Transport-number determination of a protonic ceramic electrolyte membrane via electrode-polarisation correction with the Gorelov method

Abstract

Analysis of transport numbers is critical for assessing the suitability of an ionconducting material for a given electrochemical application and the conditions for its employment. In this work, the proton, oxide-ion and electron transport numbers of the candidate protonic ceramic electrolyser and fuel cell material SrZr0.9Y0.1O3- (with the addition of 4 mol% ZnO as sintering aid) are measured in wet and dry oxidising atmospheres in the temperature range 700-850 °C. The determination of proton transport numbers is analysed in detail, encompassing the suitability of equivalent circuits in different conditions and the inclusion of an external parallel resistance for the correction of electrode-polarisation effects (Gorelov method). It is confirmed that transport numbers are highly inaccurate if no polarisation correction is applied. In dry oxidising conditions oxide-ion transport numbers, to, lie in the range 0.630.78. The conductivity in wet oxidising conditions is dominated by protons and an electronic component, with the proton transport number increasing from 0.79 to 0.88 with increasing pH2O in the range 1.1x10  ≤ pH2O ≤ 1.27x10  atm at 700 ºC.

Electromotive Force (emf) Determination of Transport Numbers for Native and Foreign Ions in Molten Alkali Metal Carbonates

“…The original derivation by Gorelov does not cover the case of multiple ions (native and foreign) responding independently to chemical gradients, but Pérez-Coll et al have recently proposed a modification for the case of oxides with oxide ion, proton, and electron transport. 33,34 For Liu's approach there have however not been attempts to expand the correction to cases with multiple ions and driving forces Figure 2. Corrected transport numbers (t corrected ) obtained using Liu's equation for different resistance ratios (R total includes R electrode ) and measured transport numbers (t measured = E obs /E N ).…”

Exploring the mixed transport properties of sulfur(vi)-doped Ba2In2O5 for intermediate-temperature electrochemical applications

“…Under these conditions, an auxiliary-variable resistance located in parallel to the sample produces a modification of the measured electromotive force of the system (E M ) according to 32,33 . Simultaneously, a gradient of pH 2 O was established by exposing each gas flow to different levels of humidification controlled by mixing wet and dry gas fractions.…”

“…Platinum paste was painted on each side of the pellets and fired at 900 ºC for 2 h to yield the contact electrodes. For this purpose the electromotive force was monitored as a function of a variable external resistance located in parallel to the system, as previously reported 32,33 . The experimental procedure was applied to dry/wet N 2 and O 2 atmospheres.…”

“…The implementation of an external-variable resistance modifies the measured value of emf according to 33 : 6 and R T is the total resistance of the sample, which is determined independently by impedance spectroscopy at the same working conditions.…”

Modeling of electrical conductivity in the proton conductor Ba0.85K0.15ZrO3−δ

“…However, major problems occur with this approach if the electronic transport number is appreciable [11]. The EMF technique is also susceptible to errors arising from electrode polarization and advanced techniques, such as the external resistor approach, must be utilized to correct for this potential error [12,13]. The ion blocking method pioneered by Hebb [14] and Wagner [15] is the most extensively used method for determining very low electronic conductivity of ionic solids and has been detailed by a number of authors [16][17][18][19].…”