Ru_0.1Mn_0.9O_<i>x</i> Electrocatalyst for Durable Oxygen Evolution in Acid Seawater

Abstract Currently, direct electrolysis of seawater for green hydrogen production is primarily focused on neutral and alkaline systems. However, the precipitation of calcium and magnesium ions restricts the advancement of this technology. An acidic system can effectively address this issue. Given that Ru/Ir‐based catalysts with high oxygen evolution reaction (OER) activity also exhibit high chlorine evolution reaction (CER) activity, acid seawater splitting requires anodes with higher selectivity and stability compared to the other two systems. In this study, we propose a non‐precious Ru 0.1 Mn 0.9 O x as the active anode for direct acid seawater electrolysis, which exhibits a high OER selectivity and remarkable stability for more than 1200 hours. Different from the Cl − ‐free system, *Cl occupied on Ru sites could shift the OER active center to Mn on Ru 0.1 Mn 0.9 O x , which prevents the lattice oxygen consumed on Ru and hinders the metal site dissolution. As the CER‐insensitive catalytic center, Mn activated by the introduction of Ru can adsorb a substantial amount of *OH, creating an OER‐favored local environment that inhibits CER. We introduce Cl − ‐assisted transfer of OER active sites to CER‐insensitive Mn as a fundamental strategy for achieving highly selective and durable oxygen evolution in acidic seawater.