Performance and aging of microtubular YSZ-based solid oxide regenerative fuel cells

Abstract

Fuel electrode supported microtubular solid oxide fuel cells (SOFC) fabricated at ICMA have been characterised in both solid oxide steam electrolyser (SOEC) and fuel cell modes. The cells consists of a fuel electrode supporting tube of Ni/YSZ with 40% porosity, ∼400 μm thickness, 2.4 mm diameter and 100–150 mm length, a 15 μm thick YSZ electrolyte and a 50 vol% LSM/YSZ composite air electrode of 20 μm thickness and LSM/YSZ (80/20 vol%) up to 2 cm2 area as current collector in the air side. Platinum paste and wires were used as interconnectors in the air chamber and Ni felt in the fuel side. SOFC and SOEC experiments were performed at temperatures between 750 and 950 °C using synthetic air in the oxygen electrode and different partial pressures of steam in the fuel side. Analysis of the polarisation contributions to the j–V curve in FC operation mode was performed using theoretical models, as discussed in the text. The effect of the steam concentration and temperature on the electrolysis and fuel cell experiments is presented and discussed. The cells are reversible in both modes of operation at low fuel conversion rates. According with previous observations, when cells are operated at high steam conversion rates the cell voltage tends to saturate. Irreversible damage was observed by SEM at the YSZ–oxygen electrode interface after operation, probably due to the electrolyte reduction produced at high voltages.