Biomass coffee grounds derived nitrogen-doped ultrafine carbon nanoparticles as an efficient electrocatalyst to oxygen reduction reaction

A nitrogen-doped carbon-based catalyst (Fe-C-CG) to oxygen reduction reaction (ORR) is synthesized by pyrolyzing a precursor from coffee grounds, iron chloride and commercial carbon black in ammonia atmosphere. The coffee grounds are pyrolyzed to carbon particles with diameters about 20 nm with the facilitation of carbon black. The carbon nanoparticles show higher reactive activity with ammonia to achieve the doping of nitrogen atoms to carbon with 3.33 at% of content in Fe-C-CG, which is greater than 0.47 at% in the product from commercial carbon black (Fe-C). Resultantly, the Fe-C-CG exhibits high ORR activity with 0.87 V of half wave potential and 5.48 mA cm ⁻² of limited diffusion current, which highly surpass the 0.71 V, 4.19 mA cm ⁻² for Fe-C, and are comparable with 0.86 V and 4.52 mA cm ⁻² for Pt/C catalyst, respectively. The Zn-air battery assembled with Fe-C-CG delivers 142 mW cm ⁻² of maximum power density and 774 mAh g ⁻¹ _Zn of specific capacity, and can stably work at 1.212–1.257 V of discharge voltage at 10 mA cm ⁻² . This work provides a strategy to prepare a nonprecious metal and nitrogen doped carbon catalyst to ORR by using biomass as the basic material.