Photoelectrochemical biofuel cells (PEBFCs) are hybrid devices which combine the utility of enzymatic redox catalysts with the photon absorbing characteristics of a dye-sensitized solar cell (DSSC).  The pairing of these two technologies has been demonstrated to result in a system that improves on the performance of either a traditional enzymatic fuel cell (EFC) or DSSC operating independently¹.  Furthermore, due to the increased potential provided by a PEBFC relative to an EFC the range of oxidizers used in the cathode can be broadened to produce a variety of useful reduced fuels.  Traditionally, PEBFCs have relied on NAD⁺/NADH intermediates for charge transfer between the anodic redox enzyme and the porphyrin sensitizer.  However, recent work by our group has shown that quinoprotein glucose dehydrogenases are capable of efficient, mediator free direct electron transfer (DET) to immobilized heme porphyrins².  DET allows for a further reduction in the electrode overpotential compared to many mediated systems and therefore provides more usable potential for energy conversion.  

In the current work a PEBFC utilizing DET mechanisms was developed with the goal of providing efficient electron transfer between the enzymatic catalyst and the porphyrin sensitizer on the anode.  The electron transfer was enhanced by photo-excitation of the sensitizer and induced charge separation to a covalently bound n-type semi-conductor (Figure 1).  The resulting oxidized sensitizer then readily accepts electrons from the quinoproteins adsorbed to the electrode surface.  The open circuit potential (V_oc) of the illuminated photo anode was more negative than the same anode in a dark condition by approximately 80 mV (top of Figure 2).  The generated current of the illuminated photoanode was also considerably higher at all potentials tested (bottom of Figure 2).  To complete the PEBFC, the photoanode is coupled with a cathode utilizing an oxidase enzymatic catalyst and overall performance in terms of surface characteristics, V_oc, and total power are characterized.  Further applications with regards to possible uses in energy conversion and reforming of simple, abundant substrates such as glucose to more readily useable fuels such as hydrogen will be discussed.

1.            M. Hambourger, G. Kodis, M. D. Vaughn, G. F. Moore, D. Gust, A. L. Moore and T. A. Moore, Dalton Transactions, 9979 (2009).

2.            R. J. Lopez, S. Babanova, K. Artyushkova and P. Atanassov, Bioelectrochemistry, 105, 78 (2015).