Precise tuning in platinum-nickel/nickel sulfide interface nanowires for synergistic hydrogen evolution catalysis

Enhancing electrochemical water-splitting efficiency with superaerophobic nickel-coated catalysts on Chinese rice paper

The quest for efficient hydrogen production highlights the need for cost-effective and high-performance catalysts to enhance the electrochemical water-splitting process. A significant challenge in developing self-supporting catalysts lies in the high cost and complex modification of traditional substrates. In this study, we developed catalysts featuring superaerophobic microstructures engineered on microspherical nickel-coated Chinese rice paper (Ni-RP), chosen for its affordability and exceptional ductility. These catalysts, due to their microspherical morphology and textured surface, exhibited significant superaerophobic properties, substantially reducing bubble adhesion. The nickel oxy-hydroxide (NiOxHy) and phosphorus-doped nickel (PNi) catalysts on Ni-RP demonstrated effective roles in oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), achieving overpotentials of 250 mV at 20 mA cm-2 and 87 mV at -10 mA cm-2 in 1 M KOH, respectively. Moreover, a custom water-splitting cell using PNi/Ni-RP and NiOxHy/Ni-RP electrodes reached an impressive average voltage of 1.55 V at 10 mA cm-2, with stable performance over 100 h in 1 M KOH. Our findings present a cost-effective, sustainable, and easily modifiable substrate that utilizes superaerophobic structures to create efficient and durable catalysts for water splitting. This work serves as a compelling example of designing high-performance self-supporting catalysts for electrocatalytic applications.

Tuning the Local Environment of Pt Species at CNT@MO2-x (M = Sn and Ce) Heterointerfaces for Boosted Alkaline Hydrogen Evolution

As the most promising hydrogen evolution reaction (HER) electrocatalysts, platinum (Pt)-based catalysts still struggle with sluggish kinetics and expensive costs in alkaline media. Herein, we accelerate the alkaline hydrogen evolution kinetics by optimizing the local environment of Pt species and metal oxide heterointerfaces. The well-dispersed PtRu bimetallic clusters with adjacent MO2-x (M = Sn and Ce) on carbon nanotubes (PtRu/CNT@MO2-x) are demonstrated to be a potential electrocatalyst for alkaline HER, exhibiting an overpotential of only 75 mV at 100 mA cm-2 in 1 M KOH. The excellent mass activity of 12.3 mA μg-1Pt+Ru and specific activity of 32.0 mA cm-2ECSA at an overpotential of 70 mV are 56 and 64 times higher than those of commercial Pt/C. Experimental and theoretical investigations reveal that the heterointerfaces between Pt clusters and MO2-x can simultaneously promote H2O adsorption and activation, while the modification with Ru further optimizes H adsorption and H2O dissociation energy barriers. Then, the matching kinetics between the accelerated elementary steps achieved superb hydrogen generation in alkaline media. This work provides new insight into catalytic local environment design to simultaneously optimize the elementary steps for obtaining ideal alkaline HER performance.

Realizing the Tailored Catalytic Performances on Atomic Pt-Promoted Transition Metal Moieties Implanted Layered Double Hydroxides for Water Electrolysis

High-performance production of green hydrogen gas is necessary to develop renewable energy generation technology and to safeguard the living environment. This study reports a controllable engineering approach to tailor the structure of nickel-layered double hydroxides via doped and absorbed platinum single atoms (PtSA) promoted by low electronegative transition metal (Mn, Fe) moieties (PtSA-Mn,Fe-Ni LDHs). We explore that the electron donation from neighboring transition metal moieties results in the well-adjusted d-band center with the low valence states of PtSA(doped) and PtSA(ads.), thus optimizing adsorption energy to effectively accelerate the H2 release. Meanwhile, a tailored local chemical environment on transition metal centers with unique charge redistribution and high valence states functions as the main center for H2O catalytic dissociation into oxygen. Therefore, the PtSA-Mn,Fe-Ni LDH material possesses a small overpotential of 42 and 288 mV to reach 10 mA·cm-2 for hydrogen and oxygen evolution, respectively, superior to most reported LDH-based catalysts. Additionally, the mass activity of PtSA-Mn,Fe-Ni LDHs proves to be 15.45 times higher than that of commercial Pt-C. The anion exchange membrane electrolyzer stack of PtSA-Mn,Fe-Ni LDHs(+,-) delivers a cell voltage of 1.79 V at 0.5 A·cm-2 and excellent durability over 600 h. This study presents a promising electrocatalyst for a practical water splitting process.

Modulating the electronic structure of VS2via Ru decoration for an efficient pH-universal electrocatalytic hydrogen evolution reaction

High-efficiency water electrolysis over a broad pH range is desirable but challenging. Herein, Ru-decorated VS2 on carbon cloth (Ru-VS2/CC) has been in situ synthesized, which features the regulated electronic structure of VS2 by introducing Ru. It is remarkable that the optimal Ru-VS2/CC displays excellent electrocatalytic hydrogen evolution activity with overpotentials of 89 and 87 mV at -10 mA cm-2 in 0.5 M H2SO4 and 1.0 M KOH, respectively. Theoretical calculations and electrocatalytic measurements have demonstrated that introducing Ru induces an enhanced charge density around the Fermi level, facilitating charge transfer and speeding up the electrocatalytic HER kinetics. The Gibbs free energy of the hydrogen intermediate (ΔGH*) of Ru-VS2/CC (0.23 eV) is much closer to zero than that of pure VS2 (0.51 eV) and Ru (-0.37 eV), demonstrating an easier hydrogen adsorption and desorption process for Ru-VS2/CC. The more favorable ΔGH*, differential charge density and the d-band center endow Ru-VS2 with enhanced intrinsic electrocatalytic activity. This study presents a feasible strategy for enhancing electrocatalytic HER activity by the regulation of the electronic structure and the rational integration of dual active components.

Crystalline nanosheets of three-dimensional supramolecular frameworks with uniform thickness and high stability

Fabricating three dimensional (3D) supramolecular frameworks (SMFs) into stable crystalline nanosheets remains a great challenge due to the homogeneous and weak inter-building block interactions along 3D directions. Herein, crystalline nanosheets of a 3D SMF with a uniform thickness of 4.8 ± 0.1 nm immobilized with Pt nanocrystals on the surface (Q[8]/Pt NSs) were fabricated via the solid-liquid reaction between cucurbit[8]uril/H2PtCl6 single crystals and hydrazine hydrate with the help of gas and heat yielded during the reaction process. A series of experiments and theoretical calculations reveal the ultrahigh stability of Q[8]/Pt NSs due to the high density hydrogen bonding interaction among neighboring Q[8] molecules. This in turn endows Q[8]/Pt NSs with excellent photocatalytic and continuous thermocatalytic CO oxidation performance, representing the thus-far reported best Pt nano-material-based catalysts.

