Optimization of active sites by sulfurization of the core–shell ZIF 67@ZIF 8 for rapid oxygen reduction kinetics in acidic media

Abstract

Achieving a highly active cathode surface with extremely efficient electrocatalysts for oxygen reduction kinetics is a fundamental necessity for durable fuel cells. Developing such active materials into desirable nanostructures is crucial in the pursuit of electrocatalysis. A facile preparation of cobalt decorated nitrogen and sulfur co-doped carbon nanostructures (Co-NSC) with the added advantage of Zeolitic imidazolate frameworks (ZIF), ZIF 67@ZIF 8 is reported here. The as-prepared Co, N, S, co-doped carbon (Co-NSC) electrocatalyst comes under platinum group metal-free (PGM-free) catalysts which intends to replace the scarce and highly expensive commercial Pt catalysts. Facile preparation of the Co-NSC catalyst that is scalable, low cost and highly ORR active makes the material advantageous. Co-doping sulfur has dramatically enhanced the intrinsic catalytic activity of the catalyst, and the degree of variation in sulfurization greatly influences the overall catalytic property. Co-NSC 200 with high sulfur doping exhibit a positively shifted onset potential of 0.81 V, and a high yielding current density of 5.5 mA cm(-2) at 20 mV s(-1).