Substitution of a tertiary amine with a softer pyridine group and the inclusion of a conjugated bipyridine unit in a Co complex was used to study the structure-activity relationship of a catalytic hydrogen evolution reaction (HER). Improved catalytic stability and activity resulted from these modifications, which was observed for both electro- and photocatalytic HER in neutral water. The new ligand referred to as Py3Me-Bpy, 6-((6-(1,1-di(pyridin-2-yl)ethyl)pyridin-2-yl)methyl)-2,2'-bipyridine, catalyzes the HER electrolytically at 1.3 V (vs. SHE) for 20 hours with a turnover number (TON) of 266,300. The photolytic HER study was stable for two days with a TON of 15,000. Both studies occurred in aqueous pH 7 solutions. Increased stability towards the CoI species is likely the result of the softer ligand scaffold. Density functional theory (DFT) calculations suggest H2 is released from the protonation of CoIIH species through a general electron transfer/proton transfer/electron transfer/proton transfer pathway.

Hydrogen evolution reaction enhancements via cobalt complexation with a softer polypyridyl ligand in neutral water

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