A multi-scale model for electrochemistry in proton exchange membrane (PEM) fuel cells has been developed. The multi-scale model involves four scales: atomic-scale for kinetics of chemical/electrochemical reaction, nano-scale for surface reactions, micro-scale for electrolyte transport, and macro-scale. The energetics of chemical and electrochemical reactions are computed using quantum computation which serves as input for the kinetics on nano-scale catalysts which is simulated using the dynamic Monte Carlo (DMC) method. A full fuel cell model will be presented where the details of all the scales have been resolved with comparisons to experiments.