Co nanoparticles-embedded N, S-codoped hierarchically porous graphene sheets as efficient bifunctional electrocatalysts for oxygen reduction reaction and hydrogen evolution reaction

Abstract

To develop efficient and low-cost bifunctional electrocatalysts towards oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is vital for the progress of fuel cell, Zn-air battery and overall water splitting. Herein, a facial method to prepare Co nanoparticles-embedded N, S-codoped hierarchically micro/meso/macroporous graphene sheets (Co@NSCs) via pyrolysis of the mixture of urea, l-cysteine, polyethylene glycol and cobalt (II) nitrate is reported. By controlling the pyrolysis temperature, Co@NSC-1000 obtained at 1000 °C performs comparable electrochemical activity on ORR and HER, with commercial Pt/C. Additionally, Co@NSC-1000 also exhibits acceptable methanol resistance on ORR and admissible long-term durability on ORR and HER after 5000 potential cycles. Synergistically, hierarchically micro/meso/macroporous nanostructure, non-precious Co nanoparticles, and N, S-codoped graphene are greatly contributed to the high electrocatalytic activity and stability. The pyrolysis temperature is the key factor for tailoring element component, nanostructure and electrochemical activities. The competitive catalytic performances on ORR and HER indicate Co@NSC-1000 is a hopeful substitute for noble benchmark Pt catalysts. Furthermore, Zn-air battery assembled with Co@NSC-1000 shows higher specific capacity, larger energy density and stronger stability than Pt/C, holding great potential in practical applications.