The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are core steps of various energy conversion and storage systems. However, their sluggish reaction kinetics, i.e., the demanding multielectron transfer processes, still render OER/ORR catalysts less efficient for practical applications. Moreover, the complexity of the catalyst–electrolyte interface makes a comprehensive understanding of the intrinsic OER/ORR mechanisms challenging. Fortunately, recent advances of in situ/operando characterization techniques have facilitated the kinetic monitoring of catalysts under reaction conditions. Here we provide selected highlights of recent in situ/operando mechanistic studies of OER/ORR catalysts with the main emphasis placed on heterogeneous systems (primarily discussing first-row transition metals which operate under basic conditions), followed by a brief outlook on molecular catalysts. Key sections in this review are focused on determination of the true active species, identification of the active sites, and monitoring of the reactive intermediates. For in-depth insights into the above factors, a short overview of the metrics for accurate characterizations of OER/ORR catalysts is provided. A combination of the obtained time-resolved reaction information and reliable activity data will then guide the rational design of new catalysts. Strategies such as optimizing the restructuring process as well as overcoming the adsorption-energy scaling relations will be discussed. Finally, pending current challenges and prospects toward the understanding and development of efficient heterogeneous catalysts and selected homogeneous catalysts are presented.

中文翻译：

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析氧/还原反应催化剂：从原位监测和反应机制到合理设计

析氧反应（OER）和氧还原反应（ORR）是各种能量转换和存储系统的核心步骤。然而，它们缓慢的反应动力学，即要求苛刻的多电子转移过程，仍然使 OER/ORR 催化剂在实际应用中效率较低。此外，催化剂-电解质界面的复杂性使得对内在 OER/ORR 机制的全面理解具有挑战性。幸运的是，原位/操作表征技术的最新进展促进了反应条件下催化剂的动力学监测。在这里，我们提供了近期原位/操作的精选亮点OER/ORR 催化剂的机理研究，主要侧重于非均相系统（主要讨论在碱性条件下运行的第一排过渡金属），然后是对分子催化剂的简要展望。本综述的关键部分侧重于确定真正的活性物质、活性位点的鉴定和反应中间体的监测。为了深入了解上述因素，提供了准确表征 OER/ORR 催化剂的指标的简短概述。获得的时间分辨反应信息和可靠的活性数据的结合将指导新催化剂的合理设计。将讨论优化重组过程以及克服吸附-能量比例关系等策略。最后，