Stable LSM/LSTM bi-layer interconnect for flat-tubular solid oxide fuel cells

A bi-layer interconnect with La_0.8Sr_0.2MnO₃ and La_0.4Sr_0.6Ti_0.6Mn_0.4O₃ (LSM/LSTM) is applied to anode-supported button cells and flat-tubular cells. Using a button cell, SEM images and gas permeation tests confirm that the bi-layer possesses a dense microstructure. The area specific resistance (ASR) of the LSM/LSTM remains nearly constant under oxidizing/reducing atmospheres with varying gas concentrations. For comparison, an LSM/LST with the same thickness is prepared; an increase in the ASR is observed as the concentration of H₂ feed to the LST side decreases. The difference in the ASR of LSM/LST can be explained by exposure to a relatively high oxygen partial pressure and partial destruction of the interfacial LST layer region where oxygen diffuses from the LSM layer. Flat-tubular cells with the LSM/LSTM bi-layer interconnect achieve a maximum power density (MPD) of 463 mW cm⁻² using humidified H₂ fuel and air at 800 °C. With decreasing H₂ concentration in the fuel, the polarization resistance increases rather than the ohmic resistance, implying that the LSM/LSTM interconnect provides stable conduction property. In comparison with the conventional LSM/LST interconnect cell, it shows improved stability and performance as the concentration of H₂ in the fuel decreases.