Inner Co Synergizing Outer Ru Supported on Carbon Nanotubes for Efficient pH-Universal Hydrogen Evolution Catalysis

Confined RuP2 Nanoparticles in N,P,S-Tridoped Carbon as Superior Electrocatalyst for pH-Wide Hydrogen Evolution

Hydrogen has been deemed as the ideal energy source and carrier due to its unmatched energy efficiency and sustainability. Nevertheless, there is a pressing need to develop cost-effective materials to replace costly Pt in the hydrogen evolution reaction (HER), and the electrocatalysts with low overpotential and robust stability under various conditions is a particularly significant concern. In this study, a straightforward and effective approach was proposed for the precise synthesis of RuP2 nanoparticles encapsulated in N, P, S-tridoped carbon, which involves utilizing zinc pyrithione, phytic acid and Ru salt as starting materials. The effect of different Ru loadings on the morphology and structures of the composite catalysts was examined carefully. The obtained composites exhibit superior alkaline activity surpassing commercial Pt/C and comparable acidic and neutral activity as well as excellent pH-wide stability. DFT computations reveal the integration of RuP2 with tridoped carbon can tailor the electronic structure of Ru active sites by interfacial electron transfer, thus optimizing the adsorption energy and promoting the HER activity. The benign graphitization of doped carbon and porous structures ensure the smooth charge and mass transfer during HER process. The cost-effective and straightforward synthesis methods presented in this work offer a promising alternative to commercial Pt/C for practical hydrogen-related applications.

Yolk-Shell CoNi@N-Doped Carbon-CoNi@CNTs for Enhanced Microwave Absorption, Photothermal, Anti-Corrosion, and Antimicrobial Properties

The previous studies mainly focused on improving microwave absorbing (MA) performances of MA materials. Even so, these designed MA materials were very difficult to be employed in complex and changing environments owing to their single-functionalities. Herein, a combined Prussian blue analogues derived and catalytical chemical vapor deposition strategy was proposed to produce hierarchical cubic sea urchin-like yolk-shell CoNi@N-doped carbon (NC)-CoNi@carbon nanotubes (CNTs) mixed-dimensional multicomponent nanocomposites (MCNCs), which were composed of zero-dimensional CoNi nanoparticles, three-dimensional NC nanocubes and one-dimensional CNTs. Because of good impedance matching and attenuation characteristics, the designed CoNi@NC-CoNi@CNTs mixed-dimensional MCNCs exhibited excellent MA performances, which achieved a minimum reflection loss (RLmin) of -71.70 dB at 2.78 mm and Radar Cross section value of -53.23 dB m2. More importantly, the acquired results demonstrated that CoNi@NC-CoNi@CNTs MCNCs presented excellent photothermal, antimicrobial and anti-corrosion properties owing to their hierarchical cubic sea urchin-like yolk-shell structure, highlighting their potential multifunctional applications. It could be seen that this finding not only presented a generalizable route to produce hierarchical cubic sea urchin-like yolk-shell magnetic NC-CNTs-based mixed-dimensional MCNCs, but also provided an effective strategy to develop multifunctional MCNCs and improve their environmental adaptabilities.

Recent advances in developing nanoscale electro-/photocatalysts for hydrogen production: modification strategies, charge-carrier characterizations, and applications

For clean hydrogen (H2) production, electrocatalysis and photocatalysis are widely regarded as promising technologies to counter the increasing energy crisis. However, developing applicable catalysts with high H2 production performances still poses a challenge. In this review, state-of-the-art nanoscale electrocatalysts for water electrolysis and photocatalysts for water splitting, tailored for different reaction environments, including acidic electrolytes, alkaline electrolytes, pure water, seawater, and hydrohalic acids, are systematically presented. In particular, modification approaches such as doping, morphology control, heterojunction/homojunction construction, as well as the integration of cocatalysts and single atoms for efficient charge transfer and separation are examined. Furthermore, the unique properties of these upgraded catalysts and the mechanisms of promoted H2 production are also analyzed by elucidating the charge carrier dynamics revealed by photophysical and photoelectrochemical characterization methods. Finally, perspectives and outlooks on future developments for H2 production using advanced electrocatalysts and photocatalysts are proposed.

