(Invited) Measurement of Polarization Resistance of LSM + YSZ Electrodes on YSZ Using AC and DC Methods

Abstract

Most of the measurements of electrode polarization are conducted using electrochemical impedance spectroscopy (EIS). The electrochemical devices, however, operate in a DC mode. Thus, frequency-dependent circuit elements (capacitances, constant phase elements, inductances) have no significance on the actual operating current and voltage of a device. The objective of the present work was to measure electrode polarization resistance using both EIS and DC technique and compare the results. A solid cylinder of 8YSZ of diameter ~1.17 cm and length ~5.00 cm was made by powder pressing in an isostatic press using a polymer mold and sintering at 1600oC in air for 4 h. Platinum electrodes/probes were painted along the circumference at four places approximately 1.2 cm apart. The strip width was ~2 mm. The sample was fired at 900oC. LSM + YSZ electrodes were applied on the two circular end faces and fired at 1000oC for 2 h. Pt wires were attached to the four Pt electrodes. Gold mesh was adhered to the circular LSM + YSZ electrodes. The sample was secured in a ceramic fixture and placed in a tubular furnace. Measurements were conducted in O2-N2 gas mixtures containing 100%, 10%, 5% and 1% O2. For DC studies, a DC voltage was applied in the range of 0.05 V and 0.38 V across the sample. At each applied voltage, the corresponding current was measured and potentials at all four probes was measured. From the measured potentials and the current, the ionic resistance of the cylinder was determined, from which the ionic resistivity was determined. From the voltage measured between one of the end electrodes and a probe, the ionic resistance between the end electrode and the probe, and the net current density, overpotential at the electrode was determined. This was done as a function of current. Also, from these measurements, electrode polarization resistance was determined. For EIS studies, done only under no applied DC voltage, spectra were obtained between electrode-1 and probe-2 and between probe-2 and electrode-2. From these measurements, the polarization resistances of the two electrodes were determined separately. EIS spectra were also obtained across electrode-1 and electrode-2. The spectra across electrode-1 and probe-2 and across probe-2 and electrode-2 were summed point by point. These spectra were then compared with the spectra across the entire sample.