Ultrasonic-assisted strategy to enhance electrocatalytic performance of CoNi N-doped carbon catalyst in alkaline oxygen reduction reaction and zinc-air batteries

Abstract

Transition metal nitrogen-doped carbon composite materials are promising candidates for electrocatalytic oxygen reduction reaction in alkaline media. Among the materials, Co-based N-doped carbon (Co-NC) catalysts attract significant attention owing to the appropriate adsorption energy of oxygen intermediates. Nevertheless, the achievement of Co-NC catalysts often suffers from serious agglomeration of cobalt sites under high-temperature pyrolysis, which greatly restricts the electrocatalytic performance of the catalysts. Therefore, increasing the active sites and the intrinsic activity of the catalysts, thus enhancing the oxygen reduction reaction activity remain a challenge. Herein, an ultrasound-assisted fabrication of zeolitic imidazole frameworks (ZIFs) doping strategy is developed to synthesize a cobalt, nickel and nitrogen co-doped carbon catalyst in oxygen electrocatalysis. The introduction of zinc and nickel domains during the synthesis process can avoid the metallic sites from agglomeration and promote the intrinsic activity of Co sites, respectively. In addition, three factors are modulated to control the intensity of the acoustic cavitation effect induced by ultrasound irradiation, including ultrasonic power, ultrasonic frequency and the surface tension of liquid media. The optimized ultrasonic conditions can regulate the pore structure of the carbon substrate, which is beneficial to expose the active sites and boost the mass transfer, thus enhancing the ORR activity maximally. Consequently, the obtained Co₃Ni₁-NC catalyst exhibits an outstanding onset potential at 0.928 V and a half-wave potential at 0.895 V and a power density at 122.73 mW cm^-2 in the zinc-air battery. This work demonstrates a reliable prospect for the relationship between the acoustic cavitation effect and the performance improvement of electrocatalysts.