Browsing by Author "Hocking, RK"

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    Characterization of energy materials with X‑ray absorption spectroscopy-advantages, challenges, and opportunities
    (American Chemical Society, 2022-02-15) Kerr, BV; King, HJ; Garibello, CF; Dissanayake, PR; Simonov, AN; Johannessen, B; Eldridge, DS; Hocking, RK
    X-ray absorption spectroscopy (XAS) plays a critical role in the characterization of energy materials, including thin-film electrocatalysts and battery materials. XAS is well-suited for this purpose because it is element-specific and can target distinct chemical environments within a material, even in a mixed or complicated matrix. Even so, some key energy materials are far from "ideal" XAS samples. This means that both sample preparation and experimental conditions need to be considered when collecting and interpreting data to ensure that conclusions are correct. This review outlines some of the key questions that an XAS experiment is well-suited to answering, including speciation of amorphous materials, understanding how multi-metal systems interact, and the different ways that we may observe single atoms. In addition, we show how XAS can be highly complementary to other analytical techniques in developing a full picture of a material over different scale bars. Importantly, we also examine instances where the sample matrix can distort XAS data, show an example where bond-length disorder can be confused with a change in the coordination number, and discuss some of the advantages and challenges of in situ electrocatalysis. Finally, we examine the future role that XAS will play in innovations in energy materials. © 2022 American Chemical Society.
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    High energy X-ray imaging of heterogeneity in charged and discharged lead-acid battery electrodes
    (Elsevier, 2023-02) Stone, CW; Hall, CJ; Pohl, OM; Hollenkamp, AF; Newnham, RH; Mahon, PJ; Hocking, RK
    Lead-acid battery technology continues to form a critical part of the global electrochemical energy storage market. Part of the reason for the lead-acid battery's success is due to its well understood electrochemistry. However, over recent years it has become clear that a poor understanding of inherent heterogeneity in chemical changes that happen during the charge and discharge cycles of these batteries is limiting innovation. In this paper we show that high-energy X-rays can be used to better understand how the chemistry within these systems is localised spatially, and how it affects battery performance. Used commercial lead-acid battery electrodes were sampled then imaged before and after the Pb K-edge (88 keV). In these electrodes, multiple features associated with battery failure were clearly observed throughout each electrode. A custom-made lead-acid battery was also imaged in-operando. Inhomogeneous utilization of the negative electrode arising from charge-transport effects could be clearly observed in the electrode face. These results show that high-energy X-ray imaging could be a powerful tool to better understand the relationship between the spatial and electrochemical dimensions in lead-acid batteries. © 2022 Elsevier B.V.
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    The impact of de-icing salts on alpine bogs in Kosciuszko National Park
    (International Union of Geodesy and Geophysics, 2011-07-04) Hocking, RK; Greene, RSB; Hughes, CE; Johnston, SG; Grover, S
    Several roads in Kosciuszko National Park (KNP), NSW, are kept open each winter with the use of snow ploughs and the de-icing salts; sodium chloride and calcium chloride. Alpine Bogs and Fens, which are endangered Sphagnum cristatum bog communities of high conservation significance, receive saline run–off from de-iced roads in KNP. Chloride de-icing salts raise the osmotic potential of soil water, degrade soil physical properties and both sodium and chloride ions are toxic to alpine flora. However, The impact of de-icing salts on alpine environments has not been previously studied in Australia. To establish salt loads and residence times in Alpine Bogs bog ground water electrical conductivity (EC) was measured weekly using a network of piezometers in sixteen roadside bogs during winter and spring 2010. A treatment of 7.5kg of NaCl and 1Gbq of tritium (3H) was diluted into 100l of water and applied to two bogs to establish if de-icing salts moved slower through the bogs than ground water. Monitoring revealed a significant flux of salt through roadside bogs. ECs were raised significantly in salted bogs with levels highest closest to the road 3520uS/cm and dropping to 100uS/cm at a distance of 120m from the road. The 3H injection suggests NaCl moves slower than ground water and salts have a shorter residence time in wetter bogs. The results indicate that Alpine Bog hydrology is significantly altered by current snow clearing practices. Peak ECs are significantly higher than the 30uS/cm of undisturbed bogs and may potentially retard bog flora vigour.
