Superior Fe-doped α -MnO 2 bifunctional catalyst for zinc–air batteries: comparative analysis of cycle stability and performance in transition metal-doped α -MnO 2 systems

Abstract Transition-metal-doped α -MnO 2 catalysts (Ni, Cu, Fe at 10 at%) were synthesized by a facile hydrothermal method and evaluated as bifunctional electrocatalysts for rechargeable zinc–air batteries (ZABs). Fe–MnO 2 exhibited the best bifunctional activity, with the most positive oxygen reduction reaction (ORR) onset potential (0.895 V vs RHE), lowest oxygen evolution reaction (OER) overpotential (510 mV at 10 mA cm −2 ), and smallest ORR/OER potential gap (Δ E = 0.964 V). Electrochemically active surface area (ECSA) normalization revealed that Fe–MnO 2 achieves an optimal balance between intrinsic per-site activity and active-site density, surpassing both undoped α -MnO 2 (high intrinsic activity but limited ECSA) and Cu–/Ni–MnO 2 (high ECSA but low intrinsic activity). In full ZAB cells at 10 mA cm −2 , Fe–MnO 2 cycled stably for 900 cycles with a charge–discharge voltage gap of…