Rationally Modulating the Functions of Ni3Sn2-NiSnOx Nanocomposite Electrocatalysts towards Enhanced Hydrogen Evolution Reaction

Surface Reconstruction of An Integrated CoO-Co2Mo3O8 Electrode Enabling Efficient Ampere-Level Hydrogen Evolution in Alkaline Water or Seawater

To accelerate the water dissociation in the Volmer step and alleviate the destruction of bubbles to the physical structure of catalysts during the alkaline hydrogen evolution, an integrated electrode of cobalt oxide and cobalt-molybdenum oxide grown on Ni foam, named CoO-Co2Mo3O8, is designed. This integrated electrode enhances the catalyst-substrate interaction confirmed by a micro-indentation tester, and thus hinders the destruction of the physical structure of catalysts caused by bubbles. Electrochemical testing shows the occurrence of a surface reconstruction of the integrated electrode, and CoO is transformed into Co(OH)2, denoted as Co(OH)2-Co2Mo3O8. Theoretical calculations determine that Co(OH)2-Co2Mo3O8 has significantly low activation barrier for water dissociation and presents easy hydroxide desorption, which accelerate the catalytic reaction. Electrochemical experiments show that Co(OH)2-Co2Mo3O8 exhibits outstanding activity, reaching current density values of -100 and -1000 mA cm-2 with overpotentials only 57.8 and 195.8 mV, respectively. Furthermore, it demonstrates excellent stability at -500 and -1000 mA cm-2 for 200 h. Combined with the previously reported anode, the two-electrode system also provides the stable operation from 100 to 1000 mA cm-2 for 600 h in alkaline solution, and over 200 h at 500 and 1000 mA cm-2 in alkaline seawater.

Partially Interstitial Silicon-Implanted Ruthenium as an Efficient Electrocatalyst for Alkaline Hydrogen Evolution

To enhance the alkaline hydrogen evolution reaction (HER), it is crucial, yet challenging, to fundamentally understand and rationally modulate potential catalytic sites. In this study, we confirm that despite calculating a low water dissociation energy barrier and an appropriate H adsorption free energy (ΔG*H) at Ru-top sites, metallic Ru exhibits a relatively inferior activity for the alkaline HER. This is primarily because the Ru-top sites, which are potential H adsorption sites, are recessive catalytic sites, compared with the adjacent Ru-hollow sites that have a strong ΔG*H. To promote the transformation of Ru-top sites from recessive to dominant catalytic sites, interstitial Si atoms are implanted into the hollow sites. However, complete interstitial implantation leads to a high water dissociation energy barrier at the RuSi intermetallic surface. Thus, we present a partial interstitial incorporation strategy to form a Ru-RuSi heterostructure that not only converts the Ru-top sites from recessive to dominant catalytic sites but also preserves the low water dissociation energy barrier at the Ru surface. Moreover, the spontaneously formed built-in electric fields bidirectionally optimize the adsorption ability of the Ru sites, thereby greatly reducing the thermodynamic energy barrier and enhancing the alkaline HER.

Review of Ni-Based Materials for Industrial Alkaline Hydrogen Production

Hydrogen has been recognized as a green energy carrier, which can relieve energy shortage and environmental pollution. Currently, alkaline water electrolysis (AWE) driven by renewable energy to produce large-scale green hydrogen is a mainstream technology. However, tardy cathodic hydrogen evolution reaction (HER) and stability issue of catalysts make it challenging to meet the industrial requirements. Ni-based materials have attracted wide attention, thanks to their low cost and rich tuning possibilities, and many efforts have focused on their activity and stability. However, due to the significant discrepancy between laboratory and industrial conditions, these catalysts have not been widely deployed in industrial AWE. In this review, we first introduce the differences between laboratory and industrial stage, especially concerning equipment, protocols and evaluation metrics. To shorten these gaps, some strategies are proposed to improve the activity and stability of the Ni-based catalysts. Besides, some key issues related to the catalysts in industrial AWE device are also emphasized, including reverse-current and foreign ions in the electrolyte. Finally, the challenges and outlooks on the industrial alkaline AWE are discussed.

