excellent dispersing agent and binder that can replace high-cost synthetic polymers to construct low-cost electrodes. Herein, a novel electrocatalyst was fabricated by combining Fe2O3 and Ni on microcrystalline cellulose (MCC) without the use of any additional binder. Structural characterization techniques confirmed the formation of the Fe2O3-Ni nanocomposite. Microstructural studies confirmed the homogeneity of the ~50 nm-sized Fe2O3-Ni on MCC. The WS performance, which involves the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), was evaluated using a 1 M KOH electrolyte solution. The Fe2O3-Ni nanocomposite on MCC displayed an efficient performance toward lowering the overpotential in both the HER (163 mV @ 10 mA cm-2) and OER (360 mV @ 10 mA cm-2). These results demonstrate that MCC facilitated the cohesive binding of electrocatalyst materials and attachment to the substrate surface. In the future, modified cellulose-based structures (such as functionalized gels and those dissolved in various media) can be used as efficient binder materials and alternative options for preparing electrodes for WS applications.

Insight into selenium vacancies enhanced CoSe2/MoSe2 heterojunction nanosheets for hydrazine-assisted electrocatalytic water splitting

The integration of interface engineering and vacancy engineering was a feasible way to develop highly efficient electrocatalysts toward water electrolysis. Herein, we designed CoSe2/MoSe2 heterojunction nanosheets with abundant Se vacancies (VSe-CoSe2/MoSe2) for electrocatalytic water splitting. In the VSe-CoSe2/MoSe2 electrocatalyst, the electrons more easily transferred from CoSe2 to MoSe2, and interface engineering not only modulated the electronic structure, but also supplied more heterointerfaces and catalytic sites. After chemical etching, partial Se atoms were eliminated, which further activated the inert plane of the VSe-CoSe2/MoSe2 electrocatalyst and induced electron redistribution. The removal of surface Se atoms was also beneficial to expose inner reactive sites, which promoted adsorption toward reaction intermediates. Density functional theory calculations revealed that interface engineering and vacancy engineering collaboratively optimized the adsorption energy of the VSe-CoSe2/MoSe2 electrocatalyst toward the intermediate H* during the hydrogen evolution reaction process, leading to better electrocatalytic activity. The density of state diagram manifested the refined electronic structure of the VSe-CoSe2/MoSe2 electrocatalyst, and it exhibited a higher electronic state near the Fermi level, which indicated superior electronic conductivity, facilitating electron transport during the catalytic process. In alkaline media, the VSe-CoSe2/MoSe2 electrocatalyst delivered low overpotentials of merely 74 and 242 mV to obtain 10 mA cm-2 toward hydrogen evolution reaction and oxygen evolution reaction. This work illustrated the feasibility of combining two or more strategies to develop high-performance catalysts for water electrolysis.

Unveiling the Structural Self-Reconstruction and Identifying the Reactive Center of a V, Fe Co-Doped Cobalt Precatalyst toward Enhanced Overall Water Splitting by Operando Raman Spectroscopy

The development of efficient and stable bifunctional electrocatalysts based on non-noble metals for water electrolysis is both urgent and challenging. However, unresolved issues remain regarding the challenge of identifying the active phase and gaining a comprehensive understanding of its surface reconstruction and functionality throughout the reaction process. In this study, we have combined doping and heterostructure construction by a one-step electrodeposition and a subsequent activation treatment to synthesize Fe, V co-doped Co3O4/Co(OH)2 and Co/Co(OH)2 heterointerfaces (referred to as A-Co60Fe1.1V). These heterointerfaces, composed of Co/Co(OH)2 and Co3O4/Co(OH)2, are proposed to facilitate charge transfer process during catalysis. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that the introduction of V and Fe dopants increases the valence state of Co centers in Co3O4 and Co(OH)2. Further operando Raman spectroscopy reveals that Co(OH)2 and Co3O4 with the high-valence Co centers remain stable during the hydrogen evolution reaction (HER) process. These high-valence Co centers are believed to promote the crucial water dissociation step and therefore enhance the overall HER catalysis. On the other hand, during the oxygen evolution reaction (OER), Fe, V co-doping leads to an earlier formation of the active CoOOH species, while Fe doping can further help stabilize the more reactive β-CoOOH species instead of the less reactive γ-CoOOH. As a result, the A-Co60Fe1.1V catalyst exhibits significantly improved catalytic activity for both HER and OER that it requires low overpotentials of 51 and 250 mV, respectively, to attain a current density of 10 mA cm-2. Moreover, when utilized as both the cathode and anode in alkaline water electrolysis, the A-Co60Fe1.1V catalyst can operate at a mere 1.54 V voltage while maintaining 10 mA cm-2, surpassing the majority of non-noble metal catalysts. Remarkably, it also exhibits stability for at least 40 h at ∼100 mA cm-2.

Engineering multilayer catalytic interfaces with N, S co-regulation for high performance water splitting

The rational design of hierarchical nano-heterojunction electrocatalysts with efficient and durable water splitting performance is a hot research topic in the field of sustainable energy conversion. Herein, chemical vapor deposition methods are exploited to dope N and S elements in a core-shell structured Co₃O₄@NiMoO₄ with a layered structure (N, S-Co₃O₄@NiMoO₄/NF₄₀₀). The close contact between Co₃O₄ nanowires and N, S co-doped NiMoO₄ cubic arrays facilitates electron transfer. The electronic structure of Ni, Co and Mo atoms could be optimized to enhance their electrical conductivity by modulation of N and S atoms. At current densities of 10 and 200 mA cm^-2, N, S-Co₃O₄@NiMoO₄/NF₄₀₀ has an overpotential of 200, 300 and 71 160 mV for the oxygen evolution reaction and hydrogen evolution reaction, respectively. Its water splitting voltages are 1.45 V and 2 V at 10 and 200 mA cm^-2. In addition, N, S-Co₃O₄@NiMoO₄/NF₄₀₀ can operate stably for 100 h at a current density of 50 mA cm^-2. This work provides a new approach to designing bifunctional catalysts with hierarchical heterogeneous structures co-regulated by dual elements.

Enhancement Mechanism of Pt/Pd-Based Catalysts for Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is one of the key catalytic reactions for hydrogen fuel cells, biofuel cells and metal-air cells. However, due to the complex four-electron catalytic process, the kinetics of the oxygen reduction reaction are sluggish. Platinum group metal (PGM) catalysts represented by platinum and palladium are considered to be the most active ORR catalysts. However, the price and reserves of Pt/Pd are major concerns and issues for their commercial application. Improving the catalytic performance of PGM catalysts can effectively reduce their loading and material cost in a catalytic system, and they will be more economical and practical. In this review, we introduce the kinetics and mechanisms of Pt/Pd-based catalysts for the ORR, summarize the main factors affecting the catalytic performance of PGMs, and discuss the recent progress of Pt/Pd-based catalysts. In addition, the remaining challenges and future prospects in the design and improvement of Pt/Pd-based catalysts of the ORR are also discussed.