In this work, a life study of a single 50 cm(2) high temperature proton exchange membrane fuel cell (HTPEMFC) has been carried out and experimental results are used to assess the causes of performance degradation in PBI HTPEMFC. Current distribution measurements, electrochemical characterization and physicochemical post-mortem analyses are combined with a CFD model that uses local parameters to determine that coalescence of catalyst particles (catalyst agglomeration) can be considered one of the main reasons responsible for the FBI fuel cell short life, according to electrochemically active area (ESA) and charge transfer resistance measurements. According to the current density distribution information, this agglomeration apparently occurs over the whole electrode surface. Increase of membrane resistance also contributes to the loss of fuel cell performance, but the significance is not as large as the effect of the catalyst. The model has been demonstrated to be a suitable diagnostic tool to identify degradation causes. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.