Polymorphism-Interface-Induced Work Function Regulating on Ru Nanocatalyst for Enhanced Alkaline Hydrogen Oxidation Reaction

Exploring high-performance Pt-free electrocatalysts for hydrogen oxidation reaction (HOR) in alkaline media is highly imperative for the development of alkaline polymer electrolyte fuel cells. Phase engineering is an effective strategy for boosting the catalytic performance of electrocatalysts; however, the fabrication of unconventional polymorphism-interfaced metal catalysts remains a significant challenge. In this study, a polymorphism-interfaced Ru nanocatalyst with a stable hexagonal close-packed (hcp) phase and a metastableface-centered-cubic (fcc) phase is successfully prepared. Owing to the built-in electric field and stacking fault on the unique polymorphic interface, the fcc-hcp-Ru catalyst exhibits outstanding alkaline HOR performance with a mass activity of 1016 A g_PGM^-1, which is six and three times higher than that of conventional hcp-Ru andcommercial Pt/C, respectively. The regulated electron distribution at the polymorphic interface is attributed to the discrepant work functions, which not only optimize the adsorption energy of hydrogen but also facilitate the water formation step to promote the alkaline HOR process. This study demonstrates that unconventional polymorphism-interfaced engineering is an efficient strategy to regulate the electronic structure of metal catalysts and identifies the prominent role of the work function in alkaline HORs, providing a new avenue for the rational design of highly efficient materials for electrocatalysis.     

Modification of the Intermediate Binding Energies on Ni/Ni3N Heterostructure for Enhanced Alkaline Hydrogen Oxidation Reaction

Developing highly efficient and stable non-precious metal-based electrocatalysts for alkaline hydrogen oxidation reaction (HOR) is essential for the commercialization of alkaline exchange membrane fuel cells but remains a big challenge. Here, a simple strategy for constructing the Ni/Ni₃N heterostructure electrocatalyst with remarkable catalytic performance toward HOR under alkaline electrolyte is reported. Density functional theory calculations and experimental results reveal that the inter-regulated d-band center of interfacial Ni and Ni₃N derived from electron transfer from Ni to Ni₃N across the interface can lead to the weakened hydrogen binding energy of Ni and strengthened hydroxyl binding energy of Ni₃N, which, together with the decreased formation energy of water species, contributes to the outstanding HOR performance.     

Single‐Atom Catalysts for Electrocatalytic Applications

The recent advances in electrocatalysis for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), carbon dioxide reduction reaction (CO₂RR), and nitrogen reduction reaction (NRR) are thoroughly reviewed. This comprehensive review focuses on the single‐atom catalysts (SACs) including Sc, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Sn, W, Bi, Ru, Rh, Pd, Ag, Ir, Pt, and Au with single‐metal sites or dual‐metal sites. The recent development of single‐atom electrocatalysts with novel configurations and compositions is documented. The understanding of the process–structure–property relationships is highlighted. For the SACs, their electrocatalytic performance and stability in fuel cells, zinc–air batteries, electrolyzers, CO₂RR, and NRR are summarized. The challenges and perspectives in the emerging field of single‐atom electrocatalysis are discussed.     

Lattice and Surface Engineering of Ruthenium Nanostructures for Enhanced Hydrogen Oxidation Catalysis

Ru has recently been considered as a promising alternative of Pt toward hydrogen oxidation reaction (HOR) due to its lower price and similar hydrogen binding energy (HBE) in comparison to Pt. Nevertheless, the catalytic performance of Ru toward HOR is far from the satisfaction of practical application. Herein, it is demonstrated that the modification of Ru multi-layered nanosheet (MLNS) with Ni can significantly promote the HOR performance. In particular, the HOR performance is strongly related to the Ni location on the surface or in the lattice of Ru MLNS. Experimental and theoretical investigations suggest that Ni in the lattice of Ru MLNS (lattice engineering) optimizes the HBE, while Ni species on the surface (surface engineering) decrease the free energy of water formation, as a result of the significantly enhanced HOR performance. The optimal catalyst, where Ni is located both on the surface and in the lattice, displays superior alkaline HOR performance to commercial Pt/C and Ru/C. The present study not only systematically reveals the significance of Ni modification on Ru toward HOR, but also promotes the fundamental researches on catalyst design for fuel cell reactions and beyond.     

