Effect of secondary metal catalysts on butane internal steam reforming operation of thin-film solid oxide fuel cells at 500–600 °C

•Pd, Ru, and Cu are studied as secondary fuel catalysts of solid oxide fuel cell.•Fuel flexibility of low-temperature solid oxide fuel cell (LT-SOFC) is studied.•Butane direct internal stream reforming (DISR) of LT-SOFC at 5–600 °C is assessed.•With Ru, 973 mW cm−2 peak power at 600 °C was achieved (∼100 % C4H10 conversion).•Cu-cell yielded comparable peak power as that of Ru-cell at 500 °C, 310 mW cm−2.