Metal-organic framework derived Co@N/C with enhanced oxygen reduction reaction in direct borohydride fuel cells

Abstract

Developing efficient and durable non-precious metals catalysts is crucial for fuel cells. Herein, we synthesize nitrogen-doped carbon-encapsulated metal cobalt nanoparticles with core–shell structure (Co@N/C-Joule) catalyst by carbothermal shock (CTS) pyrolysis of ZIF-67 under argon atmosphere. The Co@N/C-Joule exhibits superior catalytic activity and stability for the oxygen reduction reaction (ORR) in alkaline electrolyte. Co@N/C-Joule demonstrates a half-wave potential of 0.84 V (vs. the reversible hydrogen electrode, RHE). The Co@N/C-Joule also exhibits superior stability, with only a 4 mV negative shift after 30,000 cyclic voltammetry cycles. The direct borohydride fuel cells using the Co@N/C-Joule cathode achieves a maximum power density of 389 mW cm⁻² at 60°C. The rapid heating and cooling rate of CTS enables the production of small-sized Co@N/C nanocatalysts with ultra-thin nitrogen-doped graphite layer coating on Co particles, thereby increasing the surface density of active sites on Co nanoparticles and Co-N sites, which leads to improved ORR performance.