Proton conductive membranes based on doped sulfonated polytriazole M. Boaventura a , M.L. Ponce b , L. Branda ˜o a , A. Mendes a, *, S.P. Nunes b,1 a Laborato ´rio de Engenharia de Processos, Ambiente e Energia (LEPAE), Faculdade de Engenharia da Universidade do Porto, Rua Roberto Frias, 4200-465 Porto, Portugal b GKSS Research Centre Geesthacht GmbH, Max Planck Str. 1, D-21502, Geesthacht, Germany article info Article history: Received 13 April 2010 Received in revised form 26 July 2010 Accepted 21 August 2010 Available online 22 September 2010 Keywords: Sulfonated polytriazole Proton conductivity High temperature fuel cell abstract This work reports the preparation and characterization of proton conducting sulfonated polytriazole membranes doped with three different agents: 1H-benzimidazole-2-sulfonic acid, benzimidazole and phosphoric acid. The modified membranes were characterized by scanning electron microscopy (SEM), infrared spectra, thermogravimetric analysis (TGA), dynamical mechanical thermal analysis (DMTA) and electrochemical impedance spec- troscopy (EIS). The addition of doping agents resulted in a decrease of the glass transition temperature. For membranes doped with 85 wt.% phosphoric acid solution proton conductivity increased up to 2$10 3 S cm 1 at 120  C and at 5% relative humidity. The performance of the phosphoric acid doped membranes was evaluated in a fuel cell set-up at 120  C and 2.5% relative humidity. ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. 1. Introduction The most widely used proton exchange membrane in polymer electrolyte fuel cells (PEMFC), Nafion Ò , exhibits high proton conductivity under humidified conditions. The need of water to solvate the acidic protons and support proton transport limits fuel cell operation to the boiling point of water and requires a rather complicated water management system. On the other hand, the water management in high temperature fuel cells is much simpler as well as the electrochemical kinetics is higher. Moreover, the cooling system and heat recovery are simplified and CO tolerance dramatically increases [1,2]. Anhydrous proton conductive polymers have received increased attention due to its application in high temperature PEMFC (120  Ce200  C). In these materials, the proton conduction is not dependent on the hydration level; rather it is assisted by other proton solvents. One approach intensively studied to produce anhydrous proton conductive polymers is blending neutral or basic polymers with strong oxo-acids like phosphoric to obtain for example phosphoric acid doped polybenzimidazole (PBI) [3e5]. Another approach is the use of nitrogen-containing aromatic heterocycles molecules - with boiling points higher than water - as proton carriers, either as doping agents or immobilized in the poly- mer backbone, originating polymers with intrinsic proton conductivity. Kreuer and co-workers emphasized the proper- ties of nitrogen-containing aromatic heterocycles (like imid- azole, benzimidazole and pyrazole) as viable water replacers and reported the first attempt for immobilizing imidazole [6e8]. These heterocycles molecules are amphoteric and present similar transport coefficients to those of water between 150  C and 200  C. Moreover, they exhibit hydrogen bond interactions and, to a certain extent, undergo self- dissociation [9]. When heterocycles are immobilized in * Corresponding author. E-mail address: mendes@fe.up.pt (A. Mendes). 1 Present address: King Abdullah University of Science and Technology, Saudi Arabia. Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 35 (2010) 12054 e12064 0360-3199/$ e see front matter ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2010.08.123