Silica Protection of Zeolitic Imidazolate Framework (ZIF)/GO Composite as High Activity Electrocatalysts for Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is the common cathode reaction in many important electric energy devices, such as fuel cells and metal air batteries. The ORR is four electron process with sluggish kinetics and thus requires catalysts to enhance. So far Pt-based catalysts are still the most efficient catalysts. But the scarcity and high costs of platinum, together with instability and deactivation by CO poisoning and crossover effects, limit the application of fuel cells. Currently there are tremendous efforts to develop efficient low cost ORR catalysts to replace Pt based noble metal catalysts to reduce the cost of these advanced electric energy devices. Metal–organic frameworks (MOFs) have received increasing attention due to their potential applications in many areas such as gas adsorption and separation, catalysis, photoluminescence, drug delivery, photoelectrochemistry and ionic conductivity. In this work we report a highly efficient Co based catalyst for the oxygen reduction reaction (ORR) with highly dispersed Co-Nx sites on N-doped carbon. We synthesized the core-shell GO-ZIF8/ZIF-67 and silicon- core-shell GO-ZIF8/ZIF-67. Silicon protection strategy proved highly effective in preventing the irreversible fusion and aggregation of GO-Co,N-CNF during the high-temperature pyrolysis step used in GO-Co,N-CNF manufacture. Compared to unprotected core-shell GO-ZIF8/ZIF-67 an enhanced electrocatalytic activity was obtained in the case of the silicon-core-shell GO-ZIF8/ZIF-67 with optimized composition and nanostructure. In alkaline media cyclic 67 voltammetry and linear sweep voltammetry was conducted to compare the electrochemical activities for the samples. The onset Potential for silicon-core-shell GO-ZIF8/ZIF-67 (-0.1V vs AgAgCl) is better than core-shell GO-ZIF8/ZIF-67(-0.06V vs AgAgCl).