Direct Evidence for a Sequential Electron Transfer-Proton Transfer Mechanism in the PCET Reduction of a Metal Hydroxide Catalyst

Matthew C. Kessinger, Jeremiah Xu, Kai Cui, Quentin Loague, Alexander V. Soudackov, Sharon Hammes-Schiffer, Gerald J. Meyer

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

The proton-coupled electron transfer (PCET) mechanism for the reaction Mox-OH + e- + H+ → Mred-OH2 was determined through the kinetic resolution of the independent electron transfer (ET) and proton transfer (PT) steps. The reaction of interest was triggered by visible light excitation of [RuII(tpy)(bpy′)H2O]2+, RuII-OH2, where tpy is 2,2′:6′,2″-terpyridine and bpy′ is 4,4′-diaminopropylsilatrane-2,2′-bipyridine, anchored to In2O3:Sn (ITO) thin films in aqueous solutions. Interfacial kinetics for the PCET reduction reaction were quantified by nanosecond transient absorption spectroscopy as a function of solution pH and applied potential. Data acquired at pH = 5-10 revealed a stepwise electron transfer-proton transfer (ET-PT) mechanism, while kinetic measurements made below pKa(RuIII-OH/OH2) = 1.3 were used to study the analogous interfacial reaction, where electron transfer was the only mechanistic step. Analysis of this data with a recently reported multichannel kinetic model was used to construct a PCET zone diagram and supported the assignment of an ET-PT mechanism at pH = 5-10. Ultimately, this study represents a unique example among Mox-OH/Mred-OH2 reactivity where the protonation and oxidation states of the intermediate were kinetically and spectrally resolved to firmly establish the PCET mechanism.

Original languageEnglish (US)
Pages (from-to)1742-1747
Number of pages6
JournalJournal of the American Chemical Society
Volume146
Issue number3
DOIs
StatePublished - Jan 24 2024
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry

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