Fuel cell utilization for automobile and residential applications is a promising option in order to help reduce environmental concerns such as pollution. However, fuel cell development requires addressing their dynamic behavior to improve their performances and their life cycle. Since the temperature distribution in the cell is known to be an important factor to the fuel cell's efficiency, a cooling device is often added to homogenize the temperature in the cell and to ensure temperature control. A 3D dynamic thermal model of a single fuel cell is presented in this work in order to study the temperature distribution in a fuel cell cooled from the bottom to the top with air. The model is governed by the thermal energy balance, taking into account the inlet gas humidity. The model is developed with the finite difference method and is implemented in the Matlab/Simulink environment. The validation is based on the performances of the "NEXA" fuel cell produced by Ballard Power Systems. The efficiency analysis of that air cooling device reveals that the cell temperature is directly linked to the current density and to the gas humidity-varying from 30 degrees C at 5A to 80 degrees C * at 35A at low humidity. Moreover, the temperature non-uniformity in the stack is shown to be very high. As a result, temperatures are higher at the top part of the cell than at the bottom part, with a difference of up to a 5 degrees C. Moreover the non-uniforinity of the air cooling between the cells of the stack leads to large temperature variations, up to 8 degrees C, from one cell to another. These temperature variations result in large voltage disparities between the cells, which reduce the total electrical power of the entire stack. (c) 2007 Elsevier B.V. All rights reserved.