Yttrium-doped NiMo-MoO2 heterostructure electrocatalysts for hydrogen production from alkaline seawater

Active and stable electrocatalysts are essential for hydrogen production from alkaline water electrolysis. However, precisely controlling the interaction between electrocatalysts and reaction intermediates (H2O*, H*, and *OH) remains challenging. Here, we demonstrate an yttrium-doped NiMo-MoO2 heterogenous electrocatalyst that efficiently promotes water dissociation and accelerates the intermediate adsorption/desorption dynamics in alkaline electrolytes. Introducing yttrium into the NiMo/MoO2 heterostructure induces lattice expansion and optimizes the d-band center of NiMo alloy component, enhancing water dissociation and H* desorption. Yttrium doping also increases the concentration of oxygen vacancies in MoO2-x, which in turn accelerates the charge kinetics and the swift evacuation of *OH intermediates from the active sites. Consequently, the Y-NiMo/MoO2-x heterostructure exhibits notable performance by requiring only 189 and 220 mV overpotentials to achieve current density of 2.0 A cm-2 in alkaline water and seawater, respectively. This work provides a strategy to modulate heterostructure catalysts for scalable, economically viable hydrogen production from low-quality waters.

High Mass Transfer Rate in Electrocatalytic Hydrogen Evolution Achieved with Efficient Quasi-Gas Phase System

The adhesion of H2 bubbles on the electrode surface is one of the main factors limiting the performance of H2 evolution of electrolytic water, especially at high current density. To overcome this problem, here a "quasi-gas phase" electrolytic water reaction system based on capillary effect is proposed for the first time to improve the mass transfer efficiency of H2. The typical feature of this reaction system is that the main site of H2 evolution reaction is transferred from the bulk aqueous solution to the gas phase environment above the bulk aqueous solution, thus effectively inhibiting the aggregation of H2 bubbles and reducing the resistance of their diffusion away. Electrochemical test results show that the proposed quasi-gas phase system can significantly reduce the potential required in H2 evolution reaction process at high current density compared with the conventional electrolytic reaction system. Specifically, the overpotential potential is reduced by 0.31 V when the H2 evolution current density of 250 mA cm-2 is achieved.

Mo Migration-Induced Crystalline to Amorphous Conversion and Formation of RuMo/NiMoO4 Heterogeneous Nanoarray for Hydrazine-Assisted Water Splitting at Large Current Density

Manipulating the atomic structure of the catalyst and tailoring the dissociative water-hydrogen bonding network at the catalyst-electrolyte interface is essential for propelling alkaline hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR), but remains a great challenge. Herein, we constructed an advanced a-RuMo/NiMoO4/NF heterogeneous electrocatalyst with amorphous RuMo alloy nanoclusters anchored to amorphous NiMoO4 skeletons on Ni foam by a heteroatom implantation strategy. Theoretical calculations and in situ Raman tests show that the amorphous and alloying structure of a-RuMo/NiMoO4/NF not only induces the directional evolution of interfacial H2O, but also lowers the d-band center (from -0.43 to -2.22 eV) of a-RuMo/NiMoO4/NF, the Gibbs free energy of hydrogen adsorption (ΔGH*, from -1.29 to -0.06 eV), and the energy barrier of HzOR (ΔGN2(g)=1.50 eV to ΔGN2*=0.47 eV). Profiting from these favorable factors, the a-RuMo/NiMoO4/NF exhibits excellent electrocatalytic performances, especially at large current densities, with an overpotential of 13 and 129 mV to reach 10 and 1000 mA cm-2 for HER. While for HzOR, it needs only -91 and 276 mV to deliver 10 and 500 mA cm-2, respectively. Further, the constructed a-RuMo/NiMoO4/NF||a-RuMo/NiMoO4/NF electrolyzer demands only 7 and 420 mV to afford 10 and 500 mA cm-2.

The Interfacial Ni/Fe─O─Y Bonds Contribute to High-Efficiency Water Splitting

Developing economical and efficient electrocatalysts is critical for hydrogen energy industrialization through water electrolysis. Herein, a novel dual-site synergistic NiFe/Y2O3 hybrid with abundant interfacial Ni/Fe─O─Y bonds is designed by density functional theory (DFT) simulations. In situ Raman spectra combined with DFT calculations reveal that the interfacial Ni/Fe─O─Y units greatly promote H2O dissociation and optimize the adsorption of both H* and oxygen species, achieving excellent activity and durability for hydrogen evolution reaction. As expected, NiFe/Y2O3 exhibits a low overpotential of 27 mV at 10 mA cm-2 and robust stability of over 200 h at 1000 mA cm-2, and also outstanding water splitting performance with a low cell voltage of 1.64 V at 100 mA cm-2, showing significant potential for real-world applications.

