In the present work, three-dimensional CFD modelings of flow, heat transfer and electrochemical processes in a proton exchange membrane fuel cell (PEMFC) are performed for the purpose of improving PEM fuel cell efficiency. Different designs were examined and a new bipolar plate design was proposed. The predicted results from the developed model were first compared with the available measurements, and very good agreement was achieved. Numerical results showed that flow field distributions inside the cell can be greatly improved with the proposed PEMFC design and the polarization curve of the PEM fuel cell can be greatly enhanced compared with the baseline design.