Effect of Proton Conductor SrCe[sub 0.95]Yb[sub 0.05]O[sub 3−α] on Electrochemical Characteristics of Nickel/Gadolinium-Doped Ceria Anode in Dry Methane

Abstract

Ni/Gd 0.2 Ce 0.8 O 2−␦ ͑Ni/GDC͒ anodes were infiltrated with various amounts of the proton conductor SrCe 0.95 Yb 0.05 O 3−␣ ͑SCYb͒ with the goal of improving the performance of solid oxide fuel cells. First, the electrochemical characteristics of the Ni/GDC and Ni/GDC-SCYb anodes were evaluated in humidified hydrogen ͑1% H 2 O͒ fuel and in dry methane fuel at 1173 K, and then the durability of the anodes against carbon deposition was evaluated using an accelerated degradation test. Results revealed that the maximum power density of the Ni/GDC-SCYb anode was 50% higher than that of the Ni/GDC anode, namely 0.648 W/cm 2 in humidified H 2 and 0.438 W/cm 2 in dry methane. In conclusion, the performance of Ni/GDC anodes can be improved in either humidified hydrogen fuel or dry methane fuel by infiltration with SCYb. Solid oxide fuel cells ͑SOFCs͒ are typically operated at high temperature above 873 K, and therefore, can use various fuels such as hydrogen, hydrocarbons, and solid carbon. In general, high over-all energy conversion is expected when hydrocarbon fuels are used directly in SOFCs. 1-4 There are, however, some concerns that the anode of SOFCs might degrade due to carbon deposition when carbon-containing fuels are used. To prevent such degradation, the steam-reforming method and Ni-free anode were developed, 2,5,6 al-though both have shortcomings as follows. When steam-reformed hydrocarbon fuel is fed into an SOFC, not only the open-circuit voltage is reduced but also the overall size of the system increases due to the water reformer apparatus. 2,5 When a Ni-free anode is used in SOFCs, the performance is usually lower than that of SOFCs with a Ni cermet anode. 6