From 3D to 2D Co and Ni Oxyhydroxide Catalysts: Elucidation of the Active Site and Influence of Doping on the Oxygen Evolution Activity

Vladimir Tripkovic, Heine Anton Hansen, Tejs Vegge

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Abstract

Layered oxyhydroxides (ox-hys) of Ni and Co are among the most active catalysts for oxygen evolution in alkaline media. Their activities can be further tuned by delamination into single-layer oxide sheets or by means of doping. The active site for the reaction and how doping and delamination promote the intrinsic activity, however, remain elusive. To shed light on these open questions, we have undertaken a systematic analysis of the stability, catalytic activity, and electronic conductivity of Ni and Co ox-hys ranging from bulk (3D) to single-layer (2D) catalysts. In both cases, we investigate the role of terrace and edge sites and use stability, catalytic activity, and electronic conductivity as evaluation criteria to pinpoint the best catalysts. We arrive at several important conclusions: the ox-hy surface is fully oxidized under oxygen evolution conditions, bulk terraces are ostensibly the most active sites, and Ni ox-hy sheets are more electronically conductive in comparison to their Co equivalents. Furthermore, we examine 25 different doped Co and Ni ox-hy nanosheets (V, Cr, Mn, Fe, Co/Ni, Cu, Ru, Rh, Pd, Ir, Pt, Ag, Al, Ga, In, Sn, Pb, Bi, Mg, Sc, Y, Ti, Nb, Zn, and Cd) to further tailor the catalytic performance. We establish the dependence of the electronic conductivity and activity on potential and find that it is more energetically favorable to dope Ni in comparison to Co ox-hys, with first-row transition and noble metals being the most stable dopants. Finally, we extend the analysis to include bulk terminations and reveal that most dopants, which are stable in the nanosheets, have a large propensity to segregate to the surface of bulk materials, and those that are less prone to segregation (Fe or Cr) are not electronically conductive in the bulk. Overall, we identify Rh-doped Ni ox-hy to be the best catalyst material.
Original languageEnglish
JournalA C S Catalysis
Volume7
Issue number12
Pages (from-to)8558-8571
ISSN2155-5435
DOIs
Publication statusPublished - 2017

Keywords

  • Oxygen evolution reaction
  • Density functional theory
  • Doping
  • Ni oxide
  • Co oxide

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