Manganese Oxide Gas Diffusion Electrode Conditioning and Electrochemical Doping for Reversible Oxygen Reduction/Evolution Reactions

Developing durable and active bifunctional gas diffusion electrodes for reversible oxygen reduction/evolution (ORR/OER) reaction catalysis is crucial yet challenging in the development of numerous electrochemical energy conversion systems, including regenerative fuel cells and rechargeable metal-air batteries. This research is focused on developing manganese oxide-based gas diffusion electrodes for reversible oxygen electrodes. Core-porous shell Mn/Mn 3 O 4 (abbreviated as MnO x ) nanoparticles (QSI) demonstrated increased ORR/OER activities compared to γ-MnO 2 (EMD) and b-MnO 2 .[1] The unique behaviour of core-shell MnO x is attributed to the charge transfer between the low-valent Mn core and the high-valent Mn 3 O 4 shell, thereby regenerating Mn(III) active sites through comproportionation.[1] The stability of transition-metal-based reversible oxygen electrodes remains a challenge. As shown in Figure 1, the deterioration of Mn/Mn 3 O 4 during ORR and OER cycling can be attributed to three aspects: Mn active sites oxidation (Figure 1a), less active MnO x phase formation (Figure 1b), and material loss (carbon corrosion and dissolved MnO 4 - formation) (Figure 1c).[2] As a result, the QSI MnO x electrode transformed from pristine to inactive status within 15 galvanostatic ORR/OER cycles. To improve the stability of the electrode, a set of in-situ electrochemical conditioning and electric field-driven metallic cation incorporation into MnO x GDE was investigated. Among the explored metal cations, the Ni 2+ incorporation showed the most significant improvement in terms of activity and cyclic stability. The Ni-MnO x GDE demonstrated excellent stability for over 120 galvanostatic cycles at ±10 mA cm -2 in O 2 -saturated KOH without losing OER activity, surpassing the Pt/C-IrO 2 benchmark.[3] These findings position the MnO x electrodes as promising and sustainable alternatives to precious metal-based electrodes for ORR/OER catalysis and provide valuable insights into designing reversible oxygen electrodes for energy conversion and storage in alkaline systems, contributing to a green future. [1] Pei, Y., Wilkinson, D. P., & Gyenge, E. L. Insights into the electrochemical behavior of manganese oxides as catalysts for the oxygen reduction and evolution reactions: monometallic core‐shell Mn/Mn 3 O 4 . Small, 2023, 19, 2204585. [2] Pei, Y., Wilkinson, D. P., & Gyenge, E. L. Gas Diffusion Electrode Design and Conditioning with Manganese (III/IV) Oxide Catalyst for Reversible Oxygen Reduction/Evolution Reactions. ACS Energy & Fuels (2023), 37, 23, 19278–19291. [3] Pei, Y., Wu, W. Y., Wilkinson, D. P., & Gyenge, E. L. High-Performance Reversible Oxygen Reduction/Evolution Gas Diffusion Electrodes with Multivalent Cation Doped Core-Shell Mn/Mn 3 O 4 Catalysts. ChemElectroChem, in press. Figure 1