The study of hydrogenase enzymes (H2ases) is necessary because of their importance to a future hydrogen energy economy. These enzymes come in three distinct classes: [NiFe] H2ases, which have a propensity toward H2 oxidation; [FeFe] H2ases, which have a propensity toward H2 evolution; and [Fe] H2ases, which catalyze H− transfer. Modeling these enzymes has so far treated them as different species, which is understandable given the different cores and ligand sets of the natural molecules. Here, we demonstrate, using x-ray analysis and nuclear magnetic resonance, infrared, Mössbauer spectroscopies, and electrochemical measurement, that the catalytic properties of all three enzymes can be mimicked with only three isomers of the same NiFe complex.

We report an Ir complex as an anode catalyst capable of switching between a hydrogenase‐type fuel‐cell mode and a photosystem II‐type solar‐cell mode. This catalyst is connected to carbon‐black‐supported platinum as a cathode catalyst, which reduces dioxygen in a manner analogous to cytochrome c oxidase. Together, they make a system capable of switching between the two modes.

We propose a model for the water-oxidation and recovery systems of the oxygen-evolving complex (OEC) of the photosystem II (PSII) enzyme. The whole system is constructed from two catalytic cycles, conducted as a tandem reaction: (i) a water-oxidation loop uses cerium(IV) ammonium nitrate as an oxidant to activate a dimanganese complex for water-oxidation and thereby liberate a molecule of O2 and (ii) a recovery loop begins with photoinhibition of the dimanganese complex but then uses O2 to reactivate the manganese centre. The net result is a catalytic water-oxidation catalyst that can use self-generated O2 for recovery.

The development of hydrogen fuel cells is greatly hindered by the unwanted generation of H2O2 at the cathode. A non‐Pt cathode catalyst is now shown to be capable of simultaneously reducing both O2 and H2O2, thus rendering H2O2 a useful part of the feed stream. The applicability of this unique catalyst is demonstrated by employing it in a fuel cell running on H2/CO and O2/H2O2.

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