To address your question about PEM fuel cell models, you can utilize Simscape, a MATLAB tool specifically designed for modelling and simulating physical systems, rather than Simulink alone.
You can find detailed information through this example on how to model a PEM fuel cell system using Simscape on the documentation page here: https://www.mathworks.com/help/simscape/ug/pem-fuel-cell-system.html
I hope this information helps you get started with modelling PEM fuel cells using Simscape.