Fabrication of Dense Cerium Pyrophosphate-Polystyrene Composite for Application as Low-Temperature Proton-Conducting Electrolytes

Abstract

The goal of this study is to improve the applicability of cerium pyrophosphates as dense electrolytes in proton-conducting ceramicelectrolyte fuel cells (PCFCs) in 100-230 • C, by using polystyrene as a pore-filler in partially sintered cerium pyrophosphate substrates. In this study an inorganic-organic composite membrane composed of Gd 3+ -doped cerium pyrophosphate (Ce 0.9 Gd 0.1 P 2 O 7 , CGP) and highly cross-linked polystyrene is prepared by polymerization of divinylbenzene monomers in partially sintered CGP substrates. The microstructure and electrochemical behavior of the CGP-polystyrene (CGP-PS) composites are characterized to understand their proton conductivity and long-term stability. The ionic conductivity measurement using electrochemical impedance spectroscopy (EIS) shows that the CGP-PS membranes have high ionic conductivity (>10 mS cm −1 ) in 110-200 • C range under humidified condition (water vapor pressure, pH 2 O = 0.04-0.16 atm); where CGP-PS1 shows maximum conductivities of 16.1 and 14.8 mS·cm −1 in pH 2 O of 0.16 and 0.12 atm, respectively, at 190 • C. The scanning electron microscopy (SEM) analysis of the as-prepared CGP-PS composites shows that they are dense and free of pores. The stability of the CGP-PS composites is analyzed after the long-term electrical conductivity measurement in humidified atmosphere.The development of new electrolytes with ionic conductivities ≥10 mS·cm −1 in intermediate temperature range of 100-500 • C has gained increased attention in research areas of the intermediate temperature fuel cells (ITFCs). Due to the lower energy of activation of protonic conduction, fuel cells based on proton conducting electrolytes has been considered as promising candidates for ITFCs. Considering the fact that tetravalent metal pyrophosphates (TMPs) have poor sintering-ability and the substrates sintered at high temperatures have poor proton-conductivity 1-3 several strategies to utilize TMPs as dense electrolytes in PCFCs including formation of inorganic-organic composite membranes by casting process have been reported. 4-10 Li et al. 8 fabricated defect-free nanofilms of amorphous Y-doped zirconium pyrophosphate by a novel approach comprising a combination of the layer-by-layer sol-gel process and annealing. Sato et al. 10 fabricated dense MO 2 -MP 2 O 7 (where M = Sn, Si, Ti and Zr) electrolyte membranes by reacting porous MO 2 substrate with phosphoric acid, where the reaction products formed into the pores act as pore fillers. However, unfortunately not much work is reported on the fabrication of dense composite electrolytes using cerium pyrophosphate. Earlier Chatzichristodoulou et al. 11 fabricated dense CeP 2 O 7 -KH 2 PO 4 composites. But, because of water solubility of KH 2 PO 4 , the composite was not stable the long-term conductivity measurements in humidified atmosphere. Recently, the strategy of in situ solidification of phosphoric acid loaded into partially sintered cerium phosphate substrate was employed to fabricate cerium pyrophosphate-based dense composite electr...

Electrical Behavior and Stability of K2HPO4-KH5(PO4)2-Ce0.9Gd0.1P2O7Composite Electrolytes for Intermediate Temperature Proton-Conducting Fuel Cells

“…3,4,11 In order to overcome the abovementioned disadvantages associated with the solid acid phosphates and tetravalent metal phosphates (TMPs), alternative methods of utilizing their high proton conductivity in PCFC electrolytes have been proposed. [12][13][14][15][16][17] A few composite electrolytes of solid acid phosphates have been fabricated with SiO 2 based a materials as supporting matrix. [12][13][14] Similarly, alterz E-mail: song@chonnam.ac.kr native ways to form dense electrolyte substrates of TMPs have been proposed.…”

“…[12][13][14] Similarly, alterz E-mail: song@chonnam.ac.kr native ways to form dense electrolyte substrates of TMPs have been proposed. [15][16][17] In this study, we have fabricated composite electrolytes K 2 HPO 4 -KH 5 (PO 4 ) 2 -Ce 0.9 Gd 0.1 P 2 O 7 by combining solid acid phosphates K 2 HPO 4 and KH 5 (PO 4 ) 2 , and a TMP Ce 0.9 Gd 0.1 P 2 O 7 in different ratios. The high proton conductivity of cerium pyrophosphates in 100-230 • C range has been well-established in previous studies.…”