I'm assuming that the difficulty and expense of setting up a (what is currently non-existent) hydrogen infrastructure (e.g. fuelling stations) is discussed on your 'challenges' slide as a roadblock to fuel cell vehicles. However, if it is within the scope of your presentation, you could have a slide discussing what such a hydrogen infrastructure would have to include/entail.
I'm also assuming your 'challenges' slide discusses the production of hydgrogen itself, but if it doesn't, then you could have a "Where would the hydrogen come from?" slide that looks at the pros and cons of different production methods. E.g.:
1. electrolysis...clean, but requires electricity, which is not always generated cleanly.
2. extraction from hydrocarbons such as methane (not clean, but commonplace).
In other words, think critically about this technology.
Maybe you could wrap it up with a slide that looks to the future...discussing the potential of this technology, implications of it becoming widespread and envisioning a "hydrogen economy."