Available online at www.sciencedirect.com Electrochimica Acta 53 (2008) 4495–4499 A new anhydrous proton conductor based on polybenzimidazole and tridecyl phosphate Fengjing Jiang a , Hongting Pu a,∗ , Wolfgang H. Meyer b , Yisi Guan a , Decheng Wan a a Institute of Functional Polymers, School of Materials Science & Engineering, Tongji University, Shanghai 200092, China b Max Planck Institute for Polymer Research, Mainz D-55021, Germany Received 3 October 2007; received in revised form 3 January 2008; accepted 13 January 2008 Available online 19 January 2008 Abstract Most of the anhydrous proton conducting membranes are based on inorganic or partially inorganic materials, like SrCeO 3 membranes or polybenzimidazole (PBI)/H 3 PO 4 composite membranes. In present work, a new kind of anhydrous proton conducting membrane based on fully organic components of PBI and tridecyl phosphate (TP) was prepared. The interaction between PBI and TP is discussed. The temperature dependence of the proton conductivity of the composite membranes can be modeled by an Arrhenius relation. Thermogravimetric analysis (TGA) illustrates that these composite membranes are chemically stable up to 145 ◦ C. The weight loss appearing at 145 ◦ C is attributed to the selfcondensation of phosphate, which results in the proton conductivity drop of the membranes occurring at the same temperature. The DC conductivity of the composite membranes can reach ∼10 -4 S/cm for PBI/1.8TP at 140 ◦ C and increases with increasing TP content. The proton conductivity of PBI/TP and PBI/H 3 PO 4 composite membranes is compared. The former have higher proton conductivity, however, the proton conductivity of the PBI/H 3 PO 4 membranes increases with temperature more significantly. Compared with PBI/H 3 PO 4 membranes, the migration stability of TP in PBI/TP membranes is improved significantly. © 2008 Elsevier Ltd. All rights reserved. Keywords: Proton conductivity; Polybenzimidazole; Tridecyl phosphate; Migration stability 1. Introduction Polymer electrolyte membrane fuel cells (PEMFCs) oper- ating at intermediate temperature (100–200 ◦ C) have received increasing attention due to the problem of CO poisoning to catalyst. Besides this, an intermediate temperature operation eventually increases the efficiency of PEMFC. Since the high proton conductivity of conventional hydrated sulfonic acid membranes is closely related to high levels of hydration, the performance of hydrated proton conducting membranes, such as Nafion, is insufficient above 100 ◦ C due to the loss of water [1–3]. There has been considerable interest in devel- oping anhydrous proton exchange membranes on the basis of acid–base complex electrolytes. Most of anhydrous proton conducting membranes are based on inorganic or partially inor- ganic materials, like SrCeO 3 membranes or polybenzimidazole (PBI)/H 3 PO 4 composite membranes [4–8]. Polymers based on ∗ Corresponding author. Fax: +86 21 65982461. E-mail address: puhongting@mail.tongji.edu.cn (H. Pu). nitrogen-containing heterocycles, such as polybenzimidazole, poly(4-vinylimidazole), and poly(vinylpyrrolidone), have been found to exhibit a high proton conductivity under anhydrous and intermediate-temperature condition after being blended with inorganic acids, such as H 3 PO 4 and H 2 SO 4 [7–13]. Especially, the amphoteric behavior and the ability to form complex or inter- molecular hydrogen bonds in these blends are important for the proton transport [14–16]. Particularly, pure PBI has an excel- lent thermal stability and is one of the most promising polymers for anhydrous polymer electrolyte membranes [17,18]. How- ever, when blended with large amounts of H 3 PO 4 high proton conductivities are obtained, but the materials suffer from rather poor mechanical properties. The nitrogen-containing heterocy- cles in PBI possess both proton donating and accepting sites that are helpful for proton transport in acid doped membranes [19,20]. However, elution of the water soluble acids such as phosphoric acid from the membrane and dilution of the acid in the membrane can occur when the vapor produced at the cath- ode in the operation process of fuel cells is not eliminated. In this way, the stability of the membranes will be destroyed and the proton conductivity will be reduced. Tridecyl phosphate has 0013-4686/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2008.01.022