Enhanced Biofuel Cells Based on a Hybrid Enzymatic/Bimetallic Composite for Complete Lactate Catalytic Electrooxidation

We describe complete lactate electrooxidation in an enzymatic biofuel cell that combines the catalytic action of the bimetallic composite Ru@Pt-CNT and the enzyme oxalate oxidase (OxOx). The Ru@Pt-CNT/OxOx hybrid electrode was 2.0-fold more catalytically active than the electrode containing the bimetallic composite only. During chronoamperometric experiments, the hybrid electrode achieved a 35% higher maximum current density (2.65 ± 0.15 mA cm^-2) than the Ru@Pt-CNT electrode. Electrochemical impedance spectroscopy showed that the hybrid electrode had lower charge transfer resistance than the Ru@Pt-CNT electrode, confirming that OxOx had a high affinity for lactate during the bioelectrocatalytic reaction on the electrode surface. Furthermore, 18-h long-term bulk electrolysis revealed that lactate electrooxidation at the Ru@Pt-CNT/OxOx hybrid electrode provided a total charge of 1.2 ± 0.2 C, which was 3-fold higher than the total charge generated by the Ru@Pt-CNT electrode. The lactate oxidation products generated at the hybrid electrode were detected during bulk electrolysis by chromatography, which showed that the hybrid biofilm harvested all 10 electrons from lactate, completely oxidizing it to CO₂. With exceptional stability and catalytic performance, the hybrid electrode acted in the multiple catabolic steps of lactate oxidation. Overall, the interaction between Ru@Pt-CNT and OxOx enhanced the assembly of lactate biofuel cells to improve lactate electrooxidation. This could pave the way for developing efficient electronic devices with promising applications in bioelectrochemistry.