Enhanced proton conductivity of La0.95Ca0.05NixNb1-xO4 (0.01 ≤ x ≤ 0.3) through in-situ exsolution of metallic nanocatalysts

A simple and feasible catalytic route has been successfully developed through the exsolution of Ni nanoparticles to enhance the proton conductivity of a high temperature proton conducting electrolyte La0.95Ca0.05NbO4 (LCN). A series of compounds La0.95Ca0.05NixNb1-xO4 (LCNNi, x = 0.01, 0.03, 0.05, 0.1, 0.2, 0.3) are prepared by solid state reaction. Nickel is added into the solid solution of La0.95Ca0.05NbO4 in their oxidation phase, and precipitates as Ni nanoparticles upon being exposed to reducing atmosphere. Transmission electron microscopy and X-ray photoelectron spectroscopy confirmed the partial exsolution of Ni nanoparticles after exposure to 5% H2/Ar at 800 °C. The proton conductivity of LCNNi was investigated by electrochemical impedance spectroscopy in humidified Ar and 5% H2/Ar. In all cases, the total conductivities of Ni doped compositions are higher than that of the undoped one and proton conductivity is the dominant conductivity. At Ni0.05, it exhibits the maximum total conductivity (3.53 × 10−4 S cm−1), that is twice more than twice as the value of LCN (1.73 × 10−4 S cm−1) in humidified 5% H2/Ar at 800 °C. Both of the grain boundary and bulk conductivities are significantly improved in humidified 5% H2/Ar. The preliminary results demonstrate that this catalytic approach with precipitated Ni nanoparticles is viable and effective to optimize the conductivity of LCN electrolyte.