Oxygen evolution reaction (OER) in acid has been long considered a major obstacle in the generation and storage of renewable energy technology, such as regenerative fuel cells, metal-air batteries, and water electrolyzers1. Because of the sluggish reaction kinetic, highly efficient electrocatalysts play a critical role in the advancement of above energy devices. Meanwhile, the low durability of OER catalysts in acid due to rapid catalysts dissolution has rendered the OER catalysts inactive under the high potential window in which OER occurs. Ruthenium oxide and iridium oxide are the only two known compounds to perform reasonable catalytic activity along with good stability in acid electrolyte2. However, the scarceness of ruthenium and iridium metals builds up the cost of making these catalysts and thus limiting the implementation of water electrolyzer devices. To reduce the expensive metal content and increase the catalytic activity while retain stability of the catalyst are the objectives to make progression. We discovered a class of materials (pyrochlore-type ruthenate and iridium oxide) that show excellent OER catalytic activity while maintain acid stability.
Our recent results indicated the pyrochlore-type yttrium ruthenate (Y2Ru2O7) outperformed RuO2 in OER activity and stability. At 1.50 V vs. RHE, Y2Ru2O7 exhibited more than 5 times higher current density than RuO2. Moreover, after 10,000 consecutive cycles of cyclic voltammogram (CV) measurement, the OER activity loss of Y2Ru2O7 was less than 10% of its initial value, while the loss of RuO2 was more than 90%. X-ray absorption spectroscopy (XAS) analysis indicated a valence change of the Ru metal center in Y2Ru2O7, suggesting that it is likely the structure related to the enhancement of activity. Density functional theory (DFT) calculations showed a stable Ru-O bond and thus increased the stability of catalyst. Pyrochlore-type yttrium iridium oxide (Y2Ir2O7) was also synthesized and characterized, in comparison with IrO2. At 1.55 V vs. RHE, the OER current density for Y2Ir2O7 was about three times higher than IrO2. The XAS analysis was applied to understand the structural origins for the observed high OER activity. A valance change in the center Ir atom was identified by while-line integration while Ir-O bond distance alteration was recognized in extended x-ray absorption fine structure (EXAFS) analysis.
1. (a) Nocera, D. G., Acc. Chem. Res. 2012, 45 (5), 767-776; (b) Park, S.; Shao, Y.; Liu, J.; Wang, Y., Energy & Environ Sci 2012, 5 (11), 9331-9344.
2. (a) Kim, J.; Shih, P.-C.; Tsao, K.-C.; Pan, Y.-T.; Yin, X.; Sun, C.-J.; Yang, H., J Am Chem Soc 2017, 139 (34), 12076-12083; (b) Lebedev, D.; Povia, M.; Waltar, K.; Abdala, P. M.; Castelli, I. E.; Fabbri, E.; Blanco, M. V.; Fedorov, A.; Copéret, C.; Marzari, N.; Schmidt, T. J., Chem Mater 2017.