Electrocatalytic water splitting driven by renewable electricity has been recognized as a promising approach for green hydrogen production. Different from conventional strategies in developing electrocatalysts for the two half-reactions of water splitting (e.g., the hydrogen and oxygen evolution reactions, HER and OER) separately, there has been a growing interest in designing and developing bifunctional electrocatalysts, which are able to catalyze both the HER and OER. In addition, considering the high overpotentials required for OER while limited value of the produced oxygen, there is another rapidly growing interest in exploring alternative oxidation reactions to replace OER for hybrid water splitting toward energy-efficient hydrogen generation. This Review begins with an introduction on the fundamental aspects of water splitting, followed by a thorough discussion on various physicochemical characterization techniques that are frequently employed in probing the active sites, with an emphasis on the reconstruction of bifunctional electrocatalysts during redox electrolysis. The design, synthesis, and performance of diverse bifunctional electrocatalysts based on noble metals, nonprecious metals, and metal-free nanocarbons, for overall water splitting in acidic and alkaline electrolytes, are thoroughly summarized and compared. Next, their application toward hybrid water splitting is also presented, wherein the alternative anodic reactions include sacrificing agents oxidation, pollutants oxidative degradation, and organics oxidative upgrading. Finally, a concise statement on the current challenges and future opportunities of bifunctional electrocatalysts for both overall and hybrid water splitting is presented in the hope of guiding future endeavors in the quest for energy-efficient and sustainable green hydrogen production.

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用于整体和混合水分解的双功能电催化剂

由可再生电力驱动的电催化水分解已被认为是绿色氢生产的一种有前途的方法。与分别开发用于水分解的两个半反应（例如析氢和析氧反应，HER和OER）的电催化剂的传统策略不同，人们对设计和开发双功能电催化剂越来越感兴趣，它们能够催化HER 和 OER。此外，考虑到 OER 所需的高过电势而产生的氧气的价值有限，人们对探索替代氧化反应以取代 OER 用于混合水分解以实现节能制氢的兴趣迅速增长。本综述首先介绍了水分解的基本方面，然后深入讨论了探测活性位点时经常使用的各种物理化学表征技术，重点是氧化还原电解过程中双功能电催化剂的重建。全面总结和比较了基于贵金属、非贵金属和无金属纳米碳的多种双功能电催化剂的设计、合成和性能，用于酸性和碱性电解质中的整体水分解。接下来，还介绍了它们在混合水分解中的应用，其中替代阳极反应包括牺牲剂氧化、污染物氧化降解和有机物氧化升级。最后，对用于整体和混合水分解的双功能电催化剂当前的挑战和未来的机遇进行了简要陈述，希望能够指导未来寻求节能和可持续的绿色氢生产的努力。