单原子催化剂大数据库

单原子催化剂(SAC)是在基底材料上锚定孤立的金属原子,具有金属位点结构稳定以及活性中心高度均匀、配位环境可调和原子利用效率高等优点.因此, SAC有着桥接非均相和均相催化的巨大潜力.此外, SAC还为探索催化结构-性能关系以及研究原子尺度的催化机制提供了一个基本平台.近年来, SAC的合理设计和可控合成得到较大发展,它们表现出在金属表面上无法实现的显著的催化活性和选择性.尽管近期SAC研究十分热门,但仍然存在一些巨大的挑战.首先,缺乏一套统一标准为新型SAC的设计提供指导.不同的金属中心具有不同的化学和电子特性,因此合成一种SAC的指导原则不能简单地外推到另一种.其次,由于缺乏对SAC形成机制的全面了解, SAC材料中的键长、氧化态、配位数和配位阴离子种类等局部结构仍然难以调控.此外,金属单原子(SA)的负载量也难以有效控制,这主要是由于吉布斯-汤姆逊效应经常导致锚定的单原子发生团聚.虽然,氮掺杂可以缓解原子聚集,但是简单地增加氮含量并不能总是提高SA的负载量.目前,如何将不同的金属元素位点合成于一个SAC材料中还存在很多知识盲区.本文评述了Xin等(Nat. Mater., 2022, 21, 681-688)通过一种高温碳化法在氮掺杂的碳基底上合成基于37种单金属元素的单原子催化剂,作者结合原位技术对催化剂进行表征和分析,建立了一个从单金属到复杂多金属材料的单原子催化剂库.该催化剂库一方面可以为单原子催化剂的合理设计提供指导,另一方面为SAC材料中关于氧化态、配位数、键长、配位元素和单原子的金属负载量等方面的分析提供借鉴.众所周知,每个单原子元素的局部环境是决定催化性能的关键,包括单原子与距离其最外壳层最近原子间的键长、配位数等.研究发现,第5副族、第6副族和第10副族的单原子金属元素通常会失去更多的外部电子或具有更小的配位数,从而导致它们的键长更短,这说明氧化态与配位数呈负相关性.也就是说,键长越长,氧化态越低,配位数越大,反之亦然.此外,金属单原子的负载量与最大金属前驱体的比例(金属Mo元素和葡萄糖的摩尔比)呈现出正相关的关系,这表明可以通过调节金属前驱体比来有效控制负载量,并且最大金属前驱体比例和负载量与电负性均呈现出近似抛物线的关系,尽管由于金属前驱体在制备过程中挥发损失的程度不同,电负性的抛物线趋势不是很明显.该规律可用于通过金属电负性定量预测合成相应SAC的金属前驱体比上限.另外,金属单原子的负载与O含量呈正相关,而与N含量呈负相关,指明N、O含量对金属单原子负载量的调控极为关键.同时还提出SACs的最终协调环境不仅与单原子金属的种类有关,还与制备过程的反应温度有关.最后,该研究为多金属单原子催化剂的可控制备打开一扇大门,并证明使用该方法可以成功构建一种包含多达12种不同金属元素的复杂的单原子催化剂材料.

