Unveiling the Role of Manganese Substitution in Nanocast Cobalt Oxide for Alkaline Water Electrolysis Performance

Abstract The design and development of next‐generation electrocatalysts, coupled with an in‐depth understanding of their structural dynamics under operating conditions, are critical for advancing the efficiency and durability of water electrolysis technologies for green hydrogen production. Herein, the impact of manganese substitution on the morphology, electronic structure, and oxygen evolution reaction (OER) activity of cobalt‐based spinel oxides is investigated. Two‐dimensional mesoporous cobalt manganese oxides synthesized by the hard‐templating method using SBA‐15 silica templates are utilized as a well‐defined model material system. At the highest Mn content, the aligned mesoporous structure is found to be significantly less ordered. X‐ray absorption and Raman spectroscopies indicate that Mn mainly occupies the octahedral sites. OER survey shows that even small amounts of Mn substitution of Co can significantly decrease the OER performance of the catalysts due to the prevention of active species formation. Electrochemical impedance, in situ Raman spectroscopy, ICP‐OES, and postmortem XRD indicate that above 1.4 V versus RHE, Mn leaches from the bulk spinel octahedral site.