Understanding electrocatalysis at nanoscale electrodes and single atoms with operando vibrational spectroscopy

Electrocatalysis presents an environmentally benign route to carry out energy conversion reactions and organic transformations. The use of nanomaterials and single atoms as catalysts in electrochemical reactions has led to improvements in activity and selectivity over bulk electrocatalysts, however, optimal design of electrocatalytic reactions requires an in-depth understanding of the dynamic solid–liquid interface, reaction intermediates, and catalyst structural changes. Tracking bond breaking and formation events in real time is an important complement to catalyst characterization. This short review highlights advancements in fundamental understanding of electrocatalysis at nanoscale and single atom electrocatalysts obtained using operando vibrational spectroscopies. To push the boundaries of our fundamental understanding in electrocatalysis, we also emphasize a need to further develop operando vibrational techniques to reduce ensemble averaging with improvements in spatial and temporal resolution.     

Medium/High-Entropy Amalgamated Core/Shell Nanoplate Achieves Efficient Formic Acid Catalysis for Direct Formic Acid Fuel Cell

High-entropy alloys (HEAs) have been attracting extensive research interests in designing advanced nanomaterials, while their precise control is still in the infancy stage. Herein, we have reported a well-defined PtBiPbNiCo hexagonal nanoplates (HEA HPs) as high-performance electrocatalysts. Structure analysis decodes that the HEA HP is constructed with PtBiPb medium-entropy core and PtBiNiCo high-entropy shell. Significantly, the HEA HPs can reach the specific and mass activities of 27.2 mA cm⁻² and 7.1 A mg_Pt⁻¹ for formic acid oxidation reaction (FAOR), being the record catalyst ever achieved in Pt-based catalysts, and can realize the membrane electrode assembly (MEA) power density (321.2 mW cm⁻²) in fuel cell. Further experimental and theoretical analyses collectively evidence that the hexagonal intermetallic core/atomic layer shell structure and multi-element synergy greatly promote the direct dehydrogenation pathway of formic acid molecule and suppress the formation of CO*.     

高熵纳米合金在电化学催化中的应用

The implementation of clean energy techniques, including clean hydrogen generation, use of solar-driven photovoltaic hybrid systems, photochemical heat generation as well as thermoelectric conversion, is crucial for the sustainable development of our society. Among these promising techniques, electrocatalysis has received significant attention for its ability to facilitate clean energy conversion because it promotes a higher rate of reaction and efficiency for the associated chemical transformations. Noble-metal-based electrocatalysts typically show high activity for electrochemical conversion processes. However, their scarcity and high cost limit their applications in electrocatalytic devices. To overcome this limitation, binary catalysts prepared by alloying with transition metals can be used. However, optimization of the activity of the binary catalysts is considerably limited because of the presence of the miscibility gap in the phase diagram of binary alloys. The activity of binary electrocatalysts can be attributed to the adsorption energy of molecules and intermediates on the surface. High-entropy alloys (HEAs), which consist of diverse elements in a single NP, typically exhibit better physical and/or chemical properties than their single-element counterparts, because of their tunable composition and inherent surface complexity. Further, HEAs can improve the performance of binary electrocatalysts because they exhibit a near-continuous distribution of adsorption energy. Recently, HEAs have gained considerable attention for their application in electrocatalytic reactions. This review summarizes recent research advances in HEA nanostructures and their application in the field of electrocatalysis. First, we introduce the concept, structure, and four core effects of HEAs. We believe that this part will provide the basic information about HEAs. Next, we discuss the reported top-down and bottom-up synthesis strategies, emphasizing on the carbothermal shock method, nanodroplet-mediated electrodeposition, fast moving bed pyrolysis, polyol process, and dealloying. Other methods such as combinatorial co-sputtering, ultrashort-pulsed laser ablation, ultrasonication-assisted wet chemistry, and scanning-probe block copolymer lithography are also highlighted. Among these methods, wet chemistry has been reported to be effective for the formation of nano-scale HEAs because it facilitates the concurrent reduction of all metal precursors to form solid-solution alloys. Next, we present the theoretical investigation of HEA nanocatalysts, including their thermodynamics, kinetic stability, and adsorption energy tuning for optimizing their catalytic activity and selectivity. To elucidate the structure–property relationship in HEAs, we summarize the research progress related to electrocatalytic reactions promoted by HEA nanocatalysts, including the oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, methanol oxidation reaction, and CO₂ reduction reaction. Finally, we discuss the challenges and various strategies toward the development of HEAs.     

