Self-Humidifying Cs2.5H0.5PW12O40 / Nafion / PTFE Composite Membrane for Proton Exchange Membrane Fuel Cells

Abstract

A Cs 2.5 H 0.5 PW 12 O 40 /Nafion/polytetrafluoroethylene ͑PTFE͒ self-humidifying composite membrane was developed for proton exchange membrane fuel cells. It was prepared by recasting the Cs 2.5 H 0.5 PW 12 O 40 /Nafion self-humidifying layer onto the two sides of a Nafion/PTFE composite membrane with a solution-recast method. Due to the strong acidic, hydrophilic, and redox properties of Cs 2.5 H 0.5 PW 12 O 40 , the Cs 2.5 H 0.5 PW 12 O 40 /Nafion self-humidifying layer not only contributes to humidify the membrane but also contributes to the improvement of the open-circuit voltage of the fuel cell. When the self-humidifying composite membrane was employed as an electrolyte in H 2 /O 2 PEMFC, a higher maximum power density value ͑1.1 W/cm 2 ͒ was obtained than that of Nafion/PTFE composite membrane ͑0.6 W/cm 2 ͒, under the operating conditions of 70°C and at the humidified temperature of 20°C.The proton exchange membrane fuel cell ͑PEMFC͒ attracts much attention due to its high efficiency, high power density, zero emission, and low-temperature start-up as a power sources suitable for both stationary and mobile application. However, the typical membrane currently used for the PEMFC, such as Dupont's Nafion or perfluorosulfonic acid ͑PFSA͒ membrane, shows a significant loss in conductivity at a lower relative humidity ͑RH͒ environment. 1 Thus the reaction gas needs to be humidified in the PEMFC. But the humidifier will make the whole system complex and large. Therefore these needs promote the research and development selfhumidifying membrane. 2 Up to now, many materials such as Pt, 3 metal oxides, 4 heteropoly acid, 5 and ZrHPO 4 6 have been used to highly disperse in the Nafion or sulfonated poly ͑ether ether ketone͒ ͑SPEEK͒ resin to fabricate self-humidifying membrane. However, due to the poor mechanical strength and stability of those selfhumidifying membranes, the humidifier still has to be used in the PEMFC system. Cs 2.5 H 0.5 PW 12 O 40 is insoluble in water and organic solvents and has micro-and mesopores with a high surface area ͑around 130 m 2 /g͒. 7 In addition, the acidity per unit acid site of Cs 2.5 H 0.5 PW 12 O 40 was superior to Nafion-H as well as homogeneous acids, e.g., H 2 SO 4 , H 3 PW 12 O 40 , and p-toluenesulfonic acid. 8 These facts demonstrate that Cs 2.5 H 0.5 PW 12 O 40 is a promising solid acid to be used in PEMFCs. Furthermore, Cs 2.5 H 0.5 PW 12 O 40 possesses a redox property. Various catalyzed reactions such as alkylation, ester decomposition, acylation, Diels-Alder reaction, have been reported to proceed on Cs 2.5 H 0.5 PW 12 O 40 . 9-11 Recently, Limoges et al. 12 reported the heterployacides can be used as the catalyst of the anode and cathode in PEMFCs.In view of the above strong acidic, hydrophilic, and redox properties of Cs 2.5 H 0.5 PW 12 O 40 , a high performance Cs 2.5 H 0.5 PW 12 O 40 /Nafion/PTFE self-humidifying composite membrane with a sandwich structure was developed to improve the mechanical strength of the membrane and the cell performance under lower RH condit...

Phosphotungstic Acid Supported on a Nanopowdered ZrO2 as a Filler in Nafion‐Based Membranes for Polymer Electrolyte Fuel Cells

“…For example, the addition of Pt particles or HPAs allows the in situ conversion of any permeating H 2 or O 2 into water by acting through their efficient high acid catalytic activity in the peroxide decomposition [21,22]. In addition, previous works have demonstrated that HPAs have suitable properties to be used in fuel cells as solid electrolytes or aqueous solutions [23,24] and have been already introduced in perfluorinated membranes to improve the fuel cell performance [25][26][27].…”

Fabrication and characterization of a PTFE-reinforced integral composite membrane for self-humidifying PEMFC

“…However, the composite membrane has the risk of formation electron-conducting path via the network of dispersed Pt particles in the whole membrane. In the latter papers, the researchers developed Pt-containing selfhumidifying membrane mainly focusing on the following three directions: (1) decreasing the membrane thickness or incorporating some functional particles, such as SiO 2 , ZrP, and Cs 2.5 H 0.5 PW 12 O 40 to improve the cell performance under dry condition [9][10][11]; (2) designing new membranes of two-layered or three-layered structures to avoid short circuit through the membrane [12,13]; (3) using the hydrocarbon membrane which can decrease the cost of the PEM [14].…”

The Effect of Heteropoly Acids on Stability of PFSA PEMs under Fuel Cell Operation

“…PEM lifetimes and functionality for operation in hotter and drier conditions may be enhanced by the addition of catalytic amounts of Pt or the cesium salt of 12-phosphotungstic acid, a heteropoly acid ͑HPA͒ that converts any permeating H 2 or O 2 in situ in the PEM into water. 2,3 It has been implied that any peroxide in the membrane is decomposed to water. Whereas improved fuel cell performance under hotter and drier operation has been demonstrated for MEAs containing membranes with these catalytic additives, little data exists to support the assumption that these same additives enhance PEM lifetime in a fuel cell.…”