A Highly Active Bifunctional Catalyst of Mn-Co-Fe-N/S@CNT for Rechargeable Zinc-Air Batteries

Rechargeable zinc-air batteries are promising candidates for energy storage due to their high energy density, environmentally friendliness, and low cost. However, such batteries are limited by the high cost and sluggish kinetics of noble metal catalysts. Here, we present a highly active bifunctional catalyst of Mn-Co-Fe-N/S@CNT, where the catalyst is synthesized by Mn, Co, and Fe oxides doped with N and S on porous carbon nanotubes. Mn-Co-Fe-N/S@CNT has higher electrocatalytic activity than the commercial catalysts of Pt/C and RuO2, demonstrating that the half-wave potential of the oxygen reduction reaction (ORR) of Mn-Co-Fe-N/S@CNT is 0.807 V (0.9 V with Pt/C), the initial potential is 0.85 V (0.789 V with Pt/C), the limiting current is 5.66 mA cm-2 at 0.2 V (5.69 mA cm-2 with Pt/C), and oxygen evolution reaction overpotential of Mn-Co-Fe-N/S@CNT is 0.386 V at 10 mA cm-2 (0.371 V with RuO2). Moreover, a rechargeable zinc-air battery using Mn-Co-Fe-N/S@CNT outputs a discharging voltage of 1.2 V and a stable cycle life of over 150 h at 10 mA cm-2.