We conducted atomistic simulation of the interfaces between Nafion electrolyte and electrode in polymer electrolyte fuel cells (PEFCs). We have accomplished: 1) simulation of the atomic structure of the sulfuric acid/Pt, sulfuric acid/carbon, Nafion/Pt, and Nafion/carbon interfaces; 2) evaluation of the ionic potential distribution at the interfaces; 3) evaluation of the electronic potential distribution at the interfaces; 4) simulation of the dynamic trajectories at the interfaces; and 5) evaluation of the exchange current density at the interface. The following findings have been obtained. Firstly, at the interfaces, on the top of the electrode surface, water molecules and other small molecules arrayed into three highly ordered layers. The ordering or symmetry of the layers is similar to that of the electrode surface. Secondly, the potential difference or electric field is completely different for ions and electrons. Generally, the ionic potential reveals a large step at the interface. Adsorption of hydrogen and oxygen increases the height of the step. On the contrary, the electronic potential is continuous across the interface for the middle potential range but discrete for very high and low potential levels (Fig. 1). It seems that the existing definition of so-called electrochemical potential or potential difference across the electric double layer (EDL) is not valid. In fact, according to the simulation results, there are two “interface potentials”, ionic potential and electronic potential. Thirdly, the simulation proves that adsorbed hydrogen and oxygen do increase the exchange current density at the interface. The implications of the findings to the theory of electrochemical electron transfer kinetics, including the conditions for electron transfer at the interface and the popular Butler-Volmer equation are discussed.