Grafting Ultra-fine Nanoalloys with Amorphous Skin Enables Highly Active and Long-lived Acidic Hydrogen Production

Large-scale deployment of proton exchange membranes water electrolysis (PEM-WE) requires a substantial reduction in usage of platinum group metals (PGMs) as indispensable electrocatalyst for cathodic hydrogen evolution reaction (HER). Ultra-fine PGMs nanocatalysts possess abundant catalytic sites at lower loading, but usually exhibit reduced stability in long-term operations under corrosive acidic environments. Here we report grafting the ultra-fine PtRu crystalline nanoalloys with PtxRuySez "amorphous skin" (c-PtRu@a-PtxRuySez) by in situ atomic layer selenation to simultaneously improve catalytic activity and stability. We found that the c-PtRu@a-PtxRuySez-1 with ~0.6 nm thickness amorphous skin achieved an ultra-high mass activity of 26.7 A mg-1 Pt+Ru at -0.07 V as well as a state-of-the-art durability maintained for at least 1000 h at -10 mA cm-2 and 550 h at -100 mA⋅cm-2 for acid HER. Experimental and theoretical investigations suggested that the amorphous skin not only improved the electrochemical accessibility of the catalyst surface and increasing the intrinsic activity of the catalytic sites, but also mitigated the dissolution/diffusion of the active species, thus resulting in improved catalytic activity and stability under acidic electrolyte. This work demonstrates a direction of designing ultra-fine PGMs electrocatalysts both with high utilization and robust durability, offers an in situ "amorphous skin" engineering strategy.

In Situ Engineering Multifunctional Active Sites of Ruthenium-Nickel Alloys for pH-Universal Ampere-Level Current-Density Hydrogen Evolution

Developing robust non-platinum electrocatalysts with multifunctional active sites for pH-universal hydrogen evolution reaction (HER) is crucial for scalable hydrogen production through electrochemical water splitting. Here ultra-small ruthenium-nickel alloy nanoparticles steadily anchored on reduced graphene oxide papers (Ru-Ni/rGOPs) as versatile electrocatalytic materials for acidic and alkaline HER are reported. These Ru-Ni alloy nanoparticles serve as pH self-adaptive electroactive species by making use of in situ surface reconstruction, where surface Ni atoms are hydroxylated to produce bifunctional active sites of Ru-Ni(OH)2 for alkaline HER, and selectively etched to form monometallic Ru active sites for acidic HER, respectively. Owing to the presence of Ru-Ni(OH)2 multi-site surface, which not only accelerates water dissociation to generate reactive hydrogen intermediates but also facilitates their recombination into hydrogen molecules, the self-supported Ru90Ni10/rGOP hybrid electrode only takes overpotential of as low as ≈106 mV to deliver current density of 1000 mA cm-2, and maintains exceptional stability for over 1000 h in 1 m KOH. While in 0.5 m H2SO4, the Ru90Ni10/rGOP hybrid electrode exhibits acidic HER catalytic behavior comparable to commercially available Pt/C catalyst due to the formation of monometallic Ru shell. These electrochemical behaviors outperform some of the best Ru-based catalysts and make it attractive alternative to Pt-based catalysts toward highly efficient HER.

Ultrafine Ru nanoparticles stabilized by V8C7/C for enhanced hydrogen evolution reaction at all pH

The development of cost-effective electrocatalysts with high efficiency and long durability for hydrogen evolution reaction (HER) remains a great challenge in the field of water splitting. Herein, we design an ultrafine and highly dispersed Ru nanoparticles stabilized on porous V8C7/C matrix via pyrolysis of the metal-organic frameworks V-BDC (BDC: 1,4-benzenedicarboxylate). The obtained Ru-V8C7/C composite exhibits excellent HER performance in all pH ranges. At the overpotential of 40 mV, its mass activity is about 1.9, 4.1 and 9.4 times higher than that of commercial Pt/C in acidic, neutral and alkaline media, respectively. Meanwhile, Ru-V8C7/C shows the remarkably high stability in all pH ranges which, in particular, can maintain the current density of 10 mA cm-2 for over 150 h in 1.0 mol L-1 phosphate buffer saline (PBS). This outstanding HER performance can be attributed to the high intrinsic activity of Ru species and their strong interface interactions to the V8C7/C substrate. The synergistic effect of abundant active sites on the surface and the formed Ru-C-V units at the interface promotes the adsorption of reaction intermediates and the release of active sites, contributing the fast HER kinetics. This work provides a reference for developing versatile and robust HER catalysts by surface and interface regulation for pH tolerance.

Interfacial engineering of POM-stabilized Ni quantum dots on porous titanium mesh for high-rate and stable alkaline hydrogen production

The development of low-cost, high-efficiency, and stable electrocatalysts for the alkaline hydrogen evolution reaction (HER) is a key challenge because the alkaline HER kinetics is slowed by an additional water dissociation step. Herein, we report an interfacial engineering strategy for polyoxometalate (POM)-stabilized nickel (Ni) quantum dots decorated on the surface of porous titanium mesh (POMs-Ni@PTM) for high-rate and stable alkaline hydrogen production. Benefiting from the strong interfacial interactions among POMs, Ni atoms, and PTM substrates, as well as unique POM-Ni quantum dot structures, the optimized POMs-Ni@PTM electrocatalyst exhibits a remarkable alkaline HER performance with an overpotential (η10) of 30.1 mV to reach a current density of 10 mA cm-2, which is much better than those of bare Ni decorated porous titanium mesh (Ni@PTM) (η10 = 171.1 mV) and POM decorated porous titanium mesh (POMs@PTM) electrocatalysts (η10 = 493.6 mV), comparable to that of the commercial 20 wt% platinum/carbon (20% Pt/C) electrocatalyst (η10 = 20 mV). Moreover, the optimized POMs-Ni@PTM electrocatalyst demonstrates excellent stability under continuous alkaline water-splitting at a current density of ∼100 mA cm-2 for 100 h, demonstrating great potential for its practical application.

Boosting Efficient Alkaline Hydrogen Evolution Reaction of CoFe-Layered Double Hydroxides Nanosheets via Co-Coordination Mechanism of W-Doping and Oxygen Defect Engineering

While surface defects and heteroatom doping exhibit promising potential in augmenting the electrocatalytic hydrogen evolution reaction (HER), their performance remains unable to rival that of the costly Pt-based catalysts. Yet, the concurrent modification of catalysts by integrating both approaches stands as a promising strategy to effectively address the aforementioned limitation. In this work, tungsten dopants are introduced into self-supported CoFe-layered double hydroxides (LDH) on nickel foam using a hydrothermal method, and oxygen vacancies (Ov) are further introduced through calcination. The analysis results demonstrated that tungsten doping reduces the Ov formation energy of CoFeW-LDH. The Ov acted as oxophilic sites, facilitating water adsorption and dissociation, and reducing the barrier for cleaving HO─H bonds from 0.64 to 0.14 eV. Additionally, Ov regulated the electronic structure of CoFeW-LDH to endow optimized hydrogen binding ability on tungsten atoms, thereby accelerating alkaline Volmer and Heyrovsky reaction kinetics. Specifically, the abundance of Ov induced a transition of tungsten from a six-coordinated to highly active four-coordinated structure, which becomes the active site for HER. Consequently, an ultra-low overpotential of 41 mV at 10 mA cm-2 , and a low Tafel slope of 35 mV dec-1 are achieved. These findings offer crucial insights for the design of efficient HER electrocatalysts.

