Suitable alternatives are already available. One such alternative is ammonia. Ammonia can be used as an easy and safe fuel by using a catalyst that splits up the ammonia into water and hydrogen (which can then be burned).
What makes ammonia such a good alternative you might say? There are a few reasons.
1. It can be easily manufactured, it only takes water and energy to create it.
2. Emissions from an ammonia car are only water vapor and nitrogen.
3. Energy density is good (half that of gasoline).
4. Conversion kits are available for about $1000
5. Cars can be easily made dual-fuel, so one could still burn gasoline when in necessary
Ammonia cars don't produce dangerous emissions (you could run it in your living room without any problems), they have good mileage given the high energy density, allow fast refueling and still allow you to take the car to places where you don't have ammonia available - so it doesn't limit you in any way. It's cheap to convert a car - so it's viable to people besides Elon Musk.
In addition, if ammonia cars are taken up, we could use the fuel manufacturing for buffering renewable energy. Say the wind is blowing very hard or the sun is shining brightly we could up the manufacture to absorb this energy instead of offloading it for sometimes negative amounts.