Cui Wen-Gang, Gao Fan, Na Guoquan, Wang Xingqiang, Li Zhenglong, Yang Yaxiong, Niu Zhiqiang, Qu Yongquan, Wang Dingsheng, Pan Hongge
Institute of Science and Technology for New Energy, Xi'an Technological University, Xi'an, 710021, P. R. China.
Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), Nankai University, Tianjin 300071, China.
Chem Soc Rev. 2024 Oct 14;53(20):10253-10311. doi: 10.1039/d4cs00370e.
Hydrogen electrocatalytic reactions, including the hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR), play a crucial role in a wide range of energy conversion and storage technologies. However, the HER and HOR display anomalous non-Nernstian pH dependent kinetics, showing two to three orders of magnitude sluggish kinetics in alkaline media compared to that in acidic media. Fundamental understanding of the origins of the intrinsic pH effect has attracted substantial interest from the electrocatalysis community. More critically, a fundamental molecular level understanding of this effect is still debatable, but is essential for developing active, stable, and affordable fuel cells and water electrolysis technologies. Against this backdrop, in this review, we provide a comprehensive overview of the intrinsic pH effect on hydrogen electrocatalysis, covering the experimental observations, underlying principles, and strategies for catalyst design. We discuss the strengths and shortcomings of various activity descriptors, including hydrogen binding energy (HBE) theory, bifunctional theory, potential of zero free charge (pzfc) theory, 2B theory and other theories, across different electrolytes and catalyst surfaces, and outline their interrelations where possible. Additionally, we highlight the design principles and research progress in improving the alkaline HER/HOR kinetics by catalyst design and electrolyte optimization employing the aforementioned theories. Finally, the remaining controversies about the pH effects on HER/HOR kinetics as well as the challenges and possible research directions in this field are also put forward. This review aims to provide researchers with a comprehensive understanding of the intrinsic pH effect and inspire the development of more cost-effective and durable alkaline water electrolyzers (AWEs) and anion exchange membrane fuel cells (AMFCs) for a sustainable energy future.
氢电催化反应，包括析氢反应（HER）和氢氧化反应（HOR），在广泛的能量转换和存储技术中起着至关重要的作用。然而，HER和HOR表现出异常的非能斯特pH依赖性动力学，与酸性介质相比，在碱性介质中的动力学迟缓两到三个数量级。对内在pH效应起源的基本理解引起了电催化领域的广泛关注。更关键的是，对这种效应在分子水平上的基本理解仍存在争议，但对于开发活性高、稳定性好且价格合理的燃料电池和水电解技术至关重要。在此背景下，在本综述中，我们全面概述了内在pH效应在氢电催化方面的情况，涵盖实验观察、基本原理以及催化剂设计策略。我们讨论了各种活性描述符的优缺点，包括氢结合能（HBE）理论、双功能理论、零自由电荷电位（pzfc）理论、2B理论等理论，涉及不同的电解质和催化剂表面，并尽可能概述它们之间的相互关系。此外，我们强调了通过采用上述理论进行催化剂设计和电解质优化来改善碱性HER/HOR动力学的设计原则和研究进展。最后，还提出了关于pH对HER/HOR动力学影响的剩余争议以及该领域的挑战和可能的研究方向。本综述旨在为研究人员提供对内在pH效应的全面理解，并激发开发更具成本效益和耐用性的碱性水电解槽（AWE）和阴离子交换膜燃料电池（AMFC），以实现可持续能源未来。
