Song-Yul Oh

Inorganic–organic composite electrolytes consisting of polybenzimidazole and Cs-substituted heteropoly acids and their application for medium temperature fuel cells

Inorganic–organic composite electrolytes were fabricated from partially Cs+-substituted heteropoly acids (Cs-HPAs) and polybenzimidazole (PBI) for application in medium temperature fuel cells. PBI was synthesized using diaminobenzidine (DAB) and isophthalic acid (IPA) in polyphosphoric acid (PPA) in the temperature range of 170 to 200 °C under nitrogen atmosphere. Heteropoly acids, such as phosphotungstic acids (H3PW12O40), and silicotungstic acid (H4SiW12O40), were mechanochemically treated with caesium hydrogen sulfate (CsHSO4) to obtain Cs-HPAs with a molar ratio of 50/50. The PBI-Cs-HPAs composite electrolytes were fabricated by solvent casting, and FT-IR results showed that the PBI-Cs-HPAs composite formed successfully. High proton conductivity and good fuel cell performance of PBI composite electrolytes were comparable to those of phosphoric acid-doped pure PBI electrolytes, even though they have lower phosphoric acid doping level (PADL) than that of pure PBI. The high proton conductivities of 1.91 × 10−2 S cm−1 and 1.71 × 10−2 S cm−1 were achieved at 160 °C under anhydrous conditions for PBI-50H3PW12O40·50CsHSO4 with 87 wt.% PADL and PBI-50H4SiW12O40·50CsHSO4 with 82 wt.% PADL, respectively. These observations implied that the mechanochemically synthesized Cs-HPA composites are promising materials to achieve high electrochemical properties with a low level of PADL for PBI electrolytes.

Mechanochemically synthesized CsH2PO4–H3PW12O40 composites as proton-conducting electrolytes for fuel cell systems in a dry atmosphere

Abstract Cesium dihydrogen phosphate (CsH2PO4, CDP) and dodecaphosphotungstic acid (H3PW12O40·nH2O, WPA·nH2O) were mechanochemically milled to synthesize CDP–WPA composites. The ionic conductivities of these composites were measured by an ac impedance method under anhydrous conditions. Despite the synthesis temperatures being much lower than the dehydration and phase-transition temperatures of CDP under anhydrous conditions, the ionic conductivities of the studied composites increased significantly. The highest ionic conductivity of 6.58×10−4 Scm−1 was achieved for the 95CDP·5WPA composite electrolyte at 170 °C under anhydrous conditions. The ionic conduction was probably induced in the percolated interfacial phase between CDP and WPA. The phenomenon of high ionic conduction differs for the CDP–WPA composite and pure CDP or pure WPA under anhydrous conditions. The newly developed hydrogen interaction between CDP and WPA supports anhydrous proton conduction in the composites.