Fig. 1: Redox matrices for the protection of O2-sensitive catalysts.
a Structure of the [NiFe]-hydrogenase and the viologen-modified polymer (polyethylenimine backbone). b Proposed mechanism for protection from O2. The hydrogenase catalyzes the reversible oxidation of H2 in the inner parts of the film and generates electrons that are transferred to the electrode via the viologen (Vred/Vox) moieties (pathway 1) which produces the catalytic current when an oxidative potential is applied to the electrode. In addition, the presence of O2 in the electrolyte creates an oxidative driving force that diverts some of the electrons towards the electrolyte/film interface (pathway 2) where the viologen moieties act as catalysts for O2 reduction, thus protecting the catalyst in the inner film domain but also producing H2O2. Iodide catalyzes the subsequent H2O2 dismutation to H2O and half a molecule of O2, which is further reduced by the viologen.