Surface/interface engineering of high-efficiency noble metal-free electrocatalysts for energy-related electrochemical reactions

To date,much efforts have been devoted to the high-efficiency noble metal-free electrocatalysts for hydrogen-and oxygen-involving energy conversion reactions,due to their abundance,low cost and nultifunctionally.Surface/interface engineering is found to be effective in achieving novel physicochemical properties and synergistic effects in nanomaterials for electrocatalysis.Among various engineering strategies,heteroatom-doping has been regarded as a most promising method to improve the electrocatalytic performance via the regulation of electronic structure of catalysts,and numerous works were reported on the synthesis method and mechanism investigation of heteroatom-doping electrocatalysts,though the heteroatom-doping can only provide limited active sites.Engineering of other defects such as vacancies and edge sites and construction of heterostructure have shown to open up a potential avenue for the development of noble metal-free electrocatalysts.In addition,surface functionalization can attach various molecules onto the surface of materials to easily modify their physical or chemical properties,being as a promising complement or substitute for offering materials with catalytic properties.This paper gives the insights into the diverse strategies of surface/interface engineering of the highefficiency noble metal-free electrocatalysts for energy-related electrochemical reactions.The significant advances are summarized.The unique advantages and mechanisms for specific applications are highlighted.The current challenges and outlook of this growing field are also discussed.     

中空MOFs材料制备及电催化应用的研究进展

水分裂、金属-空气电池和燃料电池等能源转换技术对解决未来的能源危机和环境问题至关重要.氧还原反应(ORR)、氧析出反应(OER)和氢析出反应(HER)作为其核心反应,存在反应动力学速率较慢的问题,因此,开发研制高效的非贵金属电催化剂具有重要意义.金属有机骨架(MOFs)材料因具有高度可调的组成和多孔晶体结构,在不同的应用领域引起了越来越多的关注.中空MOFs纳米材料具有MOFs材料高度可调的组成和结构优势,又具有中空结构纳米材料的优点(如更快的物质传输、更丰富的孔隙率、灵活多变的活性组分、更多的暴露活性位点及对苛刻条件的更好相容性等),在电催化领域显现出巨大的应用潜力.本文对近几年来基于中空结构MOFs材料的制备及在电催化方面应用的研究进展进行了综合评述,并对该领域面临的挑战和发展前景进行了总结和展望.     

Noble-Metal-Free Doped Carbon Nanomaterial Electrocatalysts

Electrocatalytic processes, such as oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and carbon dioxide reduction reaction (CO₂RR), play key roles in various sustainable energy storage and production devices and their optimization in an ecological manner is of paramount importance for mankind. In this inclusive Review, we aspire to set the scene on doped carbon-based nanomaterials and their hybrids as precious-metal alternative electrocatalysts for these critical reactions in order for the research community not only to stay up-to-date, but also to get inspired and keep pushing forward towards their practical application in energy conversion.     

Solid-State Conversion Synthesis of Advanced Electrocatalysts for Water Splitting

Electrolytic water technology is promising for sustainable energy utilization, but the lack of efficient electrocatalysts retards its application. The intrinsic activity of electrocatalysts is determined by its electronic structure, whereas the apparent activity can be further optimized by reasonable design on micro-/nanostructures of electrocatalysts. The core goal of electrocatalytic research is to reveal the relationship between the structure and performance of electrocatalysts, which is also the basis of reasonable design and construction of efficient electrocatalysts. Traditional synthetic methods, namely bottom-up and top-down routes, usually induce the change of different structural parameters at the same time. The solid-state conversion strategy, which is converts solid precursors into target materials through chemical reactions, has been widely adopted to produce materials with precisely controllable structures. In this Minireview, we focus on recent advances in the solid-state conversion synthesis of water-splitting electrocatalysts. First, the basis of solid-state conversion chemistry is introduced. Then, the specific methods of precise control of electronic structure by solid-state conversion and the relationship between electronic structure and performance are summarized. Based on the understanding of the electronic structure–performance relationship, synergistic regulation of electronic structure and micro-/nanostructures by solid-state conversion to achieve the copromotion of intrinsic activity and apparent activity are described. Finally, the remaining challenges in this field are discussed, and future research directions are proposed as well.     