Synergistic Interfacial Effect of Ru/Co3O4 Heterojunctions for Boosting Overall Water Splitting

Low-cost bifunctional electrocatalysts capable of efficiently driving the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are needed for the growth of a green hydrogen economy. Herein, a Ru/Co3O4 heterojunction catalyst rich in oxygen vacancies (VO) and supported on carbon cloth (RCO-VO@CC) is prepared via a solid phase reaction (SPR) strategy. A RuO2/Co9S8@CC precursor (ROC@CC) is first prepared by loading Co9S8 nanosheets onto CC, following the addition of RuO2 nanoparticles (NPs). After the SPR process in an Ar atmosphere, Ru/Co3O4 heterojunctions with abundant VO are formed on the CC. The compositionally optimized RCO-VO@CC electrocatalyst with a Ru content of 0.55 wt.% exhibits very low overpotential values of 11 and 253 mV at 10 mA cm-2 for HER and OER, respectively, in 1 m KOH. Further, a low cell voltage of only 1.49 V is required to achieve a current density of 10 mA cm-2. Density functional theoretical calculations verify that the outstanding bifunctional electrocatalytic performance originates from synergistic charge transfer between Ru metal and VO-rich Co3O4. This work reports a novel approach toward a high-efficiency HER/OER electrocatalyst for energy storage and conversion.

Electrochemically Induced Ru/CoOOH Synergistic Catalyst as Bifunctional Electrode Materials for Alkaline Overall Water Splitting

Efficient and affordable price bifunctional electrocatalysts based on transition metal oxides for oxygen and hydrogen evolution reactions have a balanced efficiency, but it remains a significant challenge to control their activity and durability. Herein, a trace Ru (0.74 wt.%) decorated ultrathin CoOOH nanosheets (≈4 nm) supported on the surface of nickel foam (Ru/CoOOH@NF) is rationally designed via an electrochemically induced strategy to effectively drive the electrolysis of alkaline overall water splitting. The as-synthesized Ru/CoOOH@NF electrocatalysts integrate the advantages of a large number of different HER (Ru nanoclusters) and OER (CoOOH nanosheets) active sites as well as strong in-suit structure stability, thereby exhibiting exceptional catalytic activity. In particular, the ultra-low overpotential of the HER (36 mV) and the OER (264 mV) are implemented to achieve 10 mA cm-2. Experimental and theoretical calculations also reveal that Ru/CoOOH@NF possesses high intrinsic conductivity, which facilitates electron release from H2O and H-OH bond breakage and accelerates electron/mass transfer by regulating the charge distribution. This work provides a new avenue for the rational design of low-cost and high-activity bifunctional electrocatalysts for large-scale water-splitting technology and expects to help contribute to the creation of various hybrid electrocatalysts.

Molten-Salt Electrochemical Preparation of Co2B/MoB2 Heterostructured Nanoclusters for Boosted pH-Universal Hydrogen Evolution

Boosting the hydrogen evolution reaction (HER) activity of α-MoB2 at large current densities and in pH-universal medium is significant for efficient hydrogen production. In this work, Co2B/MoB2 heterostructured nanoclusters are prepared by molten-salt electrolysis (MSE) and then used as a HER catalyst. The composition, structure, and morphology of Co2B/MoB2 can be modulated by altering the stoichiometries of raw materials and synthesis temperatures. Impressively, the obtained Co2B/MoB2 at optimized conditions exhibits a low overpotential of 297 and 304 mV at 500 mA cm-2 in 0.5 m H2SO4 and 1 m KOH, respectively. Moreover, the Co2B/MoB2 catalyst possesses a long-term catalytic stability of over 190 h in both acidic and alkaline medium. The excellent HER performance is due to the modified electronic structure at the Co2B/MoB2 heterointerface where electrons are accumulated at the Mo sites to strengthen the H adsorption. Density functional theory (DFT) calculations reveal that the formation of the Co2B/MoB2 heterointerface decreases the H adsorption and H2O dissociation free energies, contributing to the boosted HER intrinsic catalytic activity of Co2B/MoB2. Overall, this work provides an experimental and theoretical paradigm for the design of efficient pH-universal boride heterostructure electrocatalysts.

