Journal
SCIENCE CHINA-MATERIALS
Volume 64, Issue 7, Pages 1653-1661Publisher
SCIENCE PRESS
DOI: 10.1007/s40843-020-1571-y
Keywords
oxygen evolution; ruthenium pyrochlore; rare earth elements; defective oxygen; d band center; valence state
Categories
Funding
- National Key Research and Development Project [2018YFB1502401]
- National Natural Science Foundation of China [21771018, 21875004]
- Royal Society and Newton Fund through Newton Advanced Fellowship award [NAFR1191294]
- Program for Changjiang Scholars and Innovation Research Team in the University [IRT1205]
- Fundamental Research Funds for the Central Universities
- Ministry of Finance
- Ministry of Education of China
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By constructing pyrochlore rare-earth ruthenate structures with a series of rare-earth elements (Nd, Sm, Gd, Er, and Yb), the electronic structure of the Ru sites could be tuned, leading to an improved OER performance in acid media by reducing the strong bonding between Ru sites and oxygen intermediates. Among them, Nd2Ru2O7 exhibited the lowest OER onset overpotential and Tafel slope, along with significantly higher intrinsic activity and durability compared to RuO2 catalyst.
Ruthenium-based catalyst is one of the most active catalysts for oxygen evolution reaction (OER) in acid media. However, the strong bonding between the Ru sites and oxygen intermediates leads to high overpotential to trigger the OER process. Hence, pyrochlore rare-earth ruthenate (RE2-Ru2O7) structures with a series of rare-earth elements (Nd, Sm, Gd, Er, and Yb) were constructed to tune the electronic structure of the Ru sites. Surface structure analysis indicated that the increase of the radius of the rare-earth cations resulted in higher content of defective oxygen (the percentage of the defective oxygen increased from 29.5% to 49.7%) in the RE2Ru2O7 structure due to the weakened hybridization of the Ru-O bond. This reduced the valence states of the Ru sites and enlarged the gap between the 4d band center and the Fermi level (E-F) of Ru, resulting in the weakened adsorption of oxygen intermediates and the improved OER performance in acid media. Among the as-prepared ruthenium pyrochlores, Nd2Ru2O7 displayed the lowest OER onset overpotential (210 mV) and Tafel slope (58.48 mV dec(-1)), as well as 30 times higher intrinsic activity and much higher durability than the state-of-art RuO2 catalyst.
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