Sol−Gel Synthesis, Electrochemical Characterization, and Stability Testing of Ti_0.7W_0.3O₂ Nanoparticles for Catalyst Support Applications in Proton-Exchange Membrane Fuel Cells

Abstract

The materials currently used in proton-exchange membrane fuel cells (PEMFCs) require complex control of operating conditions to make them sufficiently durable to permit commercial deployment. One of the major materials challenges to allow simplification of fuel cell operating strategies is the discovery of catalyst supports that are much more stable to oxidative decomposition than currently used carbon blacks. Here we report the synthesis and characterization of Ti(0.7)W(0.3)O2 nanoparticles (approximately 50 nm diameter), a promising doped metal oxide that is a candidate for such a durable catalyst support. The synthesized nanoparticles were platinized, characterized by electrochemical testing, and evaluated for stability under PEMFC and other oxidizing acidic conditions. Ti(0.7)W(0.3)O2 nanoparticles show no evidence of decomposition when heated in a Nafion solution for 3 weeks at 80 °C. In contrast, when heated in sulfuric, nitric, perchloric, or hydrochloric acid, the oxide reacts to form salts such as titanylsulfatehydrate from sulfuric acid. Electrochemical tests show that rates of hydrogen oxidation and oxygen reduction by platinum nanoparticles supported on Ti(0.7)W(0.3)O2 are comparable to those of commercial Pt on carbon black.

Preparation and characterization of novel Ti0.7W0.3O2–C composite materials for Pt-based anode electrocatalysts with enhanced CO tolerance

“…An expansion of the a-axis and a contraction of the c-axis are found due to the size difference between the W 6+ and W 4+ ions as well as W-W pairing in the doped compound [19,46]. Such pairing is also seen in WO 2 and is expected in the doped TiO 2 .…”

“…Based on these results in this study wet H 2 was used for the transformation of tungsten from W 6+ to W 4+ . However, it is necessary to mention that wet hydrogen was contacted with composite materials at 650 °C only for a very short time (10 min), because H 2 O acts as a good W-transport agent at elevated temperatures and would result in an inhomogeneous final product [19].…”

“…Moreover, dopant metals are usually selected on the basis of their ionic radii similarity to that of Ti 4+ (effective ionic radii r ion (Ti 4+ ) = 60.5 pm, r ion (W 6+ ) = 60 pm) [17][18]. Electroconductive Ti 0.7 W 0.3 O 2 mixed oxide has already been used as a support for Pt [1,19]. These materials showed unique CO-tolerant electrocatalytic activity for hydrogen oxidation compared to commercial catalysts [1].…”

Design and Preparation of CO Tolerant Anode Electrocatalysts for PEM Fuel Cells

“…After depositing Pt onto it, it was mixed with 20 wt% activated carbon to ensure the necessary electronic conductivity. Improved CO tolerance was observed during their measurements but at the same time, due to the lower active Pt specific surface area on the Ti 0.7 W 0.3 O 2 oxide than that on platinised Vulcan, the activity in hydrogen oxidation reaction decreased in comparison to commercial Pt/C [9].…”

“…Crystallite sizes were calculated from reflection line broadening using the Scherrer-equation. Since isovalent tungsten incorporation into the rutile lattice causes a characteristic distortion (expansion along the a-axis and contraction along the c-axis of the unit cell, [4,9,12]), XRD is an excellent method for assessing the extent of modification.…”