Solid oxide fuel cells (SOFCs) is now expectative as its highly efficient and the environmental friendly electric power generator for the next generation and now expectative for its application to the stationary field, such as power plants and home electricity-heat simultaneous generating systems, because of its high operating temperature and the flexibility of fuels. Unfortunately, cathode properties will drop seriously as the operating temperature decreases. One of the main subjects to overcome this problem is the development of novel cathode materials with high electrical conductivity and stability in the SOFC operating conditions. As reported, Pr₂Ni_0.71Cu_0.24Ga_0.05O₄(PNCG) showed very good oxygen diffusivity, lower polarization resistance [1~3] and appropriate thermal expansion coefficient [4]. Therefore PNCG is a good candidate for IT-SOFC.

In the present study, various oxides were prepared by using the conventional solid-state reaction methods. XRD was employed to check the crystal structure of the products. The cell tested consists of PNCG cathode, La_0.9Sr_0.1Ga_0.8Mg_0.2O₃ (LSGM) electrolyte and Ni-Fe bimetallic anode. For measuring power generating properties, pure O₂ and humidified H₂were used for oxidant and fuel, respectively. The temperature range is 773 K~1073 K, normal pressure, and 100 cc/min gas flow rate. The impedance spectra were measured to study the oxygen diffusivity and oxygen reduction reaction at cathode.

The XRD results indicate that the PNCG was obtained with K₂NiO₄ structure, no other oxides were found. When the cell voltage was 0.7 V, the cell power density was 484.2 mW/cm² at 1073 K, 239.2 mW/cm² at 973 K, 52.5 mW/cm² at 873 K and 6.7 mW/cm²at 773 K, respectively. The cell with PNCG cathode exhibited reasonable cell performances among the operating temperature range. Figure 1 shows the power generation property of the cell using PNCG cathode.

The impedance spectra were measured too. The result was shown in figure 2. The impedance spectra were fitted with Zview software. Then theoretical calculation using the Adler-Lane-Steel and Dusty gas models were employed to analyze the oxygen diffusion and oxygen reduction reaction on PNCG.

Consequently, this study reveals that PNCG does function on improving catalytic property of cathode materials for its high surface exchange coefficient and oxygen diffusion coefficient. PNCG is a good candidate cathode for SOFC.

References

[1] X. Meng et al. Ceramics International B 41, (2015):  12107-12114

[2] J. Hyodo et al. Solid State Ionics 262, (2014): 889-892

[3] J. Hyodo et al. Solid State Ionics 220, (2013): 16-20

[4] J. Xie et al. Journal of Power Sources, 228, (2013): 229-236