Design and Synthesis of Ir/Ru Pyrochlore Catalysts for the Oxygen Evolution Reaction Based on Their Bulk Thermodynamic Properties

Abstract

Density Functional Theory (DFT) has proven to be an invaluable and effective tool for identifying highly active electrocatalysts for the oxygen evolution reaction (OER). Herein we take a computational approach in order to first identify a series of rare-earth pyrochlore oxides based on Ir and Ru as potential OER catalysts. The DFT-based phase diagrams, Pourbaix diagrams (E vs. pH), projected density of states (PDOS), and band energy diagrams were used to identify prospective OER catalysts based on rare earth Ir and Ru pyrochlores. The predicted materials were synthesized using the sprayfreeze freeze-drying approach to afford nanoparticulate oxides conforming to the pyrochlore structural type A 2 B 2 O 7 where A = Nd, Gd, or Yb and B = Ir or Ru. In agreement with the computed Pourbaix diagrams, the materials were found to be moderately stable under OER conditions. All prepared materials show higher stability as compared to the benchmark IrO 2 catalyst and the OER mass activity of Yb 2 Ir 2 O 7 and the ruthenate pyrochlores (Nd 2 Ru 2 O 7 , Gd 2 Ru 2 O 7 , and Yb 2 Ru 2 O 7) were also found to exceed that of the benchmark IrO 2 catalyst. We find that the OER activity of each pyrochlore series Page 1 of 40 ACS Paragon Plus Environment ACS Applied Materials & Interfaces 2 (i.e. iridate or ruthenate) generally improves as the size of the A-site cation decreases, indicating that maintaining control over the local structure can be used to influence the electrocatalytic properties.

In situ XAFS of acid-resilient iridate pyrochlore oxygen evolution electrocatalysts under operating conditions

“…= Yb, Gd, Nd). 13 In these materials the non-precious metal cation stabilises the crystal structures of the multinary compositions, allowing access to higher oxidation states of Ru and Ir than seen in binary oxides. In our own work we studied the pyrochlores Bi 2 Ir 2 O 7 14 and (Na,Ce) 2 (Ru 1Àx Ir x )O 7 15 and showed them to be robust electrocatalysts, with the latter showing activity and stability modulated by the Ru : Ir ratio.…”

AiiDA 1.0, a scalable computational infrastructure for automated reproducible workflows and data provenance

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Highly Efficient Perovskite‐Based Electrocatalysts for Water Oxidation in Acidic Environments: A Mini Review

“…Similarly, other multi-metal-oxide compounds, pyrochlore oxides (such as Y 2 Ir 2 O 7 , Nd 2 Y 2 O 7 , and Y 2 Ru 2 O 7 ), have been found to exhibit OER activity in acidic solutions. [61][62][63] Furthermore, their electrocatalytic OER activities are correlated with the formation of IrO x or RuO x on the surface of electrocatalysts owing to the A-site cation leaching during oxidation cycling. In other words, in-depth studies on the role of perovskite oxides as acidic water oxidation electrocatalysts are still required.…”