Schottky junction enhanced H2 evolution for graphitic carbon nitride-NiS composite photocatalysts

As one of the most promising photocatalysts for H2 evolution, graphitic carbon nitride (CN) has many appealing attributes. However, the activity of pristine CN remains unsatisfactory due to severe charge carrier recombination and lack of active sites. In this study, we report a two-step approach for the synthesis of CN nanotubes (TCN) loaded with NiS nanoparticles. The resulting composite photocatalysts gave a H2 evolution rate of 752.9 μmol g-1 h-1, which is 42.3 times higher compared to the pristine CN photocatalyst. Experimental and simulation results showed that the Schottky junction which was formed between TCN and NiS was key to achieving high activity. This is because the formation of Schottky junction prevented the backflow of electrons from NiS to TCN, which improved charge separation efficiency. More importantly, it also led to the accumulation of electrons on NiS, which significantly weakened the SH bond, such that the intermediate hydrogen species desorbed more easily from NiS surface to promote H2 evolution activity.

A review of modulation strategies for improving the catalytic performance of transition metal sulfide self-supported electrodes for the hydrogen evolution reaction

Electrocatalytic water splitting is considered to be one of the most promising technologies for large-scale sustained production of H2. Developing non-noble metal-based electrocatalytic materials with low cost, high activity and long life is the key to electrolysis of water. Transition metal sulfides (TMSs) with good electrical conductivity and a tunable electronic structure are potential candidates that are expected to replace noble metal electrocatalysts. In addition, self-supported electrodes have fast electron transfer and mass transport, resulting in enhanced kinetics and stability. In this paper, TMS self-supported electrocatalysts are taken as examples and their recent progress as hydrogen evolution reaction (HER) electrocatalysts is reviewed. The HER mechanism is first introduced. Then, based on optimizing the active sites, electrical conductivity, electronic structure and adsorption/dissociation energies of water and intermediates of the electrocatalysts, the article focuses on summarizing five modulation strategies to improve the activity and stability of TMS self-supported electrode electrocatalysts in recent years. Finally, the challenges and opportunities for the future development of TMS self-supported electrodes in the field of electrocatalytic water splitting are presented.

ZnO monolayer-supported single atom catalysts for efficient electrocatalytic hydrogen evolution reaction

Hydrogen is identified as one of the most promising sustainable and clean energy sources. The development of a hydrogen evolution reaction (HER) catalyst with high activity is essential to meet future needs. Considering the novel advantages of two-dimensional materials and the high catalytic activity of atomic transition metals, in this study, using density functional theory calculations, the HER on a single transition metal (10 different TM atoms) adsorbed and doped ZnO monolayer (ZnO-m) has been investigated. The Volmer-Tafel reaction mechanisms and strain engineering of the three best HER catalysts are also discussed. The results show that Pt@ZnO-m, Co-doped ZnO-m and Ir-doped ZnO-m with high stability all have a smaller absolute H adsorption free energy than Pt, and the optimal value of Pt@ZnO-m is -0.017 eV. The calculation of the reaction energy barriers shows that the Volmer-Tafel step is favorable. Co@ZnO-m and Ir@ZnO-m have high HER activity, the widest pH range, and acid-alkali resistance. Pt@ZnO-m and Co-doped ZnO-m maintain excellent HER performances in the strain range of -4% to 4%.

Boosting Alkaline Hydrogen Oxidation Activity of Ru Single-Atom Through Promoting Hydroxyl Adsorption on Ru/WC1- x Interfaces

The sluggish kinetics of the hydrogen oxidation reaction (HOR) in alkaline conditions continue to pose a significant challenge for the practical implementation of anion-exchange membrane fuel cells. Developing single-atom catalysts can accelerate the pace of new HOR catalyst discovery for highly cost-effective and active HOR performance. However, single-atom catalysts (SACs) for the alkaline HOR have rarely been reported, and fundamental studies on the rational design of SACs are still required. Herein, the design of Ru SAC supported on the tungsten carbide (Ru SA/WC1- x ) via in situ high-temperature annealing strategy is reported. The resulting Ru SA/WC1- x catalyst exhibits remarkably enhanced HOR performance in alkaline media, a level of activity that can not be achieved with carbon-supported Ru SAC. Electrochemical results and density functional theory demonstrate that promoting the hydroxyl adsorption on Ru SA/WC1- x interfaces, which is derived from the low potential of zero charge of WC1- x support, has a significant effect on enhancing the HOR performance of SACs. This enhancement leads to 5.8 and 60.1 times higher Ru mass activity of Ru SA/WC1- x than Ru nanoparticles on carbon and Ru single-atom on N-doped carbon, respectively. This work provides new insights into the design of highly active SACs for alkaline HOR.

Deformation twin traces on gold surfaces: A pathway to tailored epitaxial growth of 1D semiconductors

The field of one-dimensional semiconducting materials holds a wide variety of captivating applications, such as photovoltaic cells, electronic devices, catalysis cells, lasers, and more. The tunability of electrical, mechanical, or optical attributes of a semiconductor crystal relies on the ability to control and pattern the crystal's growth direction, orientation, and dimensions. In this study, we harvest the unique properties of crystallographic defects in Au substrates, specifically twin boundaries, to fabricate selective epitaxial growth of semiconducting nanocrystals. Different crystallographic defects were previously shown to enhance materials properties, such as, screw dislocations providing spiral crystal growth, dislocation outcrops, and vacancies increasing their catalytic activity, dislocation strengthening, and atomic doping changing the crystal's electrical properties. Here, we present a unique phenomenon of directed growth of semiconductor crystals of gold(I)-cyanide (AuCN) on the surface of thin Au layers, using traces of deformation twins on the surface. We show that emergence of deformation twins to the {111} Au surface leads to the formation of ledges, exposing new {001} and {111} facets on the surface. We propose that this phenomenon leads to epitaxial growth of AuCN on the freshly exposed {111} facets of the twin boundary trace ledges. Specific orientations of the twin boundaries with respect to the Au surface allow for patterned growth of AuCN in the <110> orientations. Nano-scale patterning of AuCN semiconductors may provide an avenue for property tuning, particularly the band gap acquired.

Metal Alloys-Structured Electrocatalysts: Metal-Metal Interactions, Coordination Microenvironments, and Structural Property-Reactivity Relationships

Metal alloys-structured electrocatalysts (MAECs) have made essential contributions to accelerating the practical applications of electrocatalytic devices in renewable energy systems. However, due to the complex atomic structures, varied electronic states, and abundant supports, precisely decoding the metal-metal interactions and structure-activity relationships of MAECs still confronts great challenges, which is critical to direct the future engineering and optimization of MAECs. Here, this timely review comprehensively summarizes the latest advances in creating the MAECs, including the metal-metal interactions, coordination microenvironments, and structure-activity relationships. First, the fundamental classification, design, characterization, and structural reconstruction of MAECs are outlined. Then, the electrocatalytic merits and modulation strategies of recent breakthroughs for noble and non-noble metal-structured MAECs are thoroughly discussed, such as solid solution alloys, intermetallic alloys, and single-atom alloys. Particularly, unique insights into the bond interactions, theoretical understanding, and operando techniques for mechanism disclosure are given. Thereafter, the current states of diverse MAECs with a unique focus on structural property-reactivity relationships, reaction pathways, and performance comparisons are discussed. Finally, the future challenges and perspectives for MAECs are systematically discussed. It is believed that this comprehensive review can offer a substantial impact on stimulating the widespread utilization of metal alloys-structured materials in electrocatalysis.