Development of Electrocatalysts for Efficient Nitrogen Reduction Reaction under Ambient Condition

As one of the most important chemicals and an energy carrier, synthetic ammonia has been widely studied to meet the increasing demand. Among various strategies, electrochemical nitrogen reduction reaction (e-NRR) is a promising way because of its green nature and easy set-up on large-scale. However, its practical application is extremely limited because of the very-low production rate, which is strongly dependent on the electrocatalysts used. Therefore, searching novel efficient electrocatalysts for e-NRR is essential to promote the technology. In this review, it highlights the insights on the mechanism for the NH₃ electrochemical synthesis, recommend a reliable protocol for the ammonia detection, and systematically summarize the recent development on novel electrocatalysts, including noble metal-based materials, single-metal-atom catalysts, non-noble metal, and their compounds, and metal-free materials, for efficient e-NRR in both experimental and theoretical studies. Various strategies to improve the catalytic performance by increasing exposed active sites or tuning electronic structures, including surface control, defect engineering, and hybridization, are carefully discussed. Finally, perspectives and challenges are outlined. It can be expected that this review provides insightful guidance on the development of advanced catalytic systems to produce ammonia through N₂ reduction.     

Local Oxidation Induced Amorphization of 1.5-nm-Thick Pt–Ru Nanowires Enables Superactive and CO-Tolerant Hydrogen Oxidation in Alkaline Media

Low-dimensional amorphous metallic nanomaterials provide great possibility for creating high-performance electrocatalysts owing to their conspicuous reacting merits derived from the flexible coordination structures, but remain extremely challenging in synthesis. Herein, this work reports a facile synthesis of carbon-loaded amorphous 1.5-nm-thick Pt–Ru nanowires (NWs) through a local oxidation induced amorphization process. During annealing premade crystalline Pt–Ru NWs/C in air, a local-oxidation of the oxyphilic Ru generates abundant random Ru–O bonds and disturbs the order bimetallic lattices. The as-prepared amorphous Pt₅₃Ru₄₇ (a-Pt₅₃Ru₄₇) NWs/C exhibits an extremely high activity (13.7 A mg⁻¹ at 25 mV overpotential) and an excellent CO-tolerance for alkaline hydrogen oxidation reaction (HOR) electrocatalysis, drastically outperforming the crystalline counterpart and commercial benchmarks. Mechanism studies indicate the Pt–Ru bimetallic effects as well as the rich disordered “Pt–Ru–O” and/or “Pt–O–Ru” atomic heterojunctions can weaken the *H binding energy and inversely strengthen the *OH adsorption, thus promoting the alkaline HOR kinetics. More uniquely, the small interatomic spaces derived from the disordered bond nets present a H₂/*H-selected permeability, which spatially obstruct the relatively larger CO molecules to poison the internal catalytic sites during HOR. The CO-shielded internal catalytic sites and the enriched surface *OH jointly upgrade the CO-tolerance of the a-Pt₅₃Ru₄₇ NWs/C catalysts.     

Manipulating the Coordination Chemistry of Ru?N(O)?C Moieties for Fast Alkaline Hydrogen Evolution Kinetics

The coordination chemistry of the metal-support interface largely determines the electrocatalytic performance of heterostructured electrocatalysts. However, it remains a great challenge to effectively manipulate the interface chemistry of heterostructures at the atomic level. Herein, functionalized carbon-supported Ru heterostructured electrocatalysts are designed that contain abundant Ru N(O) C moieties with a view towards fast hydrogen evolution reaction (HER). The coordination chemistry of the Ru N(O) C moieties, and hence, the geometric and electronic structures of the Ru species can be precisely modulated via an appropriate annealing treatment. Specifically, the optimal heterostructured electrocatalyst delivers the highest specific activity by far among reported Ru-based electrocatalysts, and the turnover frequency value reaches 32 s⁻¹ at the overpotential (η) of 100 mV, which also surpasses the state-of-the-art Pt/C catalyst in alkaline media. The interface engineering of the heterostructured electrocatalyst not only facilitates H₂O adsorption and dissociation with help from the Ru N(O) C moieties, but also further optimizes the adsorption behavior of H on the metallic Ru species, thereby inducing accelerated hydrogen evolution kinetics in both alkaline and acidic media. The present results demonstrate the successful atomic-level interface engineering of carbon-supported Ru-based heterostructures and shed new light on the development of advanced electrocatalysts for fast hydrogen evolution, and beyond.     

