Abstract

Nickel oxyhydroxide (NiOOH)-based anodes are among the most promising materials for the electrocatalytic production of oxygen from water under alkaline conditions. We explore the stability of the low-index facets of the catalytically active β-NiOOH phase, namely the (0001), {101N} surfaces, and the as yet unexplored {112N} surfaces, via density functional theory with a Hubbard-U like correction on Ni. We find that their relative stabilities depend strongly on the coordination number of the exposed Ni (cnNi) and O (cnNi). In the vacuum, where passivation of the surface dangling bonds is limited, the stability order is as follows: (0001) > {101N} ≥ {112N}, noting that the coordination numbers for each phase are, respectively, cnNi = 6, 5, and 4, and cnO = 3-4, 2-3, and 2-3. In aqueous media, the order of stability is (0001) > {101N} ≈ {112N}, as the cnNi and cnO of the latter two surface types increase due to water coordination and dissociation. Water adsorption is found to be most favorable on the {112N} surfaces, giving rise to fivefold-coordinated Ni (Ni5c) or Ni6c from Ni4c. Our work suggests that a plethora of facets are likely to coexist on β-NiOOH crystallites with water serving to equalize the stabilities of the different surfaces.

Original languageEnglish (US)
Pages (from-to)5205-5219
Number of pages15
JournalChemistry of Materials
Volume30
Issue number15
DOIs
StatePublished - Aug 14 2018

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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