Heterogeneous photocatalysis was used to prepare bimetallic Pt-Au modified carbon-TiO 2 matrices for use in polymer electrolyte fuel cells. These new generation electrocatalysts were characterized by transmission electron microscopy, energy-dispersive X-ray analyses, X-ray diffraction, and X-ray photoelectron microscopy. The electrocatalytic activity of these materials for the oxygen reduction reaction ͑ORR͒ was assessed by rotating disk hydrodynamic voltammetry. Of the three variant scenarios that can be envisioned for photocatalytic deposition of the two metals, i.e., sequential deposition ͑with Pt first and Au second or Au first and Pt second͒ or simultaneous deposition of Pt and Au on the C-TiO 2 nanocomposite surface from a single bath, electrocatalyst samples with Pt decorating the initially deposited Au nanoclusters ͑designated as Pt/Au/C-TiO 2 ͒ performed the best in terms of ORR kinetic facility, even relative to the monometallic case of Pt supported on C-TiO 2 . The durability of these electrocatalysts ͑in terms of corrosion͒ was assessed via galvanostatic polarization tests; once again Pt/Au/C-TiO 2 fared best relative to the other two samples as well as the Pt/C-TiO 2 control case. For all the electrochemical analyses, the total metal loading in the electrocatalysts was kept constant at 20% ͑by mass͒ for meaningful comparison.In this paper, we build upon our previous studies 1-3 on new generation platinum/carbon-titanium dioxide ͑Pt/C-TiO 2 ͒ nanocomposite electrocatalysts to develop carbon-TiO 2 supported Au-Pt bimetallic electrocatalysts for polymer electrolyte fuel cells ͑PEFCs͒. As in our companion studies, 1-3 the Pt-Au electrocatalysts were prepared by photocatalytic deposition using bandgap UV excitation of TiO 2 . Three variants of this photodeposition approach can be envisioned: ͑i͒ and ͑ii͒ Pt and Au are photodeposited in a sequential manner ͑with the sequence inverted͒ on the carbon-TiO 2 nanocomposite surface and ͑iii͒ the two metals are photodeposited simultaneously. It is shown that sequential photodeposition with Au first and Pt second affords an electrocatalyst with the best activity for the oxygen reduction reaction ͑ORR͒. The ORR electrocatalytic activity of this material is better than Pt alone for comparable total noble metal loadings, signaling a strategy to reduce the expensive Pt loading in the electrocatalyst. The effect of the Au component in improving the durability of the Au-Pt/C-TiO 2 electrocatalysts, as assessed by galvanostatic polarization tests, is also presented.Matrix modification by metal oxides ͑MO x ͒ is a relatively recent development in PEFCs and is motivated by the beneficial effect of the oxide component in improving ͑i͒ membrane and electrocatalyst durability and ͑ii͒ electrocatalytic activity through electronic interactions between the noble metal electrocatalyst and the metal oxide support. 4-6 Thus metal oxides such as MnO 2 , 7 WO 3 , 8-11 TiO 2 , 1-3,12-17 and NbO x 18 have been used in conjunction with carbon to support Pt, and these modified electrocat...

New-generation Pt/C-TiO 2 nanocomposite electrocatalysts for fuel cells, prepared by a heterogeneous photocatalytic method, have been characterized using techniques such as cyclic voltammetry, rotating disk electrode (RDE) voltammetry, and electrochemical impedance spectroscopy (EIS). Importantly, galvanostatic data confirm the superior stability of these materials against corrosion under anodic polarization conditions relative to commercial benchmark fuel cell electrocatalysts. EIS spectra from ETEK 5, SIDCAT 405 and SIDCAT 410 membrane electrode assemblies (MEAs) were fit to a Randles equivalent circuit with a Warburg element to show the presence of O 2 transport limitation arising from the use of thicker electrodes (lower Pt loading on carbon). The use of a constant phase element (CPE) instead of pure capacitor was justified from the fit procedure as CPE represents the porous electrode system more precisely with its distributive elements. EIS spectra from Tanaka, SIDCAT 451 and SIDCAT 452 MEAs (thinner electrodes) were fit to a Randles circuit with a pure capacitor and no Warburg element. The use of a transmission line model for fitting these data independently provided information about the catalyst layer resistance while all other parameters matched well with that of the Randles circuit. The effective proton transport in cathodes was quantified using polarization data for both classes of MEAs. Trends in the previously reported performance of MEAs prepared using these electrocatalysts were justified based on the relative contributions of kinetic, Ohmic and mass transfer losses to the overall overpotential, which in turn were estimated from impedance and polarization data analyses.