Fundamental Reaction Limitations for Formic Acid Oxidation

Electrocatalytic conversion of formic acid oxidation to CO2 and the related CO2 reduction to formic acid represent a potential closed carbon-loop based on renewable energy. However, formic acid fuel cells are inhibited by the formation of poisoning species during the reaction. Recent studies have elucidated how the binding of carbon and hydrogen on catalyst surfaces promote CO2 reduction towards CO and formic acid. This has also given fundamental insights to the reverse reaction, i.e. the oxidation of formic acid. In this work, simulations on multiple materials have been combined with formic acid oxidation experiments on electrocatalysts to shed light on the reaction and the accompanying catalytic limitations. We found that: (i) The desired principal reaction for efficient formic acid oxidation should progress through adsorbed carboxyl, *COOH, which should then be oxidized to CO2. (ii) *H adsorbed on the surface results in *CO formation and poisoning through a chemical disproportionation step. (iii) Catalysts are poisoned by formate and/or hydroxyl. Using these results, a framework for the reaction has been developed explaining the fundamental limitations and progressing our understanding.