Enhanced electrochemical reduction of carbon dioxide to formic acid using a two-layer gas diffusion electrode in a microbial electrolysis cell

Abstract

Electrochemical reduction of CO₂ to formic acid (ERCF) is mainly hindered by CO₂ mass transfer and high energy consumption. This work developed a two-layer rolled Sn-loaded gas diffusion electrode (SGDE), consisting of a gas diffusion layer and a Sn-loaded brass mesh to improve ERCF in a microbial electrolysis cell (MEC). The morphology and chemical composition of the SGDE were characterized by scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The electrochemical behavior of the SGDE for ERCF was assessed by cyclic voltammetry and electrochemical impedance spectroscopy. The Faraday efficiency and production yield of formic acid were measured in order to evaluate ERCF. The electrochemical measurements exhibited the advantages of the SGDE, including higher ERCF current and lower charge transfer resistance, owing to the increase in the working concentration of CO₂ in the vicinity of the electrocatalytically active sites. The use of the SGDE in MEC improved Faraday efficiency and production yield of formic acid by 36.1% and 30.6%, respectively. Whereas the energy consumption for ERCF was reduced by approximately 67.2–73.6%.