Material Dynamics of Manganese-Based Oxychlorides for Oxygen Evolution Reaction in Acid

Earth-abundant manganese-based oxides have emerged as promising alternatives to noble-metal-based catalysts for the oxygen evolution reaction (OER) in acidic conditions; however, their inferior activity and stability present critical challenges for the sustainable production of hydrogen via water electrolysis. Moving beyond oxides, heteroanionic materials, which incorporate anions with lower electronegativity than oxygen, have shown potential for improving the OER performance, but a detailed understanding of the underlying mechanisms is lacking. Here, we investigate manganese-based oxychlorides (Mn₈O₁₀Cl₃ and FeMn₇O₁₀Cl₃) that exhibit excellent activity and stability for acidic OER to elucidate material property dynamics and correlate them with OER behaviors. Our rigorous electrochemical stability testing reveals that the high operating potential mitigates Mn dissolution over prolonged exposure to the OER conditions. Through a combination of ex situ and in situ surface and bulk-sensitive X-ray spectroscopy analyses, we observe a trade-off between increasing Mn valence and maintaining structural integrity, which results in dynamic bond length changes within the [MnCl₆] octahedra during the activation and degradation processes of these oxychloride catalysts. This study provides insights into the fundamental relationships between the chemical, electronic, and geometric properties of the catalysts and their electrocatalytic outcomes.