Alkaline Hydrogen Evolution Reaction Electrocatalysts for Anion Exchange Membrane Water Electrolyzers: Progress and Perspective

For the aim of achieving the carbon-free energy scenario, green hydrogen (H2) with non-CO2 emission and high energy density is regarded as a potential alternative to traditional fossil fuels. Over the last decades, significant breakthroughs have been realized on the alkaline hydrogen evolution reaction (HER), which is a fundamental advancement and efficient process to generate high-purity H2 in the laboratory. Based on this, the development of the practical industry-oriented anion exchange membrane water electrolyzer (AEMWE) is on the rise, showing competitiveness with the incumbent megawatt-scale H2 production technologies. Still, great challenges lie in exploring the electrocatalysts with remarkable activity and stability for alkaline HER, as well as bridging the gap of performance difference between the three-electrode cell and AEMWE devices. In this perspective, we systematically discuss the in-depth mechanisms for activating alkaline HER electrocatalysts, including electronic modification, defect construction, morphology control, synergistic function, field effect, etc. In addition, the current status of AEMWE is reviewed, and the underlying bottlenecks that impede the application of HER electrocatalysts in AEMWE are summarized. Finally, we share our thoughts regarding the future development directions of electrocatalysts toward both alkaline HER and AEMWE, in the hope of advancing the commercialization of water electrolysis technology for green H2 production.

Independent Control Over the H/OH Adsorption: Breaking the Trade-Off Between H/OH-Adsorption and H2O-Dissociation of Platinum-Group Metal Electrocatalyst for Hydrogen Evolution Reaction

Platinum-group metals catalysts (such as Rh, Pd, Ir, Pt) have been the most efficient hydrogen evolution reaction (HER) electrocatalysts due to their moderate H adsorption strength, while the high H2O-dissociation barrier in alkaline media restrains the catalytic performance of PGM catalysts. However, the optimization of the H2O-dissociation barrier and *H/*OH binding energy toward their individual optima is limited due to the constraints of their scaling relationship on a single active site. Here, a coordinatively unsaturated "M─Ox─W" (M = Rh, Pd, Ir, Pt) active area is constructed, where H and OH species are anchored on Pt-group metal sites and inactive W sites for individual regulation. By combining experiments and density functional theory calculations, the introduction of extra OH-adsorption sites (coordinatively unsaturated WO3-x) avoids the competitive adsorption of H and OH on the single site, while the enhanced OH-adsorption capacity on the coordinatively unsaturated WO3-x effectively facilitates the adsorption/dissociation of interfacial H2O. As a result, the representative Rh-WO3-x catalyst exhibits outstanding catalytic activity and durability for HER. The findings of this work not only provide valuable insights for the design of efficient PGM catalysts for HER but also shed light on the development of electrocatalysts for other catalytic reactions.

Vanadium-Doped Heterointerfaced Ni3N-MoOx Nanosheets with Optimized H and H2O Adsorption for Effective Alkaline Hydrogen Electrocatalysis

Nickel (Ni)-based materials represent a compelling avenue as platinum alternatives in the realm of alkaline hydrogen electrocatalysis. However, conventional nickel nitrides (Ni3N) have long been hindered by sluggish hydrogen evolution kinetics in alkaline environments, owing to inadequate adsorption strengths of both hydrogen and water molecules. Herein, a novel approach is presented involving the design of vanadium (V)-doped Ni3N/MoOx heterogeneous nanosheets (V-Ni3N@MoOx), engineered to achieve optimized adsorption strengths for hydrogen evolution and oxidation reactions (HER/HOR). Theoretical insights underscore the superior catalytic performance of this composite, attributed to a synergistic interplay between unique V doping and the heterointerfaced structure. This synergistic effect not only fine-tunes the electronic structure, establishing an optimal d band center to mitigate proton over-bonding, but also ameliorates the energy barrier through enhanced H2O dissociation capability. Consequently, V-Ni3N@MoOx manifests remarkable catalytic activities, evincing an overpotential of 56 mV at 10 mA cm-2 for HER and an exchange current density of 1.91 mA cm-2 for HOR in alkaline media. Notably, the stability assessment reveals the enduring performance of V-Ni3N@MoOx for HER/HOR, exhibiting no activity decay over extended operational durations. This study underscores the efficacy of heterogeneous interface modulation as a transformative strategy in designing Ni-based materials for alkaline hydrogen electrocatalysis.

