Synergistic effects in oxygen evolution activity of mixed iridium-ruthenium pyrochlores
Rebecca K. Pittkowski, Daniel F. Abbott, Roman Nebel, Spyridon Divanis, Emiliana Fabbri, Ivano E. Castelli, Thomas J. Schmidt, Jan Rossmeisl, Petr Krtil
Abstract
Pyrochlore oxides (A2B2O7) simultaneously containing iridium and ruthenium in the B-site are promising catalysts for oxygen evolution reaction (OER) in acid media. The catalytic activity of the pyrochlore based catalysts is increased by the coexistence of Ir and Ru in the B-site of the pyrochlore structure. Lanthanide (Yb, Gd, or Nd) stabilized mixed pyrochlores with a fraction of Ru in the B-site of xRu =0.2, 0.4, 0.6, 0.8 were synthesized by the spray-freeze freeze-dry approach. All prepared mixed pyrochlore catalysts are surpassing the OER activity of the corresponding iridium and ruthenium analogues featuring no cation mixing as well as that of the benchmark IrO2 catalyst. The synergy of Ir and Ru in the B-site of the pyrochlore structure suppresses the effect of the A-site cation radius on the OER activity. The observed OER activity scales with the Ir-Ru bond distance which represents the local structure of the prepared materials. The most active ytterbium catalyst also shows a significant stability improvement under OER operando conditions over the benchmark IrO2
Keywords
Electrocatalysis, Oxygen evolution, Pyrochlores, Local structure optimization, Synergy