Photocatalytic-induced electron transfer via anode-respiring bacteria (ARB) at an anode that intimately couples ARB and a TiO₂ photocatalyst

A novel anode that intimately couples anode-respiring bacteria (ARB) with a nitrogen-doped TiO₂ photocatalyst on a porous carbon foam electrode (the ICPB-anode) was fabricated and experimentally tested in an electrochemical cell. ARB are well known for obtaining energy by transferring bio-metabolized electrons to the anode, an external solid acceptor. The goal of this work was to identify if and how ARB play a role in transporting photo-generated electrons. When simulated visible-light illuminated an ICPB-anode, the current increased by ∼3 A/m² (∼30% of the total), due to photocatalytically generated electrons (photo-electrons). In contrast, an abiotic photocatalyst anode (photo-anode) was incapable of transfering photo-electrons. Compared to a non-photocatalytic biofilm-anode, the Coulombic efficiency increased by 15–20% with the ICPB-anode, and the effect was due to the addition of electron flow from photocatalytic water electrolysis, since oxidation of the organic electron donor was unchanged. Electrochemical impedance analyses showed that the Ohmic resistance of the ICPB-anode decreased by ∼98%, compared with the abiotic photo-anode. A redox-potential window typical of ARB's c-type cytochromes was up-regulated when the ARB transported photo-electrons, supporting that c-type cytochromes were the significant redox proteins for transferring photo-electrons. All the results combine to show that ARB were responsible for the transport of electrons generated by photocatalysis in the ICPB-anode.