Unveiling the nature of Pt-induced anti-deactivation of Ru for alkaline hydrogen oxidation reaction

While Ru owns superior catalytic activity toward hydrogen oxidation reaction and cost advantages, the catalyst deactivation under high anodic potential range severely limits its potential to replace the Pt benchmark catalyst. Unveiling the deactivation mechanism of Ru and correspondingly developing protection strategies remain a great challenge. Herein, we develop atomic Pt-functioned Ru nanoparticles with excellent anti-deactivation feature and meanwhile employ advanced operando characterization tools to probe the underlying roles of Pt in the anti-deactivation. Our studies reveal the introduced Pt single atoms effectively prevent Ru from oxidative passivation and consequently preserve the interfacial water network for the critical H* oxidative release during catalysis. Clearly understanding the deactivation nature of Ru and Pt-induced anti-deactivation under atomic levels could provide valuable insights for rationally designing stable Ru-based catalysts for hydrogen oxidation reaction and beyond.

Multi-d Electron Synergy in LaNi1-x Cox Ru Intermetallics Boosts Electrocatalytic Hydrogen Evolution

Despite the fact that d-band center theory links the d electron structure of transition metals to their catalytic activity, it is yet unknown how the synergistic effect of multi-d electrons impacts catalytic performance. Herein, novel LaNi1-x Cox Ru intermetallics containing 5d, 4d, and 3d electrons were prepared. In these compounds, the 5d orbital of La transfers electrons to the 4d orbital of Ru, which provides adsorption sites for H*. The 3d orbitals of Ni and Co interact with the 5d and 4d orbitals to generate an anisotropic electron distribution, which facilitates the adsorption and desorption of OH*. The synergistic effect of multi-d electrons ensures efficient catalytic activity. The optimized LaNi0.5 Co0.5 Ru has an overpotential of 43mV at 10 mA cm-2 for alkaline electrocatalytic hydrogen evolution reaction. Beyond offering a variety of new electrocatalysts, this work reveals the multi-d electron synergy in promoting catalytic reaction.

Frank Partial Dislocations in Coplanar Ir/C Ultrathin Nanosheets Boost Hydrogen Evolution Reaction

Developing highly active and stable acidic hydrogen evolution catalysts is of great significance and challenge for the long-term operation of commercial proton exchange membrane (PEM) electrolyzers. In this work, coplanar ultrathin nanosheets composed of rich-Frank partial dislocations (FPDs) are first synthesized. Ir nanoparticles and carbon (Dr-Ir/C NSs) use a nonequilibrium high-temperature thermal shock method (>1200 °C) and KBr template-assisted techniques. Dr-Ir/C NSs exhibit excellent hydrogen evolution reaction (HER) performance with a remarkably high mass activity of 6.64 A mg-1 at 50 mV, which is among the best Ir-based catalysts.In addition, Dr-Ir/C NSs are able to operate stably at 1.0 A cm-2 for 200 h as a cathode in a PEM electrolyser, and the original coplanar ultrathin nanosheets structure are maintained after the test, demonstrating excellent stability against stacking and agglomeration. Geometrical phase analysis and theoretical calculations show that the FPDs produce a 4% compressive strain in the Dr-Ir/C NSs, and the compressive strain weaken the adsorption of H* by Ir, thus increasing the intrinsic activity of the catalyst.

Recent progress in the development of advanced support materials for electrocatalysis

Electrocatalytic materials are pivotal for clean chemical production and energy conversion in devices like electrolyzers and fuel cells. These materials usually consist of metallic nanoparticles which serve as active reaction sites, and support materials which provide high surface area, conductivity and stability. When designing novel electrocatalytic composites, the focus is often on the metallic sites, however, the significance of the support should not be overlooked. Carbon materials, valued for their conductivity and large surface area, are commonly used as support in benchmark electrocatalysts. However, using alternative support materials instead of carbon can be beneficial in certain cases. In this minireview, we summarize recent advancements and key directions in developing novel supports for electrocatalysis, encompassing both carbon and non-carbon materials.

Engineering Morphology and Electron Redistribution of a Ni/WO3 Mott-Schottky Bifunctional Electrocatalyst for Efficient Alkaline Urea Splitting

Construction of the desired morphology and nanointerface to expose the active sites and modulate the electronic structure offers an effective approach to boosting urea splitting for energy-saving hydrogen generation. Herein, we fabricate a Ni/WO3 Mott-Schottky heterojunction electrocatalyst with a hedgehog-like structure supported on Ni foam toward alkaline urea splitting. Different Ni/WO3 morphologies, such as microspheres, hedgehog-like structures, octahedrons, and cubes, were obtained when various ratios of Ni/W feeds were used. The Mott-Schottky nanointerfaces between Ni and WO3 domains are visually confirmed by high-resolution transmission electron microscopy images, which also accelerated the charge transfer rate. Benefiting from the high electrochemically active surface area and enhanced charge transferability, the optimal Ni/WO3 electrode exhibits outstanding catalytic activity toward hydrogen generation with a low overpotential of 163 mV at 100 mA cm-2 in alkaline solution and reduced cell voltage of 1.67 V when coupled with urea oxidation reaction. Theoretical calculations reveal that the Ni sites in Ni/WO3 optimize the H adsorption energy (ΔGH*) with the |ΔGH*| value of 0.097 eV, much lower than that of Ni (0.35 eV) and WO3 (0.235 eV). This work demonstrates important guidance in designing an efficient electrocatalyst for urea splitting.

Machine Learning-Assisted Low-Dimensional Electrocatalysts Design for Hydrogen Evolution Reaction

Efficient electrocatalysts are crucial for hydrogen generation from electrolyzing water. Nevertheless, the conventional "trial and error" method for producing advanced electrocatalysts is not only cost-ineffective but also time-consuming and labor-intensive. Fortunately, the advancement of machine learning brings new opportunities for electrocatalysts discovery and design. By analyzing experimental and theoretical data, machine learning can effectively predict their hydrogen evolution reaction (HER) performance. This review summarizes recent developments in machine learning for low-dimensional electrocatalysts, including zero-dimension nanoparticles and nanoclusters, one-dimensional nanotubes and nanowires, two-dimensional nanosheets, as well as other electrocatalysts. In particular, the effects of descriptors and algorithms on screening low-dimensional electrocatalysts and investigating their HER performance are highlighted. Finally, the future directions and perspectives for machine learning in electrocatalysis are discussed, emphasizing the potential for machine learning to accelerate electrocatalyst discovery, optimize their performance, and provide new insights into electrocatalytic mechanisms. Overall, this work offers an in-depth understanding of the current state of machine learning in electrocatalysis and its potential for future research.

Bimetallic RuNi Electrocatalyst Coated MWCNTs Cathode for an Efficient and Stable Li-CO2 and Li-CO2 Mars Batteries Performance with Low Overpotential

Rechargeable lithium-CO2 (Li-CO2 ) batteries are an attractive energy storage technology that can reduce fossil fuel usage and limit the adverse environmental impact of CO2 emissions. However, the high charge overpotential, unstable cycling, and incomplete understanding of the electrochemical process limit its advancement for practical applications. Herein, we develop a Li-CO2 battery by designing a bimetallic ruthenium-nickel catalyst onto multi-walled carbon nanotubes (RuNi/MWCNTs) catalyst as cathode by solvothermal method, which exhibits a lower overpotential of 1.15 V and a discharge capacity of 15,165 mAh g-1 with outstanding coulombic efficiency of 97.4 %. The battery can also operate at high rates and have a stable cycle of more than 80 cycles at a current density of 200 mA g-1 with a fixed 500 mAh g-1 capacity. Furthermore, Mars exploration is made feasible with the Li-CO2 Mars battery composed of the RuNi/MWCNTs as cathode catalyst, which performs very similarly to that of pure CO2 atmosphere. This approach may simplify the process of developing high-performance Li-CO2 batteries to achieve carbon negativity on Earth and for future interplanetary Mars missions.

