Electrocatalytic reduction of CO2 has been taken into consideration as a fascinating option to store energy from intermittent renewable sources in the form of chemical value-added products. Among the different value-added products, formic acid or formate is particularly attractive since it can be used as a fuel for low-temperature fuel-cells and as a renewable hydrogen carrier. Very recently, a rapidly increasing number of studies have revealed Bi as a promising electrocatalytic material for the CO2 electroreduction to formate, but the performance of Bi electrodes operating in a continuous mode and high current density (j) has been hardly investigated yet. Thus, this work aims at studying the CO2 electroreduction to formate working in a continuous mode in a filter-press-reactor at a j up to 300 mA·cm-2 using Bi electrodes. Bismuth Gas Diffusion Electrodes (Bi-GDEs) were fabricated from carbon-supported Bismuth-nanoparticles. The influence of j and the electrolyte flow/area ratio in the performance of the Bi-GDEs towards formate were evaluated. Working at j of 300 mA·cm-2, a concentration of 5.2 g formate·L-1 with a faradaic efficiency (FE) and rate of 70% and 11mmol·m-2·s-1, respectively were achieved. Lowering the j to 90 mA·cm-2, formate concentrations of up to 7.5 g·L-1 could be obtained with an excellent FE of 90%. Interestingly, the highest concentration of formate obtained was 18 g·L-1, but at expenses of an important decrease in FE. Although the results of this study are interesting and promising, further research is required to increase formate concentration for a future implementation at industrial scale.

The authors of this work would like to show their gratitude to the financial support from the MINECO, through the projects CTQ2016-76231-C2-1-R and CTQ2016-76231-C2-2-R (AEI/FEDER, UE). Jose Solla-Gullón also acknowledges the financial support from VITC of the University of Alicante (UTALENTO16-02).