Recent Progress in Anode Materials for Solid Oxide Fuel Cells

摘要

In this paper, we report our recent progress in the development of anode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). Mo-doped Ce_(1-x)Mo_xO_(2+δ) (x = 0.05, 0.07, 0.1, 0.13) (CMO), Mo + RE-co-doped Ce_(0.9-x)RE_xMo_(0.1)O_(2.1-0.5x)(x = 0.2, 0.3) (RE = Y, Sm, Gd) (CRMO) and Nd_2WO_6-type Sm_(2-x)AxM_(1-y)B_yO_(6-δ) (A = Ca, Sr; M = Mo, W; B = Ce, Ni) have been investigated in our laboratory. For CMO and CRMO, the formation of fluorite-like structure was confirmed by powder X-ray diffraction (PXRD) and the change in the lattice constant was found to be consistent with the Shannon ionic radius trend. CRMO samples treated under dry H_2 at elevated temperatures were found to retain the original fluorite structure while CMO showed presence of Mo in the PXRD. Sm_(2-x)A_xMoO_(6-δ) (A = Ca, Sr) after heating under 97% H_2 +3% H_2O up to 850℃ changed from Nd_2WO_6-type structure into Sm_2MoO_5 due to the reduction of Mo~Ⅵ that was confirmed by PXRD. For CRMO and SMO, the electrical conductivity was determined using 2-probe AC and DC methods and 4-probe DC method in wet H2. The total electrical conductivity obtained from these two different techniques was found to be very close within the experimental error over the investigated temperature range. Among the CRMO samples studied, Ce_(0.7)Sm_(0.2)Mo_(0.1)O_2 exhibits the highest total conductivity of 7.8 × 10~(-2) Scm~(-1) at 450℃ in wet H_2 which is comparable to that of perovskite-type La_(0.75)Sr_(0.25)Cr_(0.5)Mn_(0.5)O_(3-δ). Nd_2WO_6-type Sm_(1.9)Ca_(0.1)MoO_(6-δ) exhibits appreciable conductivity of 8.2 × 10~(-2) Scm~(-1) at 550℃ in wet H_2 with activation energy of 0.08 eV and it appears to be chemically stable against the reaction with YSZ electrolyte at 800 ℃ for 24 h in 97% H_2 +3% H_2O.