The roles of chalcogenides in O2 protection of H2ase active sites

At some point, all HER (Hydrogen Evolution Reaction) catalysts, important in sustainable H₂O splitting technology, will encounter O₂ and O₂-damage. The NiFeSe]-H₂ases and some of the NiFeS]–H₂ases, biocatalysts for reversible H₂ production from protons and electrons, are exemplars of oxygen tolerant HER catalysts in nature. In the hydrogenase active sites oxygen damage may be extensive (irreversible) as it is for the FeFe]–H₂ase or moderate (reversible) for the NiFe]–H₂ases. The affinity of oxygen for sulfur, in NiFeS]–H₂ase, and selenium, in NiFeSe]–H₂ase, yielding oxygenated chalcogens results in maintenance of the core NiFe unit, and myriad observable but inactive states, which can be reductively repaired. In contrast, the FeFe]–H₂ase active site has less possibilities for chalcogen-oxygen uptake and a greater chance for O₂-attack on iron. Exposure to O₂ typically leads to irreversible damage. Despite the evidence of S/Se-oxygenation in the active sites of hydrogenases, there are limited reported synthetic models. This perspective will give an overview of the studies of O₂ reactions with the hydrogenases and biomimetics with focus on our recent studies that compare sulfur and selenium containing synthetic analogues of the NiFe]–H₂ase active sites.

At some point, all HER (Hydrogen Evolution Reaction) catalysts, important in sustainable H₂O splitting technology, will encounter O₂ and O₂-damage.