Recent Advances in Two-dimensional Materials for Electrochemical Energy Storage and Conversion

With the increased energy demand,developing renewable and clean energy technologies becomes more and more significant to mitigate climate warming and alleviate the environmental pollution.The key point is design and synthesis of low cost and efficient materials for a wide variety of electrochemical reactions.Over the past ten years,two-dimensional(2D)nanomaterials that graphene represents have been paid much attention as a class of the most promising candidates for heterogeneous electrocatalysts in electrochemical storage and conversion.Their unique properties,such as good chemical stability,good flexibility,and good electronic properties,along with their nanosized thickness and large specific area,make them exhibit comprehensively good performances for energy storage and conversion.Here,we present an overview on the recent advances in electrochemical applications of graphene,graphdiyne,transition metal dichalcogenides(TMDs),and MXenes for supercapacitors(SCs),oxygen reduction reaction(ORR),and hydrogen evolution reaction(HER).     

Random Occupation of Multimetal Sites in Transition Metal-Organic Frameworks for Boosting the Oxygen Evolution Reaction

Developing robust oxygen evolution reaction (OER) electrocatalysts with excellent performance is essential for the conversion of renewable electricity to clean fuel. Herein, we present a facile concept for the synthesis of efficient high-entropy metal-organic frameworks (HEMOFs) as electrocatalysts in a one-step solvothermal synthesis. This strategy allows control of the microstructure and corresponding lattice distortion by tuning the metal ion composition. As a result, the OER activity was improved by optimizing the coordination environment of the metal catalytic center. The optimized Co-rich HEMOFs exhibited a low overpotential of 310 mV at a current density of 10 mA cm⁻², better than a RuO₂ catalyst tested under the same conditions. The finding of lattice distortion of the HEMOFs provides a new strategy for developing high-performance electrocatalysts for energy conversion.     

Low-temperature plasma technology for electrocatalysis

The latest applications of plasma in energy storage and conversion are summarized here, including using it as the preparation and modification technology of the various electrocatalysts and the usage of it as the synthesis technology directly. Also, the challenges and outlook of plasma technology in energy storage and conversion were summarized, and the solutions and prospected its development in the future were present.     

The Advanced Multi‐functional Electrocatalyst Efficiently Built from Multi‐integrated Sites for Overall Water Splitting and Rechargeable Zinc‐air Battery

Exploration of cost‐effective, high‐performance and durable multifunctional electrocatalysts is of significant importance for renewable energy conversion and storage. In this work, a simple strategy is developed to tailor the nickel metal with the collaboration of nitrogen‐doped graphene and single‐walled carbon nanotubes. The resulted nickel catalyst exhibits superior trifunctional activities for oxygen evolution, hydrogen evolution and oxygen reduction reactions in the same electrolyte, even comparable to commercial Pt/C and RuO₂ respectively, which can be attributed to the synergistic advantages between nickel, nitrogen and carbon, mainly including abundant integrated active sites achieved by the irregular charge distribution among C?N and Ni?N coupling centers. Such remarkable effects on trifunctional catalysis elicit the efficient overall water splitting, and endow the assembled zinc‐air battery with a good performance. These highlight the metallic nickel as an advanced multifunctional electrocatalysts with integrated sites developed from the collaboration of two different carbon nanomaterials.     

