Structural basis for differing electrocatalytic water oxidation by the cubic, layered and spinel forms of lithium cobalt oxides

Graeme Gardner, Jafar Al-Sharab, Nemanja Danilovic, Yong Bok Go, Katherine Ayers, Martha Greenblatt, G Charles Dismukes

Research output: Contribution to journalReview article

34 Citations (Scopus)

Abstract

The two polymorphs of lithium cobalt oxide, LiCoO2, present an opportunity to contrast the structural requirements for reversible charge storage (battery function) vs. catalysis of water oxidation/oxygen evolution (OER; 2H2O → O2 + 4H+ + 4e-). Previously, we reported high OER electrocatalytic activity from nanocrystals of the cubic phase vs. poor activity from the layered phase-the archetypal lithium-ion battery cathode. Here we apply transmission electron microscopy, electron diffraction, voltammetry and elemental analysis under OER electrolysis conditions to show that labile Li+ ions partially deintercalate from layered LiCoO2, initiating structural reorganization to the cubic spinel LiCo2O4, in parallel with formation of a more active catalytic phase. Comparison of cubic LiCoO2 (50 nm) to iridium (5 nm) nanoparticles for OER catalysis (commercial benchmark for membrane-based systems) in basic and neutral electrolyte reveals excellent performance in terms of Tafel slope (48 mV dec-1), overpotential (η = ∼420 mV@10 mA cm-2 at pH = 14), faradaic yield (100%) and OER stability (no loss in 14 hours). The inherent OER activity of cubic LiCoO2 and spinel LiCo2O4 is attributed to the presence of [Co4O4]n+ cubane structural units, which provide lower oxidation potential to Co4+ and lower inter-cubane hole mobility. By contrast, the layered phase, which lacks cubane units, exhibits extensive intra-planar hole delocalization which entropically hinders the four electron/hole concerted OER reaction. An essential distinguishing trait of a truly relevant catalyst is efficient continuous operation in a real electrolyzer stack. Initial trials of cubic LiCoO2 in a solid electrolyte alkaline membrane electrolyzer indicate continuous operation for 1000 hours (without failure) at current densities up to 400 mA cm-2 and overpotential lower than proven PGM (platinum group metal) catalysts.

Original languageEnglish
Pages (from-to)184-192
Number of pages9
JournalEnergy and Environmental Science
Volume9
Issue number1
DOIs
Publication statusPublished - Jan 1 2016

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catalysis
lithium
cobalt
spinel
electrolyte
Catalysis
Cobalt
Lithium
catalyst
oxide
membrane
Membranes
oxidation
Iridium
electron
Oxidation
iridium
Catalysts
Hole mobility
Oxides

ASJC Scopus subject areas

  • Environmental Chemistry
  • Renewable Energy, Sustainability and the Environment
  • Nuclear Energy and Engineering
  • Pollution

Cite this

Structural basis for differing electrocatalytic water oxidation by the cubic, layered and spinel forms of lithium cobalt oxides. / Gardner, Graeme; Al-Sharab, Jafar; Danilovic, Nemanja; Go, Yong Bok; Ayers, Katherine; Greenblatt, Martha; Dismukes, G Charles.

In: Energy and Environmental Science, Vol. 9, No. 1, 01.01.2016, p. 184-192.

Research output: Contribution to journalReview article

Gardner, Graeme ; Al-Sharab, Jafar ; Danilovic, Nemanja ; Go, Yong Bok ; Ayers, Katherine ; Greenblatt, Martha ; Dismukes, G Charles. / Structural basis for differing electrocatalytic water oxidation by the cubic, layered and spinel forms of lithium cobalt oxides. In: Energy and Environmental Science. 2016 ; Vol. 9, No. 1. pp. 184-192.
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