Enabling direct-growth route for highly efficient ethanol upgrading to long-chain alcohols in aqueous phase

Upgrading ethanol to long-chain alcohols (LAS, C6+OH) offers an attractive and sustainable approach to carbon neutrality. Yet it remains a grand challenge to achieve efficient carbon chain propagation, particularly with noble metal-free catalysts in aqueous phase, toward LAS production. Here we report an unconventional but effective strategy for designing highly efficient catalysts for ethanol upgrading to LAS, in which Ni catalytic sites are controllably exposed on surface through sulfur modification. The optimal catalyst exhibits the performance well exceeding previous reports, achieving ultrahigh LAS selectivity (15.2% C6OH and 59.0% C8+OH) at nearly complete ethanol conversion (99.1%). Our in situ characterizations, together with theoretical simulation, reveal that the selectively exposed Ni sites which offer strong adsorption for aldehydes but are inert for side reactions can effectively stabilize and enrich aldehyde intermediates, dramatically improving direct-growth probability toward LAS production. This work opens a new paradigm for designing high-performance non-noble metal catalysts for upgrading aqueous EtOH to LAS.

Hydrogen-bonded linear chain assemblies of palladium(II)-selenoether complexes: solid state aggregates as templates for nano-structural Pd17Se15 leading to efficient electrocatalytic activity

A analogous series of 2-(3,5-dimethylpyrazol-1-yl)phenyl substituted selenoether complexes of palladium [PdCl2(RSeC6H4dmpz)]; (R = CH2COOH (1), CH2CH2COOH (2), and CH2CH2OH (3); dmpz = dimethylpyrazole) were ably synthesized in a facile manner and exhaustively characterized. Insight into molecular structures of these complexes was keenly probed through single crystal X-ray diffraction (XRD) analysis, unfolding the structural scaffolds and laying into molecular aggregation, availed through hydrogen bonding interactions borne out of tethered protic groups. The complexes were converted to capping free palladium selenide (Pd17Se15) nanoparticles through pyrolysis and evaluated for their electrocatalytic efficacy towards the hydrogen evolution reaction (HER), the oxygen evolution reaction (OER) and methanol oxidation reaction (MOR) in alkaline medium. In an alkaline medium, PSNP1 (Pd17Se15) obtained from the hydrogen bonded aggregate of complex PdCl2L1 (1) produced good HER activity. PSNP1 had a little decrease in current density after 300 continuous cycles, which proves that the catalyst presents high stability in the recycling process. For the electrocatalytic oxidation of CH3OH, the electrocatalytic rate constant (k) obtained was 0.3 × 103 cm3 mol-1 s-1.

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.

Recent Progress of Transition Metal Compounds as Electrocatalysts for Electrocatalytic Water Splitting

Hydrogen has enormous commercial potential as a secondary energy source because of its high calorific value, clean combustion byproducts, and multiple production methods. Electrocatalytic water splitting is a viable alternative to the conventional methane steam reforming technique, as it operates under mild conditions, produces high-quality hydrogen, and has a sustainable production process that requires less energy. Electrocatalysts composed of precious metals like Pt, Au, Ru, and Ag are commonly used in the investigation of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Nevertheless, their limited availability and expensive cost restrict practical use. In contrast, electrocatalysts that do not contain precious metals are readily available, cost-effective, environmentally friendly, and possess electrocatalytic performance equal to that of noble metals. However, considerable research effort must be devoted to create cost-effective and high-performing catalysts. This article provides a comprehensive examination of the reaction mechanism involved in electrocatalytic water splitting in both acidic and basic environments. Additionally, recent breakthroughs in catalysts for both the hydrogen evolution and oxygen evolution reactions are also discussed. The structure-activity relationship of the catalyst was deep-going discussed, together with the prospects of current obstacles and potential for electrocatalytic water splitting, aiming at provide valuable perspectives for the advancement of economical and efficient electrocatalysts on an industrial scale.

Metastable Hexagonal-Phase Nickel with Ultralow Pt Content for an Efficient Alkaline/Seawater Hydrogen Evolution Reaction

Hydrogen has been hailed as the core of the world's future energy architecture. It is imperative to develop catalysts with an efficient and sustained hydrogen evolution reaction (HER) to scale up alkaline/seawater electrolysis, yet significant difficulties and challenges, such as the high usage of precious metals, still remain. In this paper, a metastable-phase hexagonal close-packed (hcp) Ni-based catalyst with ultralow Pt content (3.1 at %) was designed, which has excellent catalytic performance in the alkaline/seawater HER. The optimal catalyst offers low overpotentials of 21 and 137 mV at 10 mA cm-2 and remains stable during operation for 100 and 300 h at this current density in 1.0 M KOH and real seawater, respectively. A mechanistic study shows that the metastable-phase Ni acts as an anchor site for OH-, which promotes the dissociation of water and greatly improves the formation rate of H2.

Single-Atom Cr-N4 Sites with High Oxophilicity Interfaced with Pt Atomic Clusters for Practical Alkaline Hydrogen Evolution Catalysis

Although dispersing Pt atomic clusters (ACs) on a conducting support is a promising way to minimize the Pt amount required in hydrogen evolution reaction (HER), the catalytic mass activity and durability of Pt ACs are often unsatisfactory for alkaline HER due to their unfavorable water dissociation and challenges in stabilizing them against agglomeration and detachment. Herein, we report a class of single-atom Cr-N4 sites with high oxophilicity interfaced with Pt ACs on mesoporous carbon for achieving a highly active and stable alkaline HER in an anion-exchange-membrane water electrolyzer (AEMWE). The as-made catalyst achieves the highest reported Pt mass activity (37.6 times higher than commercial Pt/C) and outstanding operational stability. Experimental and theoretical studies elucidate that the formation of a unique Pt-Cr quasi-covalent bonding interaction at the interface of Cr-N4 sites and Pt ACs effectively suppresses the migration and thermal vibration of Pt atoms to stabilize Pt ACs and contributes to the greatly enhanced catalytic stability. Moreover, oxophilic Cr-N4 sites adjacent to Pt ACs with favorable adsorption of hydroxyl species facilitate nearly barrierless water dissociation and thus enhance the HER activity. An AEMWE using this catalyst (with only 50 μgPt cm-2) can operate stably at an industrial-level current density of 500 mA cm-2 at 1.8 V for >100 h with a small degradation rate of 90 μV h-1.

