CsH₂PO₄/NdPO₄ Composites as Proton Conducting Electrolytes for Intermediate Temperature Fuel Cells

Composite proton conducting materials based on cesium dihydrogen phosphate and neodymium phosphate hydrate were prepared and investigated in terms of X-ray diffraction, thermogravimetry, conductivity, stability and fuel cell performance. At 150°C the conductivity was 1.8 × 10⁻⁶ S cm⁻¹ for the pristine cesium dihydrogen phosphate and 0.8 × 10⁻⁴ S cm⁻¹ for neodymium phosphate hydrate, while that of the composite containing 29 mol% neodymium phosphate and 71 mol% cesium dihydrogen phosphate was 0.4 × 10⁻² S cm⁻¹. It was proposed that the interaction between the two components establishes a dynamic hydrogen bonding network enabling efficient proton conduction long before the development of the extensive phase disordering of the superprotonic transition. The presence of thermally stable hydrate water present in neodymium phosphate may also play a role in improving both conductivity and stability of the solid acid. The electromotive force, open circuit voltage and fuel cell performance were measured as demonstration of the material application.