Conjugated polymers and an iron complex as electrocatalytic materials for an enzyme-based biofuel cell

Abstract

Poly-5,2′:5′,2″-terthiophen-3′-carboxylic acid (polyTTCA) and poly-Fe(III)-[N,N′-bis[4-(5,2′:5′,2″-terthien-3′-yl)salicyliden]-1,2-ethanediamine] (polyFeTSED) were synthesized and electrochemically polymerized on an Au surface for use as mediators and catalysts for a biofuel cell. The atomic force microscopy (AFM) images of (a) the TTCA homopolymer (polyTTCA) and (b) the TTCA–FeTSED copolymer (poly(TTCA–FeTSED)) layers show a nanoparticle structure. The enzymes (glucose oxidase (GOx) or horseradish peroxidase (HRP)) were immobilized onto the conducting polymer layer through covalent bond formation, which allowed for direct electron transfer processes of the enzymes. A quartz crystal microbalance (QCM) revealed that the surface coverages of GOx and HRP were 4.21×10−12M and 9.65×10−12M, respectively. The anode with immobilized GOx and the cathode with immobilized HRP were used as model enzyme systems in biofuel cells for glucose and H2O2 detection, respectively. The biofuel cell composed of the GOx/polyTTCA/Au and the HRP/poly(TTCA–FeTSED)/Au electrodes was assembled and examined for cell performance. The copolymer of polyFeTSED complex with polyTTCA revealed a catalytic activity for the electrochemical reduction of H2O2 and resulted in approximately a sevenfold increase in the power density of the biofuel cell over that of polyTTCA itself. Moreover, the conjugated polymers extend the biofuel cell lifetime to 4 months through the stabilization of immobilized enzymes. The biofuel cell operated in a solution containing glucose and anode-produced H2O2 generated an open-circuit voltage of approximately 366.0mV, while the maximum electrical power density extracted from the cell was 5.12μWcm−2 at an external optimal load of 25.0kΩ.