Issue 30, 2010

Mesoporous, high-surface-area tungsten oxide monoliths with mixed electron/proton conductivity

Abstract

Mesoporous WO3 monoliths were synthesized by a revised sol–gel technique, hydrolyzing alcoholic solutions of WCl6 in the presence of steam. Surface area and pore-size distribution were determined by nitrogen adsorption–desorption analysis. Transmission Electron Microscopy, Scanning Electron Microscopy and X-Ray Diffraction were employed for structural and morphological characterization. Oxide composition/stoichiometry as well as W oxidation states were assessed by Energy Dispersive X-Ray Spectroscopy and X-Ray Photoelectron Spectroscopy. These materials exhibit mesoporous, particulate structure with low crystallinity. Tungsten is mostly in the W6+ state, although W5+ is also present. Depending on the preparation conditions, surface area varies between 73 and 109 m2 g−1. Average pore diameter ranges between 4.7 and 10.9 nm, while pore volume ranges between 0.10 and 0.32 cm3 g−1. Electrical behaviour at several temperatures was investigated by Electrical Impedance Spectroscopy in anhydrous or wet condition. Importantly, simultaneous occurrence of both electron and proton conduction has been achieved and demonstrated for these mesoporous materials, which has implications for a variety of emerging electrochemical technologies, including Fuel Cells. At 30 °C electron conductivity is 2.0 × 10−1 S cm−1, independent of humidity conditions. At the same temperature, proton conductivity, as extracted by equivalent-circuit fitting, has a value of 4.7 × 10−3 S cm−1 in the wet state, whereas it is considerably lower in the dry state. An effective strategy to enhance the electrical properties, while retaining mesostructure is also presented and explored.

Graphical abstract: Mesoporous, high-surface-area tungsten oxide monoliths with mixed electron/proton conductivity

Article information

Article type
Paper
Submitted
17 Dec 2009
Accepted
25 Mar 2010
First published
20 Apr 2010

J. Mater. Chem., 2010,20, 6299-6308

Mesoporous, high-surface-area tungsten oxide monoliths with mixed electron/proton conductivity

G. Orsini and V. Tricoli, J. Mater. Chem., 2010, 20, 6299 DOI: 10.1039/B926641K

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