High-Performance Reversible Oxygen Reduction/Evolution Gas Diffusion Electrodes with Multivalent Cation Doped Core-Shell Mn/Mn3O4 Catalysts

The development of precious-metal-free catalysts with bifunctional activities for both oxygen reduction and evolution reactions (ORR/OER) is crucial for the advancement of regenerative fuel cells and rechargeable metal-air batteries. Manganese oxides (MnOx) have emerged as promising bifunctional catalysts. However, MnOx electrodes typically exhibit poor ORR/OER cycling stability owing to polarization-induced MnOx redox reactions and phase transition. To address this issue, we developed metallic cation (i. e., Co2+, Ni2+, Cu2+, or Bi3+) doped MnOx/carbon electrodes using potentiodynamic, potentiostatic and galvanostatic methods. Among the explored dopant cations Ni2+ intercalated into MnOx under acidic conditions using a slow-scan cyclic voltammetry method, significantly enhanced the ORR/OER activity and stability of MnOx. Alongside electrochemical doping, MnOx also underwent redox reactions leading to changes in Mn valence and phase transitions. The Ni-incorporated MnOx gas diffusion electrode (GDE) demonstrated exceptional stability for over 120 accelerated OER and ORR cycles at +/- 10 mA cm(-2) in 5 M KOH, surpassing the performance of the Pt/C-IrO2 benchmark. Furthermore, it achieved OER current densities of approximately 22 mA cm(-2) at 1.65 V-RHE, which was twice as high as that of Pt/C-IrO2.