Polyaniline-Supported Bacterial Biofilms as Active Matrices for Platinum Nanoparticles: Enhancement of Electroreduction of Carbon Dioxide

A hybrid matrix composed of a porous polyaniline underlayer, a robust bacterial biofilm and a multiwalled carbon nanotube overlayer has been demonstrated to function as highly active support for dispersed Pt catalytic nanoparticles during the electroreduction of carbon dioxide in neutral medium (phosphate buffer at pH 6.1). In contrast with bare Pt nanoparticles (deposited at a glassy carbon substrate), application of the hybrid system produces sizeable CO2-reduction currents in comparison to those originating from hydrogen evolution. The result is consistent with an enhancement in the reduction of carbon dioxide. However, the biofilm-based matrix tends to inhibit the catalytic properties of platinum towards proton discharge (competitive reaction) or even oxygen reduction. The hydrated structure permits easy unimpeded flow of aqueous electrolyte at the electrocatalytic interface. Although application of the polyaniline underlayer can be interpreted in terms of stabilization and improvement of the biofilm adherence, the use of carbon nanotubes facilitates electron transfer to Pt catalytic sites. It is apparent from the voltammetric stripping-type analytical experiments that, although formation of some methanol and methanoic acid cannot be excluded, carbon monoxide seems to be the main CO2-reduction product.