Polymer electrolyte fuel cells operating on clean and sustainable hydrogen are an attractive solution for clean transportation. However, polymer electrolyte fuel cells are costly owing to the use of considerable amounts of platinum group metal (PGM) catalysts, which are needed to catalyse the very slow oxygen reduction reaction at the cathode. The most attractive path in that regard is a complete replacement of precious metal catalysts by PGM-free materials with similar or better performance. Since 2010, numerous promising catalysts have been proposed for PGM-free electrocatalysis. However, the best-performing catalysts do not yet meet the requirements of practical systems. One important hurdle in catalyst discovery is relying heavily on empirical rather than rational design-based approaches. This Perspective article focuses on the most promising PGM-free oxygen reduction reaction catalysts based on atomically dispersed, nitrogen-coordinated single-atom metal sites (M–N–C catalysts). We specifically concentrate on the active-site structure and critical factors governing catalytic activity and performance durability. We propose potentially effective strategies for improving performance by controlling the catalyst structure at the atomic scale, mesoscale and nanoscale. We highlight the importance of overcoming often-observed activity–stability trade-offs and the importance of advanced modelling for the rational design of catalysts.

使用清洁和可持续的氢气运行的聚合物电解质燃料电池是清洁交通的一种有吸引力的解决方案。然而，聚合物电解质燃料电池由于使用大量的铂族金属（PGM）催化剂而成本高昂，而这些催化剂需要催化阴极上非常缓慢的氧还原反应。在这方面最有吸引力的途径是用性能相似或更好的不含铂族金属的材料完全替代贵金属催化剂。自 2010 年以来，人们提出了许多有前景的催化剂用于不含铂族金属的电催化。然而，性能最好的催化剂尚未满足实际系统的要求。催化剂发现的一个重要障碍是严重依赖经验而不是基于理性设计的方法。本文重点介绍最有前途的基于原子分散、氮配位单原子金属位点（M-N-C 催化剂）的不含铂族金属的氧还原反应催化剂。我们特别关注活性位点结构以及控制催化活性和性能耐久性的关键因素。我们提出了通过在原子尺度、介观尺度和纳米尺度控制催化剂结构来提高性能的潜在有效策略。我们强调了克服经常观察到的活性与稳定性权衡的重要性以及先进建模对于催化剂合理设计的重要性。