Fabrication of High Activity Electrocatalysts For Oxygen Reduction Reaction By Silica-Protection Of Zeolitic Imidazolate Framework (ZIF)- Derived

Oxygen reduction reaction (ORR) is one of the essential electrochemical reactions for the energy conversion and storage devices such as fuel cells and metal-air batteries. However, a large amount of Pt is required for catalyzing the kinetically sluggish ORR at the air cathode, therefore greatly limiting their large scale implementation. Recently, metal-organic frameworks (MOFs), constructed from bridging metal ions and ligands, have emerged as a new type of attractive precursors for the synthesis of PGM-free catalysts, which has led to encouraging performance improvement. 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 coreshell ZIF8/ZIF-67 and silicon- core-shell ZIF8/ZIF-67. Silicon protection strategy proved highly effective in preventing the irreversible fusion and aggregation of Co,N-CNF during the hightemperature pyrolysis step used in Co,N-CNF manufacture. Compared to unprotected core-shell ZIF8/ZIF-67 an enhanced electrocatalytic activity was obtained in the case of the silicon-coreshell ZIF8/ZIF-67 with optimized composition and temperatures.