Oxygen-Evolution Reaction on the Surface of Layered Manganese Oxide under Neutral Conditions: A Bioinspired Strategy Achieving Ultra-Low Overpotential

In contrast to the previous assumption that manganese (hydr)oxides in the absence of other metal ions indicate high overpotential to catalyze the oxygen-evolution reaction (OER) under neutral conditions, this study reveals that layered manganese oxide exhibits OER activity at the Mn(III) to Mn(IV) oxidation peak post charge accumulation. Although low current density was observed, this activity is realized at an exceptionally low overpotential of 20 mV within a phosphate buffer solution. A detailed mechanistic proposal for OER within this low-overpotential domain is presented, substantiated by in situ visible and Raman spectroscopic analysis focused on the Mn(III) to Mn(IV) transition and surrounding OER region. The quantification of the evolved oxygen and analysis of redox-active Mn ion concentrations near the redox peak yield a calculated turnover frequency of 3.8 × 10^–3 s^–1 at 1.35 V. The observed reduction in overpotential is ascribed to the complicated interaction between the OER process and charge accumulation, echoing mechanisms characteristic of natural systems in the oxygen-evolving complex in photosystem II, which collectively enable the remarkably low overpotential. These findings offer critical insights for advancing highly efficient and robust electrocatalysts for OER in water-splitting applications, with substantial implications for the future of energy conversion and storage technologies.