Suppressing hydrogen peroxide generation to achieve oxygen-insensitivity of a [NiFe] hydrogenase in redox active films.

Redox-active films were proposed as protective matrices for preventing oxidative deactivation of oxygen-sensitive catalysts such as hydrogenases for their use in fuel cells. However, the theoretical models predict quasi-infinite protection from oxygen and the aerobic half-life for hydrogenase-catalyzed hydrogen oxidation within redox films lasts only about a day. Here, we employ operando confocal microscopy to elucidate the deactivation processes. The hydrogen peroxide generated from incomplete reduction of oxygen induces the decomposition of the redox matrix rather than deactivation of the biocatalyst. We show that efficient dismutation of hydrogen peroxide by iodide extends the aerobic half-life of the catalytic film containing an oxygen-sensitive [NiFe] hydrogenase to over one week, approaching the experimental anaerobic half-life. Altogether, our data support the theory that redox films make the hydrogenases immune against the direct deactivation by oxygen and highlight the importance of suppressing hydrogen peroxide production in order to reach complete protection from oxidative stress.