Boosting alkaline formate electrooxidation on Pd/Co(OH)2 catalysts through synergistic enhancement of Hads removal and HCOO− adsorption

Direct formate fuel cells (DFFCs) are becoming one of the most promising next-generation energy devices owing to their high energy density, low toxicity, and carbon neutrality. However, their practical application is hindered by the sluggish kinetics of the formate oxidation reaction (FOR) on conventional palladium (Pd)-based catalysts due to the strong adsorption of hydrogen intermediates (H ads ) that block the active sites. Herein, we tackled the above problem by tailoring the Pd electrocatalytic properties through the interfacial interaction with the hydroxyl group-abundant and oxophilic Co(OH) 2 substrate. This resulted in an impressive mass activity of 5.02 A mg −1 Pd for the synthesized Pd/Co(OH) 2 , approximately three times that of commercial Pd/C. Moreover, under high formate concentration, Pd/Co(OH) 2 exhibits significantly improved stability, i.e. , up to 24000 s sustainable current density with 100% selectivity toward CO 2 (CO 2 is actually converted to carbonate in alkaline media). Kinetic isotope effect (KIE) analysis and in situ Raman spectroscopy based mechanistic study reveal the excellent FOR performance of Pd/Co(OH) 2 originates from the partially oxidized Pd facilitated H ads oxidative removal and the more hydrophilic surface induced competitive HCOO − adsorption over H ads . This study demonstrates a rational strategy to optimize the Pd-based FOR electrocatalysts through the electronic and interfacial interactions with appropriate substrate to modulate the key intermediate adsorption-reaction kinetics.