Rational Design and Engineering of Nanomaterials Derived from Prussian Blue and Its Analogs for Electrochemical Water Splitting

Electrochemical water splitting (EWS) is a sustainable and promising technology for producing hydrogen as an ideal energy carrier to address environmental and energy issues. Developing highly‐efficient electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) is critical for increasing the efficiency of water electrolysis. Recently, nanomaterials derived from Prussian blue (PB) and its analogs (PBA) have received increasing attention in EWS applications owing to their unique composition and structure properties. In this Minireview, the latest progress of PB/PBA‐derived materials for EWS is presented. Firstly, the catalyst design principles and the advantages of preparing electrocatalysts with PB/PBA as precursors are briefly introduced. Then, strategies for enhancing the electrocatalytic performance (HER, OER or overall water splitting) were discussed in detail, and the recent development and applications of PB/PBA‐derived catalysts for EWS were summarized. Finally, major challenges and possible future trends related to PB/PBA‐derived functional materials are proposed.     

基于微生物作为智能模板的电催化剂制备与应用研究进展

通过电催化实现可再生能源的存储与转化对于改善能源结构、保护生态环境、实现碳达峰和碳中和的国家战略具有重大意义。而开发低成本、高效的电催化剂成为全世界科学家共同面对的挑战。微生物在自然界中广泛存在,具有结构、组成和代谢丰富的特点,可以成为电催化剂的模板以及碳、磷、硫等非金属元素以及金属元素的来源,而且具有无毒、生产可重复性好、易于规模化等优点,已成为电催化剂制备的新趋势。对此,本文综述了微生物“智能”引导制备电催化剂的发展及在电催化析氢(HER)、电催化析氧(OER)、氧还原反应(ORR)、二氧化碳还原(CO₂RR)、锂电池(LBs)等领域的应用现状。希望有助于推动微生物代谢与催化剂微纳结构关系以及与催化反应的构效关系的深入理解,最后针对这类材料的问题挑战及其未来发展方向进行了探讨与展望。     

Recent advances of layered double hydroxides–based bifunctional electrocatalysts for ORR and OER

The oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) have attracted increasing attention for the sake of clean, renewable, and efficient energy technologies in recent years. The design of ORR/OER bifunctional electrocatalysts is a challenging task in the promotion of highly efficient rechargeable metal-air batteries as well as regenerative fuel cells. Owing to the wide adaptability of different types and ratios of metals in the interlayer space as well as the adjustable interlayer distance, composite materials with layered double hydroxides (LDHs) and their derivatives have recently been registered as electrode materials and catalysts supports for various electrochemical reactions. This study examines the recent development of bifunctional electrocatalysts based on LDHs for ORR/OER to expand the application of LDHs in the field of energy storage and conversion. Various bifunctional electrocatalysts associated with LDHs are discussed in detail to improve their performance. Finally, existing problems and future prospects for improving the performance of LDHs bifunctional electrocatalysts are proposed.     

Heteroatom Doping Promoting CoP for Driving Water Splitting

CoP nanomaterials have been extensively regarded as one of the most promising electrocatalysts for overall water splitting due to their unique bifunctionality. Although the great promise for future applications, some important issues should also be addressed. Heteroatom doping has been widely acknowledged as a potential strategy for improving the electrocatalytic performance of CoP and narrowing the gap between experimental study and industrial applications. Recent years have witnessed the rapid development of heteroatom-doped CoP electrocatalysts for water splitting. Aiming to provide guidance for the future development of more effective CoP-based electrocatalysts, we herein organize a comprehensive review of this interesting field, with the special focus on the effects of heteroatom doping on the catalytic performance of CoP. Additionally, many heteroatom-doped CoP electrocatalysts for water splitting are also discussed, and the structure-activity relationship is also manifested. Finally, a systematic conclusion and outlook is well organized to provide direction for the future development of this interesting field.     

Hierarchically Structured Nanomaterials for Electrochemical Energy Conversion

Hierarchical nanomaterials are highly suitable as electrocatalysts and electrocatalyst supports in electrochemical energy conversion devices. The intrinsic kinetics of an electrocatalyst are associated with the nanostructure of the active phase and the support, while the overall properties are also affected by the mesostructure. Therefore, both structures need to be controlled. A comparative state‐of‐the‐art review of catalysts and supports is provided along with detailed synthesis methods. To further improve the design of these hierarchical nanomaterials, in‐depth research on the effect of materials architecture on reaction and transport kinetics is necessary. Inspiration can be derived from nature, which is full of very effective hierarchical structures. Developing fundamental understanding of how desired properties of biological systems are related to their hierarchical architecture can guide the development of novel catalytic nanomaterials and nature‐inspired electrochemical devices.     

