Accelerating Electroenzymatic CO2 Reduction by Immobilizing Formate Dehydrogenase on Polyethylenimine-Modified Mesoporous Silica

Enzymatic conversion of CO2 to high value-added chemicals is in line with green chemistry. However, low solubility of CO2 under mild conditions and high cost of cofactor limit the efficiency of CO2 enzymatic conversion. Therefore, we designed a system for enzymatic electrocatalysis of CO2 by the combination of polyethylenimine (PEI)-enhanced enzyme immobilization and CO2 adsorption, and electrocatalytic nicotinamide adenine dinucleotide (NADH) regeneration. Furthermore, the PEI dendritic structure and SiO2 channel skeleton can effectively protect the enzyme structure from external damage. To be specific, PEI was first modified on mesoporous silica SBA-15 by glutaraldehyde, and then the enzyme was immobilized by electrostatic adsorption. The modified amount of PEI, the amount of enzyme for immobilization, and the amount of immobilized enzyme were optimized. The initial reaction rate increased from 1.3 to 1.9 times as the amount of PEI modification increased from 10 to 60 wt %. The optimized catalysis system could produce 1.118 mM formate after a 3 h reaction, with a productivity of 5323.8 μmol gcat–1h–1, which was 3.7 times more than that of the free enzyme system. Furthermore, the immobilized enzyme still retained over 80% activity after 12 cycles reuse with improved thermal stability.