The core of clean energy technologies such as fuel cells, water electrolyzers, and metal–air batteries depends on a series of oxygen and hydrogen-based electrocatalysis reactions, including the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), which necessitate cost-effective electrocatalysts to improve their energy efficiency. In the recent decade, complex metal oxides (beyond simple transition metal oxides, spinel oxides and ABO₃ perovskite oxides) have emerged as promising candidate materials with unexpected electrocatalytic activities for oxygen and hydrogen electrocatalysis owing to their special crystal structures and unique physicochemical properties. In this review, the current progress in complex metal oxides for ORR, OER, and HER electrocatalysis is comprehensively presented. Initially, we present a brief description of some fundamental concepts of the ORR, OER, and HER and a detailed description of complex metal oxides, including their physicochemical characteristics, synthesis methods, and structural characterization. Subsequently, we present a thorough overview of various complex metal oxides reported for ORR, OER, and HER electrocatalysis thus far, such as double/triple/quadruple perovskites, perovskite hydroxides, brownmillerites, Ruddlesden–Popper oxides, Aurivillius oxides, lithium/sodium transition metal oxides, pyrochlores, metal phosphates, polyoxometalates and other specially structured oxides, with emphasis on the designed strategies for promoting their performance and structure–property–performance relationships. Moreover, the practical device applications of complex metal oxides in fuel cells, water electrolyzers, and metal–air batteries are discussed. Finally, some concluding remarks summarizing the challenges, perspectives, and research trends of this topic are presented. We hope that this review provides a clear overview of the current status of this emerging field and stimulate future efforts to design more advanced electrocatalysts.

中文翻译：

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超越传统结构：用于高效氧和氢电催化的新兴复杂金属氧化物


燃料电池、水电解槽和金属空气电池等清洁能源技术的核心依赖于一系列氧基和氢基电催化反应，包括氧还原反应 （ORR）、析氧反应 （OER） 和析氢反应 （HER），这需要具有成本效益的电催化剂来提高其能源效率。近十年来，复杂的金属氧化物（超越简单的过渡金属氧化物、尖晶石氧化物和 ABO₃ 钙钛矿氧化物）因其特殊的晶体结构和独特的物理化学性质而成为具有前景广阔的候选材料，具有意想不到的氧和氢电催化活性。本文全面综述了复合金属氧化物在 ORR、OER 和 HER 电催化中的应用进展。最初，我们简要介绍了 ORR、OER 和 HER 的一些基本概念，并详细描述了复杂金属氧化物，包括它们的物理化学特性、合成方法和结构表征。随后，我们全面概述了迄今为止报道的用于 ORR、OER 和 HER 电催化的各种复杂金属氧化物，例如双/三/四钙钛矿、钙钛矿氢氧化物、褐米勒石、Ruddlesden-Popper 氧化物、Aurivillius 氧化物、锂/钠过渡金属氧化物、焦绿石、金属磷酸盐、多金属氧酸盐和其他特殊结构的氧化物，重点是促进其性能和结构-性能-性能的设计策略关系。此外，还讨论了复杂金属氧化物在燃料电池、水电解槽和金属空气电池中的实际器件应用。 最后，提出了一些总结性评论，总结了该主题的挑战、观点和研究趋势。我们希望这篇综述能清楚地概述这一新兴领域的现状，并激发未来设计更先进电催化剂的努力。