Morphology Controlled Synthesis of Durable TiO2 Support for Nano-Pt Catalyst for Oxygen Reduction Reaction

Owing to the sluggish kinetics of oxygen reduction reaction (ORR), conventionally, high surface carbon-supported Pt serves as an electrocatalyst. However, carbon corrosion occurs at high potentials and conditions result in agglomeration/sintering of Pt catalyst particles and subsequent decrease in electrochemical surface area (ECSA) and ORR activity. As a result, more stable and non-carbon based catalyst supports are increasingly getting attention. Among the alternative support materials, the transition metal oxides are considered to be emerging candidates for catalyst-support.¹ In these, TiO₂, being cost-effective and acid stable, is particularly attractive.²  Brewer and Wenger³ reported that the hypo d-electron character of titanium oxide facilitates its interaction with noble metals, like Pt, changing the catalytic activity of the noble metal. Suitability of TiO₂ as a catalyst support material has been studied extensively.^1,2 Although TiO₂shows higher durability in relation to conventional carbon supports, its electronic conductivity is relatively lower, resulting in increased ohmic resistance.

In the present work, TiO₂ nanorods with specific length and width are synthesized through physical vapor deposition (PVD) technique using the glancing angle deposition (GLAD). Subsequently, the interconnected Pt nanoparticles are deposited on surface of the TiO₂ nanorods for efficient catalytic activity and fine electron connectivity towards the electrode substrate. In addition, the controlled porous catalyst matrix would aid the efficient reactant and product transport. Figure 1 shows the scanning electron microscopy images of TiO₂ and Pt-TiO₂ on silica wafer substrates. These images show the nanorods of TiO₂ are encapsulated by ‘bud’ shaped inter connected Pt particles. As the surface energy of Pt is higher than TiO₂ surface,⁴ Pt does not cover the TiO₂surface homogeneously resulted structured morphologies. Generally, the electrochemical reactions are surface reactions, the Pt rich edges are possibly involve the ORR reactions and tiny bottom layers are contribute to the electron connectivity.

To study the electrochemical behavior of the synthesized Pt-TiO₂, cyclic voltammetry measurements are performed in aq. perchloric acid (0.1 M) on glassy carbon substrates and by using Pt and Ag/AgCl/Cl^- as the counter and reference electrodes, respectively.  The characteristics peaks of H₂ adsorption and desorption (Figure 2) indicate the metallic nature of Pt. The preliminary results that obtained from ORR reveal the enhanced activity and the ultra-high stability of Pt-TiO₂catalyst.

Acknowledgements

The authors gratefully acknowledge financial support from the National Science Foundation (CBET-0748063). 

References

1. Y. Wang, D. P. Wilkinson and J. Zhang, Chem. Rev., 111, 12 (2011).
2. S. Huang, P. Ganesan, S. Park and B. N. Popov, J. Am. Chem. Soc., 131, 39 (2009).
3. L. Brewer and P. R. Wengert, Metall. Trans., 4, 83 (1973).
4. C. T. Campbell, Surf. Sci. Rep. 27, 1 (1997).