Modulating the d-Band Center Enables Ultrafine Pt3 Fe Alloy Nanoparticles for pH-Universal Hydrogen Evolution Reaction

By providing dual active sites to synergistically accelerate H2 O dissociation and H+ reduction, ordered intermetallic alloys usually show extraordinary performance for pH-universal hydrogen evolution reaction (HER). Herein, activated N-doped mesoporous carbon spheres supported intermetallic Pt3 Fe alloys (Pt3 Fe/NMCS-A), as a highly-efficient electrocatalyst for pH-universal HER, are reported. The Pt3 Fe/NMCS-A exhibits low overpotentials (η10 ) of 13, 29, and 48 mV to deliver 10 mA cm-2 in 0.5 m H2 SO4 , 1.0 m KOH, and 1.0 m phosphate buffered solution (PBS), respectively, as well as robust stability to maintain the overall catalytic performances. Theoretical studies reveal that the strong Pt 5d-Fe 3d orbital electronic interactions negatively shift the d-band center (εd ) of Pt 5d orbital, resulting in reduced H* adsorption energy of Pt sites and enhanced acidic HER activity. With Pt and Fe acting as co-adsorption sites for H* and *OH intermediates, respectively, a low energy barrier is required for Pt3 Fe/NMCS-A to dissociate H2 O to afford H* intermediates, which greatly promotes the H* adsorption and H2 formation in alkaline and neutral conditions. The synthetic strategy is further extended to the synthesis of Pt3 Co and Pt3 Ni alloys with excellent HER activity in pH-universal electrolytes, demonstrating the great potential of these Pt-based alloys for practical applications.

High Valence State Sites as Favorable Reductive Centers for High-Current-Density Water Splitting

Electrochemical water splitting is a promising approach for producing sustainable and clean hydrogen. Typically, high valence state sites are favorable for oxidation evolution reaction (OER), while low valence states can facilitate hydrogen evolution reaction (HER). However, here we proposed a high valence state of Co3+ in Ni9.5 Co0.5 -S-FeOx hybrid as the favorable center for efficient and stable HER, while structural analogues with low chemical states showed much worse performance. As a result, the Ni9.5 Co0.5 -S-FeOx catalyst could drive alkaline HER with an ultra-low overpotential of 22 mV for 10 mA cm-2 , and 175 mV for 1000 mA cm-2 at the industrial temperature of 60 °C, with an excellent stability over 300 h. Moreover, this material could work for both OER and HER, with a low cell voltage being 1.730 V to achieve 1000 mA cm-2 for overall water splitting at 60 °C. X-ray absorption spectroscopy (XAS) clearly identified the high valence Co3+ sites, while in situ XAS during HER and theoretical calculations revealed the favorable electron capture at Co3+ and suitable H adsorption/desorption energy around Co3+ , which could accelerate the HER. The understanding of high valence states to drive reductive reactions may pave the way for the rational design of energy-related catalysts.

Hydrogen Evolution Reaction on Single-Atom Pt Doped in Ni Matrix under Strong Alkaline Condition

Pt catalyst has been considered as the state-of-the-art catalyst for hydrogen evolution reaction (HER) under acid condition. However, its catalytic kinetics under alkaline conditions is not well-understood. Herein, we report a Ni-Pt(SAs) (SAs = single atoms) catalyst with Pt atomically dispersed in a Ni matrix, and it possesses an impressive HER performance with an overpotential as low as 210 mV at 500 mA cm-2 in strong alkaline electrolyte (7 M KOH), which is much higher than Pt nanoparticle-modified Ni catalyst (Ni-Pt(NPs)). Kinetics analysis reveals that Pt doping in the Ni matrix can accelerate the Volmer step on the Ni-Pt surface. Moreover, Ni-Pt(SAs) displays a more favorable kinetics for H2 formation reaction at high current density than Ni-Pt(NPs). Theoretical calculations reveal that atomically dispersed Pt weakens the adsorption of both H and OH on the surface of Ni-Pt electrode and promotes H2 formation from surface H on Ni-Pt(SAs).

Supported Ruthenium Single-Atom and Clustered Catalysts Outperform Benchmark Pt for Alkaline Hydrogen Evolution

Guaranteeing satisfactory catalytic behavior while ensuring high metal utilization has become the problem that needs to be addressed when designing noble-metal-based catalysts for electrochemical reactions. Here, well-dispersed ruthenium (Ru) based clusters with adjacent Ru single atoms (SAs) on layered sodium cobalt oxide (Ru/NC) are demonstrated as a superb electrocatalyst for alkaline HER. The Ru/NC catalyst demonstrates an activity increase by a factor of two relative to the commercial Pt/C. Operando characterizations in conjunction with density functional theory (DFT) simulations uncover the origin of the superior activity and establish a structure-performance relationship, that is, under HER condition, the real active species are Ru SAs and metallic Ru clusters supported on the NC substrate. The excellent alkaline HER activity of the Ru/NC catalyst can be understood by a spatially decoupled water dissociation and hydrogen desorption mechanism, where the NC substrate accelerates the water dissociation rate, and the generated H intermediates would then migrate to the Ru SAs or clusters and recombine to have H2 evolution. More importantly, comparing the two forms of Ru sites, it is the Ru cluster that dominates the HER activity.

Decoding the Mechanisms of Reversibility Loss in Rechargeable Zinc-Air Batteries

Attaining high reversibility of the electrodes and electrolyte is essential for the longevity of secondary batteries. Rechargeable zinc-air batteries (RZABs), however, encounter drastic irreversible changes in the zinc anodes and air cathodes during cycling. To uncover the mechanisms of reversibility loss in RZABs, we investigate the evolution of the zinc anode, alkaline electrolyte, and air electrode through experiments and first-principles calculations. Morphology diagrams of zinc anodes under versatile operating conditions reveal that the nanosized mossy zinc dominates the later cycling stage. Such anodic change is induced by the increased zincate concentration due to hydrogen evolution, which is catalyzed by the mossy structure and results in oxide passivation on electrodes and eventually leads to low true Coulombic efficiencies and short life spans of batteries. Inspired by these findings, we finally present a novel overcharge-cycling protocol to compensate for the Coulombic efficiency loss caused by hydrogen evolution and significantly extend the battery life.

Construction of an Amethyst-like MoS2@Ni9S8/Co3S4 Rod Electrocatalyst for Overall Water Splitting

Transition metal sulphide electrocatalytic materials possess the bright overall water-splitting performance of practical electrocatalytic technologies. In this study, an amethyst-like MoS2@Ni9S8/Co3S4 rod electrocatalyst was constructed via a one-step hydrothermal method with in-situ-grown ZIF-67 nanoparticles on nickel foam (NF) as a precursor. The rational design and synthesis of MoS2@Ni9S8/Co3S4 endow the catalyst with neat nanorods morphology and high conductivity. The MoS2@Ni9S8/Co3S4/NF with the amethyst-like rod structure exposes abundant active sites and displays fast electron-transfer capability. The resultant MoS2@Ni9S8/Co3S4/NF exhibits outstanding hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalytic activities, with low overpotentials of 81.24 mV (HER) at 10 mA cm-2 and 159.67 mV (OER) at 50 mA cm-2 in 1.0 M KOH solution. The full-cell voltage of overall water splitting only achieves 1.45 V at 10 mA cm-2. The successful preparation of the amethyst-like MoS2@Ni9S8/Co3S4 rod electrocatalyst provides a reliable reference for obtaining efficient electrocatalysts for overall water splitting.

