I've never been enamored with the concept of using diatomic hydrogen as a fuel. It can't be liquefied at temperatures and pressure that are practical, so it must be stored as a very high pressure gas. That limits the quantity that can be stored, and means the container must be very sturdy, and should be periodically tested.
Heavier molecules are both more energy dense, and able to be compressed to a liquid.
Consider a 20lb BBQ grill propane cylinder. Using propane, liquefied, there's 456 MJ of energy available. Equal to 3.5 gallons of gasoline. The volume needed for LPG and propane are roughly similar, propane takes up about 30% more room for the same energy. The propane pressure correlates to temperature,
here's a chart. Propane cylinders are designed to have a maximum allowable working pressure of 300PSI. Not crazy high, so the metal doesn't have to be all that thick.
If we filled that same cylinder with H2 at 300PSI, how much energy would that be? By ideal gas law, we could cram about 375L of hydrogen in at STP. That's 33.7 grams. Each gram burns completely to water producing 141kJ of heat. So, 4.7MJ. Equal to 12 tablespoons of gallon in energy content. Not so good.
The solution is to raise the pressure, which is how non-condensable gasses are currently shipped and used. But, the container has to be insanely more sturdy, which adds weight, and compression losses.
Lets ask the question:
Using currently accepted, safe, industry standard high pressure gas cylinders, what would we be looking at to store say the energy content you'd get in 10 gallons of gasoline?A gallon of gasoline has 121MJ in in, so we want 1,210MJ. A Size 300 High Pressure Steel Cylinder has in internal volume of 49 liters, and can be pressurized to 2400 PSI. It weights 132lbs. At that pressure, it holds about 8000l of gas. 719g, or 101MJ.
Answer, we need 12 cylinders. That's over 1,500lb for your hydrogen "gas tank".
Here's the other thing that should cause your eyebrow to raise about hydrogen fuel... The explosive limits for gasoline are between 1.2% to 7.1%. In concentrations outside of that range, gasoline isn't explosive. Propane is between 2.1% and 9.5%. Hydrogen? 4%
to 75%.
