Electronic structure regulation in the design of low-cost efficient electrocatalysts: From theory to applications

Electrocatalysts play a pivotal role in reducing the reaction barriers for key reactions such as the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER), which are essential for the development of environment-friendly energy conversion devices including metal air batteries (MABs), proton exchange membrane fuel cells (PEMFCs), oxyhydrogen fuel cells (OFC), and water electrolyzers (WE). Despite the acknowledged effectiveness of noble metals (Pt, Ir, Ru-based) as electrocatalysts, their high cost and scarcity greatly limit their large-scale application. Thus, there is an urgent need to design low precious metal loading/noble metal-free electrocatalysts. The electronic structure plays a crucial role in determining the efficiency of electron transfer during electrochemical reactions. Modifying the electronic structure can facilitate charge transfer processes or create efficient active sites with low reaction energy barriers, both of which are beneficial for designing low precious metal loading/noble metal-free electrocatalysts with high catalytic activity. In this article, we review strategies for modifying materials without introducing other phases (known as self-modification) and introducing other phases (known as multi-phase modification). Specifically, self-modification strategies including heteroatom doping, edge/vacancy engineering, functional group introducing, tuning the exposed crystal planes, and multi-phase modification strategies regarding heterostructure creation are analyzed in detail. These strategies are useful for designing electrocatalysts that reinforce the electron transfer process during electrochemical reactions. Additionally, two approaches for accelerating the electron transfer on the electrode including designing bind-free/integrated electrode structure and constructing membrane electrode assembly, have also been discussed for pushing forward the practical application. At last, we provide a comprehensive summary and future perspectives of both self-modification/multi-phase modification strategies and practical application of these efficient low-cost electrocatalysts in this article.