[Ni(PPh 2NBn 2) 2(CH3CN)]2+ as an electrocatalyst for H 2 production: Dependence on acid strength and isomer distribution

Aaron Appel, Douglas H. Pool, Molly O'Hagan, Wendy J. Shaw, Jenny Y. Yang, M. Rakowski Dubois, Daniel L DuBois, R Morris Bullock

Research output: Contribution to journalArticle

72 Citations (Scopus)

Abstract

[Ni(PPh 2NBn 2) 2(CH3CN)]2+ (where PPh 2NBn 2 is 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3, 7-diphosphacyclooctane), has been studied as an electrocatalyst for the production of hydrogen in acetonitrile. Strong acids, such as p-cyanoanilinium, protonate [Ni(PPh 2NBn 2) 2(CH3CN)]2+ prior to reduction under catalytic conditions, and an effective pKa of 6.7 ± 0.4 was determined for the protonation product. Through multinuclear NMR spectroscopy studies, the nickel(II) complex was found to be doubly protonated without any observed singly protonated species. In the doubly protonated complex, both protons are positioned exo with respect to the metal center and are stabilized by an N-H-N hydrogen bond. The formation of exo protonated isomers is proposed to limit the rate of hydrogen production because the protons are unable to gain suitable proximity to the reduced metal center to generate H2. Preprotonation of [Ni(PPh 2NBn 2)2(CH 3CN)]2+ has been found to shift the catalytic operating potential to more positive potentials by up to 440 mV, depending upon the conditions. The half-wave potential for the catalytic production of H 2 depends linearly on the pH of the solution and indicates a proton-coupled electron transfer reaction. The overpotential remains low and nearly constant at 74 ± 44 mV over the pH range of 6.2-11.9. The catalytic rate was found to increase by an order of magnitude by increasing the solution pH or through the addition of water.

Original languageEnglish
Pages (from-to)777-785
Number of pages9
JournalACS Catalysis
Volume1
Issue number7
DOIs
Publication statusPublished - Jul 1 2011

Fingerprint

Electrocatalysts
Isomers
Protons
Acids
Metals
Protonation
Hydrogen production
Nickel
Acetonitrile
Nuclear magnetic resonance spectroscopy
Hydrogen
Hydrogen bonds
Electrons
Water

Keywords

  • catalyst
  • Electrocatalysis
  • hydrogen production
  • PCET
  • pendant amine
  • potential

ASJC Scopus subject areas

  • Catalysis

Cite this

[Ni(PPh 2NBn 2) 2(CH3CN)]2+ as an electrocatalyst for H 2 production : Dependence on acid strength and isomer distribution. / Appel, Aaron; Pool, Douglas H.; O'Hagan, Molly; Shaw, Wendy J.; Yang, Jenny Y.; Rakowski Dubois, M.; DuBois, Daniel L; Bullock, R Morris.

In: ACS Catalysis, Vol. 1, No. 7, 01.07.2011, p. 777-785.

Research output: Contribution to journalArticle

Appel, Aaron ; Pool, Douglas H. ; O'Hagan, Molly ; Shaw, Wendy J. ; Yang, Jenny Y. ; Rakowski Dubois, M. ; DuBois, Daniel L ; Bullock, R Morris. / [Ni(PPh 2NBn 2) 2(CH3CN)]2+ as an electrocatalyst for H 2 production : Dependence on acid strength and isomer distribution. In: ACS Catalysis. 2011 ; Vol. 1, No. 7. pp. 777-785.
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abstract = "[Ni(PPh 2NBn 2) 2(CH3CN)]2+ (where PPh 2NBn 2 is 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3, 7-diphosphacyclooctane), has been studied as an electrocatalyst for the production of hydrogen in acetonitrile. Strong acids, such as p-cyanoanilinium, protonate [Ni(PPh 2NBn 2) 2(CH3CN)]2+ prior to reduction under catalytic conditions, and an effective pKa of 6.7 ± 0.4 was determined for the protonation product. Through multinuclear NMR spectroscopy studies, the nickel(II) complex was found to be doubly protonated without any observed singly protonated species. In the doubly protonated complex, both protons are positioned exo with respect to the metal center and are stabilized by an N-H-N hydrogen bond. The formation of exo protonated isomers is proposed to limit the rate of hydrogen production because the protons are unable to gain suitable proximity to the reduced metal center to generate H2. Preprotonation of [Ni(PPh 2NBn 2)2(CH 3CN)]2+ has been found to shift the catalytic operating potential to more positive potentials by up to 440 mV, depending upon the conditions. The half-wave potential for the catalytic production of H 2 depends linearly on the pH of the solution and indicates a proton-coupled electron transfer reaction. The overpotential remains low and nearly constant at 74 ± 44 mV over the pH range of 6.2-11.9. The catalytic rate was found to increase by an order of magnitude by increasing the solution pH or through the addition of water.",
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T1 - [Ni(PPh 2NBn 2) 2(CH3CN)]2+ as an electrocatalyst for H 2 production

