Systematic Water Uptake Energetics of Yttrium-Doped Barium Zirconate—A High Resolution Thermochemical Study

Mayra D Gonçalves,Aleksandra Mielewczyk-Gryń,Alexandra Navrotsky,Maria Gazda,Łukasz Kryścio,Pardha S Maram

doi:10.1021/acs.jpcc.0c01049

Abstract

A combination of surface area analyzer and microcalorimetry was employed to investigate the in situ water uptake energetics and the mechanism of proton incorporation in yttrium-doped barium zircona...

Highlights

Yttrium-doped barium zirconate (BZY) is the most promising proton conducting electrolyte for solid oxide fuel cells due to its high chemical stability under CO2-rich atmospheres, mechanical strength, and relatively high proton conductivity at 400−600 °C.1,2 The Ba(Zr0.8Y0.2)O3−s (BZY20) composition was reported to achieve a proton conductivity of 0.1 S/cm at 450 °C.2,3 Along with optimizing synthetic routes, processing parameters, and morphology, understanding the BZY defect chemistry has been achieved.[7]
The defect chemistry is closely related to the incorporation and mobility of the charge carriers, affecting the thermodynamic stability, water uptake, and behavior of proton conductivity as a function of temperature, water fugacity, and electrolyte composition.[7−10] When partially substituting Zr4+ ions by the acceptor Y3+, oxygen vacancies are formed for charge balance (1)
Isothermal microcalorimetry in combination with a Brunauer−Emmett− Teller (BET) surface area analyzer is a promising approach to such determinations, since it allows precise quantification of water uptake and simultaneous in situ measurement of heats of reaction upon changing the water vapor pressure.[8−11] the goal of this study is a systematic evaluation of hydration enthalpies, which will be useful for investigating the energetics of protonic defect environments and how their stability changes with composition and temperature.[11]

Summary

■ INTRODUCTION

Yttrium-doped barium zirconate (BZY) is the most promising proton conducting electrolyte for solid oxide fuel cells due to its high chemical stability under CO2-rich atmospheres, mechanical strength, and relatively high proton conductivity at 400−600 °C.1,2 The Ba(Zr0.8Y0.2)O3−s (BZY20) composition was reported to achieve a proton conductivity of 0.1 S/cm at 450 °C.2,3 Along with optimizing synthetic routes, processing parameters, and morphology, understanding the BZY defect chemistry has been achieved.[7]. Isothermal microcalorimetry in combination with a BET surface area analyzer is a promising approach to such determinations, since it allows precise quantification of water uptake and simultaneous in situ measurement of heats of reaction upon changing the water vapor pressure.[8−11] the goal of this study is a systematic evaluation of hydration enthalpies, which will be useful for investigating the energetics of protonic defect environments and how their stability changes with composition and temperature.[11] This study is the first one to compare heats of hydration obtained using the traditional thermogravimetry method and in situ direct isothermal water hydration calorimetry (stepwise hydration of BZY). For the first time, such an experimental approach allowed us to support previous simulation studies

■ EXPERIMENTAL PROCEDURES

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES