Acidic Oxygen Evolution Reaction Activity-Stability Relationships in Ru-Based Pyrochlores

McKenzie A. Hubert, Anjli M. Patel, Alessandro Gallo, Yunzhi Liu, Eduardo Valle, Micha Ben-Naim, Joel Sanchez, Dimosthenis Sokaras, Robert Sinclair*, Jens K. Nørskov, Laurie A. King*, Michal Bajdich*, Thomas F. Jaramillo*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Ru-based oxygen evolution reaction (OER) catalysts show significant promise for efficient water electrolysis, but rapid degradation poses a major challenge for commercial applications. In this work, we explore several Ru-based pyrochlores (A2Ru2O7, A = Y, Nd, Gd, Bi) as OER catalysts and demonstrate improved activity and stability of catalytic Ru sites relative to RuO2. Furthermore, we combine complementary experimental and theoretical analysis to understand how the A-site element impacts activity and stability under acidic OER conditions. Among the A2Ru2O7 studied herein, we find that a longer Ru-O bond and a weaker interaction of the Ru 4d and O 2p orbitals compared with RuO2 results in enhanced initial activity. We observe that the OER activity of the catalysts changes over time and is accompanied by both A-site and Ru dissolution at different relative rates depending on the identity of the A-site. Pourbaix diagrams constructed using density functional theory (DFT) calculations reveal a driving force for this experimentally observed dissolution, indicating that all compositions studied herein are thermodynamically unstable in acidic OER conditions. Theoretical activity predictions show consistent trends between A-site cation leaching and OER activity. These trends coupled with Bader charge analysis suggest that dissolution exposes highly oxidized Ru sites that exhibit enhanced activity. Overall, using the stability number (molO2 evolved/molRu dissolved) as a comparative metric, the A2Ru2O7 materials studied in this work show substantially greater stability than a standard RuO2 and commensurate stability to some Ir mixed metal oxides. The insights described herein provide a pathway to enhanced Ru catalyst activity and durability, ultimately improving the efficiency of water electrolyzers.
Original languageEnglish
JournalACS Catalysis
Volume10
Issue number20
Pages (from-to)12182-12196
ISSN2155-5435
DOIs
Publication statusPublished - 2020

Keywords

  • Water splitting
  • Oxygen evolution
  • Ruthenium
  • Pyrochlore
  • Theoretical Pourbaix stability
  • Dissolution
  • Activity descriptors

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