A review of transition metal‐based bifunctional oxygen electrocatalysts

Electrochemical energy storage and conversion devices play a key role in the development of clean, sustainable, and efficient energy systems to meet the sustainable growth of our society. However, challenging issues including the sluggish kinetics of oxygen electrode reactions involving the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are present, limiting the implementation of devices such as metal‐air batteries, water electrolyzers, and regenerative fuel cells. In this review, various monometallic and bimetallic transition metal oxides (TMOs) and hydroxides are summarized in terms of their application for ORR/OER, in which the merits and demerits of various precious metal and carbon‐based metal oxide materials are discussed, with requirements for better electrocatalysts and catalyst support being introduced as well. Following this, different approaches to improve catalytic activity such as the introduction of doping and defects, the manipulation of crystal facets, and the engineering of supports, compositions, and morphologies are summarized in which TMOs with improved ORR/OER catalytic activities can be synthesized, further improving the speed, stability, and polarization of electrochemical energy storage and conversion devices. Finally, perspectives into the improvement of performance and the better understanding of ORR/OER mechanisms for bifunctional electrocatalysts using in situ spectroscopic techniques and density functional theory calculations are also discussed.     

Colloidal surfactant-free syntheses of precious metal nanoparticles for electrocatalysis

The successful study, understanding, optimization, and ultimately scaling up of electroactive and stable electrodes strongly rely on the careful design and preparation of electrocatalytic materials. In particular, precious metal nanoparticles are key electrocatalysts for a wide range of reactions. Colloidal syntheses offer several advantages to develop precious metal nanoparticles but unfortunately often require capping agents to stabilize the nanoparticles. These ligands or surfactants often block the surface active sites and need to be removed by time and/or energy demanding steps. These extra steps potentially (unnecessarily) complicate studies, might impair reproducibility and limit a direct transfer of fundamental breakthroughs to real-life applications. Fortunately, a range of surfactant-free syntheses have been reported and are well-suited to develop electrocatalysts with improved activity. Surfactant-free syntheses also bear promising features towards high-throughput screening of multi-metallic nanomaterials to explore new concepts in electrode design.     

钯基氧还原和乙醇氧化反应电催化剂:关于结构和机理研究的一些近期见解

质子交换膜燃料电池和直接乙醇燃料电池已成为可持续性清洁能源研究的一个聚焦点.在燃料电池中,氧还原反应和乙醇氧化反应是两个重要的反应,其相关高活性、高稳定性并且廉价的催化剂的研发仍然存在很多问题,极大地制约了燃料电池的大规模商业化应用.其中的挑战主要来自于对纳米催化剂结构和反应机理的有限认识.由于实验表征理论计算的结合,...     

Superhydrophilic Phytic‐Acid‐Doped Conductive Hydrogels as Metal‐Free and Binder‐Free Electrocatalysts for Efficient Water Oxidation

Recently, metal‐free, heteroatom‐doped carbon nanomaterials have emerged as promising electrocatalysts for the oxygen evolution reaction (OER), but their synthesis is a tedious process involving energy‐wasting calcination. Molecular electrocatalysts offer attractive catalysts for the OER. Here, phytic acid (PA) was selected to investigate the OER activity of carbons in organic molecules by DFT calculations and experiments. Positively charged carbons on PA were very active towards the OER. The PA molecules were fixed into a porous, conductive hydrogel with a superhydrophilic surface. This outperformed most metal‐free electrocatalysts. Besides the active sites on PA, the high OER activity was also related to the porous and conductive networks on the hydrogel, which allowed fast charge and mass transport during the OER. Therefore, this work provides a metal‐free, organic‐molecule‐based electrocatalyst to replace carbon nanomaterials for efficient OER.