Toward quantification of active site density and size-dependent ORR activity of ZIF-derived carbons in alkaline electrolyte

Abstract

ZIF-derived carbons (ZDCs) represent a novel category of non-precious metal catalysts (NPMCs) for the oxygen reduction reaction (ORR). Nevertheless, establishing the correlation between their structure and performance is challenging due to their diverse structural properties and ill-defined active site moieties. Here we investigate the effect of ZIF-67 derived carbon’s particle size and corresponding distribution of assorted nitrogen functionalities on the ORR. Our findings reveal a substantial increase in ORR activity with decreasing ZDC particle size, while the exact influence of nitrogen functionalities remains uncertain. Most importantly, the present work unveils a correlation between the ORR activity and the site density (SD) of Co-Nx within the ZDC materials, which can be attributed to the concurrently increasing SD and accessibility of Co-Nx on the ZDC particles with small sizes. The present work provides novel insights into the optimization of ZDCs as high-performance NPMCs for ORR in alkaline electrolytes.