Recent Progress on High Entropy Alloy Water Electrolytic Electrode

The efficiency of hydrogen generation can be improved by developing suitable catalytic materials and preparing the catalytic electrode with high performance, large scale, and low cost. As a new platform for catalysis, high entropy alloy (HEA) has attracted extensive attention for its high catalytic activity. The work aims to review the recent advances in the HEA water electrolytic electrodes for catalyzing the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Firstly, a brief introduction to the industrial background and electrochemical principles of water electrolysis was made. The sources of high activity of HEA, i.e., rational adsorption energy and a large number of active sites attributed to hybridized energy bond, were analyzed. The strategies of HEA composition design, including the replacement of noble metals and the effects of alloying elements on catalytic activity, were discussed. The applications of first-principle calculation in the study of the catalytic mechanism, regulation of adsorption energy, and high-throughput screening of composition, were introduced. The processing and challenges of catalytic electrodes with different macrostructure, including the plate, porous, and nanoparticle-loaded electrodes, were summarized. Finally, the perspectives and research direction were featured. At present, two ways to improve the catalytic activity of HEA electrodes, are to increase the intrinsic activity by designing the rational composition, and to increase the number of active sites by optimizing the processing. For composition design, Pt-group HEA (IrPdPtRhRu) shows the highest HER activity corresponding to the lowest overpotential. Meanwhile, the 3d transition metals have a significant advantage in reducing costs. Pd-doped 3d transition metal HEA (FeCoNiCuPd) also shows the best performance for catalyzing OER. On the other hand, first-principle calculation plays a vital role in composition design. It can be used to predict the adsorption energy to establish the volcano curves or to screen the composition. It can also be used to calculate the reaction pathway to infer the reaction barrier, rate determine step, BEP relationship, or other reaction mechanisms. For HEA electrode processing, plat electrodes can be prepared by vacuum arc melting, cold spray, thermal spray, laser cladding, and magnetron sputtering, which possess high conductivity, large scale, and high preparation efficiency. Porous electrodes can be prepared by the de-alloying method, its macrostructure increases the specific surface area and exposes more active edge sites, which improves the catalytic activity. Nanoparticle-loaded electrodes are mostly employed in HEA catalytic electrodes. They can be prepared by a "top-down" or "down-top" pathway. The former includes laser ablation and photo-etching method, and the latter includes hydrothermal, solvothermal, or carbon-thermal shock synthesis. The high activity of nanoparticle-loaded electrodes can be attributed to the high surface area, size effect, and ligand effect. Although many HEA electrode shows outstanding activity and stability, more efforts on catalytic the mechanism are necessary to illustrate the complicated electronic structure and varied surface active sites. A rational and representative structure model of the HEA surface should be established to calculate the adsorption energy or reaction barriers accurately. A more comprehensive active descriptor should be explored to screen the composition. Meanwhile, the studies on the preparation should be more microscopic, for example, focusing on electron transfer in the electrode and proton transfer on the surface. In this way, the performance of HEA electrolytic electrodes can be further improved to facilitate their commercial and industrial applications. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.