Fig. 8 shows the electrochemical impedance spectroscopy (EIS) results of Ni/YSZ and LCN-modified Ni/YSZ with the YSZ electrolyte and LSM cathode with varying Ni amounts in (a) H
2 (~5 vol.% of H
2O) and (b) CH
4 (~5 vol.% of H
2O) at 800°C. H
2 and CH
4 were humidified in a bubbler before being inserted into the reactor at the rate of 200 ml/min and pure O
2 was used as an oxidant gas at the same rate. EIS results were obtained under open circuit voltage (OCV) conditions. Nyquist plots of Z
real (Re Z′) vs. Z
imaginary (Im Z″) as a function of frequency (0.01 to 10
6 Hz) under 10 mV current conditions were drawn to ensure linear response. Because analysis of the impedance spectra of a multi-layered fuel cell is very complicated and mostly uncertain, we discuss and explain the overall polarization resistance of the sample. The effects of impedance spectra can be attributed to the anode because the cathode and the electrolyte are the same in all the samples. In our experimental, the SMR can be limited because of low amounts of H
2O (~ 5wt%). Therefore, the electrochemical oxidation of H
2 via the
reaction (4) will compete to CH
4 oxidation via the
reaction (6), which also occurs CH
4 pyrolysis. Because of the slower reaction of CH
4 electrochemical oxidation than H
2 electrochemical oxidation and carbon deposition by CH
4 pyrolysis, the overall polarization resistance increased in CH
4 fuel condition. Under H
2 conditions, the polarization resistances of the bare, LCN01-modified, LCN04-modified, and LCN12-modified Ni/YSZ anodes were 4.52, 3.88, 0.88, and 0.56 Ωcm
2, respectively. The polarization resistances decreased with increasing amounts of Ni substitution in the LCN. Under CH
4 conditions, the polarization resistances of the bare, LCN01-modified, LCN04-modified, and LCN12-modified Ni/YSZ anodes were 54.3, 38.7, 31.2, and 6.9 Ωcm
2, respectively. Lower reaction kinetics and slower gas diffusion were exhibited under CH
4 conditions than those under H
2, thereby increasing the polarization resistance under CH
4. The polarization resistance of the bare Ni/YSZ anode was significantly increased compared to that of the LCN12-modified Ni/YSZ anode under CH
4 conditions. CH
4 decomposed to C and H
2 via pyrolysis of methane in the Ni phase of the Ni/YSZ anode leading to carbon deposition. The deposited carbon deactivated the TPB area and increased the mass transport resistance in the anode, resulting in the increase of low frequency arc (>1 Hz) in the impedance spectra. However, in the LCN12-modified Ni/YSZ anode, CH
4 decomposed to H
2 and CO via SMR in the LCN12 layer, and subsequently, the decomposed H
2 and CO reacted with O
2− electrochemically in the Ni/YSZ layer. H
2O for the SMR was obtained from humidified CH
4 and the electrochemical reaction of H
2 in the Ni/YSZ anode. In addition, CH
4 reacted with CO
2 from the electrochemical reaction of CO in the Ni/YSZ anode and WGS reaction via
reaction (3). The existence of dry methane reforming (CH
4 + CO
2 →2CO + 2H
2) in the LCN12-modified Ni/YSZ anode will contribute to our further research.