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  1. Article: Exploiting the flexibility of the pyrochlore composition for acid-resilient iridium oxide electrocatalysts in proton exchange membranes

    Burnett, David L. / Petrucco, Enrico / Kashtiban, Reza J. / Parker, Stewart F. / Sharman, Jonathan D. B. / Walton, Richard I.

    Journal of materials chemistry A. 2021 Nov. 16, v. 9, no. 44

    2021  

    Abstract: Iridate pyrochlore oxides (Na,Ca)₂₋ₓ(Ir₂₋yMy)O₆·nH₂O (M = Sb, Zr, Ru, Rh) are studied as electrocatalysts for the oxygen evolution reaction under acid conditions. The materials crystallise from aqueous solution under alkali hydrothermal conditions with ... ...

    Abstract Iridate pyrochlore oxides (Na,Ca)₂₋ₓ(Ir₂₋yMy)O₆·nH₂O (M = Sb, Zr, Ru, Rh) are studied as electrocatalysts for the oxygen evolution reaction under acid conditions. The materials crystallise from aqueous solution under alkali hydrothermal conditions with 10–40 nm crystallite size. Refinement of their crystal structures using both powder neutron and X-ray diffraction determined the composition of the materials, and Ir LIII-edge XANES spectroscopy shows the average Ir oxidation state to be close to 4.5 in all materials, consistent with bond valence sums. All materials show high electrocatalytic activity for the oxygen evolution reaction and the electrocatalyst which best maintains activity on cycling is the sodium-free Ca₂₋ₓIr₂O₆·nH₂O, while the (Na,Ca)₂₋ₓIr₂O₆·nH₂O material shows highest activity when normalised for surface area. In membrane electrode assemblies, carbon corrosion is minimised, making the materials suitable for use in catalyst layers in proton exchange membrane devices, such as electrolysers and fuel cells. Under strongly acidic conditions it is proved that while A-site Ca and Na are readily leached, the average pyrochlore structure is maintained, as is electrocatalytic activity, with charge balance achieved by inclusion of protons in the pyrochlore structure in the form of bridging hydroxyls, as seen using inelastic neutron scattering spectroscopy.
    Keywords X-ray absorption spectroscopy ; X-ray diffraction ; aqueous solutions ; carbon ; catalysts ; corrosion ; crystallites ; crystallization ; electrodes ; iridium ; neutrons ; oxidation ; oxygen production ; surface area
    Language English
    Dates of publication 2021-1116
    Size p. 25114-25127.
    Publishing place The Royal Society of Chemistry
    Document type Article
    ZDB-ID 2702232-8
    ISSN 2050-7496 ; 2050-7488
    ISSN (online) 2050-7496
    ISSN 2050-7488
    DOI 10.1039/d1ta05457k
    Database NAL-Catalogue (AGRICOLA)

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  2. Article ; Online: In situ XAFS of acid-resilient iridate pyrochlore oxygen evolution electrocatalysts under operating conditions.

    Burnett, David L / Petrucco, Enrico / Russell, Andrea E / Kashtiban, Reza J / Sharman, Jonathan D B / Walton, Richard I

    Physical chemistry chemical physics : PCCP

    2020  Volume 22, Issue 34, Page(s) 18770–18773

    Abstract: Pyrochlore iridates (Na,Ca) ...

    Abstract Pyrochlore iridates (Na,Ca)
    Language English
    Publishing date 2020-05-18
    Publishing country England
    Document type Journal Article
    ZDB-ID 1476244-4
    ISSN 1463-9084 ; 1463-9076
    ISSN (online) 1463-9084
    ISSN 1463-9076
    DOI 10.1039/d0cp01378a
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article ; Online: Exploring cycling induced crystallographic change in NMC with X-ray diffraction computed tomography.

