Na3[Ru2(µ-CO3)4] as a homogeneous catalyst for water oxidation; HCO3 as a co-catalyst

Shanti Gopal Patra, Totan Mondal, Krishnamoorthy Sathiyan, Amir Mizrahi, Haya Kornweitz, Dan Meyerstein

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1 Scopus citations

Abstract

In neutral medium (pH 7.0) [RuIIIRuII(µ-CO3)4(OH)]4− undergoes one electron oxidation to form [RuIIIRuIII(µ-CO3)4(OH)2]4− at an E1/2 of 0.85 V vs. NHE followed by electro-catalytic water oxidation at a potential ≥ 1.5 V. When the same electrochemical measurements are performed in bicar-bonate medium (pH 8.3), the complex first undergoes one electron oxidation at an Epa of 0.86 V to form [RuIIIRuIII(µ-CO3)4(OH)2]4−. This complex further undergoes two step one electron oxidations to form RuIVRuIII and RuIVRuIV species at potentials (Epa) 1.18 and 1.35 V, respectively. The RuIVRuIII and RuIVRuIV species in bicarbonate solutions are [RuIVRuIII(µ-CO3)4(OH)(CO3)]4− and [RuIVRuIV(µ-CO3)4(O)(CO3)]4− based on density functional theory (DFT) calculations. The formation of HCO4 in the course of the oxidation has been demonstrated by DFT. The catalyst acts as homogeneous water oxidation catalyst, and after long term chronoamperometry, the absorption spectra does not change significantly. Each step has been found to follow a proton coupled electron transfer process (PCET) as obtained from the pH dependent studies. The catalytic current is found to follow linear relation with the concentration of the catalyst and bicarbonate. Thus, bicarbonate is involved in the catalytic process that is also evident from the generation of higher oxidation peaks in cyclic voltammetry. The detailed mechanism has been derived by DFT. A catalyst with no organic ligands has the ad-vantage of long-time stability.

Original languageEnglish
Article number281
Pages (from-to)1-21
Number of pages21
JournalCatalysts
Volume11
Issue number2
DOIs
StatePublished - 1 Feb 2021

Keywords

  • Carbonate
  • DFT
  • Electrocatalysis
  • Peroxomonocarbonate
  • Ruthenium carbonate
  • Water oxidation

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