Miniaturised glucose-oxygen biofuel cells

Miniaturized glucose-oxygen biofuel cells are useful to power implantable medical devices such as biosensors. They are small, more biocompatible and run continuously on glucose and oxygen, providing cleaner energy at neutral environment. A typical glucose-oxygen biofuel cell consists of an anode with glucose oxidase (GOx) and a cathode with various oxygen reducing catalysts. This thesis describes experimental investigations of the major issues of such systems, viz.: complex electrode fabrication, enzyme instability and inefficient oxygen reduction. Electrodes were built using the simple and scaleable bulk modification method, where all the material was simply mixed and bound together into composites with epoxy resin. For the anodes, the composite made of 10% GOx with 7:7 TTF-TCNQ was found optimal. The GOx electrodes were modified with various enzyme stabilisers (PEI, DTT, PEG, GLC, FAD and mixture of PEI:DTT and PEI:FAD) and 2% of PEI-DTT (1:1 w/w) was most effective in the presence of O2. Its maximum output current density was 1.8 x 10-2 ± 9.9 x 10-3 A.m-2. It also showed the resistant against O2 electron deprivation and enzyme inhibition. Its KM.was 5 mM. For the cathodes, various oxygen reducing catalysts (metalised carbon, anthroquinone modified carbon, laccase and bilirubin oxidase) were incorporated into graphite composite and the electrodes were pretreated in different media in order to enhance their catalytic activity. None showed four-electron O2 reduction. NaOH-pretreated cobalt (II) salophen composite electrodes showed two-electron O2 reduction and were most catalytic. Its standard catalytic rate constant was 1.2 x 10-5 ± 1.2 x 10-6 m.s-1. Of the catalysts examined, metal complex composites gave the best results for oxygen-reducing cathodes and their pretreatment led to the synergetic effect because it increased the concentration of catalytic surface oxygen groups and enhanced oxygen reduction