Enhancing Enzymatic Electrocatalysis of CO ₂ to Formate Using Graphene-Grown Carbon Fiber as a Conductive Carrier

The bioelectrochemical system was constructed to enable efficient formate synthesis from CO₂ while decreasing the high cost to the natural cofactor nicotinamide adenine dinucleotide. The enzyme cathode was prepared using the carbon fiber (CF) with in situ grown graphene (rGO/CF), where copper nanoparticles were deposited as the electronic mediator to enable the electric-driven cofactor regeneration. Additionally, ionic liquids were employed as electrolytes to improve the CO₂ capture efficiency and enhance the electron transfer capacity. Compared to the common CF, the rGO/CF significantly improved the enzyme stability due to its larger surface area and higher catalytic loading capacity. The immobilization efficiency of rGO/CF reached 67.41% at 55 °C with the enzyme activity of 10.86 U·g^-1. Compared to the free enzyme, the superior pH stability and thermal resistance maintaining 54.7% relative conversion after 7 reuse cycles and 84.61% activity after 40 days of storage were performed with the enzyme immobilization. Under optimal conditions at pH 6.0, the system achieved maximum formate production of 258.56 mM within 450 min, with ionic liquids further enhancing the catalytic performance. This approach presents an efficient method for promoting the conversion of CO₂.