Proton conductor NASICON-structure Li1+xCdx/2Zr2−x/2(PO4)3 as solid electrolyte for intermediate-temperature fuel cells

Abstract

Low ionic conductivity of solid electrolytes at intermediate temperatures hinders the commercialization process of solid fuel cell technology. A sodium superionic conductor (NASICON)-structure with a rigid three-dimensional network and an interconnected interstitial space is expected to be an ideal solid electrolyte for fuel cells. Based on the H+/Li+ exchange engineering strategy, here we report a NASICON-structure proton conductor Li1+xCdx/2Zr2−x/2(PO4)3 (x = 0.5, 1, 1.5, 2) derived from CdZr4(PO4)6 to construct a fuel cell device. Among all samples, the Li3Cd1Zr1(PO4)3 cell device exhibits a high performance including peak power density 815 mW cm−2, proton conductivity 0.165 S cm−1 and activation energy 0.372 eV at 550 °C. Theoretical and experimental studies both suggest that the high proton conductivity benefits from the unique 3D interstitial space and rapid H+/Li+ exchange in the NASICON material. Under fuel cell operating conditions, the interstitial space of Li1+xCdx/2Zr2−x/2(PO4)3 (x = 2) substitutes mobile Li+ with H+ enabling fast proton transport. The new transport mechanism and excellent proton conductivity suggest that Li1+xCdx/2Zr2−x/2(PO4)3 provides new opportunities for enriching novel electrolyte materials in intermediate temperature protonic ceramic fuel cells (IT-PCFCs).