    Daemi, Sohrab R / Tan, Chun / Vamvakeros, Antonis / Heenan, Thomas M M / Finegan, Donal P / Di Michiel, Marco / Beale, Andrew M / Cookson, James / Petrucco, Enrico / Weaving, Julia S / Jacques, Simon / Jervis, Rhodri / Brett, Dan J L / Shearing, Paul R

    Physical chemistry chemical physics : PCCP

    2020  Volume 22, Issue 32, Page(s) 17814–17823

    Abstract: This study presents the application of X-ray diffraction computed tomography for the first time to analyze the crystal dimensions of LiNi0.33Mn0.33Co0.33O2 electrodes cycled to 4.2 and 4.7 V in full cells with graphite as negative electrodes at 1 μm ... ...

    Abstract This study presents the application of X-ray diffraction computed tomography for the first time to analyze the crystal dimensions of LiNi0.33Mn0.33Co0.33O2 electrodes cycled to 4.2 and 4.7 V in full cells with graphite as negative electrodes at 1 μm spatial resolution to determine the change in unit cell dimensions as a result of electrochemical cycling. The nature of the technique permits the spatial localization of the diffraction information in 3D and mapping of heterogeneities from the electrode to the particle level. An overall decrease of 0.4% and 0.6% was observed for the unit cell volume after 100 cycles for the electrodes cycled to 4.2 and 4.7 V. Additionally, focused ion beam-scanning electron microscope cross-sections indicate extensive particle cracking as a function of upper cut-off voltage, further confirming that severe cycling stresses exacerbate degradation. Finally, the technique facilitates the detection of parts of the electrode that have inhomogeneous lattice parameters that deviate from the bulk of the sample, further highlighting the effectiveness of the technique as a diagnostic tool, bridging the gap between crystal structure and electrochemical performance.
    Language English
    Publishing date 2020-06-24
    Publishing country England
    Document type Journal Article
    ZDB-ID 1476244-4
    ISSN 1463-9084 ; 1463-9076
    ISSN (online) 1463-9084
    ISSN 1463-9076
    DOI 10.1039/d0cp01851a
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  4. Article ; Online: Water-splitting electrocatalysis in acid conditions using ruthenate-iridate pyrochlores.

    Sardar, Kripasindhu / Petrucco, Enrico / Hiley, Craig I / Sharman, Jonathan D B / Wells, Peter P / Russell, Andrea E / Kashtiban, Reza J / Sloan, Jeremy / Walton, Richard I

    Angewandte Chemie (International ed. in English)

    2014  Volume 53, Issue 41, Page(s) 10960–10964

    Abstract: The pyrochlore solid solution (Na(0.33)Ce(0.67))2(Ir(1-x)Ru(x))2O7 (0≤x≤1), containing B-site Ru(IV) and Ir(IV) is prepared by hydrothermal synthesis and used as a catalyst layer for electrochemical oxygen evolution from water at pH<7. The materials have ...

    Abstract The pyrochlore solid solution (Na(0.33)Ce(0.67))2(Ir(1-x)Ru(x))2O7 (0≤x≤1), containing B-site Ru(IV) and Ir(IV) is prepared by hydrothermal synthesis and used as a catalyst layer for electrochemical oxygen evolution from water at pH<7. The materials have atomically mixed Ru and Ir and their nanocrystalline form allows effective fabrication of electrode coatings with improved charge densities over a typical (Ru,Ir)O2 catalyst. An in situ study of the catalyst layers using XANES spectroscopy at the Ir L(III) and Ru K edges shows that both Ru and Ir participate in redox chemistry at oxygen evolution conditions and that Ru is more active than Ir, being oxidized by almost one oxidation state at maximum applied potential, with no evidence for ruthenate or iridate in +6 or higher oxidation states.
    Language English
    Publishing date 2014-09-04
    Publishing country Germany
    Document type Journal Article
    ZDB-ID 2011836-3
    ISSN 1521-3773 ; 1433-7851
    ISSN (online) 1521-3773
    ISSN 1433-7851
    DOI 10.1002/anie.201406668
    Database MEDical Literature Analysis and Retrieval System OnLINE

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