Boosting Current Density of Electrocatalytic CO₂ Reduction using Metal-Enzyme Hybrid Cathodes

As a promising solution to global warming, electrocatalytic reduction of carbon dioxide (CO₂RR) to liquid fuel has attracted great attention. A primary challenge in industrializing CO₂RR technologies for producing liquid fuel is the mass transfer limitation of CO₂, which significantly reduces the current density of CO₂RR. This study proposes a new enzyme-enhanced electrocatalysis platform for boosting CO₂RR current density. This platform integrates an enzyme of bovine carbonic anhydrase (bCA), stabilized on carbon nanotubes (bCA@CNT), into formate/formic acid selective metal catalysts such as tin (Sn) and bismuth (Bi) to prepare Metal-bCA (M-bCA) hybrid cathodes. The incorporation of bCA enhances both the CO₂ hydration and the reversible dehydration of bicarbonate to CO₂ in the cathode. This dynamic catalysis of bCA facilitates rapid local regeneration of dissolved CO₂ from bicarbonate at the catalyst surface, thereby boosting the current density of CO₂RR. Consequently, the formate current density of the Sn-bCA cathode was 3.3 times higher than that of the bare Sn cathode in a membrane-electrode assembly (MEA)-type cell. Furthermore, the Bi-bCA cathode achieved an excellent current density of 442 mA cm^-2, 1.5 times higher than the bare Bi cathode, for direct production of highly concentrated (3.4 mol L^-1) formic acid in a 3-compartment cell.