Rational Design of Nanoarray Architectures for Electrocatalytic Water Splitting

Electrochemical water splitting is recognized as a practical strategy for impelling the transformation of sustainable energy sources such as solar energy from electricity to clean hydrogen fuel. To actualize the large‐scale hydrogen production, it is paramount to develop low‐cost, earth‐abundant, efficient, and stable electrocatalysts. Among those electrocatalysts, alternative architectural arrays grown on conductive substrates have been proven to be highly efficient toward water splitting due to large surface area, abundant active sites, and synergistic effects between the electrocatalysts and the substrates. Herein, the advancement of nanoarray architectures in electrocatalytic applications is reviewed. The categories of different nanoarrays and the reliable and versatile synthetic approaches of electrocatalysts are summarized. A unique emphasis is highlighted on the promising strategies to enhance the electrocatalytic activities and stability of architectural arrays by component manipulation, heterostructure regulation, and vacancy engineering. The intrinsic mechanism analysis of electronic structure optimization, intermediates' adsorption facilitation, and coordination environments' amelioration is also discussed with regard to theoretical simulation and in situ identification. Finally, the challenges and opportunities on the valuable directions and promising pathways of architectural arrays toward outstanding electrocatalytic performance are provided in the energy conversion field, facilitating the development of promising water splitting systems.     

One‐Step Synthesis of W2C@N,P‐C Nanocatalysts for Efficient Hydrogen Electrooxidation across the Whole pH Range

Highly active and low‐cost non‐noble metal electrocatalysts for hydrogen oxidation reaction (HOR) are crucial for the large‐scale applications of fuel cells, which, unfortunately, are rarely documented up to now. Here, a facile one‐step strategy to fabricate W₂C nanoparticles (≈3 nm) encased in N, P‐doped few layer carbon materials (W₂C@N,P‐C, WNPC) as an efficient non‐noble metal HOR electrocatalyst simply by calcining the mixture of recrystallized phosphotungstic acid and dicyandiamide is reported. The obtained WNPC catalyst shows extraordinarily high HOR activities (1.03/0.91/0.84 mA cm^?2 at 0.05 V vs reversible hydrogen electrode in 0.1 m HClO₄/0.1 m KOH/0.1 m neutral phosphate buffered saline electrolytes, respectively), excellent durability during accelerated degradation tests for 10 000 cycles, and outstanding CO tolerance. These high performances are attributed to the uniform structure of WNPC, and more essentially, the synergistic effect among N, P, and C species which elevates the reducibility of WNPC, favoring the generation of abundant HOR active sites.     

Designing High-Valence Metal Sites for Electrochemical Water Splitting

Electrochemical water splitting is a critical energy conversion process for producing clean and sustainable hydrogen; this process relies on low-cost, highly active, and durable oxygen evolution reaction/hydrogen evolution reaction electrocatalysts. Metal cations (including transition metal and noble metal cations), particularly high-valence metal cations that show high catalytic activity and can serve as the main active sites in electrochemical processes, have received special attention for developing advanced electrocatalysts. In this review, heterogenous electrocatalyst design strategies based on high-valence metal sites are presented, and associated materials designed for water splitting are summarized. In the discussion, emphasis is given to high-valence metal sites combined with the modulation of the phase/electronic/defect structure and strategies of performance improvement. Specifically, the importance of using advanced in situ and operando techniques to track the real high-valence metal-based active sites during the electrochemical process is highlighted. Remaining challenges and future research directions are also proposed. It is expected that this comprehensive discussion of electrocatalysts containing high-valence metal sites can be instructive to further explore advanced electrocatalysts for water splitting and other energy-related reactions.     

