Ampere-level co-electrosynthesis of formate from CO2 reduction paired with formaldehyde dehydrogenation reactions

Abstract

Current catalysts face challenges with low formate selectivity at high current densities during the CO2 electroreduction. Here, we showcase a versatile strategy to enhance the formate production on p-block metal-based catalysts by incorporating noble metal atoms on their surface, refining oxygen affinity, and tuning adsorption of the critical oxygen-bound *OCHO intermediate. The formate yield is observed to afford a volcano-like dependence on the *OCHO binding strength across a series of modified catalysts. The rhodium-dispersed indium oxide (Rh/In2O3) catalyst exhibits impressive performances, achieving Faradaic efficiencies (FEs) of formate exceeding 90% across a broad current density range of 0.20 to 1.21 A cm−2. In situ Raman spectroscopy and theoretical calculations reveal that the oxophilic Rh site facilitates *OCHO formation by optimizing its adsorption energy, placing Rh/In2O3 near the volcano-shaped apex. A bipolar electrosynthesis system, coupling the CO2 reduction at the cathode with the formaldehyde oxidative dehydrogenation at the anode, further boosts the FE of formate to nearly 190% with pure hydrogen generation under an ampere-level current density and a low cell voltage of 2.5 V in a membrane electrode assembly cell. Developing high-productive and energy-saving systems in formate electrosynthesis is attractive but challenging. Here, the authors report an efficient Rh-dispersed In2O3 catalyst for CO2 reduction, benefiting the ampere-level formate coproduction when pairing with anodic aldehyde oxidative dehydrogenation.