Browsing by Author "Simonov, AN"

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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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    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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    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.