Journal of Power Sources 160 (2006) 27–36 Improving the performance of high-temperature PEM fuel cells based on PBI electrolyte F. Seland ∗ , T. Berning 1 , B. Børresen, R. Tunold Electrochemistry Group, Department of Materials Science and Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway Received 12 January 2005; received in revised form 30 December 2005; accepted 4 January 2006 Available online 28 February 2006 Abstract This paper describes the testing of the gas-diffusion electrodes for polymer electrolyte membrane fuel cells utilizing phosphoric acid doped polybenzimidazole (PBI) electrolyte, which allows for an operating temperature as high as 200 ◦ C. In order to determine the optimum structure of our anodes and cathodes, the platinum content in the Pt/C catalyst and catalyst loading were varied, as well as the loading of the PBI electrolyte dispersed in the catalyst layer. The different MEAs were tested in terms of their performance by recording polarization curves using pure oxygen and hydrogen. It was found that a high platinum content and a thin catalyst layer on both anode and cathode, gave the overall best performance. This was attributed to the different catalyst surface areas, the location of the catalyst in relation to the electrolyte membrane and particularly the amount of PBI dispersed in the catalyst layer. Scanning electron microscopy (SEM) was used in order to examine the cross-section of the MEAs and measure the thickness of the catalyst layers. With this information, it was possible to give an estimate of the porosity of the catalyst layer. © 2006 Elsevier B.V. All rights reserved. Keywords: PEM; Fuel cell; Polybenzimidazole; PBI; CO poisoning; Electrocatalysis 1. Introduction As PEM fuel cells approach commercialization there is an increased desire to raise the operating temperature to above 100 ◦ C. To date, most PEM fuel cells are based on an electrolyte that relies on addition of liquid water to facilitate protonic con- duction. Operating these fuel cells at a temperature close to the boiling point of water introduces a dual phase water system that must be controlled carefully. Common problems are the pos- sible drying out of the electrolyte membrane at the anode at high current densities and possible flooding of the gas-diffusion electrodes due to water condensation. A lot of work has been focussed on resolving the water-management issues related to these fuel cells, e.g. [1–4]. Polymer electrolyte fuel cells based on polybenzimidazole (PBI) electrolyte represent a new generation of PEM fuel ∗ Corresponding author. Tel.: +47 73594040; fax: +47 73594083. E-mail addresses: frode.seland@material.ntnu.no (F. Seland), torsten.berning@de.opel.com (T. Berning), borre.borresen@material.ntnu.no (B. Børresen), reidar.tunold@material.ntnu.no (R. Tunold). 1 Present address: Adam Opel AG, International Technical Development Cen- ter, D-65423 R¨ usselsheim, Germany. cells that can be operated at temperatures up to 200 ◦ C. An increased operating temperature significantly increases the toler- ance towards carbon monoxide, as has previously been shown by Li et al. [5] and Holladay et al. [6]. Li et al. report a CO tolerance of 3% CO in hydrogen at current densities up to 0.8 A cm -2 at 200 ◦ C and 0.1% CO in hydrogen at 125 ◦ C and current densities lower than 0.3 A cm -2 , where CO tolerance is defined by a volt- age loss less than 10 mV. Furthermore, the electro-osmotic drag coefficient for water and methanol in phosphoric acid doped PBI membranes has been reported by Weng et al. [7] to be essentially zero under all conditions. This greatly simplifies the material balances and mass transport management and reduces the cross- over of methanol in direct methanol fuel cells. High-temperature PBI fuel cells offer a viable alternative to low-temperature PEM fuel cells that demand an extensive and expensive pre-treatment of the fuel. Polybenzimidazole, PBI, is an amorphous basic polymer with a high thermal stability and a reported glass transition tempera- ture of 420 ◦ C [8]. The conductivity of different PBI membranes in the pure state is very low and about 10 -12 S cm -1 [9,10]. However, there are many ways of substantially increase the con- ductivity of PBI membranes, and this has been the focus in several recent published works, e.g. [11–16]. Polybenzimida- 0378-7753/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2006.01.047