Pt/TiO₂ composites were synthesized by single-step ultrasonic spray pyrolysis (USP) at different temperatures. In an in-situ method, Pt and TiO₂ particles were generated from tetra-n-butyl orthotitanate and chloroplatinic acid, and hydrothermally-prepared TiO₂ colloidal dispersion served as Pt support in an ex-situ USP approach. USP-synthesized Pt/TiO₂ composites were generated in the form of a solid mixture, morphologically organized in nesting huge hollow and small solid spheres, or TiO₂ core/Pt shell regular spheroids by in-situ or ex-situ method, respectively. This paper exclusively reports on characteristic mechanisms of the formation of novel two-component solid composites, which are intrinsic from the USP approach and controlled precursor composition. The generation of the two morphological components within the in-situ approach, the hollow spheres and all-solid spheres, was indicated to be caused by characteristic sol-gel/solid phase transition of TiO₂. Both the walls of the hollow spheres and the cores of all-solid ones consist of TiO₂ matrix populated by 10 nm-sized Pt. On the other hand, spherical, uniformly-sized, Pt particles of a few nanometers in size created a shell uniformly deposited onto TiO₂ spheres of ca. 150 nm size. Activities of the prepared samples in an oxygen reduction reaction and combined oxygen reduction and hydrogen evolution reactions were electrochemically tested. The ex-situ synthesized Pt/TiO₂ was more active for oxygen reduction and combined oxygen reduction and hydrogen reactions in comparison to the in-situ Pt/TiO₂ samples, due to better availability of Pt within a core/shell structure for the reactions.

Polygonal Pt nanoparticles were synthesized using ultrasonic spray pyrolysis (USP) at different precursor concentrations. Physicochemical analysis of the synthesized Pt particles involved thermogravimetric, microscopic, electron diffractive, and light absorptive/refractive characteristics. Electrochemical properties and activity in the oxygen reduction reaction (ORR) of the prepared material were compared to commercial Pt black. Registered electrochemical behavior is correlated to the structural properties of synthesized powders by impedance characteristics in ORR. The reported results confirmed that Pt nanoparticles of a characteristic and uniform size and shape, suitable for incorporation on the surfaces of interactive hosts as catalyst supports, were synthesized. It is found that USP-synthesized Pt involves larger particles than Pt black, with the size being slightly dependent on precursor concentration. Among ORR-active planes, the least active (111) structurally defined the synthesized particles. These two morphological and structural characteristics caused the USP-Pt to be made of lower Pt-intrinsic capacitive and redox currents, as well as of lower ORR activity. Although being of lower activity, USP-Pt is less sensitive to the rate of ORR current perturbations at higher overpotentials. This issue is assigned to less-compact catalyst layers and uniform particle size distribution, and consequently, of activity throughout the catalyst layer with respect to Pt black. These features are considered to positively affect catalyst stability and thus promote USP synthesis for improved properties of host-supported Pt catalysts.

TiO2 powder was synthesized by a forced hydrolysis process and used for the synthesis of Pt/TiO2 composite that is to be foreseen as an advanced electrode material. Pt was incorporated into the synthesized TiO2 from a Pt colloidal dispersion as a precursor prepared by a microwave-assisted polyol process. Physicochemical properties of TiO2 and TiO2-supported Pt were investigated by scanning electron microscopy, dynamic light scattering and X-ray spectroscopy and diffraction techniques. The properties of Pt/TiO2 composite are correlated to the basic voltammetric response of its thin-layer form. It was found that subsequent thermal treatment of synthesized TiO2, which caused crystallization into mainly rutile phase, is required for appropriate Pt incorporation. Although being appropriately loaded by Pt, and the voltammetric response is typical for Pt-based material, the voltammetry of Pt/TiO2 corresponded to much lower loadings. The possibility for Pt particles to be trapped inside TiO2 agglomerates is indicated. The catalyst usage from the synthesized Pt/TiO2 was found quite moderate due to this trapping. This work is licensed under a Creative Commons Attribution 4.0 International License

Determination of the extractive behavior of ionic species from lateritic ore leachates is complex, since the leachates are pregnant with tens of different ions in, as a rule, multiple oxide states. To examine the possible pathways of intrinsic electrochemical extraction of the crucial elements Ni and Co, it was necessary to make model solutions of these elements and to subject them to electrochemical examination techniques in order to obtain a benchmark. Beside Ni and Co, the model system for Fe had to be evaluated. Iron, as a dominant ore component by far, is the main interfering factor in the extraction processes of Ni and Co in rather low amounts from leaching solution. The leachate examination results were compared to separate model solutions, as well as to their combinations in concentrations and to pH values comparable to those of the leachate. The separation of the leachate components was initially performed by continuous increase in pH upon leaching with NaOH solution, and afterwards the pH-adjusted solutions were subjected to electrochemical investigation. With the purpose of connecting and quantifying the visual changes in leachate upon increase in pH, conductometric measurements were performed. Reactions of oxidation/precipitations were indicated, which led to the essential Fe removal by precipitation. Resulting solutions were found suitable for Ni and Co electrochemical extraction.

The influence of different hydroxides, applied to activate carbon black, on the electrochemical properties of activated carbon was investigated. The carbon material was prepared by hydrothermal treatment of sucrose and afterwards thermally activated using KOH, NaOH and LiOH. The electrochemical properties of the obtained samples were examined by cyclic voltammetry and electrochemical impedance spectroscopy and correlated to their physicochemical properties. All samples showed characteristic capacitor-like behaviour. The highest specific capacitance was obtained for the KOH-treated sample, while the increase in capacitance follows the sequence of the growth of ionic radius of a metal from an alkali which is used for activation. It was found that the dependence on the type of hydroxide is due to differences in the radii of a metal. The alkalies of larger radii of metal generated make pores wider and consequently the structure of a porous layer become more accessible to the charge transfer of capacitive response.