Optimized cobalt and graphitic carbon hybrid catalysts derived from zeolite imidazolate framework for oxygen evolution reaction

Catalysts with cobalt (Co) and graphitic carbon hybrid structure are receiving significant attention in various electrocatalysis applications because of their stability and high activities. In addition, the size and the well dispersed distribution of metal active site are some of the most important factors for electrocatalyst. In this paper, we successfully synthesized ultra-small and well dispersed Co nanoparticle on nitrogen-doped carbon structure (Co/NC) adding and evaporating a Zinc (Zn) and found the optimized ratio of Co and Zn. We used a bottom-up method to synthesize catalysts with Co on carbon substrate structure from zeolitic imidazolate frameworks (ZIF). Zinc (Zn) was also added and evaporated by pyrolysis. By addition and evaporation of Zn, Co nanoparticle became smaller and more evenly dispersed. As a result, the OER performance was significantly improved than the catalyst without Zn. Also, an optimized catalyst with abundant uniformly dispersed Co was successfully synthesized by appropriately controlling the ratio of Co and Zn comprising the ZIFs. As the ratio of Zn increased, the size and the amount of Co nanoparticles were decreased, and Co nanoparticles were more evenly dispersed. Furthermore, carbon substrate has more porous structure due to the evaporation of Zn atoms. When the Co:Zn ratio was 1:3, Co/NC showed the best electrocatalytic performance due to optimized active sites and large surface area. The optimized Co/NC showed an overpotential of 1.56 V (vs RHE) to acquire a current density of 10 mA cm−2, which is higher activity than commercial RuO2. We also analyzed the material characterization occurred as the ratio of Zn in ZIF increased, revealing the factors enhancing the OER activity. Optimized Co/NC (Co:Zn = 1:3) exhibited improved OER activity and long-term and cycle stability in the OER.