Abstract
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.
Highlights
A popular topic nowadays is the investigation of fuel cells (FC) as alternative power devices
Spherical Pt/TiO2 composite materials of novel structure and characteristic component distribution were synthesized at different temperatures using ultrasonic spray pyrolysis (USP)
In the ex-situ synthesis, TiO2 colloid and chloroplatinic acid were used as precursors, while the in-situ approach was based on tetra-n-butyl orthotitanate and chloroplatinic acid in an hydrochloric acid solution as precursors
Summary
A popular topic nowadays is the investigation of fuel cells (FC) as alternative power devices. Some of the most investigated electrode materials [4,5,6,7] in an FC are platinum-based nanoparticles supported on carbons, due to the high activity of Pt in the kind of reactions FC functioning are based on. Bearing in mind the low abundance and high cost of platinum, a lot of research aims to reduce the platinum amount in FC catalysts [12,13,14,15,16]. Carbon’s advantages, if compared to other supporting materials, are good conductivity and high surface area [17]. The usage of carbon as a Pt support has disadvantages, due its low stability and tendency to corrode [18,19,20]
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