Metal nanoparticle growth through in situ exsolution from barium cerate zirconate

Abstract

Protonic ceramic fuel cells (PCFCs) have great potential in applications compared with oxygen-ion-conducting-electrolyte based cells due to their relatively high ionic conductivity under intermediate and low temperature operating conditions. In addition, water is produced at the air electrode side of a proton-conducting fuel cell without diluting the fuel in the fuel electrode side, which provides higher operating voltage than an oxygen ion conducting SOFC. Among the proton-conducting materials, the most traditionally and widely used one is barium cerate-zirconate based perovskite oxide. It is simple to tailor its proton conductivity and stability by adjusting the doping concentration of Ce⁴⁺ and Zr⁴⁺. In a highly performed cell, the fuel electrode plays a vital role. The conventional fuel electrode is fabricated by metal-electrolyte composites, where the metal particles provide the catalytic activity and electronic conductivity and the electrolyte material ensures the proton conductivity. The main drawbacks of this cermet electrode are metal sintering and carbon coking, which degrades the cell performance in a long run.

In past decades, exsolution has been proposed as an effective way for in situ nanoparticles growth from perovskite oxide by a controlled phase decomposition process. Exsolved nanoparticles are socketed strongly in parent perovskite and show better resistance towards coarsening and coking compared with conventional electrodes. The nanoparticles exsolution from perovskite can be simply accomplished by doping the catalytically active transition metal into the perovskite structure, followed by chemical or electrochemical reduction.

The exsolution phenomenon has been well investigated on perovskite titanate oxide. However, little study has been focused on the exsolution from protonic conducting oxides and their applications in PCFCs. This thesis explores the exsolution behavior from the doped barium cerate zirconate oxide. Generally, nicely distributed particles are obtained on the BCZY perovskite through the in situ exsolution approach.