Positively Charged Hollow Co Nanoshells by Kirkendall Effect Stabilized by Electron Sink for Alkaline Water Dissociation

While cobalt (Co) exhibits a comparable energy barrier for H* adsorption/desorption to platinum in theory, it is generally not suitable for alkaline hydrogen evolution reaction (HER) because of unfavorable water dissociation. Here, the Kirkendall effect is adopted to fabricate positive-charged hollow metal Co (PHCo) nanoshells that are stabilized by MoO2 and chainmail carbon as the electron sink. Compared to the zero-valent Co, the PHCo accelerates the water dissociation and changes the rate-determining step from Volmer to Heyrovsky process. Alkaline HER occurs with a low overpotential of 59.0 mV at 10 mA cm-2. Operando Raman and first principles calculations reveal that the interfacial water to the PHCo sites and the accelerated proton transfer are conducive to the adsorption and dissociation of H2O molecules. Meanwhile, the upshifted d-band center of PHCo optimizes the adsorption/desorption of H*. This work provides a unique synthesis of hollow Co nanoshells via the Kirkendall effect and insights to water dissociation on catalyst surfaces with tailored charge states.

Lattice Strain with Stabilized Oxygen Vacancies Boosts Ceria for Robust Alkaline Hydrogen Evolution Outperforming Benchmark Pt

Earth-abundant metal oxides are usually considered as stable but catalytically inert toward hydrogen evolution reaction (HER) due to their unfavorable hydrogen intermediate adsorption performance. Herein, a heavy rare earth (Y) and transition metal (Co) dual-doping induced lattice strain and oxygen vacancy stabilization strategy is proposed to boost CeO2 toward robust alkaline HER. The induced lattice compression and increased oxygen vacancy (Ov) concentration in CeO2 synergistically improve the water dissociation on Ov sites and sequential hydrogen adsorption at activated Ov-neighboring sites, leading to significantly enhanced HER kinetics. Meanwhile, Y doping offers stabilization effect on Ov by its stronger Y─O bonding over Ce─O, which endows the catalyst with excellent stability. The Y,Co-CeO2 electrocatalyst exhibits an ultra-low HER overpotential (27 mV at 10 mA cm-2) and Tafel slope (48 mV dec-1), outperforming the benchmark Pt electrocatalyst. Moreover, the anion exchange membrane water electrolyzer incorporated with Y,Co-CeO2 achieves excellent stability of 500 h under 600 mA cm-2. This synergistic lattice strain and oxygen vacancy stabilization strategy sheds new light on the rational development of efficient and stable oxide-based HER electrocatalysts.

Engineering interfacial sulfur migration in transition-metal sulfide enables low overpotential for durable hydrogen evolution in seawater

Hydrogen production from seawater remains challenging due to the deactivation of the hydrogen evolution reaction (HER) electrode under high current density. To overcome the activity-stability trade-offs in transition-metal sulfides, we propose a strategy to engineer sulfur migration by constructing a nickel-cobalt sulfides heterostructure with nitrogen-doped carbon shell encapsulation (CN@NiCoS) electrocatalyst. State-of-the-art ex situ/in situ characterizations and density functional theory calculations reveal the restructuring of the CN@NiCoS interface, clearly identifying dynamic sulfur migration. The NiCoS heterostructure stimulates sulfur migration by creating sulfur vacancies at the Ni3S2-Co9S8 heterointerface, while the migrated sulfur atoms are subsequently captured by the CN shell via strong C-S bond, preventing sulfide dissolution into alkaline electrolyte. Remarkably, the dynamically formed sulfur-doped CN shell and sulfur vacancies pairing sites significantly enhances HER activity by altering the d-band center near Fermi level, resulting in a low overpotential of 4.6 and 8 mV at 10 mA cm-2 in alkaline freshwater and seawater media, and long-term stability up to 1000 h. This work thus provides a guidance for the design of high-performance HER electrocatalyst by engineering interfacial atomic migration.

