Development of enzymatic fuel cells with pyranose-2-oxidase

Abstract

Power harvesting from biological sources has been very popular recently because of the advancements in implantable medical devices. Among all different biofuel cells, utilising enzymes for glucose oxidation plays essential role in developing micro-power sources due to their high bio-catalytic activity. The aim of this study is to develop enzyme electrodes using pyranose-2-oxidase (P2O, wild type and mutants) and investigate the potential use in enzymatic biofuel cell applications as alternative to commercially available glucose oxidase (GOx) for glucose oxidation. Additional work was also carried out with bilirubin oxidase (BOD) for oxygen reduction. The effect of oxygen on enzyme performance, immobilization of the enzymes on carbon surface and biofuel cell performance were mainly investigated. The electrochemical techniques employed in this study were cyclic voltammetry, linear sweep voltammetry and chronoamperometry. Fuel cell test were carried out in glass cells and custom-made stack cells by recording cell potential on different resistances. Polarization curves were obtained by plotting voltage, current and power values. P2O and GOx were first tested in solution in the presence of electron mediator ferrocene carboxylic acid (FcCOOH) to investigate the effect of oxygen on enzyme performances. P2O and its mutants showed similar electrochemical behaviour compared to commercial GOx where P2O-T169G mutant showed better performance, especially when oxygen is saturated in the solution. The immobilization of the mutant P2O-T169G and GOx were then achieved using crosslinking on pyrenyl carbon structures, where either FcCOOH was used in solution or ferrocene (Fc) immobilised with nafion® polymer and carbon nanotubes on electrode surface. BOD was also immobilised on electrode using same method without mediator. Results indicate that enhanced current values was achieved compared to solution studies with good affinity towards glucose for both of the enzymes. Proof of concept biofuel cells were set up using P2O-T169G/GOx and BOD as anodes and cathode, respectively. Initial tests showed that P2O-T169G based enzymatic fuel cell can reach up to a power density of 9.56 μW cm-2 which is ~ 25 % more power output than it was obtained for GOx in aerobic conditions. Finally, a biofuel cell anode using P2O-T169G was combined with air breathing BOD cathode in a stack design enzymatic biofuel cell with an open circuit potential of 0.558 V and maximum power density of 29.8±6.1 μW cm-2 at 0.318 V.