This report shows the synthesis of a new family of “core-shell” carbon nitride (CN)-based electrocatalysts (ECs) for the oxygen reduction reaction (ORR) in acid medium. The ECs comprise “cores” of carbon black nanoparticles (NPs) that are covered by a CN “shell” embedding the active sites. The latter include Pt as the “active metal” and Co as the “co-catalyst.” The interplay between the synthesis parameters, the chemical composition, and the ORR performance of the final ECs is elucidated. In particular, the ORR performance and reaction mechanism are studied both in an: (i) “ex-situ” setup, by means of cyclic voltammetry with thin-film rotating ring-disk electrode (CV-TF-RRDE) measurements; and (ii) “in-situ” experiment, i.e., in single proton exchange membrane fuel cells (PEMFCs) tested under operating conditions. A structural hypothesis is proposed that explains both the “ex situ” and the “in situ” ORR results on the basis of: (i) the relative amounts of the reactants used in the precursor synthesis; and (ii) the main temperature of the pyrolysis process (T_f) adopted in the preparation of the ECs. It is shown that the understanding of the fundamental features of the physicochemical processes involved in the preparation of the ECs is crucial in order to improve the proposed synthesis route and to yield ORR ECs exhibiting a performance level beyond the state of the art.

Graphical Abstract

该报告显示了用于酸性介质中氧还原反应（ORR）的新型“核-壳”氮化碳（CN）基电催化剂（EC）的合成。EC包含炭黑纳米颗粒（NP）的“核心”，这些核心被嵌入活性位点的CN“壳”覆盖。后者包括Pt作为“活性金属”和“钴”作为“助催化剂”。阐明了最终EC的合成参数，化学组成和ORR性能之间的相互作用。特别是，在以下两种情况下都研究了ORR性能和反应机理：（i）“非原位”设置，通过循环伏安法和薄膜旋转环形盘电极（CV-TF-RRDE）测量；（ii）“原位”实验，即在运行条件下测试的单个质子交换膜燃料电池（PEMFC）中。提出了一种结构假说，该假说解释了“异位”和“原位” ORR结果，其依据是：（i）前体合成中所用反应物的相对量；（ii）热解过程的主要温度（T _f），以在EC的准备工作中采用。结果表明，对制备EC所涉及的物理化学过程基本特征的理解对于改善拟议的合成路线和生产表现出超出现有技术水平的ORR EC至关重要。

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