Hydrogen is a clean energy alternative to fossil fuels, which can be generated from solar-driven water splitting. However, more efficient and inexpensive catalysts for the hydrogen evolution reaction (HER) are needed. In this context, we have developed original cobalt complexes supported by tetradentate pyridyl-N-heterocylic carbene (NHC)-based ligands, which allow access to both cis and trans labile coordination sites at cobalt. The trans-Co catalyst shows remarkable activity for proton reduction in aqueous solutions with overpotentials as low as 300 mV. Moreover, controlled potential electrolyses coupled with gas chromatography show that hydrogen is produced with a Faradaic efficiency of 99% and turnover frequency of 50 h-1. Indeed, introduction of NHC donors into the ligand framework leads to low overpotentials and high activity for the trans catalyst relative to related polypyridyl complexes, whereas long-term stability of the cis-Co catalyst is limited. Results from electrochemical studies in aqueous solutions as a function of pH and in nonaqueous solutions with added organic acids are presented.

Water reduction at low overpotentials with cobalt pyridyl-NHC electrocatalysts

255th National Meeting (2018)

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