Hierarchically porous metal organic framework immobilized formate dehydrogenase for enzyme electrocatalytic CO2 reduction

The utilization of CO2 has become an important issue aiming to the achievement of carbon neutrality. The enzyme electrocatalytic CO2 reduction to produce carbonaceous fuels has been increasingly appealing. While the low CO2 aqueous solubility severely limits the CO2 reduction efficiency, and the expensive cofactor restricts the application potential. In this study, microporous UiO-66-NH2 was firstly converted into hierarchically porous structure (HP-UiO-66-NH2) containing both micropores and mesopores to simultaneously enhance the enrichment of CO2 and the immobilization of formate dehydrogenase by optimizing the pore structure. The relative contents of the protein secondary structures were similar after immobilization. The mechanism of enzyme electrocatalytic CO2 reduction was proposed. The enzyme stability was highly enhanced after immobilization and the CO2 reduction was enhanced by the enzyme electrocatalytic system through the combination of CO2 enrichment and electrocatalytic NADH regeneration. The optimized catalytic system can obtain formate yield of 1.826 mM in 3 h (5.57 times higher than the free enzyme system) with a generation rate of 6086.7 μmol gcat‑1h‑1.