Suppression of Anode Degradation by Sulfur using an Anionic Catalyst

Abstract

Fuel cells can be regarded as catalysed chemical reactors. They can therefore be highly sensitive to the purity of the relevant reagent, the fuel. The anode catalyst in the standard SOFC is a metal-ceramic composite characterised by rapid and significant deterioration of its activity when exposed to sulfur contaminants in the fuel, even in ppm. concentrations. However commercial hydrocarbon liquid fuels regularly contain some quantity of sulfur compounds as impurities, and sulfur compounds are even deliberately added as odorants for safety reasons in gaseous fuels. Therefore a desulfuriser unit is a normal subsystem in any SOFC installation. An anode with high intrinsic sulfur tolerance would clearly simplify SOFC system design, as well as offering lower capital and operation costs. In a technology transfer from petrochemicals practice, hydrodesulfurisation catalysts using heavy metals have been investigated and showed partial protection of the anode. However a recent observation established an even more effective desensitisation to sulfur of a Ni-YSZ cermet anode modified by an anionic activator.