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    Impurity tolerance of unsaturated Ni-N‑C active sites for practical electrochemical CO2 reduction
    (American Chemical Society (ACS), 2022-02-09) Leverett, J; Yuwono, JA; Kumar, P; Tran-Phu, T; Qu, JT; Cairney, JM; Wang, X; Simonov, AN; Hocking, RK; Johannessen, B; Dai, L; Daiyan, R; Amal, R
    Demonstrating the potential of the electrochemical carbon dioxide reduction reaction (CO2RR) in industrially relevant conditions is a promising route for achieving net-zero emissions through decarbonization. This requires a catalyst system that displays not only high activity and stability but also the capacity to deliver a consistent performance in the presence of waste stream impurities. To explore these opportunities, we investigate the role that the Ni coordination structure plays on the impurity tolerance of highly active single-atom catalysts (SACs) during CO2RR. The as-synthesized materials are highly active for CO2RR to CO, achieving a current density of 470 mA cm-2 and a CO selectivity of 99% in a CO2 electrolyzer. We demonstrate, through high-temperature pyrolysis, that a higher concentration of “unsaturated” Ni-N4-x-Cx sites significantly improves the tolerance to NOx, SOx, volatile organic compounds, and SCN- impurities in aqueous electrolyte, paving the way for SACs capable of CO2RR in industrial conditions. © 2022 American Chemical Society.
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    Iron-monosulfide oxidation in natural sediments: resolving microbially mediated S transformations using XANES, electron microscopy, and selective extractions
    (American Chemical Society, 2009-05-01) Burton, ED; Bush, RT; Sullivan, LA; Hocking, RK; Mitchell, DRG; Johnston, SG; Fitzpatrick, RW; Raven, M; McClure, S; Jang, LY
    Iron-monosulfide oxidation and associated S transformations in a natural sediment were examined by combining selective extractions, electron microscopy and S K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The sediment examined in this study was collected from a waterway receiving acid−sulfate soil drainage. It contained a high acid-volatile sulfide content (1031 μmol g−1), reflecting an abundance of iron-monosulfide. The iron-monosulfide speciation in the initial sediment sample was dominated by nanocrystalline mackinawite (tetragonal FeS). At near-neutral pH and an O2 partial pressure of 0.2 atm, the mackinawite was found to oxidize rapidly, with a half-time of 29 ± 2 min. This oxidation rate did not differ significantly (P < 0.05) between abiotic versus biotic conditions, demonstrating that oxidation of nanocrystalline mackinawite was not microbially mediated. The extraction results suggested that elemental S (S08) was a key intermediate S oxidation product. Transmission electron microscopy showed the S08 to be amorphous nanoglobules, 100−200 nm in diameter. The quantitative importance of S08 was confirmed by linear combination XANES spectroscopy, after accounting for the inherent effect of the nanoscale S08 particle-size on the corresponding XANES spectrum. Both the selective extraction and XANES data showed that oxidation of S08 to SO42− was mediated by microbial activity. In addition to directly revealing important S transformations, the XANES results support the accuracy of the selective extraction scheme employed here. © 2009, American Chemical Society
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    Mixed metal–antimony oxide nanocomposites: low pH water oxidation electrocatalysts with outstanding durability at ambient and elevated temperatures
    (Royal Society of Chemistry, 2021-11-16) Luke, S; Chatti, M; Yadav, A; Kerr, BV; Kangsabanik, J; Williams, T; Cherepanov, PV; Johannessen, B; Tanksale, A; MacFarlane, DR; Hocking, RK; Alam, A; Yella, A; Simonov, AN
    Proton-exchange membrane water electrolysers provide many advantages for the energy-efficient production of H2, but the current technology relies on high loadings of expensive iridium at the anodes, which are often unstable in operation. To address this, the present work scrutinises the properties of antimony–metal (Co, Mn, Ni, Fe, Ru) oxides synthesised as flat thin film electrodes by a solution-based method for water electrooxidation in 0.5 M H2SO4. Among the noble-metal-free catalysts, cobalt–antimony and manganese–antimony oxides demonstrate robust performance under ambient conditions, but slowly lose activity at elevated temperatures. A distinctive feature of the ruthenium–antimony system is its outstanding stability demonstrated herein through up to 8 day-long tests at 80 ± 1 °C, during which the reaction rate of 10 mA cm−2 was maintained at a stable overpotential of 0.34 ± 0.01 V. The S-number for this catalyst is on par with those for the high-performance benchmark Ir-based systems. Density functional theory analysis and detailed physical characterisation reveal that this high stability is supported by the enhanced hybridisation of the oxygen p- and metal d-orbitals induced by antimony and can arise from two distinct structural scenarios: either formation of an antimonate phase, or nanoscale intermixing of metal and antimony oxide crystallites. © Royal Society of Chemistry 2025.