Enzyme immobilization in covalent organic frameworks for efficient bioelectrocatalytic CO₂ reduction to formic acid...

The conversion of atmospheric CO₂ into value-added chemicals represents a critical strategy for climate impact. Bioelectrocatalytic reduction of CO₂ to C₁ and C_n compounds holds significant promise, yet enzymatic instability remains a major constraint for practical deployment. In this study, three immobilized enzymes-FDH@COF-LZU1, FDH@COF-TpPA, and FDH@COF-TpBD-were synthesized and compared using a biocompatible, polyvinylpyrrolidone (PVP)-assisted one-pot encapsulation strategy under ambient conditions. The immobilized enzymes exhibited significantly enhanced thermal stability, pH tolerance, storage stability, reusability, along with apparently lower product inhibition compared to free enzymes. Based on comprehensive performance evaluation, COF-TpPA was identified as the optimal carrier for multi-enzyme immobilization (7 enzymes) toward efficient formic acid-to-glycine conversion. The bioelectrocatalytic system was established for CO₂-to-formic acid and formic acid-to-glycine conversion with in situ NADH regeneration. The FDH@COF-LZU1 and FDH@COF-TpPA systems achieved formic acid production of 101 mM and 88 mM, respectively, yielding approximately double the cumulative formic acid yield of free enzyme after 10 h. The multi-enzyme@COF-TpPA system produced 0.51 mM glycine after 10 h. This study provides an effective strategy for CO₂ conversion to formic acid and higher-value compounds such as glycine, while also offering new insights into enzyme immobilization strategies.