Phosphorus-induced activation of Ir metallene for efficient acidic overall water electrolysis

In this work, we synthesize P-doped Ir metallene (P-Ir metallene) with rich defects as a highly active bifunctional catalyst towards the hydrogen evolution reaction and oxygen evolution reaction, requiring overpotentials of 28 and 279 mV to drive 10 mA cm-2 in 0.5 M H2SO4, respectively. Moreover, P-Ir metallene exhibits excellent electrocatalytic performance for overall water splitting, producing hydrogen at 10 mA cm-2 with a low operation voltage of 1.508 V. This study proposes the incorporation of phosphorus into noble metals to improve the electrocatalytic performance for water splitting.

Synergistic Effect of Dual-Doped Carbon on Mo2C Nanocrystals Facilitates Alkaline Hydrogen Evolution

Molybdenum carbide (Mo2C) materials are promising electrocatalysts with potential applications in hydrogen evolution reaction (HER) due to low cost and Pt-like electronic structures. Nevertheless, their HER activity is usually hindered by the strong hydrogen binding energy. Moreover, the lack of water-cleaving sites makes it difficult for the catalysts to work in alkaline solutions. Here, we designed and synthesized a B and N dual-doped carbon layer that encapsulated on Mo2C nanocrystals (Mo2C@BNC) for accelerating HER under alkaline condition. The electronic interactions between the Mo2C nanocrystals and the multiple-doped carbon layer endow a near-zero H adsorption Gibbs free energy on the defective C atoms over the carbon shell. Meanwhile, the introduced B atoms afford optimal H2O adsorption sites for the water-cleaving step. Accordingly, the dual-doped Mo2C catalyst with synergistic effect of non-metal sites delivers superior HER performances of a low overpotential (99 mV@10 mA cm-2) and a small Tafel slope (58.1 mV dec-1) in 1 M KOH solution. Furthermore, it presents a remarkable activity that outperforming the commercial 10% Pt/C catalyst at large current density, demonstrating its applicability in industrial water splitting. This study provides a reasonable design strategy towards noble-metal-free HER catalysts with high activity.

Electrochemically Grown Ultrathin Platinum Nanosheet Electrodes with Ultralow Loadings for Energy-Saving and Industrial-Level Hydrogen Evolution

Nanostructured catalyst-integrated electrodes with remarkably reduced catalyst loadings, high catalyst utilization and facile fabrication are urgently needed to enable cost-effective, green hydrogen production via proton exchange membrane electrolyzer cells (PEMECs). Herein, benefitting from a thin seeding layer, bottom-up grown ultrathin Pt nanosheets (Pt-NSs) were first deposited on thin Ti substrates for PEMECs via a fast, template- and surfactant-free electrochemical growth process at room temperature, showing highly uniform Pt surface coverage with ultralow loadings and vertically well-aligned nanosheet morphologies. Combined with an anode-only Nafion 117 catalyst-coated membrane (CCM), the Pt-NS electrode with an ultralow loading of 0.015 mgPt cm-2 demonstrates superior cell performance to the commercial CCM (3.0 mgPt cm-2), achieving 99.5% catalyst savings and more than 237-fold higher catalyst utilization. The remarkable performance with high catalyst utilization is mainly due to the vertically well-aligned ultrathin nanosheets with good surface coverage exposing abundant active sites for the electrochemical reaction. Overall, this study not only paves a new way for optimizing the catalyst uniformity and surface coverage with ultralow loadings but also provides new insights into nanostructured electrode design and facile fabrication for highly efficient and low-cost PEMECs and other energy storage/conversion devices.

