I've been wondering why it never really caught on. I have no idea about the science of what it takes to put hydrogen into tanks that can be put into a car's tank. I assume that may have something to do with it, but I'm guessing there's more to it than just that.

Everyone thinks Electrolysis! is the only way to make hydrogen. Nope, and it's not really efficient either.

The most common way to make hydrogen is to steam-reform methane. You mix methane with 1100°C superheated steam and drag it across a nickel catalyst, and you get hydrogen plus carbon monoxide.

Oil refineries can catalytically reform naphtha to hydrogen and gasoline blendstock. I know...OMG you're aiding and abetting the Nasty Old Oil Industry! This also takes a lot of energy to do.

Or you can recover hydrogen as a waste product from the chloralkali process used to make lye and chlorine. There's only one tiny problem with pulling hydrogen out of the chloralkali process: it's more valuable if you use the hydrogen as feedstock for either ammonia or hydrochloric acid.

And then there's good old electrolysis, which is the least efficient way to get to Rock Ridge.

All four processes have the same root problem: extreme energy inefficiency. (There's also the parts about hydrogen being a nasty chemical to work with, starting with the problem of containing the shit - it LOVES to eat holes in your plumbing. But we won't talk about that now.) Hydrogen is so reactive it takes a LOT of power to convince it to leave its comfortable home on the side of a molecule - and it's so light you need to have a lot of it by volume to get any work out of it. If you're going to spend a lot of electricity to push cars down the road, it's more economical to install batteries and use the electricity directly - which is the way most people are going.

TANSTAAFL - There Ain't No Such Thing as a Free Lunch. I don't know why people do not grasp that while hydrogen is plentiful in water that it takes lots of energy to break to bonds with oxygen. And superheating methane must take a lot of energy and then what to do with the CO.

The hard part is, where do you come up with a cheap source of 1100-degree steam?

There has to be some excess power always produced to handle increased loads. This standby power could be producing the hydrogen and quickly switch to the grid when needed.

During high wind periods or mid-day, these produce more electrical power than the grid needs.

...is damn near free and space efficient.

The other factors involving hydrogen can be said in part about other fules

Hydrogen's Gasoline Gallon Equivalent or GGE is one kilogram of hydrogen per gallon of gasoline. That sounds great until you realize how much volume a kilo of hydrogen has.

One mole of any gas at Standard Temperature and Pressure (STP - roughly 15 psi) is 22.4 liters of gas. Since hydrogen gas ALWAYS exists as a diatomic molecule each mole of gas weighs 2 grams. A quick back-of-envelope calculation shows a kilo of H2 at STP is 11,200 liters of gas. At the 700 bar they store hydrogen at, 1 kilo of gas fills 16 liters. (As opposed to the 3.8 liters required to store 1 GGE's worth of Texaco's Finest.) And no, liquifying it isn't going to save you: a kilo of liquid hydrogen is 14.114 liters of product...and if you think the general public needs free access to cryogenic liquid you're crazier than you look.

Now that we know you need a shitload of hydrogen to get any work done with it, how much area do our electrolysis plates need? Well...I have learned through debunking the "run your car on water" children that an optimally designed electrolyzer needs 1/2 watt per square inch of plate surface and produces 10 cm3 of H2 per square inch. To make one GGE's worth of H2 per minute we need 1120 square inches of plate surface and 560 watts of power to drive it. (And we need a compressor but that's a different issue.)

... period of time will make enough for adequate refuls ..

the other stuff you're making my argument for me; the perfect and good should NOT be the enemy of adequate, you're still solving for perfect with the amount of H that YOU state is needed no?

BTW: I am kinda of cheating, I have a friend who works for a major auto comp in the US... they've already done the calcs and the customer studies so I already know what their parameters are and know most who know anything about alternative fuels will solve for something way outside of those parameters for the avg customer needs.

my confession

electric vehicles. It takes roughly 3x the energy to use electricity to produce hydrogen to run a fuel cell to produce electricity to turn a motor as it does to just use electricity to turn a motor.

Do you like expensive cars, with low efficiency, and insanely expensive fuel? If so then you will love hydrogen. If you don't like those things then you will probably not like hydrogen.

This isn't a challenge to what you've said. I'm genuinely asking to be educated.

I have a lot to learn about this.

...so I'm giving up a for b

after a prior hydrogen-powered vehicle. I wonder how the Hindenburg would sell?

Oops!

Although they say the fire was caused by the paint not the hydrogen. Oh the Humanity!

and then looked up the disaster itself on Wikipedia. It occurred to me that for people of the time seeing the newsreel footage must have been like us watching the WTC fall.

Oh, the humanity, indeed.

It was a gloomy, nasty day when the Hindenburg came in for the last time. There was probably electricity in the air. They spent several hours dumping ballast water to try to level out the ship because the tail was riding low. To me, this suggests they tore one of the 16 gas bags in the aft end of the craft and lost a lot of rear lift. Finally they decided to land. Several ropes (it's raining, remember) and a steel cable were lowered to the ground. So...the hull was carrying a charge, they grounded it, a spark happened...boom.

We do not have large scale hydrogen reserves the way we have petroleum or coal reserves. Hydrogen can be easily made from electrolysis of water or by other processes, but it requires energy input. With this in mind, hydrogen should be viewed as an energy storage method and not a new source of energy. Perhaps hydrogen fuel cells will end up supplanting batteries to run electric cars. It can also be used in internal combustion engines designed for it, and water vapor is the only waste product (theoretically at least). As another post implied, there is the flammability hazard that people will have to learn to be okay with. Gasoline is not benign either and is more toxic to humans and the environment.

... Even if it's inefficient

In this case the perfect and good shouldn't be the enemy of adequate

And an electric car is even cheaper than a hybrid. Sure cost will go down, but it might be a while before hydrogen is cheaper than gas.

Hydrogen is horribly inefficient. Round trip efficiency is somewhere close to 30%. So it would require at least 3x as much energy to run a car by hydrogen then simply powering it by electricity (battery electric vehicle like Bolt) directly.