TiO 2 and Nb-TiO 2 were investigated as stable supports for Pt-Ru electrocatalysts towards methanol oxidation. X-ray photo-electron spectroscopy (XPS) data for all these TiO 2 -based supports show oxidation states of Ti 4+ , with no Ti 3+ , suggesting low electronic conductivity. However, the deposition of metal nanoparticles onto the supports at loadings of 60 wt% metal dramatically increased conductivity, making these electrodes (metal particles + support) suitable for electrochemistry even though the supports have low conductivity. For some of these TiO 2 -based supports, the activity of Pt-Ru towards methanol oxidation was excellent, even surpassing the activity of the same electrocatalysts supported on carbon. The activity of the electrocatalyst depended on TiO 2 crystalline structure, the addition of Nb into the support and the weight loading of metal. For example, using anatase Nb-TiO 2 as a support increased the electrochemical activity of Pt-Ru by 83% compared to the same electrocatalysts supported on either carbon Vulcan XC-72R or rutile Nb-TiO 2 . This electrode was also 64% more active than the one that had anatase TiO 2 as the support with no Nb. Finally, increasing the weight loading of metal from 5 to 60% increased the conductivity by 5 orders of magnitude and the activity by a factor of 20.
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Fuentes et al. (2011) studied this question.
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