Bismuth Iridium Oxide Oxygen Evolution Catalyst from Hydrothermal Synthesis

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• 作者：Kripasindhu Sardar ; Sarah C. Ball ; Jonathan D.B. Sharman ; David Thompsett ; Janet M. Fisher ; Richard A.P. Smith ; Pabitra K. Biswas ; Martin R. Lees ; Reza J. Kashtiban ; Jeremy Sloan ; Richard I. Walton
• 刊名：Chemistry of Materials
• 出版年：2012
• 出版时间：November 13, 2012
• 年：2012
• 卷：24
• 期：21
• 页码：4192-4200
• 全文大小：578K
• 年卷期：v.24,no.21(November 13, 2012)
• ISSN：1520-5002

文摘

We present a detailed characterization of the pyrochlore Bi₂Ir₂O₇ prepared by a one-step hydrothermal synthesis route from aqueous sodium hydroxide solution of NaBiO₃路2H₂O and IrCl₃路5H₂O in the presence of Na₂O₂ at 240 掳C. Using 5 M NaOH solution as the reaction medium, a fine powder of polycrystalline Bi₂Ir₂O₇ with an average crystal size of 10 nm and surface area of 46 m² g^鈥? is produced. Structure refinement against powder neutron diffraction reveals a stoichiometric pyrochlore with no evidence for significant oxide-ion defects. X-ray absorption near-edge structure (XANES) spectra recorded at both metal L_III-edges show that, although Bi is present solely as Bi³⁺, there is evidence for the oxidation of iridium slightly beyond +4. This would suggest some surface oxidation of iridium, which is also shown by X-ray photoelectron spectroscopy (XPS) measurements. Magnetization data, as a function of temperature, show that the system is paramagnetic down to a temperature of 2 K, while the electrical conductivity shows hydrothermal Bi₂Ir₂O₇ to be a metallic conductor. In electrochemical tests, performed on rotating disk electrodes fabricated from the powdered iridate and Nafion solution, the material shows oxygen evolution activity in acidic solution, comparable to the most active precious-metal oxide materials, with reproducibility over >1000 cycles, demonstrating the formation of robust electrodes.

Keywords:

pyrochlore; neutron diffraction; electrocatalysis; oxygen evolution; XANES