Nanometer-thick films of titanium oxide acting as electrolyte in the polymer electrolyte fuel cell

• Published in: Electrochimica acta Vol. 52; no. 12; pp. 4239 - 4245
• Main Authors: Ekström, Henrik, Wickman, Björn, Gustavsson, Marie, Hanarp, Per, Eurenius, Lisa, Olsson, Eva, Lindbergh, Göran
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.03.2007; Elsevier
• Subjects: Analytical chemistry; Analytisk kemi; Applied sciences; Chemistry; Electrochemistry; Elektrokemi; Energy; Energy. Thermal use of fuels; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fuel cell; Fuel cells; Kemi; NATURAL SCIENCES; NATURVETENSKAP; Oxygen reduction; Proton conduction; Thermal evaporation; Titanium oxide; Oxygen reduction; Titanium oxide; Proton conduction; Fuel cell; Thermal evaporation; Ultrathin films; Ionomer; Scanning electron microscopy; Oxygen; Electrical properties; X ray; Evaporation; Surface structure; Sulfonate copolymer; Chemical reduction; Tetrafluoroethylene copolymer; Transmission electron microscopy; Electrolyte; Morphology; Cation exchange membrane; Proton conductivity; Photoelectron spectrometry; Electrochemical reaction; proton conduction; fuel cell; thermal evaporation; titanium oxide; oxygen reduction
• ISSN: 0013-4686; 1873-3859; 1873-3859
• DOI: 10.1016/j.electacta.2006.12.002

0–18 nm-thick titanium, zirconium and tantalum oxide films are thermally evaporated on Nafion 117 membranes, and used as thin spacer electrolyte layers between the Nafion and a 3 nm Pt catalyst film. Electrochemical characterisation of the films in terms of oxygen reduction activity, high frequency impedance and cyclic voltammetry in nitrogen is performed in a fuel cell at 80 °C and full humidification. Titanium oxide films with thicknesses up to 18 nm are shown to conduct protons, whereas zirconium oxide and tantalum oxide block proton transport already at a thickness of 1.5 nm. The performance for oxygen reduction is higher for a bi-layered film of 3 nm platinum on 1.5 or 18 nm titanium oxide, than for a pure 3 nm platinum film with no spacer layer. The improvement in oxygen reduction performance is ascribed to a higher active surface area of platinum, i.e. no beneficial effect of combining platinum with zirconium, tantalum or titanium oxides on the intrinsic oxygen reduction activity is seen. The results suggest that TiO 2 may be used as electrolyte in fuel cell electrodes, and that low-temperature proton exchange fuel cells could be possible using TiO 2 as electrolyte.