通过表面镧改性和体相锰掺杂协助钴尖晶石酸性下析氧

电解水作为一种高效环保的制氢技术,有望解决日益严重的能源危机和环境污染的问题.目前,商业电解池根据电解质的不同可分为碱性液态电解池和质子交换膜电解池(PEMWE).与前者相比,PEMWE不仅设备结构紧凑节省空间,而且在电流密度、电阻损失和产氢纯度等方面具有优势.然而,阳极析氧反应(OER)复杂而缓慢的动力学过程严重制约了PEMWE的大规模商业应用.由于PEMWE在酸性和高氧化环境中工作,电催化活性和稳定性比在碱性介质中面临着更大的挑战.目前,商业OER催化剂仅限于包括IrO_(2)和RuO_(2)的资源稀缺的铂族金属基(PGM)材料.尽管廉价的非PGM基氧化物已被开发应用于碱性电解质的OER,但其在酸性环境中的催化性能远低于预期.因此,需要设计合理的策略来优化非PGM基氧化物的酸性OER活性和稳定性以推动PEMWE技术的发展.本文对Liu等的工作(Science,2023,380,609-616)进行了深度评述.文章报道了一种La和Mn共掺杂的Co尖晶石纤维(LMCF)材料,其中La掺杂在表面,Mn掺杂于体相,为PEMWE阳极催化剂设计引入新思路.首先,采用传统的湿化学方法将La和Mn掺杂到Co-ZIF前驱体中,然后将其混入聚丙烯腈(PAN)聚合物浆料中,再通过静电纺丝工艺拉丝,将纺制的纤维在360°C的流动空气中活化以去除有机成分,最终得到LMCF材料.在PEMWE电解槽中对LMCF进行了催化性能评价,发现LMCF在强酸性环境下显示出较好的OER活性和稳定性,甚至不逊于PGM基OER催化剂.文中催化剂设计亮点包括:(1)选用Co-ZIF作为前驱体,不仅能在低温氧化制备过程中转化为相互连接、部分保留高孔隙率和菱形十二面体结构的空心Co_(3)O_(4)纳米颗粒,有利于电荷转移和传质传输,还使LMCF具有自支撑性而无需负载于碳基衬底之上,可以避免由于碳基衬底在高工作电位下氧化而导致的催化活性锐减.(2)表面掺杂La^(3+)元素,因其足够稳定进而有助于提高LMCF整体的耐酸性,且较大的离子半径可以诱导表面氧空位的生成从而降低OER能垒.(3)体相掺杂Mn^(2+)元素,在氧化过程中,Mn^(2+)会转化为与CO_(2)+大小相近的Mn^(3+),可均匀掺杂到Co_(3)O_(4)晶格中,进而显著提高了整体电导率,并优化活性中间物种的吸附能.综上,该文章通过精心设计多种优化策略从根本上提高适用于强酸性环境的Co尖晶石的稳定性和活性,对后续研究具有参考意义,为PEMWE非PGM基阳极催化剂的合理设计提供参考.

Applications of Atomically Dispersed Oxygen Reduction Catalysts in Fuel Cells and Zinc–Air Batteries

Due to severe energy crisis and environmental problems,green and renewable electrochemical energy devices such as fuel cells and metal–air batteries have attracted great attention,where oxygen reduction reaction(ORR)plays a vital role.The rational design of efficient and robust singleatom catalysts(SACs)is vital but challenging toward ORR.Here,recent developments of single-atom ORR catalysts in fuel cells and Zn–air batteries are systematically summarized,focusing on transition-metal-based electrocatalysts including single or dual Fe,Co,Ni,Cu,Zn,Pd,Ag,and Pt sites.At the atomic level,different synthesis methods and characterization techniques are introduced.Theoretical studies of ORR mechanisms are documented.The active sites and structure–property relationships of SACs for ORR are highlighted,and the performances of proton exchange membrane fuel cells(PEMFCs),anion exchange membrane fuel cells(AEMFCs),and Zn–air batteries are discussed.The great challenges and future directions of SACs in fuel cells and Zn–air batteries are presented.

Surface reconstruction and structural transformation of twodimensional Ni-Fe MOFs for oxygen evolution in seawater media

