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Acidic ionic liquid/water solution as both medium and proton source for electrocatalytic H₂ evolution by [Ni(P₂N₂)₂]²⁺ complexes

Pool, Douglas H., Stewart, Michael P., O’Hagan, Molly, Shaw, Wendy J., Roberts, John A. S., Bullock, R. Morris, DuBois, Daniel L.
Proceedings of the National Academy of Sciences of the United States of America 2012 v.109 no.39 pp. 15634-15639
acetonitrile, aqueous solutions, bromine, catalysts, evolution, hydrogen, hydrogen production, hydrophobicity, ionic liquids, nickel, protons
The electrocatalytic reduction of protons to H ₂ by [Formula] (where [Formula] in the highly acidic ionic liquid dibutylformamidium bis(trifluoromethanesulfonyl)amide shows a strong dependence on added water. A turnover frequency of 43,000–53,000 s ⁻¹ has been measured for hydrogen production at 25 °C when the mole fraction of water (χ H₂O) is 0.72. The same catalyst in acetonitrile with added dimethylformamidium trifluoromethanesulfonate and water has a turnover frequency of 720 s ⁻¹. Thus, the use of an ionic liquid/aqueous solution enhances the observed catalytic rate by more than a factor of 50, compared to a similar acid in a traditional organic solvent. Complexes [Formula] (X = H, OMe,CH ₂P(O)(OEt) ₂, Br) are also catalysts in the ionic liquid/water mixture, and the observed catalytic rates correlate with the hydrophobicity of X .