Browsing by Author "Golovko, VB"

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    Electrochemical CO2 reduction on Au cluster-based electrodes: investigating the role of nafion ionomer
    (The Electrochemical Society, 2023-07-25) Sharma, SK; Johannessen, B; Golovko, VB; Marshall, AT
    The performance of electrocatalytic CO2 reduction (CO2RR) depends not only on the catalytic material but also on the neighbouring chemical environment around the active sites. The surrounding local environment can perturb the electronic properties of active sites and alter the adsorption/desorption behaviour of reactant/intermediate/product, thus changing CO2RR characteristics. Herein, we studied electrochemical reduction of CO2 onto supported atomically precise [Au9(PPh3)8](NO3)3 clusters and observed an unusual increase in catalytic activity over time. Additionally, electrochemical activation of the electrodes by applying a more negative potential was found to improve activity of the electrode. Investigations using UV–vis and X-ray absorption spectroscopy revealed that these observations may be attributed to the interaction of the Nafion ionomer with the catalytic Au9 clusters. These interactions may cause partial blocking of the Au9 active sites, and the prolonged application of negative potentials leads to favourable interface reconstructions. In addition, a method was developed to minimise the interaction between the Au9 clusters and Nafion ionomer by first depositing a layer of carbon black followed by dropcasting the active catalyst. Our study highlights that polymeric binders modulate the electronic properties of the electrocatalysts, which can change the product distribution during CO2 electrolysis. © 2023 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.
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    Influence of carbon support on the pyrolysis of cobalt phthalocyanine for the efficient electroreduction of CO2
    (American Chemical Society, 2022-11-14) Hamonnet, J; Bennington, MS; Johannessen, B; Hamilton, JL; Brooksby, PA; Brooker, S; Golovko, VB; Marshall, AT
    Understanding the nature of the reactive sites of CO2reduction catalysts is crucial to developing efficient and selective materials to help mitigate the greenhouse effect. In this research, materials based on cobalt phthalocyanine supported by carbon black and pyrolyzed at various temperatures under argon are fabricated and tested for CO2electroreduction. The results show that the high reactivity of the catalysts for the electroreduction of CO2to CO is maintained for materials prepared at temperatures up to 700 °C, with CO Faradaic efficiencies of >85% and CO current densities consistently at >40 mA cm-2at -0.86 V vs RHE. The materials annealed up to 900 °C are also remarkably active, with CO Faradaic efficiencies of >40% and CO current densities of >12 mA cm-2. The combination of X-ray diffraction, infrared and Raman spectroscopies, and X-ray absorption analysis show that the annealed materials exhibit chemical structures drastically different from those of the original CoPC and unsupported pyrolyzed catalyst while highlighting the role of the carbon black support in the formation of active species. These results give crucial insight into the reactive structure of CoPC and open the way for the development of pyrolyzed Co-N4macrocycles as a new class of materials efficient for the electroreduction of CO2,. © 2022 American Chemical Society.
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    Towards better understanding of atomically precise gold clusters and titania made using surface modifying agents
    (Australian Institute of Physics, 2014-02-04) Golovko, VB; Ruzicka, JY; Abu Bakar, A; Anderson, DP; Adnan, R; Donoeva, B; Ovoshchnikov, D; Metha, GF; Andersson, GG; Thomsen, L; Cowie, B; McNicoll, C; Ingham, B; Kemmitt, T; Fang, V; Kennedy, J
    Controlled synthesis of titania nanoparticles using recently perfected sol-gel methodology, synthesis of atomically precise metal clusters, their deposition and activation on oxide supports and studies of properties of the resulting materials as promising catalysts and sensors will be briefly discussed. Our work on synthesis of titania nanoparticles is focused on careful tuning of the reaction conditions and use of selected surface modifying agents capable of directing and controlling growth of nanoparticles with specific size, phase and even population of Ti+3 sites at the surface. Promising performance of titania made using our methodology as near-IR reflective coating will be briefly highlighted. From pre-historic times gold was known as a chemically inert, “noble” metal until, in 1987, Haruta et al. proved that gold nanoparticles can be catalytically active. Results of research focused on the use of size-controlled, chemically pre-synthesised nanoparticles (colloids and clusters) with core sizes ranging from classical 1.5 nm “Au55” systems to atomically precise, uniquely small clusters (Au9 etc.) including a range of mixed-metal clusters will be presented. Immobilization of such clusters on a variety of supports had been pursued in an attempt to fabricate a family of site-isolated catalysts, where properties of the active site are defined by the nature of the precursor with great precision. Catalytic performance in selected reactions will be highlighted. New insights in the nature of our precisely defined precursors (pure and immobilised onto supports) obtained using relevant materials characterization techniques, such as Synchrotron X-ray Photoelectron Spectroscopy will be presented.
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    XPS and NEXAFS study of fluorine modified TiO2 nano-ovoids reveals dependence of Ti3+ surface population on the modifying agent
    (Royal Society of Chemistry, 2014-04-04) Ruzicka, JY; Bakar, FA; Thomsen, L; Cowie, BCC; McNicoll, C; Kemmitt, T; Brand, HEA; Ingham, B; Andersson, GG; Golovko, VB
    Crystalline titanium dioxide was synthesised under mild conditions by the thermal degradation of peroxotitanic acid in the presence of a number of fluoride-containing surface modifying agents (NH4F, NH4BF4, NH4PF6, NBu4F, NBu4BF4, NBu4PF6). The resulting materials were characterised by PXRD, SEM, HRTEM, XPS and NEXAFS. Particle phase, size, and surface area were noticeably affected by the choice of surface modifying agent. Both the cation and anion comprising the modifying agent affect the surface Ti3+ population of the materials, with two apparent trends observed: F− > BF4− > PF6− and NBu4+ > NH4+. All materials displayed evidence of fluorine doping on their surfaces, although no evidence of bulk doping was observed. © 2014 The Royal Society of Chemistry (Open Access)