Production of formate by CO₂ electrochemical reduction and its application in energy storage

Production of liquid fuels by electrochemical CO₂ reduction (eCO₂R) is an attractive option for energy storage in the form of renewable energy. This study focuses on efficient formate production using an eCO₂R system and its application in generating power using a direct formate fuel cell (DFFC). A carbon black supported SnO₂ catalyst was used for the eCO₂R in a gas diffusion reactor using a 1.0 M KOH electrolyte. An average faradaic efficiency of 80% for formate production was achieved over a wide electrode potential range (-0.63 to -1.43 V vs. RHE). Since the overall current density varied linearly with the overpotential, the rate of formate production could be easily controlled by varying the applied potential. At a current density of 251 mA cm^-2 (-1.43 V), a high formate production rate was achieved at 3 mg min^-1 cm_WE^-2 resulting in 0.5 M formate being produced within 1 hour. This formate solution was directly used as the fuel for a DFFC, without pre-treatment. The fuel cell consisted of a Pd-CeO₂/C anode and FeCo/C cathode and produced a peak power density of 92 mW cm^-2. A closed loop of "electricity-formate-electricity" has been realized in this study, signifying the promising future of sustainable CO₂ conversion to liquid fuels for CO₂ fixation as well as for energy storage.