High-entropy alloys in water electrolysis: Recent advances, fundamentals, and challenges

REVIEWS SCIENCE CHINA Materials mater.scichina.com link.springer.com Published online 27 March 2023 | https://doi.org/10.1007/s40843-022-2379-8 High-entropy alloys in water electrolysis: Recent advances, fundamentals, and challenges Quan Zhang1, Kang Lian1,2, Gaocan Qi3*, Shusheng Zhang4, Qian Liu5, Yang Luo6,7*, Jun Luo1,8 and Xijun Liu2* ABSTRACT As a clean energy carrier, hydrogen energy has become part of the global clean energy strategy and one of the necessary routes to achieve global carbon neutrality. Driven by renewable electricity, water electrolysis promises to be an ideal long-term hydrogen production method that can realize net zero carbon emissions. Compared with conventional alloys, high-entropy alloys (HEAs) have much more catalytic active sites due to their unique structural features including occupation disorder and lattice ordering. They have various promising applications in the field of hydrolysis catalysts. Herein, in this review, the mechanisms of electrolysis of water, catalytic principles of HEAs in hydrolysis processes and latest research progress of HEAs as water electrolysis catalysts are summarized. We also provide perspectives on the difficulties and potential linked to novel HEA design approaches in this attractive sector, with a focus on the connection between both the surface morphology and the catalysis activity. The compositions and possible applications of HEAs in water electrolysis and other emerging fields are outlined. Keywords: high-entropy alloys, electrolytic water splitting, catalysts design, hydrogen evolution reaction, oxygen evolution reaction INTRODUCTION With the massive burning of traditional fossil fuels, a large amount of greenhouse gases are being emitted, causing global warming, which leads to problems such as rising sea levels and the appearance of extreme weather. The carbon dioxide emissions caused by the use of fossil fuels have caused many adverse effects on the earth’s ecological balance, causing irreversible damage. Moreover, as urbanization and industrialization intensify, the demand for new and clean energy sources is also increasing, and the accompanying energy crisis is becoming more serious. New energy sources including solar, hydrogen, and tidal energy are being explored gradually. Solar cells [1,2], hydrogen hydrolysis devices and supercapacitors [3] have a promising future. Hydrogen is viewed as a suitable substitute for conventional fossil fuels as it is a clean energy source which is easily stored and is also predicted to play a significant part in the development of brand-new sources of power in the future [4–6]. Hydrogen has the highest energy density (146 kJ g−1) compared with other fuels used. The only product of H2 combustion is water, which contains no greenhouse gases (i.e., carbon dioxide, methane, or other harmful gases). Hydrogen can be reproduced from water by electrolysis [7–9], photolysis, and photo electrolysis, which can result in hydrogen recycling [10–14]. Photolytic and photo electrolytic water splitting will take some time to achieve industrial application due to their limitations and high cost. Hydrogen production from water electrolysis, as a more mature method of hydrogen production, has a crucial role in developing hydrogen energy [15,16]. The purpose of energy storage is achieved through energy conversion by changing electrical energy into hydrogen energy for storage employing hydrogen production from water electrolysis [17,18]. In the process of hydrogen production from electrolysis, only ecofriendly oxygen is produced as a by-product. Electrolysis of water is a prospective and swiftly developing method of generating hydrogen. One of the core problems that need to be solved is reducing electricity consumption in the process of hydrogen preparation [19–22]. It is crucial to design a more reasonable industrial electrolyzer and develop preferable catalysts for hydrogen production. With better catalysts, the advantages of electrolytic hydrogen production will be more and more prominent [23–26]. Electrolysis of water to produce hydrogen is the current cleaner and eco-friendly pathway to obtain clean energy. Pt is the main catalyst for the acquisition of hydrogen, while Ru and Ir are important catalysts for the preparation of oxygen. The 1 Institute for New Energy Materials & Low-Carbon Technologies, School of Materials Science and Engineering, Tianjin University of Technology, Tianjin 300384, China 2 MOE Key Laboratory of New Processing Technology for Non-Ferrous Metals and Materials, and Guangxi Key Laboratory of Processing for Non-Ferrous Metals and Featured Materials, School of Resource, Environments and Materials, Guangxi University, Nanning 530004, China 3 School of Materials Science and Engineering, Tianjin University of Technology, Tianjin 300384, China 4 College of Chemistry, Zhengzhou University, Zhengzhou 450000, China 5 Institute for Advanced Study, Chengdu University, Chengdu 610106, China 6 Department of Materials, ETH Zürich, Zürich 8093, Switzerland 7 Department of Physics, City University of Hong Kong, Hong Kong SAR 999077, China 8 ShenSi Lab, Shenzhen Institute for Advanced Study, University of Electronic Science and Technology of China, Shenzhen 518110, China * Corresponding authors (emails: (Qi G); (Luo Y); (Liu X)) © Science China Press 2023 1 REVIEWS SCIENCE CHINA Materials scarcity of these three noble-metal catalysts will make the production cost higher, which hinders industrial-scale production. Water electrolysis kinetics can be enhanced by the numerous and diverse active sites, elemental variety, multifunctionality, lattice distortion, and natural surface complexity of high-entropy alloys (HEAs), which also modify the adsorption of reactants while delaying the adsorption of intermediates. Regarding the industrial application field, the most widely used hydrolysis catalysts are mainly precious metals and their oxides, including IrO2, RuO2 and Pt. However, the rarity and high-cost of precious metal elements limit their large-scale preparation. More and more researchers focus their research on the preparation of nonprecious metal catalysts [27]. In order to retain a powerful catalytic action of hydrolysis while using less precious metals, some researchers are currently utilizing unique metal-organic framework (MOF) structures that are filled with metal components [28]. The number of active sites involved in the catalytic reaction can be adjusted by changing the structure of the material [29,30]. To create well-aligned Ni-benzenedicarboxylic acid (BDC)based MOF nanosheet arrays with S introduction, Cheng et al. [31] designed a universal ligand control approach (S-NiBDC). The S-NiBDC array demonstrates a low overpotential of 310 mV to obtain a current density of 1.0 A cm−2 with great stability in alkaline electrolytes, taking advantage of the closer p-band center to the Fermi level with strong electron transferability. By encapsulating poorly (...truncated)