A yttria-stabilized zirconia (YSZ) tube with platinum electrodes was used for measurement of potential with one electrode exposed to air and the other to H2-H2O gas mixtures. Measurements were conducted over a temperature range from 30°C to 475°C using two different meters, one with input impedance of 10 GΩ and the other with input impedance > 200 TΩ. With the high impedance meter (electrometer), a voltage of 0.93 V was measured at 30°C, while it was much lower using the low impedance meter. Above ~177°C readings from both meters converged. From the measurements, the actual cell voltage and the net cell resistance including all polarization resistances were estimated. Above 275°C, the measured voltage was in agreement with the expected Nernst voltage. At lower temperatures, the voltage even with the electrometer was lower than the calculated Nernst voltage indicating that H2-H2O gas phase mixture did not reach equilibrium. Electrochemical impedance spectra (EIS) were obtained. From the EIS spectra, the ohmic resistance was obtained. Above 75°C much of the cell resistance is attributed to electrode polarization.