Size-dependent subnanometer Pd cluster (Pd4, Pd6, and Pd17) water oxidation electrocatalysis

Gihan Kwon, Glen A. Ferguson, Christopher J. Heard, Eric C. Tyo, Chunrong Yin, Janae Debartolo, Sönke Seifert, Randall E. Winans, A. Jeremy Kropf, Jeffrey Greeley, Roy L. Johnston, Larry A. Curtiss, Michael J. Pellin, Stefan Vajda

Research output: Contribution to journalArticlepeer-review

135 Scopus citations


Water oxidation is a key catalytic step for electrical fuel generation. Recently, significant progress has been made in synthesizing electrocatalytic materials with reduced overpotentials and increased turnover rates, both key parameters enabling commercial use in electrolysis or solar to fuels applications. The complexity of both the catalytic materials and the water oxidation reaction makes understanding the catalytic site critical to improving the process. Here we study water oxidation in alkaline conditions using size-selected clusters of Pd to probe the relationship between cluster size and the water oxidation reaction. We find that Pd4 shows no reaction, while Pd6 and Pd17 deposited clusters are among the most active (in terms of turnover rate per Pd atom) catalysts known. Theoretical calculations suggest that this striking difference may be a demonstration that bridging Pd-Pd sites (which are only present in three-dimensional clusters) are active for the oxygen evolution reaction in Pd6O6. The ability to experimentally synthesize size-specific clusters allows direct comparison to this theory. The support electrode for these investigations is ultrananocrystalline diamond (UNCD). This material is thin enough to be electrically conducting and is chemically/electrochemically very stable. Even under the harsh experimental conditions (basic, high potential) typically employed for water oxidation catalysts, UNCD demonstrates a very wide potential electrochemical working window and shows only minor evidence of reaction. The system (soft-landed Pd4, Pd6, or Pd17 clusters on a UNCD Si-coated electrode) shows stable electrochemical potentials over several cycles, and synchrotron studies of the electrodes show no evidence for evolution or dissolution of either the electrode material or the clusters.

Original languageEnglish (US)
Pages (from-to)5808-5817
Number of pages10
JournalACS Nano
Issue number7
StatePublished - Jul 23 2013
Externally publishedYes


  • X-ray absorption
  • X-ray scattering
  • catalysis
  • electrocatalysis
  • hybrid nanostructures
  • nanocrystalline diamond
  • nanoparticles
  • palladium
  • subnanometer clusters
  • water oxidation
  • water splitting

ASJC Scopus subject areas

  • General Materials Science
  • General Engineering
  • General Physics and Astronomy


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