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We propose the very first “Nernstian biosupercapacitor”, a biodevice based on only one redox polymer: poly(vinyl imidazole‐co‐allylamine)[Os(bpy)2Cl], and two biocatalysts. At the bioanode PQQ‐dependent glucose dehydrogenase reduces the Os3+ moieties at the polymer to Os2+ shifting the Nernst potential of the Os3+/Os2+ redox couple to negative values. Concomitantly, at the biocathode the reduction of O2 by means of bilirubin oxidase embedded in the same redox polymer leads to the oxidation of Os2+ to Os3+ shifting the Nernst potential to higher values. Despite the use of just one redox polymer an open circuit voltage of more than 0.45 V was obtained during charging and the charge is stored in the redox polymer at both the bioanode and the biocathode. By connecting both electrodes via a predefined resistor a high power density is obtained for a short time exceeding the steady state power of a corresponding biofuel cell by a factor of 8.

Abstract:We present an intrinsic self-charging biosupercapacitor built on a unique concept for the fabrication of biodevices based on redox polymers. The biosupercapacitor consists of a high-potential redox polymer based bioanode and a low-potential redox polymer based biocathode in which the potentials of the electrodes in the discharged state show an apparent potential mismatch E anode > E cathode and prevent the use of the device as a conventional biofuel cell. Upon charging the potentials of the electrodes are shifted to more positive (cathode) and more negative (anode) values because of a change in the a ox -to-a red ratio within the redox polymer matrix. Hence, a potential inversion occurs in the charged state (E anode < E cathode ) and an open circuit voltage of > 0.4 V is achieved and the biodevice acts as a true biosupercapacitor. The bioanode consists of a novel specifically designed high potential Os-complex modified polymer for the efficient immobilization and electrical wiring of glucose converting enzymes, such as glucose oxidase and FAD-dependent glucose dehydrogenase. The cathodic side is constructed from a low potential Os-complex modified polymer integrating the O 2 reducing enzyme, bilirubin oxidase. The large potential differences between the redox polymers and the prosthetic groups of the biocatalysts ensure fast and efficient charging of the biodevice.

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We report the fabrication of a polymer/enzyme-based biosupercapacitor (BSC)/biofuel cell (BFC) hybrid device with an optimized cell voltage that can be switched on demand from energy conversion to energy storage mode. The redox polymer matrices used for the immobilization of the biocatalyst at the bioanode and biocathode act simultaneously as electron relays between the integrated redox enzymes and the electrode surface (BFC) and as pseudocapacitive charge storing elements (BSC). Moreover, owing to the self-charging effect based on the continuously proceeding enzymatic reaction, a Nernstian shift in the pseudocapacitive elements, that is, in the redox polymers, at the individual bioelectrodes leads to a maximized open circuit voltage of the device in both operating modes. Comparison with a conventional fuel cell design, that is, using redox mediators with redox potentials that are close to the potentials of the used redox proteins, indicates that the novel hybrid device shows a similar voltage output. Moreover, our results demonstrate that the conventional design criteria commonly used for the development of redox polymers for the use in biofuel cells have to be extended by considering the effect of a Nernstian shift towards the potentials of the used biocatalysts in those pseudocapacitive elements.