Page 8 - Introduction to Transfer Phenomena in PEM Fuel Cells

vi Introduction to Transfer Phenomena in PEM Fuel Cells
2.2.4. Empty voltage ................................ 57
2.2.5. Effect of pressure .............................. 58
2.2.6. Effect of temperature ............................ 59
2.2.7. Theoretical efficiency ........................... 63
2.3. The flow rates of reactants and products ................... 65
2.3.1. Oxygen flow rate .............................. 65
2.3.2. Hydrogen flow rate ............................. 66
2.3.3. Amount of water produced ........................ 67
2.4. Electrochemistry of the fuel cell ....................... 67
2.4.1. Electrode kinetics .............................. 67
2.4.2. Activation energy .............................. 68
2.4.3. Reaction rate ................................. 69
2.4.4. Exchange current .............................. 69
2.4.5. Current density ............................... 71
2.5. Polarization phenomena ............................ 72
2.5.1. Activation polarization ........................... 72
2.5.2. Ohmic polarization ............................. 74
2.5.3. Concentration polarization ........................ 75
2.5.4. Real cell voltage .............................. 77
2.5.5. Polarization curve .............................. 77
2.5.6. Optimum operating range ......................... 79
2.6. Modeling of charge transfer .......................... 79
2.7. Overview of analytical models ........................ 79
2.7.1. Simple analytical models ......................... 80
2.7.2. Complex analytical models ........................ 80
2.8. Empirical models ................................ 80
2.9. Current transport and charge conservation ................. 81
2.10. Conclusion ................................... 82

Chapter 3. Mass Transfer Phenomena ..................... 85
3.1. Introduction .................................... 85
3.2. Flow of matter .................................. 85
3.3. Mass transfer by convection .......................... 90
3.4. Mass transfer in porous diffusers ....................... 92
3.4.1. Conservation of mass ........................... 92
3.4.2. The conservation of species ........................ 93
3.4.3. Some parametric laws ........................... 98
3.5. Mass transfer in the catalyst layers (electrodes) ............. 101
3.5.1. Low current model (Butler–Volmer) ................. 102
3.5.2. Agglomerate model with strong current ................ 103