As concerns about climate change continue to mount, research into production of carbon-free fuels such as hydrogen has become increasingly urgent. One promising route is electrocatalytic generation of hydrogen mediated by small inorganic complexes, where secondary coordination sphere interactions have been found to dramatically influence reactivity. In this study, a series of hydrogen evolving cobalt-peptide complexes active in water were investigated to elucidate the role of secondary coordination sphere interactions with the catalytic active site by varying peptide ligand amino acid side chains. Cobalt bound by Gly-Gly-His (GGH), Lys-Lys-His (KKH), Arg-Arg-His (RRH), and Gly-Gly-His-Asn (GGHN) were studied. To evaluate the performance of the catalysts, the catalytic rate constant for hydrogen production was determined in the presence and absence of buffer for each derivative using cyclic voltammetry. All of the derivatives were observed to have comparable reaction rates in the presence of buffer, with rate constants dependent on buffer pK<sub>a</sub>, suggesting that buffer is the primary proton source in the hydrogen evolution reaction under those conditions. However, in the absence of buffer, the variants showed significantly different reaction rates, which indicates that the secondary coordination sphere has an impact on the reaction under these conditions. CoKKH has the highest rate in the absence of buffer followed by CoRRH, CoGGH and finally CoGGHN. We suggest that the Arg or Lys side chain plays a role in assisting proton delivery to the metal in CoKKH and CoRRH.

Secondary coordination sphere effect on hydrogen evolution electrocatalysis by cobalt-ATCUN complexes

ACS Spring Meeting 2021

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