Concentrated formate produced through co-electrolysis of CO₂ and methanol in a zero-gap electrolyzer

Recent progresses have highlighted the enormous potentials of renewable electricities driven carbon dioxide (CO2) electrolysis in achieving carbon neutrality. However, its further industrial application is limited by low liquid product concentrations, which requires energy-intensive downstream separation processing. Herein we report a CO2 and methanol co-electrolysis strategy to produce formate at both electrodes and collect highly concentrated formate in zero-gap CO2 electrolyzers. An anion exchange membrane was employed to enable formate product crossover from cathode to anode. A bismuth silicate derived nanofiber electrocatalyst with rich grain boundaries was synthesized and exhibited excellent formate selectivity (Faradaic efficiency >95%), high activity (partial current density >500 mA cm(-2)), as well as good stability (>120 h). Coupled with NiOX anode catalyst for methanol selective oxidation to formate in a zero-gap electrolyzer, we demonstrate a similar to 180% of formate Faradaic efficiency and a full-cell voltage of 2.43 V at an industrially relevant current density of 0.2 A cm(-2). By decoupling product generation and collection, our electrolyzer produced a highly concentrated formate of 3.24 M, which could be directly used as anode fuel for fuel cells.