Transforming Damage into Benefit: Corrosion Engineering Enabled Electrocatalysts for Water Splitting

Producing high-purity hydrogen from water electrocatalysis is essential for the flourishing hydrogen energy economy. It is of critical importance to develop low-cost yet efficient electrocatalysts to overcome the high activation barriers during water electrocatalysis. Among the various approaches of catalyst preparation, corrosion engineering that employs the autogenous corrosion reactions to achieve electrocatalysts has emerged as a burgeoning strategy over the past few years. Benefiting from the advantages of simple synthesis, effective regulation, easy scale-up production, and extremely low cost, corrosion engineering converts the harmful corrosion process into the useful catalyst preparation, achieving the goal of “transforming damage into benefit.” Herein, the concept of corrosion engineering, fundamental reaction mechanisms, and affecting factors are firstly introduced. Then, recent progresses on corrosion engineering for fabricating electrocatalysts toward water splitting are summarized and discussed. Specific attentions are devoted to the formation mechanisms, catalytic performances, and structure–activity relations of these catalysts as well as the approaches employed for performance improvements. At last, the current challenges and future exploiting directions are proposed for achieving highly active and durable electrocatalysts. It is envisioned to shed light on the multidisciplinary corrosion engineering that is closely associated with corrosion and material science for energy and environmental applications.     

A Self-Supported High-Entropy Metallic Glass with a Nanosponge Architecture for Efficient Hydrogen Evolution under Alkaline and Acidic Conditions

Developing highly efficient and durable electrocatalysts for hydrogen evolution reaction (HER) under both alkaline and acidic media is crucial for the future development of a hydrogen economy. However, state-of-the-art high-performance electrocatalysts recently developed are based on carbon carriers mediated by binding noble elements and their complicated processing methods are a major impediment to commercialization. Here, inspired by the high-entropy alloy concept with its inherent multinary nature and using a glassy alloy design with its chemical homogeneity and tunability, we present a scalable strategy to alloy five equiatomic elements, PdPtCuNiP, into a high-entropy metallic glass (HEMG) for HER in both alkaline and acidic conditions. Surface dealloying of the HEMG creates a nanosponge-like architecture with nanopores and embedded nanocrystals that provides abundant active sites to achieve outstanding HER activity. The obtained overpotentials at a current density of 10 mA cm⁻² are 32 and 62 mV in 1.0 m KOH and 0.5 m H₂SO₄ solutions, respectively, outperforming most currently available electrocatalysts. Density functional theory reveals that a lattice distortion and the chemical complexity of the nanocrystals lead to a strong synergistic effect on the electronic structure that further stabilizes hydrogen proton adsorption/desorption. This HEMG strategy establishes a new paradigm for designing compositionally complex alloys for electrochemical reactions.     

Kinetic‐Oriented Construction of MoS2 Synergistic Interface to Boost pH‐Universal Hydrogen Evolution

As a prerequisite for a sustainable energy economy in the future, designing earth‐abundant MoS₂ catalysts with a comparable hydrogen evolution catalytic performance in both acidic and alkaline environments is still an urgent challenge. Decreasing the energy barriers could enhance the catalysts' activity but is not often a strategy for doing so. Here, the first kinetic‐oriented design of the MoS₂‐based heterostructure is presented for pH‐universal hydrogen evolution catalysis by optimizing the electronic structure based on the simultaneous modulation of the 3d‐band‐offsets of Ni, Co, and Mo near the interface. Benefiting from this desirable electronic structure, the obtained MoS₂/CoNi₂S₄ catalyst achieves an ultralow overpotential of 78 and 81 mV at 10 mA cm^?2, and turnover frequency as high as 2.7 and 1.7 s^?1 at the overpotential of 200 mV in alkaline and acidic media, respectively. The MoS₂/CoNi₂S₄ catalyst represents one of the best hydrogen evolution reaction performing ones among MoS₂‐based catalysts reported to date in both alkaline and acidic environments, and equally important is the remarkable long‐term stability with negligible activity loss after maintaining at 10 mA cm^?2 for 48 h in both acid and base. This work highlights the potential to deeply understand and rationally design highly efficient pH‐universal electrocatalysts for future energy storage and delivery.     

