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Adrian Ruff, Julian Szczesny, Maria Vega, Sónia Zacarias, Pedro M. Matias, Sébastien Gounel, Nicolas Mano, Inês A. C. Pereira, Wolfgang Schuhmann

• Variants of the highly active [NiFeSe] hydrogenase from \(\textit {D. vulgaris Hildenborough}\) that exhibit enhanced O\(_2\) tolerance were used as H\(_2\)-oxidation catalysts in H\(_2\)/O\(_2\) biofuel cells. Two [NiFeSe] variants were electrically wired by means of low-potential viologen-modified redox polymers and evaluated with respect to H\(_2\)-oxidation and stability against O\(_2\) in the immobilized state. The two variants showed maximum current densities of (450\(\pm\)84) \(\mu\)A cm\(^{−2}\) for G491A and (476\(\pm\)172) \(\mu\)A cm\(^{−2}\) for variant G941S on glassy carbon electrodes and a higher O\(_2\) tolerance than the wild type. In addition, the polymer protected the enzyme from O\(_2\) damage and high-potential inactivation, establishing a triple protection for the bioanode. The use of gas-diffusion bioanodes provided current densities for H\(_2\)-oxidation of up to 6.3 mA cm\(^{−2}\). Combination of the gas-diffusion bioanode with a bilirubin oxidase-based gas-diffusion O\(_2\)-reducing biocathode in a membrane-free biofuel cell under anode-limiting conditions showed unprecedented benchmark power densities of 4.4 mW cm\(^{−2}\) at 0.7 V and an open-circuit voltage of 1.14 V even at moderate catalyst loadings, outperforming the previously reported system obtained with the [NiFeSe] wild type and the [NiFe] hydrogenase from \(\textit {D. vulgaris}\) Miyazaki F.