Assembly of an improved hybrid cascade system for complete ethylene glycol oxidation: Enhanced catalytic performance for an enzymatic biofuel cell

We report an Enzymatic Fuel Cell (EFC) combining an enzyme that can cleave carbon-carbon bonds (oxalate oxidase (OxOx)) with an organic catalyst (Pyrene-TEMPO (TEMPO = 2,2,6,6-tetramethyl piperidinyl-N-oxyl)) immobilized on the surface of modified carboxylated multi-walled carbon nanotubes (MWCNT-COOH). This combination gave a hybrid bi-catalyst electrode for complete ethylene glycol (EG) oxidation. The hybrid electrode provided ninefold enhanced catalytic activity (0.17 +/- 6 x 10-3 mA cm(-2)) in the presence of EG as compared to the electrode in the absence of EG (0.018 & PLUSMN; 3 x 10-5 mA cm-2), indicating that the enzyme combined with the organic catalyst improved energy generation through deep EG electrooxidation. Electro-chemical impedance spectroscopy reveals that the addition of the enzyme in the electrode containing MWCNT-COOH-Pyrene-TEMPO increased the charge transfer resistance (Rct) and the capacitance of the double layer. Long-term electrolysis for 15 h showed that the hybrid electrode presented outstanding current density and stability. The EG oxidation products were identified and quantified by high-performance liquid chromatography (HPLC-UV/RID). The results confirmed complete EG oxidation in the presence of CO2 in the solution, allowing 10 electrons to be collected from the fuel. Overall, this study illustrates the development of a simple and improved hybrid bi-catalyst electrode for promising applications in small electronic devices.