In this study, we aimed to examine the effect of dopant type and concentration on the ionic conductivity of ceria‐based electrolytes. Ceria electrolytes doped with samarium (SDC), gadolinium (GDC), neodymium (NDC), and lanthanum (LDC) for solid oxide fuel cells were prepared through the polyol process. Acetate compounds of cerium and dopants were used as starting materials, and triethylene glycol was used as a solvent. Prepared powders and pellets were characterized by TG/DTA, XRD, FTIR, SEM, EIS, and EDS techniques. The results of the TG/DTA and XRD indicated that a single‐phase fluorite structure formed at the relatively low calcination temperature of 500°C. The relative densities of the pellets were higher than 90% and these finding were supported by the SEM images. The lattice parameters of the samples increased with the dopant concentration. According to the electrochemical analysis results, the samples with maximum conductivity values were SDC‐20, GDC‐15, NDC‐15, and LDC‐15. The results of the impedance spectroscopy revealed that the SDC‐20 sample exhibited the highest ionic conductivity with a value of 4.29 × 10−2 S/cm at 800°C in air.
In this study, proton‐conducting sulfonated polyether ether ketone (sPEEK) membranes including tungstic acid, organically modified montmorillonite, and silicon dioxide were prepared using solution casting method for direct methanol fuel cells. All obtained composite membranes had adequate thermal stability for fuel cells, and their surfaces became more hydrophilic due to the incorporation of additives. The ion exchange capacities of the composite membranes were found to be very close to the sPEEK membrane. While the proton conductivity of the sPEEK membrane was 8.6 mS cm−1, the addition of additives led to an enhancement in the proton conductivity values. Among the prepared composite membranes, sPEEK‐H2WO4‐5 had the highest proton conductivity (36.5 mS cm−1) which was comparable to Nafion117 in water at room temperature. On the other hand, the methanol permeabilities of the composite membranes were in the same order compared to sPEEK but showed minor changes depending on the added materials and their compositions. Among the membranes obtained by solution casting, sPEEK‐H2WO4‐5 was found to be the best composite membrane due to its high proton conductivity and acceptable methanol permeability. Layer‐by‐layer modified sPEEK membranes were also obtained in the study for comparison and it was found that sPEEK‐PAH/H2WO4‐2 displayed the best selectivity value.
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