AbstractEarth-abundant electrocatalysts for the oxygen evolution reaction (OER) able to work in acidic working conditions are elusive. While many first-row transition metal oxides are competitive in alkaline media, most of them just dissolve or become inactive at high proton concentrations where hydrogen evolution is preferred. Only noble-metal catalysts, such as IrO₂, are fast and stable enough in acidic media. Herein, we report the excellent activity and long-term stability of Co₃O₄-based anodes in 1 M H₂SO₄ (pH 0.1) when processed in a partially hydrophobic carbon-based protecting matrix. These Co₃O₄@C composites reliably drive O₂ evolution a 10 mA cm^–2 current density for >40 h without appearance of performance fatigue, successfully passing benchmarking protocols without incorporating noble metals. Our strategy opens an alternative venue towards fast, energy efficient acid-media water oxidation electrodes.