Photocatalytically Generated Bimetallic (Pt–Au∕C–TiO[sub 2]) Electrocatalysts for Polymer Electrolyte Fuel Cell Applications

Abstract

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...

Electrocatalytic Reduction of Carbon Dioxide Using Pt∕C-TiO2 Nanocomposite Cathode

“…1,2 This in situ catalyst photodeposition strategy first consisted of ultrasonically dispersing: (i) a suitable carbon black; (ii) the metal oxide (in desired proportions); (iii) the catalyst precursor salt (e.g., H 2 PtCl 6 , PdCl 2 ); (iv) an electron donor or hole scavenger (e.g., formate); and (v) a surfactant (as needed). This dispersion was introduced into a custom-built photochemical reactor 8 equipped with a medium pressure Hg arc lamp as a UV irradiation source.…”

“…A crucial aspect of this synthetic approach is that photoinduced electron transfer from the TiO 2 phase to the carbon support results in the uniform deposition of the metal catalyst throughout the composite as a whole rather than being localized on the titania surface. 1,2 Commercial carbon blacks (from Sid Richardson Carbon Co., Fort Worth; see Ref. 1 for carbon black details) were used in the photocatalytic preparation of the Pt/C-TiO 2 nanocomposite cathode.…”

“…1,2 The current/potential profiles at different rotation speeds were recorded in a 0.2 M NaF (pH 5.2) solution containing 10 mM pyridine and saturated with CO 2 . A potential scan rate of 10 mV s −1 and a potential range from −0.2 V to −1.0 V were used.…”

“…This new-generation cathode material was prepared by heterogeneous photocatalysis as described in our companion studies. 1,2 Electrocatalytic reduction of CO 2 to useful fuels and small organic molecules could help lead to a carbon-neutral fuel cycle, and represents a value-added approach to the environmental remediation of this greenhouse gas. 3 A variety of electrode materials has been deployed for this purpose including a variety of metal candidates.…”

Entropy Effects in Atom Distribution and Electrochemical Properties of AuxPt1−x/Pt(111) Surface Alloys

“…Apart from new insights into the electrochemical adlayer formation on Pt(111), Au x Pt 1Àx /Pt(111) surface alloys are also promising model surfaces for bimetallic Au-Pt (electro)catalysts, which themselves are attracting increasing interest during the last years. [11,14,[32][33][34][35][36] 2. Results and Discussion…”