Polymer electrolyte fuel cells (PEFCs) are promising power sources in portable and transportation applications because of their high energy densities, low operating temperatures and ease of transportation and storage. However, high cost, low activity and short durability of electrocatalysts are restricting the commercialization of PEFCs. Metal oxides have abundant sources, low cost, high chemical and electrochemical stability, abundant hydroxyl groups on their surfaces, and strong interactions with metal nanoparticles, and thus are promising to reduce the current problems of PEFCs. In this review, binary metal oxides such as titanium oxide, tungsten oxide, molybdenum oxide, ruthenium oxide, tin oxide, cerium oxide and manganese oxide, and multi-component perovskite oxides are chosen based on the selection criteria of metal oxides and introduced as independent electrocatalysts, co-catalysts and supports for various anode oxidation and cathode reduction reactions in PEFCs. The effects of composition, morphology, doping and mixing of metal oxides on their electrocatalytic performance in PEFCs have also been summarized. Finally, several of the most promising metal oxides and possible research trends of metal oxides are recommended for future PEFCs.

An overview of metal oxide materials as electrocatalysts and supports for polymer electrolyte fuel cells

Electrochemical characteristics of Pt–WO3/C and Pt–TiO2/C electrocatalysts in a polymer electrolyte fuel cell

Hydrogen spill-over effect on Pt/WO3 anode catalysts

The current materials used in proton-exchange membrane fuel cells (PEMFCs) are not sufficiently durable for commercial deployment. One of the major challenges lies in the development of an inexpensive, efficient, and CO-tolerant anode catalyst. Here we report the unique CO-tolerant property of Pt nanoparticles supported on Ti0.7W0.3O2. The Ti0.7W0.3O2 nanoparticles (50 nm) were synthesized via a sol−gel process and platinized using an impregnation−reduction technique. Electrochemical studies of Pt/Ti0.7W0.3O2 show unique CO-tolerant electrocatalytic activity for hydrogen oxidation compared to commercial E-TEK PtRu/C catalysts. Differential electrochemical mass spectrometry measurements show the onset potential for CO oxidation on Pt/Ti0.7W0.3O2 to be below 0.1 V (vs RHE). Pt/Ti0.7W0.3O2 is a promising new anode catalyst for PEMFC applications.

Highly stable and CO-tolerant Pt/Ti0.7W0.3O2 electrocatalyst for proton-exchange membrane fuel cells.

Tungsten-based materials can play different roles in fuel cell systems. They are the only compounds which can be used as catalysts, co-catalysts, catalyst supports and electrolytes in different types of fuels cells. In particular, tungsten-based materials fulfill the requirements for their use as thermally stable carbon-alternative catalyst supports and Nafion ® -alternative proton conducting electrolytes in fuel cells operating at intermediate temperature. In this work an overview of the use of tungsten-containing materials in fuel cells is presented.

Tungsten-based materials for fuel cell applications

HYDROCARBON fuels (methane, propane and so on) are relatively inert and can only be electrochemically oxidized using either high loading noble metal-black electrodes in phosphoric acid at 150° C or high temperature molten carbonate (or solid oxide) electrolyte cells at 600–1,000° C (ref. 1). Alternatively the fuel may be “reformed”, producing impure hydrogen (containing carbon dioxide and some carbon monoxide) which may be fed into a low temperature (> 100° C) acid fuel cell. Carbon monoxide, however, poisons platinum black by strongly adsorbing on its surface (with high coverage) at normal fuel cell anode potentials. Little opportunity exists for water molecules to adsorb on sites adjacent to surface CO molecules—a necessary condition for the removal of the latter by anodic oxidation2

High Performance, Platinum Activated Tungsten Oxide Fuel Cell Electrodes

HYDROPHOBIC gas electrodes can demonstrate high performance even at ambient temperatures1. These electrodes are made by mixing a finely divided catalyst, such as Pt black, with polytetrafluoroethylene (PTFE) dispersion and applying the mixture to a porous conducting substrate, such as a metal screen. The electrodes are dried and cured at 300° C for 1 h.

Structure and Performance of Hydrophobic Gas Electrodes

THE performance of low temperature fuel cells is usually limited by the speed of the cathodic reduction of oxygen, One explanation of the slowness of the reaction is the need to break the O—O bond, which requires considerable energy, even for oxygen in the adsorbed state. An alternative explanation1–3 is that the reaction is slow because it can occur only at scarce favourable sites on the electrode surface. This mechanism, called pseudo-splitting, accounts for the nature of oxygen electrode polarization curves and predicts that the electrode current density i will be proportional to the square root of p, the oxygen partial pressure.

A. C. C. Tseung

Papers

High Performance, Platinum Activated Tungsten Oxide Fuel Cell Electrodes

Structure and Performance of Hydrophobic Gas Electrodes

A Joint Pseudo-splitting/Peroxide Mechanism for Oxygen Reduction at Fuel Cell Cathodes