As a four-electron transfer reaction,oxygen evolution reaction(OER)is limited by large overpotential and slow kinetics.Here,we in-situ synthesized two-dimensional(2D)Ni-Fe metal-organic framework nanosheets on nickel foam(NixFe-TPA/NF,TPA=terephthalic acid)for oxygen evolution in alkaline and alkaline seawater electrolytes.In 1 M KOH,Ni3Fe-TPA/NF shows a low overpotential(η10)of 189 mV at 10 mA·cm^(-2) and an ultra-low overpotential of only 260 mV at 500 mA·cm^(-2).In alkaline seawater,Ni3Fe-TPA/NF still provides impressive OER performance,with anη10 of 265 mV.In-situ Raman characterization results show that the phase transition occurs during the OER,and Ni3FeOOH with more oxygen vacancies is in-situ formed,reducing the OER energy barrier.Density functional theory(DFT)reveals that the synergy between Ni and Fe reduces the energy barrier and accelerates the rate-determining step.In addition,the ultra-thin 2D sheet structure and the close combination of Ni3FeOOH and highly conductive NF support ensure the high catalytic OER activity.Therefore,the surface reconstruction and structural modification strategy can be used to design and prepare high-performance OER electrocatalysts for energy-related applications.

Diatomic Fe-Co catalysts synergistically catalyze oxygen evolution reaction

The design of diatomic catalysts with uniformly dispersed metal atoms is expected to improve catalytic performance,which is conducive to the intensive comprehending of the synergistic mechanism between dual-metal sites for the oxygen evolution reaction(OER)at the atomic level.Herein,we design a strategy to immobilize bimetallic Fe-Co atoms onto nitrogen-doped graphene to obtain a diatomic catalyst(DA-FC-NG)with FeN_(3)-CoN_(3) configuration.The DA-FC-NG shows excellent OER activity with a low overpotential(η_(10)=268 mV),which is superior to commercial iridium dioxide catalysts.Theoretical calculations uncover that the excellent activity of DA-FC-NG is due to the interaction between Fe and Co diatoms,which causes charge rearrangement and induces the adsorption of intermediates on the Fe-O-Co bridge structure,thus improving the catalytic OER performance.This work is of great significance for the design of highly active diatomic catalysts to replace noble metal catalysts for energy-related applications.

Interface engineering of Fe-Sn-Co sulfide/oxyhydroxide heterostructural electrocatalyst for synergistic water splitting

To realize large-scale hydrogen production by electrolysis of water,it is essential to develop non-precious metal catalysts for oxygen evolution reaction(OER)and hydrogen evolution reaction(HER).Here,we fabricate Sn-,Fe-,and Co-based sulfide/oxyhydroxide heterostructural catalyst on nickel foam(FeSnCo_(0.2)S_(x)O_(y)/NF)by solvothermal method.The FeSnCo_(0.2)S_(x)O_(y)/NF requires low overpotentials of 48 and 186 mV at 10 mA·cm^(-2),respectively,for HER and OER.When it is assembled into an electrolytic cell as a bifunctional electrocatalyst,it only needs 1.54 V to reach 10 mA·cm^(-2),far better than IrO_(2)||Pt/C electrolyzer.The formation of sulfide/hydroxide heterostructural interfaces improves the electron transfer and reduces the reaction energy barrier,thus promoting the electrocatalytic processes.

Multicomponent transition metal oxides and(oxy)hydroxides for oxygen evolution

Oxygen evolution reaction(OER)is the core electrode reaction in energy-related technologies,such as electrolytic water,electrocatalytic carbon dioxide reduction,rechargeable metal-air batteries,and renewable fuel cells.Development of well-stocked,cost-effective,and high-performance OER electrocatalysts is the key to the improvement of energy efficiency and the large-scale commercial implementation of these technologies.Multicomponent transition metal oxides and(oxy)hydroxides are the most promising OER catalysts due to their low cost,adjustable structure,high electrocatalytic activity,and outstanding durability.In this review,a brief overview about the mechanisms of OER is first offered,accompanied with the theory and calculation criteria.Then,the latest advances in the rational design of the related OER electrocatalysts and the modulation of the electronic structure of active sites are comprehensively summarized.Specifically,various strategies(including element doping,defect engineering,and fabrication of binderless catalysts)used to improve the OER performance are detailedly discussed,emphasizing the structure–function relationships.Finally,the challenges and perspectives on this promising field are proposed.

