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

Abstract

The incorporation of highly active but also highly sensitive catalysts (e.g. the [FeFe] hydrogenase from Desulfovibrio desulfuricans) in biofuel cells is still one of the major challenges in sustainable energy conversion. We report the fabrication of a dual‐gas diffusion electrode H2/O2 biofuel cell equipped with a [FeFe] hydrogenase/redox polymer‐based high‐current‐density H2‐oxidation bioanode. The bioanodes show benchmark current densities of around 14 mA cm−2 and the corresponding fuel cell tests exhibit a benchmark for a hydrogenase/redox polymer‐based biofuel cell with outstanding power densities of 5.4 mW cm−2 at 0.7 V cell voltage. Furthermore, the highly sensitive [FeFe] hydrogenase is protected against oxygen damage by the redox polymer and can function under 5 % O2.

Insight into the Redox Behavior of the [4Fe–4S] Subcluster in [FeFe] Hydrogenases

“…Additionally, we observed complex redox behavior in Cp HydA1 PDT , the hydrogenase containing F-clusters, which can only be explained through a redox anticooperative interaction between [4Fe–4S] H and the F-clusters. Because [FeFe] hydrogenases have recently come to the fore as potentially useful catalysts for incorporation into redox-hydrogel-based fuel cells, − understanding their mechanism and how their structure influences their activity is of particular relevance.…”

Enhancing the catalytic current response of H2 oxidation gas diffusion bioelectrodes using an optimized viologen‐based redox polymer and [NiFe] hydrogenase

“…This potential difference is sufficiently large to invoke a high driving force for H 2 oxidation, but it is still low enough to guarantee a large open‐circuit voltage in a corresponding biofuel cell. [ 33 ] The optimization of the polymer loading on the electrode in a two‐layer approach (Figure 2b), similar to the ones described in our previous work, [ 16–18 ] yielded highly stable GDEs with immobilized [NiFe] hydrogenase from Desulfovibrio vulgaris Miyazaki F ( Dv MF).…”

“…In our previous work, we combined the benefits of redox polymers, namely protection of the enzyme and high catalyst loading, with the concept of gas diffusion electrodes to fabricate high performance H 2 oxidation bioanodes using various hydrogenases as biocatalysts. [ 17,18,30 ] Surprisingly, the catalytic current response of these electrodes did not scale with the intrinsic activity of the employed hydrogenase. [ 17 ] Since H 2 mass transport limitation could be ruled out when using GDEs, the limited current densities achieved, especially in the case of the most active [FeFe] hydrogenase, [ 18 ] may be attributed to insufficient electron transfer kinetics within the redox polymer film.…”

“…[ 17,18,30 ] Surprisingly, the catalytic current response of these electrodes did not scale with the intrinsic activity of the employed hydrogenase. [ 17 ] Since H 2 mass transport limitation could be ruled out when using GDEs, the limited current densities achieved, especially in the case of the most active [FeFe] hydrogenase, [ 18 ] may be attributed to insufficient electron transfer kinetics within the redox polymer film. [ 17 ] To prevent direct electron transfer with the immobilized hydrogenase, which would lead to undesired enzyme inactivation, an initial coating of the GDE surface with a layer of only the redox polymer without any enzyme was used as an adhesion layer between the electrode surface and the catalytically active layer comprising a mixture of redox polymer and hydrogenase.…”

“…We assume that by this the probability of the collision between adjacent viologen units within the redox polymer layer is insufficient to allow charge transfer at the rate necessary for the most active hydrogenase at high enzyme loading and unlimited H 2 supply within the GDE. [ 17,18,30 ]…”