CO-Terminated Platinum Electrodeposition on Nb-Doped Bulk Rutile TiO2

Nanoparticulate platinum on carbon as oxygen reduction electrocatalyst suffers from two major drawbacks, namely, low specific activity of the Pt particles and corrosion instability of the carbon support under hydrogen starvation conditions (reverse current degradation). Both issues can be tackled by Pt thin films on TiO2 support. Platinum films were synthesized on commercially available Nb-doped bulk TiO2 electrodes via electrodeposition from Ar- (bulk amounts) and CO-saturated solutions (monolayer amounts). The platinized electrodes were tested for ORR activity in a voltammetric fashion, and the field-free semiconductor properties were evaluated by a combination of X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), photoelectron yield spectroscopy (PYS), electrochemical impedance spectroscopy (EIS), and bulk conductivity measurements. The deposition of bulk amounts of Pt leads to a situation where the catalytic activity is directly correlated to the conductivity of the electrode. Raising the majority carrier density in the Nb-doped TiO2, via proton intercalation in aqueous HClO4 or glycol, drastically increased the activity. In case of monolayer deposits (CO-terminated deposition), intercalation has practically no effect on activity. Thus, the hypothesis is formed that unfavorable electronic interaction of the TiO2 support with small amounts of platinum drastically reduces ORR activity, an effect which is not observed for monolayer amounts of Pt deposited on gold.