Paired Electrosynthesis of H₂ and Acetic Acid at A/cm² Current Densities

Industrial water splitting pairs cathodic hydrogen evolution with oxygen evolution at the anode, the latter generating low-value oxygen as the oxidative product. We reasoned that replacing the oxygen evolution reaction (OER) with anodic electrosynthesis of acetic acid from ethanol at industrial current densities could be a route to increase the economic efficiency of green hydrogen production. We partition the selective oxidation of ethanol to acetic acid into two mechanistically distinct transformations: first ethanol oxidation followed by the production of *OH. Density functional theory (DFT) studies show that the aldehyde-derived intermediate CH 3 CO* from ethanol oxidation and the *OH radical from water dissociation are both needed in the electroproduction of acetic acid. Operando Fourier transform infrared (FTIR) spectroscopy identifies the corresponding aldehyde intermediates on the anode surface. Based on these mechanistic findings, we develop a vacancy-rich IrRuO x catalyst and achieve selective electrotransformation of ethanol to acetic acid at a generation rate of 30 mmol/cm 2 /h and a partial current density of 3 A/cm 2, fully 10× higher than in the previous highest-activity reports.