Rational Design of Transition Metal Phosphide-Based Electrocatalysts for Hydrogen Evolution

Developing efficient and inexpensive electrocatalysts for the hydrogen evolution reaction (HER) is critical to the commercial viability of electrochemical clean energy technologies. Transition metal phosphides (TMPs), with the merits of abundant reserves, unique structure, tunable composition, and high electronic conductivity, are recognized as attractive HER catalytic materials. Nevertheless, the HER electrocatalytic activity of TMPs is still limited by various thorough issues and inherent performance bottlenecks. In this review, these issues are carefully sorted, and the corresponding reasonable explanations and solutions are elucidated on the basis of the HER catalytic activity origins of TMPs. Subsequently, highly targeted multiscale strategies to improve the HER performance of TMPs are comprehensively presented. Additionally, critical scientific issues for constructing high-efficiency TMP-based electrocatalysts are proposed. Finally, the HER reaction process, catalytic mechanism research, TMP-based catalyst construction, and their application expansion are mentioned as challenges and future directions for this research field. Expectedly, this review offers professional and targeted guidelines for the rational design and practical application of TMP-based HER catalysts.     

Non‐Noble‐Metal‐Based Electrocatalysts toward the Oxygen Evolution Reaction

The development of low‐cost, high‐efficiency, and robust electrocatalysts for the oxygen evolution reaction (OER) is urgently needed to address the energy crisis. In recent years, non‐noble‐metal‐based OER electrocatalysts have attracted tremendous research attention. Beginning with the introduction of some evaluation criteria for the OER, the current OER electrocatalysts are reviewed, with the classification of metals/alloys, oxides, hydroxides, chalcogenides, phosphides, phosphates/borates, and other compounds, along with their advantages and shortcomings. The current knowledge of the reaction mechanisms and practical applications of the OER is also summarized for developing more efficient OER electrocatalysts. Finally, the current states, challenges, and some perspectives for non‐noble‐metal‐based OER electrocatalysts are discussed.     

Emerging Applications,Developments, Prospects,and Challenges of Electrochemical Nitrate-to-Ammonia Conversion

Ammonia is not only an important feedstock for chemical industry but also a carbon-free energy carrier and a safe storage media for hydrogen. Due to the advantages compared to Haber–Bosch process, electrochemical NO₃⁻-to-NH₃ conversion via nitrate reduction reaction (NO₃⁻RR) received attention. Recently, “green hydrogen” generated from water electrolysis shows promise to become the energy for future but limited by the safety of storage and transportation. This review proposes electrochemical NO₃⁻-to-NH₃ conversion can store renewable electric energy and “green hydrogen” into NH₃, which is a potential solution for solving the puzzle of “green hydrogen” storage and transportation. Moreover, the theoretical insights of NO₃⁻RR and electrocatalyst design are discussed. Finally, the challenges and opportunities in this field are elucidated. This review provides a novel perspective for NO₃⁻RR and accelerates the development of effective electrocatalysts for NO₃⁻-to-NH₃ conversion.     

面向电解水的激光制备微纳米结构催化电极

相对于使用化石燃料的制氢方式,电解水不存在碳排放,是一种真正绿色环保的制氢技术,对发展氢能源具有重要意义。电解水的能耗和成本都较大,需要使用高效稳定的非贵金属催化剂,以降低过电压。激光具有高效、灵活、非接触、高度可控等优点,近年来已成为制备电解水催化剂的有效工具,但在一体化微纳米结构催化电极的制备方面存在不足之处。本文基于激光微纳制备方法,总结了激光液相合成粉末催化剂和激光制备自支撑微纳米结构催化电极的最新研究进展,并讨论了该领域未来的研究方向。     

Hierarchical Porous NC@CuCo Nitride Nanosheet Networks: Highly Efficient Bifunctional Electrocatalyst for Overall Water Splitting and Selective Electrooxidation of Benzyl Alcohol

