高熵合金纳米电催化剂的合成

Recent Progress on High-Entropy Nanoalloy for Electrocatalytic Applications

相较于单金属和双金属催化剂,高熵合金(HEAs)催化剂因具有多种活性位点而表现出优异的协同效应和催化活性,当其粒径细化至纳米尺度时,纳米尺寸效应与多元活性位点赋予了高熵合金纳米颗粒(np-HEAs)催化剂较低的过电位,近年来在电化学领域逐渐成为研究热点。目前,np-HEAs催化剂的合成方法有脱合金法、热冲击法、低温液相共还原法、机械合金法、激光烧蚀法及溅射沉积法等。综述了近年来np-HEAs催化剂合成的研究现状,总结了提高其催化活性的策略及措施,并展望了np-HEAs催化剂的未来发展方向。

As one of the important ways to develop green energy,electrocatalysis has the advantages of environmental friendliness,cleanliness and sustainability,whose key lies on the exploitation of catalysts with low overpotential.Compared with mono-or bimetallic catalysts,high entropy alloys(HEAs) nano-catalysts exhibit the strong electrolytic activity owing to their multiple active sites,and have gradually become a research hotspot in recent years,especially in hydrogen production from water.In the electrocatalytic process,the multi-metals can adjust the adsorption energies of reactant molecules and intermediates on the nano-catalyst surface,and thus enhance the electrocatalytic performance of HEAs nanoalloy(np-HEAs) catalysts through synergistic effects.With a comprehensive review of the fabrication of np-HEAs and the latest research in the field of electrocatalysis,this work summarized the methods for preparation of np-HEAs including the de-alloying method,thermal shock method,low-temperature liquid-phase co-reduction method,mechanical alloying method,laser ablation method and sputtering deposition method.The principles,conditions and characteristics of various preparation methods and the catalytic mechanisms of the as-obtained np-HEAs in the electrocatalytic process were presented.The inherent connection between the preparation methods and the electrocatalytic performance of np-HEAs was described,and the problems and shortcomings of the present study and the future research directions were pointed out.The de-alloying method was to selectively dissolve and remove the more active elements in the precursor through selective chemical(or electrochemical) corrosion,leaving behind the chemically stable elements,which could synthesize HEAs with the controllable composition and nanopores,and the as-synthesized np-HEAs had the relatively large specific surface area.The thermal shock method was to prepare np-HEAs by a rapid heating and cooling process using carbon materials as the heating source and catalyst carrier with Joule-heating condition.The lowtemperature liquid-phase co-reduction method,as a bottom-up synthesis method,generally involved dissolving soluble metal salts in a solution which are subsequently reduced at room temperature.The conventionally mechanical alloying process utilized the hysteresis dispersal effect of HEAs and prepares np-HEAs through an iterative process including the calendaring,compaction,crushing and recompression between metal powder particles,as well as the local friction and heating.The laser ablation method was to ablate the metal target using a high-energy laser,which instantly reduced the metal and np-HEAs were finally formed in the target.The sputtering deposition generally involved the deposition of np-HEAs on substrate materials by magnetron sputtering at a wide range of voltages.The advantages and disadvantages of these preparation methods as well as the catalytic mechanisms of np-HEAs had been analyzed based on the existing experimental and theoretical foundations of the recent works.All these methods contributed to the development and utilization of np-HEAs to some extent.In the catalytic strategy of np-HEAs,it could be roughly summarized that the elements that played the dominated catalytic role were the noble metals Pt,Pd,Ir,and etc.,and the others elements Co,Ni,Mn,and etc.,which showed the synergistic effect that jointly promote the electrocatalytic reaction.Although these developments had significantly contributed to the development of np-HEAs,it had suffered from low purity,harsh preparation conditions and high cost in the synthesis process.The research on the relevant catalytic mechanisms of np-HEAs was relatively scarce and immature,and the most current works were focused on the surface Co,Ni and noble metals,and the theoretical calculation of other high-entropy elements was less.The synergistic effect between each elemental atom of np-HEAs was not yet clear,and the related catalytic mechanisms were inevitably contradictory.So it was believed that the further explorations were expected from the following aspects:1) A novel technique was still required to prepare np-HEAs,which could work stably and continuously at higher voltages in the actual applications;2) The precious metals were still dominated for the enhanced catalytic behavior of current np-HEAs,thus the developing of inexpensive transition metal np-HEAs was highly urgent to reduce their cost for the practical industrial applications;3) The catalytic mechanism of np-HEAs was not well established,and the study of the tedious and comprehensive synergistic effects was not clear.Thus,the density functional theory(DFT) combined with molecular dynamics simulation(MD) was expected to be used to explore the behavior mechanism of np-HEAs and the actual catalytic process,to establish the corresponding reaction kinetic model,elucidate the synergistic effects between different metal elements,and provide a better guidance for the development and application of np-HEAs.By summarizing the relevant scientific research,the recent research progress in the preparation of np-HEAs would be introduced to the general researchers,which would help the development of np-HEAs in the field of electrocatalysis,and be also expected to provide new ideas and perspectives to solve the "neck" problem of np-HEAs in electrocatalysis.