Does the increase in Y-dopant concentration improve the proton conductivity of BaZr_1-xY_xO_{3 -δ} fuel cell electrolytes?

Y-doped barium zirconate (BZY) is a widely investigated proton conducting electrolyte for intermediate temperature solid oxide fuel cell applications. Yttrium is generally recognized as the most suitable dopant into the barium zirconate structure to achieve proper proton conductivity. The influence of Y concentration on the BZY electrical properties is here investigated. Single phase BaZr_1-xY_xO_3-δ powders were obtained using a wet chemistry process in a wide compositional range (0.2 ≤ x ≤ 0.5). Inductively coupled plasma (ICP) and X-ray diffraction (XRD) analysis suggested complete Y solubility into the BZY powders for all the tested compositions. Proton concentration as a function of Y content was evaluated in the 200-800 °C temperature range using thermogravimetric analysis performed under a water partial pressure of ∼ 0.03 atm. The larger the Y content, the larger the proton concentration. By means of electrochemical impedance spectroscopy, the electrical conductivity of BZY sintered pellets was measured under humidified 10% H₂/Ar atmosphere. Despite the increase in defect concentration, the conductivity decreased with increasing the Y concentration, due to both hindered mobility and reduced charge carrier concentration.