Fig. 1
Schematic of the proposed hydrogenase/horseradish peroxidase biofuel cell. The bioanode consists of a polymer double-layer system comprising an underlying layer composed of the [NiFe] or [NiFeSe] hydrogenase from Desulfovibrio vulgaris Miyazaki F (DvMF-[NiFe]) and from Desulfovibrio vulgaris Hildenborough (DvH-[NiFeSe]) integrated into the viologen-modified polymer P(N3MA-BA-GMA)-vio (poly(3-azido-propyl methacrylate-co-butyl acrylate-co-glycidyl methacrylate)-viologen (the viologen moieties are depicted in blue) and a protection top layer consisting of a bienzymatic system that contains an oxidase (glucose oxidase, GOx, or pyranose oxidase, Py2Ox) and catalase (CAT) embedded in the redox-silent polymer P(SS-GMA-BA) (poly(4-styrene sulfonate-co-glycidyl methacrylate-co-butyl acrylate)). Oxygen is removed by converting glucose to gluconolactone by the concomitant reduction of O2 to H2O2. The biocathode is built on a carbon cloth electrode that was modified with carbon microfibers (CMFs) that were decorated with carbon nanotubes (CNTs). The latter ensure wiring of the horseradish peroxidase (HRP) via the iron-oxo complex compound I. The cathode was first modified with pyrene butyric acid (hydrophilization) and then via a sequential drop cast process with a HRP layer followed by a top layer containing the oxidase (GOx or Py2Ox) that ensures the in situ H2O2 formation. Note that for clarity only the combination of a DvH-[NiFeSe]/GOx/CAT and GOx/HRP based electrodes are shown in the scheme
