Investigating the origin of Co(IV)’s high electrocatalytic activity in the oxygen evolution reaction at a NaxCoO2 interface

Huiwen Ji, Girija Sahasrabudhe, Matthew K. Vallon, Jeffrey Schwartz, Andrew Bruce Bocarsly, Robert Joseph Cava

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We present a study based on the layered oxide system NaxCoO2 as an oxygen evolution reaction (OER) catalyst, where the formal oxidation state of Co can be continuously increased, above 3+, through Na-ion deintercalation. Accompanying this increase of formal Co oxidation state, the overpotential for the catalytic oxygen evolution reaction (OER) at 10 mA/cm2 decreases from 470 mV to 415 mV, while all the NaxCoO2 materials (x = 0.75, 0.65, 0.52, 0.36) share a common Tafel slope of 41(±5) mV/decade, implying a common rate-limiting process for the whole series. Our use of X-ray photoelectron spectroscopy (XPS) on the de-intercalation-derived NaxCoO2 catalysts, on the other hand, led to the unexpected observation that the percentage of surface Co(III) increases from 23% to 37% even as the Na deintercalation increases the formal Co oxidation state above 3+. These observations suggest that when the formal oxidation state of the central metal is pushed to an unusually high value, i.e. Co(IV) in this case, oxygen vacancies on the materials surface formed from the relaxation of the highly oxidized metal to a more stable oxidation state are the key to improving catalytic OER activity.

Original languageEnglish (US)
Pages (from-to)285-291
Number of pages7
JournalMaterials Research Bulletin
StatePublished - Nov 2017

All Science Journal Classification (ASJC) codes

  • General Materials Science
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering


  • Cobalt oxide
  • Electrocatalysis
  • Oxygen evolution
  • Oxygen vacancies
  • Transition metal oxide


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