Self-supported transition metal chalcogenides for oxygen evolution

Owing to stable spatial framework and large electrochemical interface,self-supported transition metal chalcogenides have been actively explored in renewable energy fields,especially in oxygen evolution reaction(OER).Here,we review the research progress of self-supported transition metal chalcogenides(including sulfides,selenides,and tellurides)for the OER in recent years.The basic principle and evaluation parameters of OER are first introduced,and then the preparation methods of transition metal chalcogenides on various self-supporting substrates(including Ni foam(NF),carbon cloth(CC),carbon fiber paper(CFP),metal mesh/plate,etc.)are systematically summarized.Subsequently,advanced optimization strategies(including interface and defect engineering,heteroatom doping,edge engineering,surface morphology engineering,and construction of heterostructure)are introduced in detail to improve the inherent catalytic activity of self-supported electrocatalysts.Finally,the challenges and prospects of developing more promising self-supported chalcogenide electrocatalysts are proposed.

Synergy between isolated Fe and Co sites accelerates oxygen evolution

Dual-metal catalysts with synergistic effect exhibit enormous potential for sustainable electrocatalytic applications and mechanism research.Compared with mono-metal-site catalysts,dual-metal-site catalysts exhibit higher efficiency for the oxygen evolution reaction(OER)due to reduced energy barrier of the process involving proton-coupled multi-electron transfer.Herein,we construct dual-metal Fe-Co sites coordinated with nitrogen in graphene(FeCo-NG),which exhibits high OER performance with onset overpotential of only 126 mV and Tafel slope of 120 mV·dec^(−1),showing that the rate-determining step is controlled by the single-electron transfer step.Theoretical calculations reveal that the FeN_(4)site exhibits lower OER overpotential than the CoN_(4)site due to appropriate adsorption energy of OOH*on the former,while the O^(*)adsorbed on the adjacent Co site could stabilize the OOH*on the FeN_(4)site through hydrogen bond interaction.

The d-orbital regulation of isolated manganese sites for enhanced oxygen evolution

Developing transition metal-nitrogen-carbon materials(M-N-C)as electrocatalysts for the oxygen evolution reaction(OER)is significant for low-cost energy conversion systems.Further d-orbital adjustment of M center in M-N-C is beneficial to the improvement of OER performance.Herein,we synthesize a single-Mn-atom catalyst based on carbon skeleton(Mn_(1)-N_(2)S_(2)C_(x))with isolated Mn-N_(2)S_(2)sites,which exhibits high alkaline OER activity(η10=280 mV),low Tafel slope(44 mV·dec^(−1)),and excellent stability.Theoretical calculations reveal the pivotal function of isolated Mn-N_(2)S_(2)sites in promoting OER,including the adsorption kinetics of intermediates and activation mechanism of active sites.The doping of S causes the increase in both charge density and work function of active Mn center,and ortho-Mn_(1)-N_(2)S_(2)C_(x)expresses the fastest OER kinetics due to the asymmetric plane.

Recent progress and prospect of carbon-free single-site catalysts for the hydrogen and oxygen evolution reactions

The key challenge for scalable production of hydrogen from water lies in the rational design and preparation of high-performance and earth-abundant electrocatalysts to replace precious metal Pt and IrO_(2) for hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).Although atomic M-N-C materials have been extensively studied in heterogeneous catalysis field,the insufficient antioxidant capacity of carbonous substrates hinders their practical application in OER.Developing highly active and stable OER electrocatalysts is the key for electrochemical water splitting.This review presents feasible design strategies for fabricating carbon-free single-site catalysts and their applications in HER/OER and overall water splitting.The constitutive relationships between structure,composition,and catalytic performance for HER and OER are detailly discussed,providing ponderable insights into rationally constructing high-performance HER and OER electrocatalysts.The perspectives on the challenges and future research orientations in single-site catalysts for electrochemical water splitting are suggested.