Next-Generation Green Hydrogen: Progress and Perspective from Electricity, Catalyst to Electrolyte in Electrocatalytic Water Splitting

Green hydrogen from electrolysis of water has attracted widespread attention as a renewable power source. Among several hydrogen production methods, it has become the most promising technology. However, there is no large-scale renewable hydrogen production system currently that can compete with conventional fossil fuel hydrogen production. Renewable energy electrocatalytic water splitting is an ideal production technology with environmental cleanliness protection and good hydrogen purity, which meet the requirements of future development. This review summarizes and introduces the current status of hydrogen production by water splitting from three aspects: electricity, catalyst and electrolyte. In particular, the present situation and the latest progress of the key sources of power, catalytic materials and electrolyzers for electrocatalytic water splitting are introduced. Finally, the problems of hydrogen generation from electrolytic water splitting and directions of next-generation green hydrogen in the future are discussed and outlooked. It is expected that this review will have an important impact on the field of hydrogen production from water.

Enhancing Ni/Co Activity by Neighboring Pt Atoms in NiCoP/MXene Electrocatalyst for Alkaline Hydrogen Evolution

Density functional theory (DFT) calculations demonstrate neighboring Pt atoms can enhance the metal activity of NiCoP for hydrogen evolution reaction (HER). However, it remains a great challenge to link Pt and NiCoP. Herein, we introduced curvature of bowl-like structure to construct Pt/NiCoP interface by adding a minimal 1 ‰-molar-ratio Pt. The as-prepared sample only requires an overpotential of 26.5 and 181.6 mV to accordingly achieve the current density of 10 and 500 mA cm-2 in 1 M KOH. The water dissociation energy barrier (Ea) has a ~43 % decrease compared with NiCoP counterpart. It also shows an ultrahigh stability with a small degradation rate of 10.6 μV h-1 at harsh conditions (500 mA cm-2 and 50 °C) after 3000 hrs. X-ray photoelectron spectroscopy (XPS), soft X-ray absorption spectroscopy (sXAS), and X-ray absorption fine structure (XAFS) verify the interface electron transfer lowers the valence state of Co/Ni and activates them. DFT calculations also confirm the catalytic transition step of NiCoP can change from Heyrovsky (2.71 eV) to Tafel step (0.51 eV) in the neighborhood of Pt, in accord with the result of the improved Hads at the interface disclosed by in situ electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) tests.

Surface Reconstruction for Selective Oxidation of Tetrahydroisoquinoline

Integration of hydrogen evolution with the oxidation of organic substances in one electrochemical system is highly desirable. However, achieving selective oxidation of organic substances in the integrated system is still highly challenging. In this study, a phosphorylated NiMoO4 nanoneedle-like array was designed as the catalytic active electrode for the integration of highly selective electrochemical dehydrogenation of tetrahydroisoquinolines (THIQs) with hydrogen production. The leaching of anions, including MoO42- and PO43-, facilitates the reconstruction of the catalyst. As a result, nickel oxyhydroxides with the doping of PO43- and richness of defects are in situ formed. In situ Raman and density functional theory calculations have shown that the high catalytic activity is attributed to the in situ formed PO43- involved NiOOH substance. In the dehydrogenation process, the involved C-H bond but not the N-H bond is first destroyed. A two-electrode system was then fabricated with the optimized electrode that shows a benchmark current density of 10 mA cm-2 at 1.783 V, providing a yield of 70% for dihydroisoquinolines. A robust stability was also shown for this integrated electrochemical system. The understanding of the reconstruction behavior and the achievement of selective dehydrogenation will provide some hints for electrochemical synthesis.

