Hydrogen production using nickel electrocatalysts with pendant amines: Ligand effects on rates and overpotentials

Stefan Wiese, Uriah J. Kilgore, Ming Hsun Ho, Simone Raugei, Daniel L. Dubois, R. Morris Bullock, Monte L. Helm

Research output: Contribution to journalArticle

44 Citations (Scopus)

Abstract

A Ni-based electrocatalyst for H2 production, [Ni(8P Ph2NC6H4Br)2](BF 4)2, featuring eight-membered cyclic diphosphine ligands incorporating a single amine base, 1-para-bromophenyl-3,7-triphenyl-1-aza-3,7- diphosphacycloheptane (8PPh2NC6H4Br) has been synthesized and characterized. X-ray diffraction studies reveal that the cation of [Ni(8PPh2NC6H4Br) 2(CH3CN)](BF4)2 has a distorted trigonal bipyramidal geometry. In CH3CN, [Ni(8PPh 2NC6H4Br)2]2+ is an electrocatalyst for reduction of protons, and it has a maximum turnover frequency for H2 production of 800 s-1 with a 700 mV overpotential (at Ecat/2) when using [(DMF)H]OTf as the acid. Addition of H2O to acidic CH3CN solutions of [Ni(8P Ph2NC6H4Br)2] 2+ results in an increase in the turnover frequency for H2 production to a maximum of 3300 s-1 with an overpotential of 760 mV at Ecat/2. Computational studies carried out on [Ni(8P Ph2NC6H4Br)2] 2+ indicate the observed catalytic rate is limited by formation of nonproductive protonated isomers, diverting active catalyst from the catalytic cycle. The results of this research show that proton delivery from the exogenous acid to the correct position on the proton relay of the metal complex is essential for fast H2 production.

Original languageEnglish
Pages (from-to)2527-2535
Number of pages9
JournalACS Catalysis
Volume3
Issue number11
DOIs
Publication statusPublished - Nov 1 2013

Keywords

  • electrocatalysis
  • hydrogen production
  • nickel phosphine complexes
  • pendant amines
  • proton reduction
  • proton relay

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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