5. To explain how the hydrogen protons migrate through the PEM with the help of water molecules, at least three models have been presented, such as Grotthuss hopping model, Vehicle diffusion model, and Direct transport model. (a) What are the details of these three models. (b) Are there any other models proposed which are available in the literature? 5. To explain how the hydrogen protons migrate through the PEM with the help of water molecules, at least three models have been presented, such as Grotthuss hopping model, Vehicle diffusion model, and Direct transport model. (a) What are the details of these three models. (b) Are there any other models proposed which are available in the literature