Performance Enhanced Solid Oxide Fuel Cell Cathodes By Electrocatalyst Surface Modification

Abstract

Solid oxide fuel cells (SOFCs) are a promising energy conversion device due to their fuel flexibility and high efficiency. However, commercialization of SOFCs has been hindered by high operating costs due to high balance of plant and high degradation rates, mainly caused by the high operating temperature. However, the sluggish cathode activity limits the performance of low temperature SOFC operation. Here we show our recent results on cathode surface modification. Different modification techniques were used and different metal oxide electrocatalysts were introduced on the surface of common SOFC cathodes, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and Sm0.5Sr0.5CoO3 (SSC). These nano-sized electrocatalysts significantly enhance the cathode performance by increasing oxygen activity and reaction sites due to the high intrinsic catalytic activity and the increase in triple phase boundary length. The overall activity of SOFC cathodes at lower temperatures is significantly enhanced, providing a cost effect route to enhancing cathode activity for low temperature SOFC operation. The effect of number of available valence states in a metal may play a role in the facilitating the cathode reaction. Specifically, higher valence state metals could accept and transport oxygen more rapidly than lower valence state metals. Correlating electrochemical performance with the available valence states of metal cations may help elucidate the mechanism of the cathode reaction in SOFCs. The most promising metal oxide candidates were also tested to investigate CO2 poisoning and strontium oxide segregation to increase durability of SOFC cathodes. Our results demonstrate surface modification to existing SOFC cathodes could potentially increase the activity at lower temperatures while limiting unwanted material interaction between cell components.