Rational design of Co3O4–CNT–N-doped carbon system for superior OER: Bridging in situ/ex situ studies with DFT

This paper reveals that the controlled strategy of high-temperature carbonization of ZIF-67 is a facile route to deliver active species boosting oxygen evolution reaction (OER) performance. The optimized sample (treated at 750 °C) is composed of a nitrogen-doped carbon matrix with embedded metallic Co nanoparticles with Co₃O₄ islets and decorated by carbon nanotubes (CNT). Among them, Co₃O₄ islets significantly promote oxygen evolution. Their enhanced activity is explained via density-functional theory (DFT) calculations describing the reaction mechanism involving two different active sites of islets. The experimental results demonstrate an overpotential of 288 mV, a Tafel slope of 69 mV/dec, and a potential retention of 97.2 % after a 100h test at 50 mA/cm². Systematic microscopic, in situ & ex-situ spectroscopic (Raman), and theoretical studies allowed us to unveil the intermediates responsible for the promotion of electroactivity. The theoretical model predicts the predominant catalytic activity of terminal O atoms (Ot) at the Co₃O₄ surface. These results offer a promising "proof of concept" for developing more efficient zeolitic imidazole framework (ZIF)-based electrocatalysts.