Amorphous nickel hydroxide shell tailors local chemical environment on platinum surface for alkaline hydrogen evolution reaction

In analogy to natural enzymes, an elaborated design of catalytic systems with a specifically tailored local chemical environment could substantially improve reaction kinetics, effectively combat catalyst poisoning effect and boost catalyst lifetime under unfavourable reaction conditions. Here we report a unique design of 'Ni(OH)2-clothed Pt-tetrapods' with an amorphous Ni(OH)2 shell as a water dissociation catalyst and a proton conductive encapsulation layer to isolate the Pt core from bulk alkaline electrolyte while ensuring efficient proton supply to the active Pt sites. This design creates a favourable local chemical environment to result in acidic-like hydrogen evolution reaction kinetics with a lowest Tafel slope of 27 mV per decade and a record-high specific activity and mass activity in alkaline electrolyte. The proton conductive Ni(OH)2 shell can also effectively reject impurity ions and retard the Oswald ripening, endowing a high tolerance to solution impurities and exceptional long-term durability that is difficult to achieve in the naked Pt catalysts. The markedly improved hydrogen evolution reaction activity and durability in an alkaline medium promise an attractive catalyst material for alkaline water electrolysers and renewable chemical fuel generation.

Dual roles of sub-nanometer NiO in alkaline hydrogen evolution reaction: breaking the Volmer limitation and optimizing d-orbital electronic configuration

Pt-based nanoclusters toward the hydrogen evolution reaction (HER) remain the most promising electrocatalysts. However, the sluggish alkaline Volmer-step kinetics and the high-cost have hampered progress in developing high-performance HER catalysts. Herein, we propose to construct sub-nanometer NiO to tune the d-orbital electronic structure of nanocluster-level Pt for breaking the Volmer-step limitation and reducing the Pt-loading. Theoretical simulations firstly suggest that electron transfer from NiO to Pt nanoclusters could downshift the Ed-band of Pt and result in the well-optimized adsorption/desorption strength of the hydrogen intermediate (H*), therefore accelerating the hydrogen generation rate. NiO and Pt nanoclusters confined into the inherent pores of N-doped carbon derived from ZIF-8 (Pt/NiO/NPC) were designed to realize the structure of computational prediction and boost the alkaline hydrogen evolution. The optimal 1.5%Pt/NiO/NPC exhibited an excellent HER performance and stability with a low Tafel slope (only 22.5 mv dec-1) and an overpotential of 25.2 mV at 10 mA cm-2. Importantly, the 1.5%Pt/NiO/NPC possesses a mass activity of 17.37 A mg-1 at the overpotential of 20 mV, over 54 times higher than the benchmark 20 wt% Pt/C. Furthermore, DFT calculations illustrate that the Volmer-step could be accelerated owing to the high OH- attraction of NiO nanoclusters, leading to the Pt nanoclusters exhibiting a balance of H* adsorption and desorption (ΔGH* = -0.082 eV). Our findings provide new insights into breaking the water dissociation limit of Pt-based catalysts by coupling with a metal oxide.

Three-dimensional ordered macroporous molybdenum doped NiCoP honeycomb electrode for two-step water electrolysis

Two-step alkaline water electrolysis is considered a safe and efficient method for producing hydrogen from renewable energy. Reversal of the current polarity in a bifunctional electrocatalyst used as a gas evolution electrode (GEE) in two-step water electrolysis can generate H₂/O₂ at different times and in different spaces. The design of a bifunctional electrocatalyst with high durability and excellent activity is imperative to achieving continuous, safe, and pure H₂ generation via two-step alkaline water electrolysis. Here, we present for the first time a novel 3D Mo-doped NiCo phosphide honeycomb electrocatalyst that was grown on nickel foam (3D Mo-NiCoP/NF) and fabricated using polystyrene as a template. The electrocatalyst exhibited extremely low overpotentials in both the hydrogen evolution reaction (HER; 117 mV at 10 mA/cm²) and the oxygen evolution reaction (OER; 344 mV at 100 mA/cm²). As a bifunctional electrocatalyst for two-step alkaline water electrolysis, the device had a 1.784 V cell voltage at 10 mA/cm², 95% decoupling efficiency, and ∼83% energy conversion efficiency. Taken together, the use of 3D Mo-NiCoP/NF as a GEE reduced the complexity and lowered the cost of the electrolyzer. The latter could be used to construct highly competitive water-splitting systems for continuous H₂ production and green energy harvesting.

Cu-Doped Heterointerfaced Ru/RuSe2 Nanosheets with Optimized H and H2 O Adsorption Boost Hydrogen Evolution Catalysis

Ruthenium chalcogenide is a highly promising catalytic system as a Pt alternative for hydrogen evolution reaction (HER). However, well-studied ruthenium selenide (RuSe₂ ) still exhibits sluggish HER kinetics in alkaline media due to the inappropriate adsorption strength of H and H₂ O. Herein, xx report a new design of Cu-doped Ru/RuSe₂ heterogeneous nanosheets (NSs) with optimized H and H₂ O adsorption strength for highly efficient HER catalysis in alkaline media. Theoretical calculations reveal that the superior HER performance is attributed to a synergistic effect of the unique heterointerfaced structure and Cu doping, which not only optimizes the electronic structure with a suitable d-band center to suppress proton overbinding but also alleviates the energy barrier with enhanced H₂ O adsorption. As a result, Cu-doped heterogeneous Ru/RuSe₂ NSs exhibit a small overpotential of 23 mV at 10 mA cm^-2 , a low Tafel slope of 58.5 mV dec^-1 and a high turnover frequency (TOF) value of 0.88 s^-1 at 100 mV for HER in alkaline media, which is among the best catalysts in noble metal-based electrocatalysts toward HER. The present Cu-doped Ru/RuSe₂ NSs interface catalyst is very stable for HER by showing no activity decay after 5000-cycle potential sweeps. This work heralds that heterogeneous interface modulation opens up a new strategy for the designing of more efficient electrocatalysts.

Significantly Stabilizing Hydrogen Evolution Reaction Induced by Nb-Doping Pt/Co(OH)2 Nanosheets

High stability and efficiency of electrocatalysts are crucial for hydrogen evolution reaction (HER) toward water splitting in an alkaline media. Herein, a novel nano-Pt/Nb-doped Co(OH)₂ (Pt/NbCo(OH)₂ ) nanosheet is designed and synthesized using water-bath treatment and solvothermal reduction approaches. With nano-Pt uniformly anchored onto NbCo(OH)₂ nanosheet, the synthesized Pt/NbCo(OH)₂ shows outstanding electrocatalytic performances for alkaline HER, achieving a high stability for at least 33 h, a high mass activity of 0.65 mA µg^-1 Pt, and a good catalytic activity with a low overpotential of 112 mV at 10 mA cm^-2 . Both experimental and theoretical results prove that Nb-doping significantly optimizes the hydrogen adsorption free energy to accelerate the Heyrovsky step for HER, and boosts the adsorption of H₂ O, which further enhances the water activation. This study provides a new design methodology for the Nb-doped electrocatalysts in an alkaline HER field by facile and green way.

