Determination of proton transference number of Ba(Zr_0.84Y _0.15Cu_0.01)O_3-δ via electrochemical concentration cell test

Electromotive force (EMF) measurements using electrochemical concentration cells are often used to estimate the transport number of conducting species in ionic and mixed conductors. In this study, the proton transference number of an electrolyte based on CuO-modified Y-doped BaZrO₃ (Ba(Zr _0.84Y_0.15Cu_0.01)O_3-δ, BZYCu) is determined using steam concentration cells based on Wagner's theory. According to the investigation, proton concentration cells including water vapor provide good estimates of the proton transference number of the BZYCu electrolyte, showing that the number increases as the water partial pressure, P(H₂O), increases; the proton transference number also increases as the oxygen partial pressure P(O₂) decreases, owing to the relatively lower hole conductivity of BZYCu at low P(O₂) conditions. From the combination of proton transference number with the measured total conductivity, the proton conductivity of the BZYCu electrolyte is estimated as 0.0031 S/cm at 650 C in wet argon atmosphere. The EMF values measured under real operating conditions of the PCFC test (fuel side, 3 % H₂O + hydrogen; oxidant side, dry air) are found to be increased from 0.98 to 1.08 V as the temperature decreases from 650 to 550 C.