Gold's future role in fuel cell systems

Innovative recent research has suggested that gold-based catalysts are potentially capable of being effectively employed in fuel cells and related hydrogen fuel processing. The justification for developing the gold catalyst technologies described, is not only based on their promising technical performance, but also the relatively low stable price and greater availability of gold compared with the platinum group metals. The employment of gold catalysts could therefore produce a welcome reduction in the capital cost of fuel cell installations. The most likely first use for gold catalysts is for the removal of carbon monoxide impurities from the hydrogen feedstock streams used for fuel cells. Such hydrogen is usually obtained from reforming reactions (from hydrocarbons or methanol) either from free-standing plant or from an onboard reformer in a vehicle in the case of transport applications. Absence of carbon monoxide would enable fuel cells to run at lower temperatures and with improved efficiency. Effectiveness of gold catalysts in this application has already been demonstrated. Preferential oxidation (PROX) of carbon monoxide in hydrogen-rich reformer gas is best effected by a gold catalyst (Au/alpha-Fe2O3) which is significantly more active at lower temperatures than the commercial PROX catalyst, i.e. Pt/gamma-Al2O3 currently used for this purpose. Supported gold catalysts are also very active in the water gas shift reaction used for producing hydrogen from carbon monoxide and water. Research has shown that gold supported on iron oxide (Au/alpha-Fe2O3) catalyst is more active at lower temperatures than both the alpha-Fe2O3 support and the mixed copper/zinc oxide (CuO/ZnO) catalyst currently used commercially. Preparation of gold on iron oxide and gold on titania (Au/Fe2O3 and Au/TiO2) by deposition-precipitation produces more active catalysts than by conventional co-precipitation. Other applications for gold in fuel cells are described and include its use as a corrosion resistant material and the incorporation of gold catalysts to provide useful improvements in electrode conductivity. (C) 2003 Elsevier Science B.V. All rights reserved.