Sr2+-doped cerium pyrophosphate (Ce1–x Sr x P2O7, x = 0.05, 0.1, 0.15, and 0.2) electrolytes are synthesized by digesting cerium oxide and strontium nitrate with 85% H3PO4. The ionic conductivity behavior of Ce1–x Sr x P2O7-sintered pellets is analyzed by electrochemical impedance spectroscopy in a dry and humid air atmosphere. The time-dependent variation of ionic conductivity during humidification process and the variation of conductivity with temperature are studied. In humid atmosphere in the 90–230 °C range, the variation of ionic conductivity is explained on the basis of the combined effect of ionic mobility and the availability of charge carriers in the samples. The ionic conductivity shows dependence on dopant concentration and water vapor pressure (pH2O). In dry air, conductivity of Ce1–x Sr x P2O7 is very low, with Ce0.9Sr0.1P2O7 showing a maximum conductivity of 4.3 × 10–6 S/cm at 430 °C. Among various Ce1–x Sr x P2O7 samples, Ce0.9Sr0.1P2O7 shows the highest conductivity in humid air (pH2O = 0.12 atm) with a maximum conductivity of 6.3 × 10–3 S/cm at 90 °C, and the conductivity of Ce0.9Sr0.1P2O7 was 3.5 × 10–3 S/cm at 190 °C and pH2O = 0.12 atm. On the basis of XRD results, the stability of Ce1–x Sr x P2O7 in a humid atmosphere is analyzed.

The proton conducting electrolyte cerium pyrophosphate was synthesized by digesting cerium oxide with 85% H 3 PO 4 . The crystal structure and phase stability of the material were analyzed by X-ray diffraction and thermogravimetric analysis/differential thermal analysis (TGA/DTA), and the microstructure was analyzed by scanning electron microscopy (SEM). The electric conductivity behavior of CeP 2 O 7 sintered pellets was analyzed by electrochemical impedance spectroscopy (EIS) and modulus spectroscopy. The activation energies for migration (E ω ) and dc conduction (E σ ) calculations indicates that the charge carriers responsible for conductivity and relaxation are same and the concentration of charge carries is independent of temperature. The variation of conductivity with temperature was studied in dry and humid atmosphere for the possible application as electrolyte in proton conducting ceramic electrolyte fuel cells (PCFCs) in the temperature range of 100-220 • C, which showed that the conductivity of CeP 2 O 7 was mainly due to the incorporation of water and the maximum conductivity was found to be 2.1 × 10 −4 S cm −1 at 175 • C and P H2O = 0.06 atm. The presence of water in CeP 2 O 7 matrix increases the number of jump sites and facilitates the hopping of protons, leading to an increase in the conductivity.

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Protonic ceramic electrochemical cells (PCECs) have attracted considerable attention owing to their ability to reversibly convert chemical fuels into electricity at low temperatures below 600 °C. However, extreme sintering conditions during conventional convectionbased heating induce critical problems for PCECs such as nonstoichiometric electrolytes and microstructural coarsening of the electrodes, leading to performance deterioration. Therefore, we fabricated PCECs via a microwave-assisted sintering process (MW-PCEC). Owing to the ultrafast ramping rate (∼50 °C/min) with bipolar rotation and the resistive heating nature of microwave-assisted sintering, undesirable cation diffusion and grain growth were effectively suppressed, thus producing PCECs with stoichiometric electrolytes and nanostructured fuel electrodes. The MW-PCEC achieved electrochemical performance in both in fuel cell (0.85 W cm −2 ) and in electrolysis cell (1.88 A cm −2 ) modes at 600 °C (70% and 254% higher than the conventionally sintered PCEC, respectively) demonstrating the effectiveness of using an ultrafast sintering technique to fabricate high-performance PCECs.

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