Construction of Nitrogen-Doped Biphasic Transition-Metal Sulfide Nanosheet Electrode for Energy-Efficient Hydrogen Production via Urea Electrolysis

Urea-assisted hybrid water splitting is a promising technology for hydrogen (H₂ ) production, but the lack of cost-effective electrocatalysts hinders its extensive application. Herein, it is reported that Nitrogen-doped Co₉ S₈ /Ni₃ S₂ hybrid nanosheet arrays on nickel foam (N-Co₉ S₈ /Ni₃ S₂ /NF) can act as an active and robust bifunctional catalyst for both urea oxidation reaction (UOR) and hydrogen evolution reaction (HER), which could drive an ultrahigh current density of 400 mA cm^-2 at a low working potential of 1.47 V versus RHE for UOR, and gives a low overpotential of 111 mV to reach 10 mA cm^-2 toward HER. Further, a hybrid water electrolysis cell utilizing the synthesized N-Co₉ S₈ /Ni₃ S₂ /NF electrode as both the cathode and anode displays a low cell voltage of 1.40 V to reach 10 mA cm^-2 , which can be powered by an AA battery with a nominal voltage of 1.5 V. The density functional theory (DFT) calculations decipher that N-doped heterointerfaces can synergistically optimize Gibbs free energy of hydrogen and urea, thus accelerating the catalytic kinetics of HER and UOR. This work significantly advances the development of the promising cobalt-nickel-based sulfide as a bifunctional electrocatalyst for energy-saving electrolytic H₂ production and urea-rich innocent wastewater treatment.

Diversity of platinum-sites at platinum/fullerene interface accelerates alkaline hydrogen evolution

Membrane-based alkaline water electrolyser is promising for cost-effective green hydrogen production. One of its key technological obstacles is the development of active catalyst-materials for alkaline hydrogen-evolution-reaction (HER). Here, we show that the activity of platinum towards alkaline HER can be significantly enhanced by anchoring platinum-clusters onto two-dimensional fullerene nanosheets. The unusually large lattice distance (~0.8 nm) of the fullerene nanosheets and the ultra-small size of the platinum-clusters (~2 nm) leads to strong confinement of platinum clusters accompanied by pronounced charge redistributions at the intimate platinum/fullerene interface. As a result, the platinum-fullerene composite exhibits 12 times higher intrinsic activity for alkaline HER than the state-of-the-art platinum/carbon black catalyst. Detailed kinetic and computational investigations revealed the origin of the enhanced activity to be the diverse binding properties of the platinum-sites at the interface of platinum/fullerene, which generates highly active sites for all elementary steps in alkaline HER, particularly the sluggish Volmer step. Furthermore, encouraging energy efficiency of 74% and stability were achieved for alkaline water electrolyser assembled using platinum-fullerene composite under industrially relevant testing conditions.

Alloying Pt into Ni partially amorphous for promoted alkaline hydrogen production

Aiming at the sluggish water dissociation step in alkaline hydrogen evolution reaction (HER), the platinum-nickel alloy material (PtNi₁₀/C) featuring unique crystalline/amorphous structure supported on carbon black is deliberately designed and fabricated via a reversely rapid co-precipitation and mild thermal reduction strategy. Electrochemical results show that only 66 mV of overpotential is needed for PtNi₁₀/C to drive a current density of 10 mA cm^-2 at a lower platinum loading (8.3 μg_Pt cm-2 geo), which is much lower than that of other catalysts with a single metal source(S-Ni/C and S-Pt/C) and even the commercial Pt/C catalyst (20 wt%). The target catalyst also exhibits smaller tafel slope value (16.73 mV dec^-1) and electrochemical impedance value, enabling a fast kinetics rate for water dissociation. Partial crystallization facilitates moderate adsorption of intermediates, while the high-valence Ni(II) and Pt(II) species serve as pivotal driving force for the kinetic dissociation of water. The unique microstructure of PtNi₁₀/C shows a remarkable advantage toward HER in alkaline but acidic medium. In addition, other transition metal-based catalysts following the similar protocol are also fabricated and present varying degrees of HER performance. Hence, the facile and rapid co-precipitation/thermal reduction strategy proposed in this study provides some guidelines for designing high-efficiency alkaline HER catalysts.

·H effectively enhance electrocatalytic nitrogen fixation

Nowadays, most reported ammonia (NH₃) yields and Faradaic efficiency (FE) of electrocatalysts are very low in the field of electrocatalytic nitrogen reduction reactions (NRR). Here, we are reported ·H for the first time in the field of electrocatalytic NRR, which are generated by sulfite (SO₃^2-) and H₂O in electrolyte solutions upon exposure to UV light. The high NH₃ yields can achieve 100.7 μg h^-1 mg_cat^-1, while stability can achieve 64 h and the FE can achieve 27.1% at -0.3 V (vs. RHE) with UV irradiation. In situ Fourier transform infrared spectroscopy (FTIR), electron spin resonance (ESR), density functional theory (DFT) and ¹H nuclear magnetic resonance (NMR) tests showed that the ∙H effectively lowered the reaction energy barrier at each step of the NRR process and inhibits the occurrence of competitive hydrogen evolution reaction (HER). This explores the path and provides ideas for the field of electrocatalysis involving water.

Interfacial Engineering of Polycrystalline Pt5 P2 Nanocrystals and Amorphous Nickel Phosphate Nanorods for Electrocatalytic Alkaline Hydrogen Evolution

Electrocatalytic hydrogen evolution reaction (HER) in alkaline media is important for hydrogen economy but suffers from sluggish reaction kinetics due to a large water dissociation energy barrier. Herein, Pt₅ P₂ nanocrystals anchoring on amorphous nickel phosphate nanorods as a high-performance interfacial electrocatalyst system (Pt₅ P₂ NCs/a-NiPi) for the alkaline HER are demonstrated. At the unique polycrystalline/amorphous interface with abundant defects, strong electronic interaction, and optimized intermediate adsorption strength, water dissociation is accelerated over abundant oxophilic Ni sites of amorphous NiPi, while hydride coupling is promoted on the adjacent electron-rich Pt sites of Pt₅ P₂ . Meanwhile, the ultra-small-sized Pt₅ P₂ nanocrystals and amorphous NiPi nanorods maximize the density of interfacial active sites for the Volmer-Tafel reaction. Pt₅ P₂ NCs/a-NiPi exhibits small overpotentials of merely 9 and 41 mV at -10 and -100 mA cm^-2 in 1 M KOH, respectively. Notably, Pt₅ P₂ NCs/a-NiPi exhibits an unprecedentedly high mass activity (MA) of 14.9 mA µg_Pt ^-1 at an overpotential of 70 mV, which is 80 times higher than that of Pt/C and represents the highest MA of reported Pt-based electrocatalysts for the alkaline HER. This work demonstrates a phosphorization and interfacing strategy for promoting Pt utilization and in-depth mechanistic insights for the alkaline HER.