T2 - Dependence on acid strength and isomer distribution

AU - Appel, Aaron

AU - Pool, Douglas H.

AU - O'Hagan, Molly

AU - Shaw, Wendy J.

AU - Yang, Jenny Y.

AU - Rakowski Dubois, M.

AU - DuBois, Daniel L

AU - Bullock, R Morris

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N2 - [Ni(PPh 2NBn 2) 2(CH3CN)]2+ (where PPh 2NBn 2 is 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3, 7-diphosphacyclooctane), has been studied as an electrocatalyst for the production of hydrogen in acetonitrile. Strong acids, such as p-cyanoanilinium, protonate [Ni(PPh 2NBn 2) 2(CH3CN)]2+ prior to reduction under catalytic conditions, and an effective pKa of 6.7 ± 0.4 was determined for the protonation product. Through multinuclear NMR spectroscopy studies, the nickel(II) complex was found to be doubly protonated without any observed singly protonated species. In the doubly protonated complex, both protons are positioned exo with respect to the metal center and are stabilized by an N-H-N hydrogen bond. The formation of exo protonated isomers is proposed to limit the rate of hydrogen production because the protons are unable to gain suitable proximity to the reduced metal center to generate H2. Preprotonation of [Ni(PPh 2NBn 2)2(CH 3CN)]2+ has been found to shift the catalytic operating potential to more positive potentials by up to 440 mV, depending upon the conditions. The half-wave potential for the catalytic production of H 2 depends linearly on the pH of the solution and indicates a proton-coupled electron transfer reaction. The overpotential remains low and nearly constant at 74 ± 44 mV over the pH range of 6.2-11.9. The catalytic rate was found to increase by an order of magnitude by increasing the solution pH or through the addition of water.

AB - [Ni(PPh 2NBn 2) 2(CH3CN)]2+ (where PPh 2NBn 2 is 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3, 7-diphosphacyclooctane), has been studied as an electrocatalyst for the production of hydrogen in acetonitrile. Strong acids, such as p-cyanoanilinium, protonate [Ni(PPh 2NBn 2) 2(CH3CN)]2+ prior to reduction under catalytic conditions, and an effective pKa of 6.7 ± 0.4 was determined for the protonation product. Through multinuclear NMR spectroscopy studies, the nickel(II) complex was found to be doubly protonated without any observed singly protonated species. In the doubly protonated complex, both protons are positioned exo with respect to the metal center and are stabilized by an N-H-N hydrogen bond. The formation of exo protonated isomers is proposed to limit the rate of hydrogen production because the protons are unable to gain suitable proximity to the reduced metal center to generate H2. Preprotonation of [Ni(PPh 2NBn 2)2(CH 3CN)]2+ has been found to shift the catalytic operating potential to more positive potentials by up to 440 mV, depending upon the conditions. The half-wave potential for the catalytic production of H 2 depends linearly on the pH of the solution and indicates a proton-coupled electron transfer reaction. The overpotential remains low and nearly constant at 74 ± 44 mV over the pH range of 6.2-11.9. The catalytic rate was found to increase by an order of magnitude by increasing the solution pH or through the addition of water.

KW - catalyst

KW - Electrocatalysis

KW - hydrogen production

KW - PCET

KW - pendant amine

KW - potential

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