[Ni(PPh2NBn2)2(CH3CN)]2+ as an Electrocatalyst for H2 Production: Dependence on Acid Strength and Isomer Distribution
[Ni(PPh2NBz2)2(CH3CN)](BF4)2, Ni(PPh2NBz2)22+ (where PPh2NBz2 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. Using strong acids, such as p cyanoanilinium, Ni(PPh2NBz2)22+ has been shown to be protonated under catalytic conditions prior to reduction, with an effective pKa of 6.7±0.4. 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 dihydrogen. Pre-protonation of Ni(PPh2NBz2)22+ has been found to shift the catalytic operating potential to more positive potentials by up to 440 mV, depending upon the conditions. The catalytic rate was found to increase by an order of magnitude by increasing the solution pH or through the addition of water. This material is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1023175
- Report Number(s):
- PNNL-SA-77921; KC0307010; TRN: US201118%%478
- Journal Information:
- ACS Catalysis, 1(7):777-785, Vol. 1, Issue 7
- Country of Publication:
- United States
- Language:
- English
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