Earth-abundant electrocatalysts for the oxygen evolution reaction (OER) able to work in acidic working conditions are elusive. While many first-row transi- tion 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 pro- tocols without incorporating noble metals. Our strategy opens an alternative venue towards fast, energy efficient acid-media water oxidation electrodes.