Composite electrolytes composed of Cs-substituted phosphotungstic acid and sulfonated poly(ether–ether ketone) for fuel cell systems

Abstract

Abstract Composite electrolytes composed of cesium hydrogen sulfate containing phosphotungstic acids (CsHSO 4 –H 3 PW 12 O 40 ) and sulfonated poly(ether–ether ketone) (SPEEK) were prepared by casting the corresponding precursor for application in fuel cells. Partially Cs-substituted phosphotungstic acids (Cs x H 3− x PW 12 O 40 ) were formed in the CsHSO 4 –H 3 PW 12 O 40 system by mechanochemical treatment. SPEEK was prepared from PEEK by sulfonation using concentrated sulfuric acid. Flexible composite electrolytes were obtained and their electrochemical properties were markedly improved with the addition of Cs x H 3− x PW 12 O 40 , into the SPEEK matrix. A maximum power density of 213 mW cm −2 was obtained from the single cell test for 50H 3 PW 12 O 40 –50CsHSO 4 in SPEEK (1/5 by weight) composite electrolyte at 80 °C and at 80 RH%. Electrochemical properties and transmission electron microscopy (TEM) results suggest that three-dimensional cluster particles were formed and homogeneously distributed in the SPEEK matrix. The mechanochemically synthesized Cs x H 3− x PW 12 O 40 incorporated into the SPEEK matrix increased the number of protonate sites in the electrolyte. The composite electrolytes were successfully formed with Cs x H 3− x PW 12 O 40 , which consist of hydrogen bonding between surface of inorganic solid acids and not only –HSO 4 − dissociated from CsHSO 4 but also –SO 3 H groups in the SPEEK.