In this work, the effect of porphyrin loading and template size is varied systematically to study its impact on the oxygen reduction reaction (ORR) activity and selectivity as followed by rotating ring disc electrode experiments in both acidic and alkaline electrolytes. The structural composition and morphology are investigated by ⁵⁷Fe Mössbauer spectroscopy, transmission electron microscopy, Raman spectroscopy and Brunauer–Emmett–Teller analysis. It is shown that with decreasing template size, specifically the ORR performance towards fuel cell application gets improved, while at constant area loading of the iron precursor (here expressed in number of porphyrin layers), the iron signature does not change much. Moreover, it is well illustrated that too large area loadings result in the formation of undesired side phases that also cause a decrease in the performance, specifically in acidic electrolyte. Thus, if the impact of morphology is the focus of research it is important to consider the area loading rather than its weight loading. At constant weight loading, beside morphology the structural composition can also change and impact the catalytic performance.

This article is part of the theme issue ‘Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 2)’.

在这项工作中，卟啉负载和模板尺寸的影响系统地变化，以研究其对氧还原反应 (ORR) 活性和选择性的影响，然后在酸性和碱性电解质中进行旋转环盘电极实验。结构组成和形貌由⁵⁷Fe Mössbauer 光谱、透射电子显微镜、拉曼光谱和 Brunauer-Emmett-Teller 分析。结果表明，随着模板尺寸的减小，特别是燃料电池应用的 ORR 性能得到改善，而在铁前体的恒定面积负载（此处以卟啉层数表示）的情况下，铁特征没有太大变化。此外，它很好地说明了太大的面积负载会导致形成不需要的副相，这也会导致性能下降，特别是在酸性电解质中。因此，如果形态的影响是研究的重点，那么考虑面积载荷而不是重量载荷是很重要的。在恒重负载下，除了形态外，结构组成也会改变并影响催化性能。

本文是主题问题“用于新兴技术的生物衍生和仿生可持续先进材料（第 2 部分）”的一部分。