Formate (HCOO^-) has been proposed as an intermediate compound to store energy and carbon for microbial conversion to fuels and chemicals¹. Formate can be generated by electrochemical reduction of CO₂ and subsequently assimilated by microbes that are able to use it as a sole source of energy and carbon for growth and, as recently demonstrated, to produce higher-value chemicals like higher alcohols². Using formate as an intermediate molecule could provide several advantages over direct conversion from gaseous feeds, such as utilizing renewable energy sources by uncoupling the power availability from the fluctuations inherent to renewable energy sources such as wind, solar, or tidal¹. To enable formate as a foundation for the storage of carbon and energy and subsequent conversion to value-added fuels and chemicals, CO₂ mass transport limitation issues need to be overcome.

High current densities are required for CO₂ electrolyzers to be relevant for industrial applications. Due to the solubility limit of CO₂, current densities are restricted to about 30 mA/cm² in a liquid/planar electrode configuration³. Proof of principle results have shown the mass transport issues can be overcome through utilization of gas diffusion electrodes (GDE) with high interphase (gas/liquid/solid) surface area⁴.

Here we will discuss how higher current densities and faradaic efficiencies for the gas-phase CO₂ to formate conversion process can be achieved through the utilization of novel bipolar membrane (BPM) architectures and reactor designs coupled with optimized reaction condition parameters. We will also show an introductory view of developed testing methods and equipment coupled with in-situ product analysis for electrocatalytic conversions not limited to formate production.

References

[1] Yishai, O., Lindner, S. N., Gonzalez de la Cruz, J., Tenenboim, H. & Bar-Even, A. The formate bio-economy. Curr Opin Chem Biol 35, 1–9 (2016).

[2] Li, H. et al. Integrated electromicrobial conversion of CO₂ to higher alcohols. Science 335, 1596–1596 (2012).

[3] Salvatore, D. A. et al. Electrolysis of gaseous CO₂ to CO in a flow cell with a bipolar membrane. ACS Energy Lett. 3, 149–154 (2017).

[4] Kopljar, D., Inan, A., Vindayer, P., Wagner, N. & Klemm, E. Electrochemical reduction of CO2 to formate at high current density using gas diffusion electrodes. J Appl Electrochem 44, 1107–1116 (2014).