Rational Combination of Promiscuous Enzymes Yields a Versatile Enzymatic Fuel Cell with Improved Coulombic Efficiency

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Enzymatic fuel cells (EFCs) utilize enzymatic catalysts to convert chemical energy to electrical energy, typically by performing a 2e− oxidation of saccharides. In the case of sugars, a single 2e− oxidation does not fully exploit this energy-dense fuel that is capable of producing 24e− from its complete oxidation to CO2. Here, we propose an efficient approach to design a versatile EFC that can produce electrical energy from 12 (oligo)saccharides by combining two enzymes that possess diverse substrate specificities: pyranose dehydrogenase (PDH) and a broad glucose oxidase (bGOx). Additionally, PDH is able to perform single or two sequential oxidations of glucose (at C2 and/or C3) yielding up to 4e−, whereas bGOx only performs a single 2e− oxidation at the anomeric (C1) position. By combining PDH and bGOx, we demonstrate the ability to achieve deep oxidation of glucose and xylose, whereby each is able to undergo sequential oxidations by PDH and bGOx. Additionally, we demonstrate that this deep oxidation can yield improved performances of EFCs. For example, an EFC comprised of a bi-enzymatic PDH/bGOx bioanode using xylose as a fuel yields a maximum current density of 586 ± 3 μAcm−2 whereas mono-enzymatic PDH or bGOx EFC bioanodes result in current densities of 440 ± 4 μAcm−2 and 120 ± 1 μAcm−2, respectively.