Co9S8 nanoparticles embedded in egg white-derived porous carbon as an efficient bifunctional cathode catalyst for Zn–air batteries

Abstract

Low-cost cobalt sulfide materials are deemed to be promising cathode catalysts for rechargeable Zn–air batteries (ZABs) due to their intrinsic activity in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, the aggregation tendency, low conductivity and poor stability hinder their electrocatalytic performance. Herein, a composite catalyst of Co₉S₈ nanoparticles embedded in N, S doped porous carbon (Co₉S₈/EWPC) was synthesized by pyrolyzing and sulfurating a prepared hydrogel of egg white, NaCl and Co(NO₃)₂. After subsequent removal of NaCl templates and activation by KOH, the obtained Co₉S₈/EWPC achieves a hierarchical porous structure with a large specific surface area of 500.59 m² g⁻¹. Owing to the synergistic effects of the evenly embedded Co₉S₈ nanoparticles, N, S doped carbon matrix and large specific surface area, Co₉S₈/EWPC exhibits excellent bifunctional electrocatalytic performance for the ORR (half-wave potential of 0.83 V) and OER (overpotential of 390 mV at 10 mA cm⁻²). An aqueous ZAB assembled with the Co₉S₈/EWPC cathode catalyst displays a high peak power density of 125 mW cm⁻² and durable cycling stability over 268 cycles. Moreover, based on Co₉S₈/EWPC, a designed 2D coplanar flexible ZAB presents excellent electrochemical performance and favorable mechanical flexibility.