Christophe Léger & Vincent Fourmond. ChemElectroChem 8, 2607-2615 (2021) doi: 10.1002/celc.202100586

Redox catalysts, including hydrogenases, can be embedded into films made of redox polymers, whose side chains mediate electrons between the catalyst and an electrode. These films can be used as bioanodes in H₂-based biofuel cells, because they protect the catalyst from O₂-induced inactivation: self-protection occurs because a fraction of the incoming H₂ is used in the outer region of the film to catalytically produce electrons that reduce the O₂ molecules that penetrate the film. Here, we focus on the case of unidirectional catalysis (e. g. H₂ oxidation) by an enzyme that is irreversibly inactivated by O₂, embedded in a film of arbitrary thickness. We analytically solve the reaction/diffusion system to fully describe the time evolution of the penetration of O₂ and we discuss the amount of H₂ consumed by the protection mechanism. We establish the relations between film thickness, electron conduction, catalyst use and life time. This provides the theoretical framework required to optimize the design of these systems.