Comparative analysis of the electroactive area of Pt/C PEMFC electrodes in liquid and solid polymer contact by underpotential hydrogen adsorption/desorption A.M. Chaparro a, *, A.J. Martı´n a , M.A. Folgado a , B. Gallardo a , L. Daza a,b a Dep. de Energı´a, CIEMAT, Avda. Complutense, 22, 28040 Madrid, Spain b Instituto de Cata ´lisis y Petroleoquı´mica (CSIC), Marie Curie 2, Campus Cantoblanco, 28049 Madrid, Spain article info Article history: Received 21 January 2009 Received in revised form 25 March 2009 Accepted 29 March 2009 Available online 24 April 2009 Keywords: Electroactive area Pt/C Fuel cell PEMFC Hydrogen adsorption Corrosion abstract Because of the different experimental conditions found in literature for the measurement of the electroactive area of Pt/C electrodes of proton exchange membrane fuel cells (PEMFC) by means of underpotential hydrogen adsorption (H UPD ) voltammetry, specially concerning sweep rate and temperature, it was found necessary to perform an analysis of these parameters. With this aim, the electroactive area of PEMFC electrodes has been measured by means of H UPD voltammetry at different sweep rates and temperatures, in liquid elec- trolyte and solid polymer contact. Both configurations show that H UPD adsorption and desorption charges are strongly dependent on sweep rate voltage and temperature. The most common behaviour observed is a maximum in H UPD desorption charge, typically in the 100–10 mV s 1 sweep rate range, whereas H UPD adsorption charge shows continuous increase with decreasing sweep rate. The decrease of desorption charge at low sweep rates is attributed to adsorbing species related with carbon support reactivity. These processes are also responsible for the increase in desorption H UPD charge at low sweep rate. At high sweep rate, both adsorption and desorption H UPD charges decrease due to limiting diffusion of protons through the microporous electrode. As a consequence, it is found that the closest approximation to the real electroactive area (i.e. the area accessible to protons) corresponds to the maximum in the H UPD desorption charge in the range of 10–100 mV s 1 sweep rate. The influence of measuring temperature is also tested in the range 25  C–80  C. A dependence of the adsorption and desorption hydrogen charges is found, due to ther- modynamic and kinetics factors. We observe that the processes competing with hydrogen adsorption, i.e. generation and adsorption of carbon species are enhanced with tempera- ture, so a low measuring temperature is found as most appropriate. ª 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. 1. Introduction The electroactive area may be defined as the amount of surface of an electrode in conditions to promote a desired electrochemical reaction. It may be a blurred concept, as noted by Trasatti and Petrii [1], that depends on the electro- chemical reaction considered and the method of measure- ment. For electrodes containing an electrocatalyst, like used for low temperature proton exchange membrane fuel cells (PEMFC), the electroactive area corresponds to the area of the * Corresponding author. Tel.: þ34 913467897; fax: þ34 913466269. E-mail address: antonio.mchaparro@ciemat.es (A.M. Chaparro). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he 0360-3199/$ – see front matter ª 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2009.03.053 international journal of hydrogen energy 34 (2009) 4838–4846