Studies on Ionic Conductivity of Sr²⁺-Doped CeP₂O₇ Electrolyte in Humid Atmosphere

Abstract

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.

Ionic Conductivity of Gd3+Doped Cerium Pyrophosphate Electrolytes with Core-Shell Structure

“…22,23 In order to minimize the effect of incomplete initial humidification, all CGP samples were humidified for relatively longer duration (>100 h) at 90 • C until a stable EIS response is obtained. Figure 9a and 9b show Cole-Cole plot for EIS measurement on CGP at 90 and 190 • C in humidified air atmosphere.…”

“…Gd 3+ -doped CeP 2 O 7 were synthesized by digesting GDC powder with 85% H 3 PO 4 via slight modification of the earlier reported single step digestion procedure. 14,22 Briefly, the GDC powder and H 3 PO 4 were mixed in different P/(Ce+Gd) molar ratio (2.3-2.8) in a covered alumina crucible at ∼95 • C for ∼8 h with constant stirring using magnetic stirrer to get a highly viscous paste. The temperature was then raised to ∼150 • C to get a dry yellow solid.…”

“…Also, they have shown strong dependency of proton conductivity on the use of excess phosphorous in material synthesis. [14][15][16][22][23][24] The excess phosphorous is supposed to be present as amorphous P m O n phase in the as-synthesized material. 25 However, the fabrication of dense crystalline CeP 2 O 7 samples has been an issue, as the methods used for the preparation of dense samples involve heat-treatment at >600 • C, but cerium pyrophosphates are known to be thermally unstable at temperatures >400 • C and slowly decompose to CeO 2 , P 2 O 5 and a number of other secondary phosphates such as cerium metaphosphate (Ce 3 P 3 O 9 ), cerium orthophosphate (CePO 4 ) and cerium polyphosphates (Ce 3 (PO 4 ) 3 ).…”

Effect of partial substitution of Sn4+ by M4+ (M=Si, ti, and Ce) on sinterability and ionic conductivity of SnP2O7

“…We have been working on the synthesis and characterization of cerium pyrophosphates for the application as electrolyte in low-temperature PCFCs [8][9][10]. Though the cerium pyrophosphates are thermally unstable at 4400 1C and therefore their sintering at the higher temperature is avoided [10,11], it has been observed that they give fairly dense specimens even on sintering at temperatures $ 400 1C [5,[8][9][10][11].…”

“…Though the cerium pyrophosphates are thermally unstable at 4400 1C and therefore their sintering at the higher temperature is avoided [10,11], it has been observed that they give fairly dense specimens even on sintering at temperatures $ 400 1C [5,[8][9][10][11]. Considering the fact that pyrophosphates of cerium and tin are generally isomorphous, with both having cubic lattice and Pa3 space group [12,13], it is expected that on partially replacing Sn 4 þ ion in SnP 2 O 7 by Ce 4 þ ion, Ce 4 þ ion would be easily incorporated into tin pyrophosphate lattice, although the ionic radius of Ce 4 þ ion (r=0.87 Å) is larger than that of Sn 4 þ ion (r=0.69 Å) [14], and improve the sinterability of tin pyrophosphate.…”