If the efficiency of propane production (from atmospheric CO2) can be made even close to that for hydrogen from hydrolysis, then the systems benefits of propane over compressed and/or liquid hydrogen will blow liquid hydrogen out of the water. Hydrogen is an awful fuel. It's only real advantage is the potential for being carbon neutral, and the fact that it doesn't create noxious air pollution when used in a fuel cell. It's claimed advantage of energy density is at best a wash in most applications - higher density by mass, but much lower by volume. But everything to do with hydrogen as a fuel system is hard, complicated, and expensive, compared to the alternatives.