Thermal and water management is a critical issue in PEFCs. In this research, the thermal behavior of PEFC is focused. The objective is to understand the influence of heat on cell performance both by experiment and theoretical analysis, as well as improving cell performance and reliability. In order to investigate the theoretical behavior, especially in the catalyst layer where the electrochemical reactions occur, a detailed modeling of heterogeneous surface reaction coupled with reactant transport is needed. In this paper, a theoretical model that improves the dependency of the exchange current density with reactant concentrations by applying data from a known surface reaction steps found in catalysis is developed. It served as a preliminary step before the thermal-electrochemical behavior of a PEFC can be fully understood.