Design Strategies towards Advanced Hydrogen Evolution Reaction Electrocatalysts at Large Current Densities

Hydrogen (H2), produced by water electrolysis with the electricity from renewable sources, is an ideal energy carrier for achieving a carbon-neutral and sustainable society. Hydrogen evolution reaction (HER) is the cathodic half-reaction of water electrolysis, which requires active and robust electrocatalysts to reduce the energy consumption for H2 generation. Despite numerous electrocatalysts have been reported by the academia for HER, most of them were only tested under relatively small current densities for a short period, which cannot meet the requirements for industrial water electrolysis. To bridge the gap between academia and industry, it is crucial to develop highly active HER electrocatalysts which can operate at large current densities for a long time. In this review, the mechanisms of HER in acidic and alkaline electrolytes are firstly introduced. Then, design strategies towards high-performance large-current-density HER electrocatalysts from five aspects including number of active sites, intrinsic activity of each site, charge transfer, mass transfer, and stability are discussed via featured examples. Finally, our own insights about the challenges and future opportunities in this emerging field are presented.

NiRu-Mo2Ti2C3O2 as an efficient catalyst for alkaline hydrogen evolution reactions: the role of bimetallic site interactions in promoting Volmer-step kinetics

The Volmer step in alkaline hydrogen evolution reactions (HERs), which supplies H* to the following steps by cleaving H-O-H bonds, is considered the rate-determining step of the overall reaction. The Volmer step involves water dissociation and adsorbed hydroxyl (*OH) desorption; Ru-based catalysts display a compelling water dissociation process in an alkaline HER. Unfortunately, the strong affinity of Ru for *OH blocks the active sites, resulting in unsatisfactory performance during HER processes. Hence, this study investigates a series of key descriptors (ΔG*H2O, ΔG*H-OH, ΔG*H, and ΔG*OH) of TM (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, or Pt)-Ru/Mo2Ti2C3O2 to systematically explore the effects of bimetallic site interactions on the kinetics of the Volmer step. The results indicate that bimetallic catalysts effectively reduced the strong adsorption of *OH on Ru sites; especially, the NiRu diatomic state shows the highest electron-donating ability, which promoted the smooth migration of *OH from Ru sites to Ni sites. Therefore, Ru, Ni and MXenes are suitable to serve as water adsorption and dissociation sites, *OH desorption sites, and H2 release sites, respectively. Ultimately, NiRu/Mo2Ti2C3O2 promotes Volmer kinetics and has the potential to improve alkaline HERs. This work provides theoretical support for the construction of synergistic MXene-based diatomic catalysts and their wide application in the field of alkaline HERs.

Light-driven assembly of Pt clusters on Mo-NiOx nanosheets to achieve Pt/Mo-NiOx hybrid with dense heterointerfaces and optimized charge redistribution for alkaline hydrogen evolution

Designing cost-effective alkaline hydrogen evolution reaction (HER) catalysts with high water dissociation ability, enhanced hydroxyl transfer rate and optimized hydrogen adsorption free energy (ΔGH*) by a time and energy efficient strategy is pivotal, but still challenging for alkaline water electrolysis. Herein, Pt/Mo-NiOx hybrid consisting of Pt clusters assembled on Mo-doped NiOx nanosheet arrays is prepared on the surface of raw NiMo foam (NMF) by a light-driven strategy to address this challenge. Benefitting from the electronic interaction between Mo-NiOx and Pt, the Pt/Mo-NiOx composite owns optimized ΔGH* and is beneficial for accelerating water dissociation and hydroxyl transfer. As a result, the optimized Pt/Mo-NiOx/NMF electrode displays an exceptional alkaline HER activity with a low overpotential of 62 mV to obtain 100 mA cm-2 and a high Pt mass activity (13.2 times as high as that of commercial 20 wt% Pt/C). Furthermore, the assembled two-electrode cell of Pt/Mo-NiOx/NMF||NiFe-LDH/NF requires a voltage of only 1.549 V to deliver 100 mA cm-2, along with negligible activity decay after 70 h stability test. The present study provides a promising strategy for exploiting high-performance electrocatalysts towards alkaline HER.