Directed electron regulation promoted sandwich-like CoO@FeBTC/NF with p-n heterojunctions by gel electrodeposition for oxygen evolution reaction

Metal organic framework (MOF) is currently-one of the key catalysts for oxygen evolution reaction (OER), but its catalytic performance is severely limited by electronic configuration. In this study, cobalt oxide (CoO) on nickel foam (NF) was first prepared, which then wrapped it with FeBTC synthesized by ligating isophthalic acid (BTC) with iron ions by electrodeposition to obtain CoO@FeBTC/NF p-n heterojunction structure. The catalyst requires only 255 mV overpotential to reach a current density of 100 mA cm^-2, and can maintain 100 h long time stability at 500 mA cm^-2 high current density. The catalytic properties are mainly related to the strong induced modulation of electrons in FeBTC by holes in the p-type CoO, which results in stronger bonding and faster electron transfer between FeBTC and hydroxide. At the same time, the uncoordinated BTC at the solid-liquid interface ionizes acidic radicals which form hydrogen bonds with the hydroxyl radicals in solution, capturing them onto the catalyst surface for the catalytic reaction. In addition, CoO@FeBTC/NF also has strong application prospects in alkaline electrolyzers, which only needs 1.78 V to reach a current density of 1 A cm^-2, and it can maintain long-term stability for 12 h at this current. This study provides a new convenient and efficient approach for the control design of the electronic structure of MOF, leading to a more efficient electrocatalytic process.

Revealing the Crystal Phase-Activity Relationship on NiRu Alloy Nanoparticles Encapsulated in N-Doped Carbon towards Efficient Hydrogen Evolution Reaction

Adjusting the crystal phase of a metal alloy is an important method to optimize catalytic performance. However, detailed understanding about the phase-property relationship for the hydrogen evolution reaction (HER) is still limited. In this work, the crystal phase-activity relationship of NiRu nanoparticles is studied employing N-doped carbon shell coated NiRu nanoparticles with different phase contents. It is found that the NiRu@NC (mix) with both face-centred cubic (fcc) and thermodynamically unstable hexagonal close-packed (hcp) phase NiRu give the best HER performance. Further activity studies demonstrate that hcp NiRu has better HER performance, and NiRu@NC (mix) with rich (∼70 %) hcp phase presented outstanding performance with an overpotential of only 27 mV @ 10 mA ⋅ cm^-2 . The high HER activity of NiRu@NC (mix) is attributed to the formation of hcp phase. This finding indicates that the regulation of crystal structure can provide a new strategy for optimizing HER activity.

Facet Engineering of Advanced Electrocatalysts Toward Hydrogen/Oxygen Evolution Reactions

The crystal facets featured with facet-dependent physical and chemical properties can exhibit varied electrocatalytic activity toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) attributed to their anisotropy. The highly active exposed crystal facets enable increased mass activity of active sites, lower reaction energy barriers, and enhanced catalytic reaction rates for HER and OER. The formation mechanism and control strategy of the crystal facet, significant contributions as well as challenges and perspectives of facet-engineered catalysts for HER and OER are provided.

The electrocatalytic water splitting technology can generate high-purity hydrogen without emitting carbon dioxide, which is in favor of relieving environmental pollution and energy crisis and achieving carbon neutrality. Electrocatalysts can effectively reduce the reaction energy barrier and increase the reaction efficiency. Facet engineering is considered as a promising strategy in controlling the ratio of desired crystal planes on the surface. Owing to the anisotropy, crystal planes with different orientations usually feature facet-dependent physical and chemical properties, leading to differences in the adsorption energies of oxygen or hydrogen intermediates, and thus exhibit varied electrocatalytic activity toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this review, a brief introduction of the basic concepts, fundamental understanding of the reaction mechanisms as well as key evaluating parameters for both HER and OER are provided. The formation mechanisms of the crystal facets are comprehensively overviewed aiming to give scientific theory guides to realize dominant crystal planes. Subsequently, three strategies of selective capping agent, selective etching agent, and coordination modulation to tune crystal planes are comprehensively summarized. Then, we present an overview of significant contributions of facet-engineered catalysts toward HER, OER, and overall water splitting. In particular, we highlight that density functional theory calculations play an indispensable role in unveiling the structure–activity correlation between the crystal plane and catalytic activity. Finally, the remaining challenges in facet-engineered catalysts for HER and OER are provided and future prospects for designing advanced facet-engineered electrocatalysts are discussed.