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

Douglas H. Pool, Michael P. Stewart, Molly O'Hagan, Wendy J. Shaw, John A.S. Roberts, R. Morris Bullock, Daniel L. DuBois

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Abstract

The electrocatalytic reduction of protons to H2 by [Ni(P Ph2NC6H4-hex2)2](BF 4)2 (where PPh2N C6H4-hex2 = 1,5-di(4-n-hexylphenyl)-3,7-diphenyl-1,5- diaza-3,7-diphosphacyclooctane) 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 (χH2O) 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 [Ni(PPh 2NC6H4X2)2](BF4) 2 (X = H, OMe,CH2P(O)(OEt)2, Br) are also catalysts in the ionic liquid/water mixture, and the observed catalytic rates correlate with the hydrophobicity of X.

Original languageEnglish
Pages (from-to)15634-15639
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume109
Issue number39
DOIs
Publication statusPublished - Sep 25 2012

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Keywords

  • Electrocatalysis
  • Homogeneous
  • Hydrogenase
  • Proton relay
  • Renewable energy

ASJC Scopus subject areas

  • General

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