Orderly Nanodendritic Nickel Substitute for Raney Nickel Catalyst Improving Alkali Water Electrolyzer

The development of nonprecious metal catalysts to meet the activity-stability balance at industrial-grade large current densities remains a challenge toward practical alkali-water electrolysis. Here, this work develops an orderly nanodendritic nickel (ND-Ni) catalyst that consists of ultrafine nanograins in chain-like conformation, which shows both excellent activity and robust stability for large current density hydrogen evolution reaction (HER) in alkaline media, superior to currently applied Raney nickel (R-Ni) catalyst in commercial alkali-water electrolyzer (AWE). The ND-Ni catalyst featured by a three-dimensional (3D) interconnecting microporous structure endows with high specific surface area and excellent conductivity and hydrophilicity, which together afford superior charge/mass transport favorable to HER kinetics at high current densities. An actual AWE with ND-Ni catalyst demonstrates durable water splitting with 1.0 A cm-2 at 1.71 V under industrial conditions and renders a record-low power consumption of 3.95 kW h Nm-3 with an energy efficiency close to 90%. The hydrogen price per gallon of gasoline equivalent (GGE) is calculated to be ≈$0.95, which is less than the target of $2.0 per GGE by 2026 from the U.S. Department of Energy. The results suggest the feasibility of ND-Ni substitute for R-Ni catalyst in commercial AWE.

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.

Optimizing Pt-Based Alloy Electrocatalysts for Improved Hydrogen Evolution Performance in Alkaline Electrolytes: A Comprehensive Review

The splitting of water through electrocatalysis offers a sustainable method for the production of hydrogen. In alkaline electrolytes, the lack of protons forces water dissociation to occur before the hydrogen evolution reaction (HER). While pure Pt is the gold standard electrocatalyst in acidic electrolytes, since the 5d orbital in Pt is nearly fully occupied, when it overlaps with the molecular orbital of water, it generates a Pauli repulsion. As a result, the formation of a Pt-H* bond in an alkaline environment is difficult, which slows the HER and negates the benefits of using a pure Pt catalyst. To overcome this limitation, Pt can be alloyed with transition metals, such as Fe, Co, and Ni. This approach has the potential not only to enhance the performance but also to increase the Pt dispersion and decrease its usage, thus overall improving the catalyst's cost-effectiveness. The excellent water adsorption and dissociation ability of transition metals contributes to the generation of a proton-rich local environment near the Pt-based alloy that promotes HER. Significant progress has been achieved in comprehending the alkaline HER mechanism through the manipulation of the structure and composition of electrocatalysts based on the Pt alloy. The objective of this review is to analyze and condense the latest developments in the production of Pt-based alloy electrocatalysts for alkaline HER. It focuses on the modified performance of Pt-based alloys and clarifies the design principles and catalytic mechanism of the catalysts from both an experimental and theoretical perspective. This review also highlights some of the difficulties encountered during the HER and the opportunities for increasing the HER performance. Finally, guidance for the development of more efficient Pt-based alloy electrocatalysts is provided.

Enhanced Metal-Support Interactions Boost the Electrocatalytic Water Splitting of Supported Ruthenium Nanoparticles on a Ni3 N/NiO Heterojunction at Industrial Current Density

Developing highly efficient and stable hydrogen production catalysts for electrochemical water splitting (EWS) at industrial current densities remains a great challenge. Herein, we proposed a heterostructure-induced-strategy to optimize the metal-support interaction (MSI) and the EWS activity of Ru-Ni3 N/NiO. Density functional theory (DFT) calculations firstly predicted that the Ni3 N/NiO-heterostructures can improve the structural stability, electronic distributions, and orbital coupling of Ru-Ni3 N/NiO compared to Ru-Ni3 N and Ru-NiO, which accordingly decreases energy barriers and increases the electroactivity for EWS. As a proof-of-concept, the Ru-Ni3 N/NiO catalyst with a 2D Ni3 N/NiO-heterostructures nanosheet array, uniformly dispersed Ru nanoparticles, and strong MSI, was successfully constructed in the experiment, which exhibited excellent HER and OER activity with overpotentials of 190 mV and 385 mV at 1000 mA cm-2 , respectively. Furthermore, the Ru-Ni3 N/NiO-based EWS device can realize an industrial current density (1000 mA cm-2 ) at 1.74 V and 1.80 V under alkaline pure water and seawater conditions, respectively. Additionally, it also achieves a high durability of 1000 h (@ 500 mA cm-2 ) in alkaline pure water.