Catalytic Activity of Titanium Dioxide Nanoparticles As a Non-Platinum Cathode Catalyst for Oxygen Reduction Reaction
Authors: Mirshekari Gholamreza , Shirvanian Pezhman 
Published: February 2020

Fuel cells offer potentially efficient, silent and low-pollution electrical power generation. Technical and economic problems have however, restricted their widespread development. One of the principal factors hampering the extensive commercialization of fuel cells is their dependence on platinum as electrocatalysts [1]. In recent years, many attempts have been made to reduce the platinum usage by introducing some metal oxide-based electrocatalysts. As a search of new metal oxide-based electrocatalysts, titanium oxide catalysts were studied for their catalytic activity during the oxygen reduction reaction (ORR) and stability in acid media, especially as a support material. It was reported that titanium oxide supported the oxygen reaction in acid [2] and alkaline [3] media. Early studies on titanium oxide catalysts showed that the catalytic activity for the ORR was low [2], however, Kim et al. [4] later showed that it depends on oxidation state, crystalline structure and work function of the titanium oxide catalysts. Moreover, although previous studies showed that the particle size of nanoparticles electrocatalysts can significantly affect their activity for the ORR [5], no work has been done to investigate the effect of particle size on catalytic performance of titanium oxide nanoparticles electrocatalysts. Therefore, due to some ambiguities and lack of knowledge in this research field, titanium oxide is worth being studied as an independent non-platinum electrocatalyst.
In this study, titanium dioxide (TiO2) nanoparticle powders with four different average particle size were purchased and characterized by X-ray diffraction analysis (XRD), small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM). The SAXS profiles showed that the particle size maximum probability for TiO2 powders with average particle size of 5 nm, 18 nm, 50 nm and 100 nm were 4 nm, 12 nm, 43 nm and 96 nm, respectively. The SEM images of TiO2 nanoparticle powders showed agglomerated particles with spherical structure that this agglomeration increased with decreasing the size of particles. The XRD patterns indicated anatase and rutile phases for TiO2 nanoparticles. The diffraction intensity of crystal planes for both anatase and rutile phases increased with increasing the particle size which can impact the catalytic activity of TiO2 catalysts for the ORR. The catalytic activity of the catalysts for the ORR was evaluated using cyclic voltammograms (CVs) and linear sweep voltammograms (LSVs) in 0.1 M HClO4 acid solution at 25 ºC. The results shed light on the effect of TiO2 particle size for the ORR.

References

[1] C.D.A. Brady, E.J. Rees, G.T. Burstein, Electrocatalysis by Nanocrystalline Tungsten Carbides and the Effects of Codeposited Silver, J. Power Sources 179 (2008) 17-26.
[2] V.B. Baez, E. Graves, D. Pletcher, The Reduction of Oxygen on Titanium Oxide Electrodes, J. Electroanal. Chem. 340 (1992) 273-286.
[3] A. Fujishima, K. Honda, Electrochemical Photolysis of Water at a Semiconductor Electrode, Nature 238 (1972) 37-38.
[4] J-H Kim, A. Ishihara, S. Mitsushima, N. Kamiya, K-I Ota, Catalytic activity of titanium oxide for oxygen reduction reaction as a non-platinum catalyst for PEFC, Electrochim. Acta 52 (2007) 2492-2497.
[5] K. Kinoshita, Particle size Effects for Oxygen Reduction on Highly Dispersed Platinum in Acid Electrolytes, J. Electrochem. Soc. 137 (1990) 845-848.