Bioinspired Metal Selenolate Polymers with Tunable Mechanistic Pathways for Efficient H2 Evolution

The efficient reduction of water into hydrogen has emerged as an attractive strategy for the conversion of solar energy into chemical bonds. Hydrogenase enzymes efficiently catalyze this reaction. The [NiFeSe] hydrogenases, a subclass of the [NiFe] hydrogenases with a selenocysteine replacing a cysteine residue, display higher activities and O2 tolerance than the conventional sulfur-only [NiFe] hydrogenases. Inspired by the enhanced activity upon replacement of sulfur with selenium seen in nature, we report here the syntheses and characterization of cobalt and nickel selenolate coordination polymers (CPs) based on benzene-1,2,4,5-tetraselenolate (BTSe), which are efficient catalysts for the hydrogen evolution reaction (HER) from water. To reach a current density of 10 mA/cm2, the benchmarking metric for HER, both cobalt and nickel systems display overpotentials of only ∼350 mV, displaying a reduction in overpotential in comparison to the previously reported cobalt and nickel CPs based on benzene-1,2,4,5-tetrathiolate (BTT). In addition, the cobalt selenolate polymer displays a 217 mV improvement in the overpotential in comparison to its sulfur-only analogue that arises from the ability to promote an alternative mechanism at high catalyst loadings that was not available for the cobalt BTT CP.