Highly active and stable bifunctional electrocatalysts for overall water splitting are important for clean and renewable energy technologies. The development of energy‐saving electrocatalysts for hydrogen evolution reaction (HER) by replacing the sluggish oxygen evolution reaction (OER) with a thermodynamically favorable electrochemical oxidation (ECO) reaction has attracted increasing attention. In this study, a self‐supported, hierarchical, porous, nitrogen‐doped carbon (NC)@CuCo₂N_x/carbon fiber (CF) is fabricated and used as an efficient bifunctional electrocatalyst for both HER and OER in alkaline solutions with excellent activity and stability. Moreover, a two‐electrode electrolyzer is assembled using the NC@CuCo₂N_x/CF as an electrocatalyst at both cathode and anode electrodes for H₂ production and selective ECO of benzyl alcohol with high conversion and selectivity. The excellent electrocatalytic activity is proposed to be mainly due to the hierarchical architecture beneficial for exposing more catalytic active sites, enhancing mass transport. Density functional theoretical calculations reveal that the adsorption energies of key species can be modulated due to the synergistic effect between CoN and CuN. This work provides a reference for the development of high‐performance bifunctional electrocatalysts for simultaneous production of H₂ and high‐value‐added fine chemicals.     

All-pH Stable Sandwich-Structured MoO2/MoS2/C Hollow Nanoreactors for Enhanced Electrochemical Hydrogen Evolution

Molybdenum sulfide has great potential for the electrocatalytic hydrogen evolution, but its structural instability in acidic media and high barriers in alkaline/neutral media limits its practical applications. Herein, the design of monodispersed sandwich-structured MoO₂/MoS₂/C hollow nanoreactors is reported with a triple layer “conductor/catalyst/protector” configuration for efficient electrochemical hydrogen evolution over all pH values. Metallic MoO₂ substrates with ultrahigh pristine electroconductivity can promote the charge transfer while sulfur vacancies are introduced to activate the highly exposed (002) facets of MoS₂. The optimized MoO₂/MoS₂/C nanoreactor exhibits overpotentials of 77, 91, and 97 mV (10 mA cm⁻²) and Tafel slopes of 41, 49, and 53 mV dec⁻¹ in acidic, alkaline, and neutral media, respectively, which are much better than most of the MoS₂-based electrocatalysts. Moreover, defective carbon shells are in situ generated, preventing the electrocatalysts from corrosion in acidic and alkaline media; the structural stability is verified via in situ Raman and XRD characterizations. Based on the density functional theory calculations, vacancy engineering can regulate the band structures, electron density differences, total density of states, and the H* and H₂O adsorption-dissociation ability over the entire pH range. The findings may shed light on the rational development of practical pH-universal electrocatalysts for durable hydrogen evolution.     

Bifunctional Heterostructured Transition Metal Phosphides for Efficient Electrochemical Water Splitting

Reducing green hydrogen production costs is essential for developing a hydrogen economy. Developing cost‐effective electrocatalysts for water electrolysis is thus of great research interest. Among various material candidates, transition metal phosphides (TMP) have emerged as robust bifunctional electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) due to their various phases and tunable electronic structure. Recently, heterostructured catalysts have exhibited significantly enhanced activities toward HER/OER. The enhancement can be attributed to the increased amount of accessible active sites, accelerated mass/charge transfer, and optimized adsorption of intermediates, which arise from the synergistic effects of the heterostructure. Herein, a comprehensive overview of the recent progress of bifunctional TMP‐based heterostructure is introduced to provide an insight into their preparation and corresponding reaction mechanisms. It starts with summarizing general fundamental aspects of HER/OER and the synergistic effect of heterostructures for enhanced catalytic activity. Next, the innovational strategies to design and construct bifunctional TMP‐based heterostructures with enhanced overall water splitting activity, as well as the related mechanisms, are discussed in detail. Finally, a summary and perspective for further opportunities and challenges are highlighted for the further development of bifunctional TMP‐based heterostructures from the points of practical application and mechanistic studies.