Introducing Pseudocapacitive Bioelectrodes into a Biofuel Cell/Biosupercapacitor Hybrid Device for Optimized Open Circuit Voltage

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.