Intensifying Hydrogen Spillover for Boosting Electrocatalytic Hydrogen Evolution Reaction

Hydrogen spillover has attracted increasing interests in the field of electrocatalytic hydrogen evolution reaction (HER) in recent years because of their distinct reaction mechanism and beneficial terms for simultaneously weakening the strong hydrogen adsorption on metal and strengthening the weak hydrogen adsorption on support. By taking advantageous merits of efficient hydrogen transfer, hydrogen spillover-based binary catalysts have been widely investigated, which paves a new way for boosting the development of hydrogen production by water electrolysis. In this paper, we summarize the recent progress of this interesting field by focusing on the advanced strategies for intensifying the hydrogen spillover towards HER. In addition, the challenging issues and some perspective insights in the future development of hydrogen spillover-based electrocatalysts are also systematically discussed.

Merging Platinum Single Atoms to Achieve Ultrahigh Mass Activity and Low Hydrogen Production Cost

Single atom catalysts (SACs) with isolated active sites exhibit the highest reported mass activity for hydrogen evolution catalysis, which is crucial for practical applications. Here, we demonstrate that ultrahigh mass activity can also be achieved by rationally merging the isolated platinum (Pt) active sites in SAC. The catalyst was obtained by the thermodynamically driven diffusing and merging phosphorus-doped carbon (PC) supported Pt single atoms (Pt₁@PC) into Pt nanoclusters (Pt_M@PC). X-ray absorption spectroscopy analysis revealed that the merged nanoclusters exhibit much stronger interactions with the support than the traditional method, enabling more efficient electron transfer. The optimized Pt_M@PC exhibited an order of magnitude higher mass activity (12.7 A mg_Pt^-1) than Pt₁@PC (0.9 A mg_Pt^-1) at an overpotential of 10 mV in acidic media, which is the highest record to date, far exceeding reports for other outstanding SACs. Theoretical study revealed that the collective active sites in Pt_M@PC exhibit both favorable hydrogen binding energy and fast reaction kinetics, leading to the significantly enhanced mass activity. Despite its low Pt content (2.2 wt %), a low hydrogen production cost of ∼3 USD kg^-1 was finally achieved in the full-water splitting at a laboratory scale.

Recent progress on the synthesis of metal alloy nanowires as electrocatalysts

Benefiting from both one-dimensional (1D) morphology and alloy composition, metal alloy nanowires have been exploited as advanced electrocatalysts in various electrochemical processes. In this review, the synthesis approaches for metal alloy nanowires are classified into two categories: direct syntheses and syntheses based on preformed 1D nanostructures. Ligand systems that are of critical importance to the formation of alloy nanowires are summarized and reviewed, together with the strategies imposed to achieve the co-reduction of different metals. Meanwhile, different scenarios that form alloy nanowires from pre-synthesized 1D nanostructures are compared and contrasted. In addition, the characterization and electrocatalytic applications of metal alloy nanowires are briefly discussed.

Amorphous Mo-doped NiS0.5 Se0.5 Nanosheets@Crystalline NiS0.5 Se0.5 Nanorods for High Current-density Electrocatalytic Water Splitting in Neutral Media

It is vitally important to develop highly active, robust and low-cost transition metal-based electrocatalysts for overall water splitting in neutral solution especially at large current density. In this work, amorphous Mo-doped NiS_0.5 Se_0.5 nanosheets@crystalline NiS_0.5 Se_0.5 nanorods (Am-Mo-NiS_0.5 Se_0.5 ) was synthesized using a facil one-step strategy. In phosphate buffer saline solution, the Am-Mo-NiS_0.5 Se_0.5 shows tiny overpotentials of 48 and 209 mV for hydrogen evolution reaction (HER), 238 and 514 mV for oxygen evolution reaction (OER) at 10 and 1000 mA cm^-2 , respectively. Moreover, Am-Mo-NiS_0.5 Se_0.5 delivers excellent stability for at least 300 h without obvious degradation. Theoretical calculations revealed that the Ni sites in the defect-rich amorphous structure of Am-Mo-NiS_0.5 Se_0.5 owns higher electron state density and strengthened the binding energy of H₂ O, which will optimize H adsorption/desorption energy barriers and reduce the adsorption energy of OER determining step.

Tunable Aryl Alkyl Ionic Liquid Supported Synthesis of Platinum Nanoparticles and Their Catalytic Activity in the Hydrogen Evolution Reaction and in Hydrosilylation

Tunable aryl alkyl ionic liquids (TAAILs) are ionic liquids (ILs) with a 1-aryl-3-alkylimidazolium cation having differently substituted aryl groups. Herein, nine TAAILs with the bis(trifluoromethylsulfonyl)imide anion are utilized in combination with and without ethylene glycol (EG) as reaction media for the rapid microwave synthesis of platinum nanoparticles (Pt-NPs). TAAILs allow the synthesis of small NPs and are efficient solvents for microwave absorption. Transmission electron microscopy (TEM) shows that small primary NPs with sizes of 2 nm to 5 nm are obtained in TAAILs and EG/TAAIL mixtures. The Pt-NPs feature excellent activity as electrocatalysts in the hydrogen evolution reaction (HER) under acidic conditions, with an overpotential at a current density of 10 mA cm^-2 as low as 32 mV vs the reversible hydrogen electrode (RHE), which is significantly lower than the standard Pt/C 20% with 42 mV. Pt-NPs obtained in TAAILs also achieved quantitative conversion in the hydrosilylation reaction of phenylacetylene with triethylsilane after just 5 min at 200 °C.

Promising transition metal decorated borophene catalyst for water splitting†

Borophene has been recently reported to be a promising catalyst for water splitting. However, as a newly synthesized two-dimensional material, there are several issues that remain to be explored. In the present study, we investigate the catalytic performance of three kinds of pristine and decorated borophenes using first-principles calculations. Our calculations show that Ni-doped α borophene can be a highly active catalyst for water splitting. Doping or decorating with different transition metals such as Co or Ni at different sites shows a strong effect on the catalytic performance of α, β₁₂ and χ₃ borophenes. Ni-doped α borophene shows low Gibbs free energy of hydrogen adsorption (ΔG_H ∼ 0.055 eV) for the hydrogen evolution reaction (HER) and promising overpotential (0.455 V) for the oxygen evolution reaction (OER). This study provides some critical insights into the catalytic activity of borophene for water splitting by selecting suitable decorated metal.

Promising Ni metal decorated borophene catalyst for water splitting.

Observation of a robust and active catalyst for hydrogen evolution under high current densities

Despite the fruitful achievements in the development of hydrogen production catalysts with record-breaking performances, there is still a lack of durable catalysts that could work under large current densities (>1000 mA cm^-2). Here, we investigated the catalytic behaviors of Sr₂RuO₄ bulk single crystals. This crystal has demonstrated remarkable activities under the current density of 1000 mA cm^-2, which require overpotentials of 182 and 278 mV in 0.5 M H₂SO₄ and 1 M KOH electrolytes, respectively. These materials are stable for 56 days of continuous testing at a high current density of above 1000 mA cm^-2 and then under operating temperatures of 70 °C. The in-situ formation of ferromagnetic Ru clusters at the crystal surface is observed, endowing the single-crystal catalyst with low charge transfer resistance and high wettability for rapid gas bubble removal. These experiments exemplify the potential of designing HER catalysts that work under industrial-scale current density.