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

Abstract

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.

Redox‐Polymer‐Based High‐Current‐Density Gas‐Diffusion H2‐Oxidation Bioanode Using [FeFe] Hydrogenase from Desulfovibrio desulfuricans in a Membrane‐free Biofuel Cell

“…The OCV was 1.13 V (recorded after a constant voltage was obtained at open circuit, reached within 3 min) and is only slightly lower than the theoretical value of 1.23 V. Moreover, the value is similar to that of [NiFe]‐ and [NiFeSe]‐based dual‐gas diffusion biofuel cells operated in a mediated electron transfer regime and in a direct electron transfer regime . Evidently, the pseudo‐capacitive effect of the polymer matrix compensates for the fact that the redox potential of the viologen is slightly higher than that of the hydrogenase. Cyclic voltammograms recorded with the bioanode after biofuel cell tests show identical current values under turnover and non‐turnover conditions (Figure S2 a).…”

“…We want to emphasize that redox polymers additionally act as pseudo‐capacitive elements which further increase the OCV due to charging of the immobilized polymer matrix leading to a shift in open circuit potential under turnover conditions (see Note S1 in the Supporting Information and refs. ).…”

Eine Redoxpolymer‐basierte Gasdiffusions‐H2‐Oxidationsbioanode mit hoher Stromdichte unter Verwendung von [FeFe]‐Hydrogenase aus Desulfovibrio desulfuricans integriert in einer membranfreien Biobrennstoffzelle

“…Wir möchten betonen, dass Redoxpolymere zusätzlich als pseudokapazitive Elemente wirken, die die OCV weiter erhöhen, da die Aufladung der immobilisierten Polymermatrix zu einer Verschiebung des Leerlaufpotentials unter Umsatzbedingungen führt (siehe Anmerkung S1 in den Hintergrundinformationen und Lit. ).…”

“…Die OCV lag bei 1.13 V (aufgezeichnet, nachdem eine konstante Spannung bei offenem Stromkreis innerhalb von 3 min erreicht wurde) und ist nur geringfügig niedriger als der theoretische Wert von 1.23 V. Darüber hinaus ist der Wert ähnlich wie bei den auf [NiFe]‐ und [NiFeSe]‐Hydrogenase basierenden dualen Gasdiffusions‐Biobrennstoffzellen, die in einem mediiertem Elektronentransfer oder unter direktem Elektronentransfer betrieben werden. Offensichtlich kompensiert der pseudokapazitive Effekt der Polymermatrix das etwas höhere Redoxpotential der Viologene im Vergleich zu dem der Hydrogenase. Cyclovoltammogramme, die mit der Bioanode nach Biobrennstoffzellentests aufgezeichnet wurden, zeigen identische Stromwerte unter Umsatz‐ und Nichtumsatzbedingungen (Abbildung S2 a).…”

Recent Progress in Applications of Enzymatic Bioelectrocatalysis

“…In addition, once both enzymes and mediators are stably immobilized on electrodes, the measurement systems work as pseudo-DET-type systems [10,11,36]. Particularly, redox polymers anchoring osmium complexes [3,[37][38][39][40][41][42][43][44][45], ferricyanide [46,47], metallocenes [48][49][50][51], and viologen units [52][53][54][55] are constructed as polymeric mediators immobilized on electrodes. In summary, a DET-type system is often more ideal than a MET-type system, whereas it seems to be practical to utilize an MET-type system for several objectives.…”