A solid oxide fuel cell (SOFC) is a highly efficient energy converting device which can convert chemical energy in fuels directly into electrical energy with little emission^[1]. In order to lower the temperature of SOFC, ceramic-molten salt composite electrolyte materials with efficient ionic conductivity has been widely investigated. However, the corresponding NiO anode could not be sintered efficiently in the SOFC, leading to a low conductivity and activity. In this work, we synthesize NiO-Sm_0.2Ce_0.8O_1.9 (NiO-SDC) composite anode powders with nano-sized particles through a hydrothermal technique for the first time^[2]. The anode sintered at 700 ˚C exhibits an electrical conductivity of above 100 S×cm^-1, three orders of magnitude higher than that of a similar solid-mixed composite anode. The SDC-carbonate composite electrolyte supported single cell with the composite anode exhibits a maximum power density (P_max) of 738 mW×cm^-2 at 700 ˚C with H₂ as fuel, much higher than that of a similar cell with a solid-mixed anode. The nano-sized particles and uniform distribution of different phase increase the conductivity and the activity of the anode.

In order to improve the stability of the anode with hydrocarbon fuels, Nb is doped into the NiO-SDC anode. The cell with 5Nb-NiO-SDC (the molar ratio of Nb/Ni is 0.05:1) as the anode shows a higher P_max (687 mW×cm^-2) and stability than that with the NiO-SDC as the anode with methanol as the fuel (Fig. 1). In Nb-NiO-SDC anode, Nb₂O₅ adsorbs water vapor produced from the electrochemical reaction and provides surface hydroxyl, which could oxidize the carbon deposited on the Ni surface.

Fig. 1. I-V and I-P curves of single cells with Nb-NiO-SDC anodes at 700 ^oC with methanol as the fuel

Keywords: SOFC; Nickel anode; Niobium; Methanol; Carbon deposition

References

[1] M. G. Bellino, J. G. Sacanell, D. G. Lamas, et al., Journal of the American Chemical Society, 2007, 129: 3066-3067.

[2] X. L. Yao, P. Li, B. L. Yu, et al., International Journal of Hydrogen Energy, 2017, 42: 22192-22200.