The exploration of highly active, durable, and cost-effective electrocatalysts for the oxygen reduction reaction (ORR) is indispensable for several important energy conversion technologies. Significant achievements have been made with numerous efforts devoted by the academic and industrial researchers. In this review, from a more practical point of view, the tests and experiments at the membrane electrode assembly (MEA) level are accentuated due to the fact that the rotating disk electrode (RDE) level performance cannot be transformed directly into the MEA level. Four major categories of the current ORR electrocatalysts are discussed, namely, platinum group metal (PGM or noble) catalysts, non-PGM catalysts, carbon-based catalysts, and single-atom-based catalysts. The advantages and shortcomings, along with the performance achieved by the catalysts, are briefly reviewed, and the improvement in the rational design approaches is emphasized at the full-cell level. Finally, the present challenges and prospects are discussed for developing advanced ORR electrocatalysts.

对于几种重要的能量转化技术而言，探索用于氧还原反应（ORR）的高活性，耐用且具有成本效益的电催化剂是必不可少的。在学术界和工业界研究人员的大量努力下，已经取得了重大成就。在这篇评论中，从更实际的角度来看，由于不能将圆盘电极（RDE）的性能直接转换为MEA级别，因此在膜电极组件（MEA）级别的测试和实验得到了强调。讨论了当前ORR电催化剂的四个主要类别，即铂族金属（PGM或贵金属）催化剂，非PGM催化剂，碳基催化剂和单原子基催化剂。催化剂的优点和缺点以及性能，简要回顾一下，并在全单元级别上强调合理设计方法的改进。最后，讨论了开发高级ORR电催化剂的当前挑战和前景。