Enzyme-Metal Oxide Composite As Catalysts for Enzymatic Oxygen Reduction

Abstract

Laccase is widely used in enzymatic fuel cell as cathode catalyst. There has been a lot of work using carbon nanostructures as immobilization support for laccase to demonstrate bio-electrocatalytic activity towards oxygen reduction reaction.1,2,3 The metal oxide nanoparticles studied were TiO2, ZnO and SnO2. The immobilization of laccase on these metal oxide nanoparticles were achieved. The coupling agent was silane and the crosslinking agents were dithiobis[succinimidyl propionate] (DSP), 1,5-Difluoro-2,4-dinitrobenzene (DFDNB) and succinimidyl iodoacetate (SIA). Attenuated total resonance fourier transform infrared spectroscopy (ATR-FTIR) was performed on the nanocomposites and the results confirmed that laccase was attached on to the metal oxide nanoparticles through the molecular crosslinkers. The resulting laccase-metal oxide nanocomposites were deposited onto screen printed carbon electrode and tested for oxygen reduction electro-catalysis in an electrochemical cell using 0.2 M sodium acetate buffer as the electrolyte. The composite modified electrode showed an open circuit potential of 0.61V vs Ag/AgCl. Cyclic voltammograms showed a clear difference between unmodified and laccase modified TiO2 in the oxygen reduction region with an onset potential of 0.57 V. In comparison the laccase physisorbed onto TiO2without the molecular crosslinkers showed no obvious electrocatalytic activity. The work adds significant value to the biofuel cell community as it introduces a new class of material as enzymatic support for bio-electrochemical reactions. Fig. 1: Schematic representation of Laccase immobilized onto metal oxide nanoparticles through molecular crosslinkers. Fig. 2 : Cyclic voltammetry of crosslinked and physisorbed laccase on TiO2 nanoparticle electrodes in O2 saturated sodium acetate buffer electrolyte. Acknowledgements: The authors would like to thank University of Georgia for providing seed funds to carry out this research.