Applications of single-atom catalysts

Owing to unsaturated coordination environment,quantum size effect and metal-support interaction,single-or dual-atom metal sites,such as Mn,Fe,Co,Ni,Cu,Zn,Mo,Ru,Rh,Pd,Ag,Sn,Ir,Pt,Au,Bi,and Er coordinated with nonmetallic elements such as O,N,P,and S,exhibit different electronic configurations,which endow them with high catalytic performances in multiple redox reactions and versatile applications in organic synthesis,environmental remediation,energy conversion,and biomedicine.Despite intense research,the relation of structure-activity for single-atom catalysts(SACs)still bedazzles researchers,since diversified configurations of active sites would bring about difficulty in structural identification and theoretical simulations.Here,recent results on the applications of SACs are reviewed with an emphasis on identifying the active sites and discussing the relation between structure and property.

Atomic manganese coordinated to nitrogen and sulfur for oxygen evolution

Lack of high-efficiency,cost-efficient,and well-stocked oxygen evolution reaction(OER)electrocatalysts is a main challenge in large-scale implementation of electrolytic water.By regulating the electronic structure of isolated single-atom metal sites,highperformance transition-metal-based catalysts can be fabricated to greatly improve the OER performance.Herein,we demonstrate single-atom manganese coordinated to nitrogen and sulfur species in two-dimensional graphene nanosheets MnNSG(NSG means N-and S-codoped graphene)as an active and durable OER catalyst with a low overpotential of 296 mV in alkaline media,compared to that of the benchmark IrO_(2) catalyst.Theoretical calculations and experimental measurements reveal that the Mn-N3S sites in the graphene matrix are the most active sites for the OER due to modified electronic structure of the Mn site by three nitrogen and one sulfur atoms coordination,which show lower theoretical overpotential than the Mn-N4 sites and over which the O–O formation step is the rate-determining step.

Cu Nanoparticles Embedded in N-Doped Carbon Materials for Oxygen Reduction Reaction

Summary of main observation and conclusion Development of eco-friendly,cost-effective,and high-performance electrocatalysts to replace precious metal platinum for oxygen reduction reaction(ORR)has received increasing attention.Herein,we adopt a facile one-pot strategy to embed Cu nanoparticles onto N-doped carbon-graphene(Cu@NC-700).The Cu@NC-700 exhibits robust and efficient ORR catalysis with positive half-wave potential(-0.86 V vs.RHE)and lowTafel slope(33.9 mV-dec^-1)in 0.1 M KOH solution.Meanwhile,it manifests remarkable electrochemical stability,and strong tolerance to methanol crossover and carbon monoxide poisoning.The synergistic effect between Cu-N-C sites,Cu nanoparticles,and N-doped carbon support speeds up ORR electrocatalysis.

Advances and challenges in two-dimensional materials for oxygen evolution

Oxygen evolution reaction(OER)plays an important role in many energy conversions and storage technologies,such as water splitting,rechargeable metal air batteries,renewable fuel cells,and electrocatalytic carbon dioxide reduction and nitrogen reduction,but its slow kinetics and high overpotential seriously affect the energy efficiency.Fabrication of high-performance and well-stocked OER catalysts is the key to the large-scale implementation of these energy-related technologies.Two-dimensional(2D)materials get a lot of attention as OER catalysts due to their large specific surface area,abundant active sites,and adjustable structures and compositions.Here,an overview is presented for the latest achievements in design and synthesis of 2D materials(including layered double hydroxides,metal-organic frameworks and their derivatives,covalent-organic frameworks,graphene,and black phosphorus)for the OER,emphasizing novel strategies(including metal/nonmetal doping,defect engineering,interface engineering,lattice strain,and fabrication of heterojunction)for achieving high electrocatalytic activity.Peculiarly,the structure–function relationship is analyzed in detail to gain deeper insight into the reaction mechanism,which is crucial to rational design of more high-performance 2D materials for the OER.Finally,the remaining challenges to improve the OER performance of 2D electrocatalysts are put forward to indicate possible future development of 2D materials.