Enhancing oxygen reduction reaction activity in ZIF-derived catalysts through thermal oxidation-induced micropore enlargement

Abstract

Non-precious metal-based catalysts derived from metal–organic frameworks (MOFs), particularly zeolitic imidazolate frameworks (ZIFs), have gained attention as promising electrocatalysts for enhancing the oxygen reduction reaction (ORR) efficiency in energy conversion systems. However, the intrinsic microporous structure of ZIF-derived catalysts can hinder the mass transport of reactants to the active sites, thereby reducing the ORR mass activity (MA). In this paper, we present a novel strategy for improving the MA of ZIF-derived catalysts, which is an essential advancement in renewable energy storage and conversion technologies. While direct carbonization of ZIF precursors typically preserves this microporosity, limiting performance, we present a novel strategy to overcome this by employing a controlled thermal oxidation pre-treatment on Zn,Co-ZIF precursors. This pre-treatment introduces oxygen species and lattice strain into the framework, which act as in situ etching agents during subsequent pyrolysis, effectively converting micropores into mesopores. The resulting optimized catalyst (Co/N–C_3) exhibited a significant increase in mesopore volume and specific external surface area compared to the non-oxidized counterpart. Consequently, it demonstrated superior MA (205.98 A g⁻¹_catal) and stability (maintaining nearly 100% activity for 48 h), outperforming commercial Pt/C (56.24 A g⁻¹_catal). This study highlights that oxidation-induced pore engineering is critical for optimizing the mass transport properties of ZIF-derived catalysts, paving the way for their application in high performance energy conversion technologies.