Hydrogen Fuel Cells Will Never Be Practical For Cars

The thought of filling up your car at the local hydrogen pump may sound appealing on the surface.  After all, hydrogen is non-toxic, and cars running off the gas would produce no carbon dioxide emissions.  Upon closer inspection, though, the superficial benefits of hydrogen as an automotive fuel are little more than wishful thinking unless major breakthroughs can be made in how the gas is stored.

Simply put, native H2 gas is a horrible fuel for automobiles, regardless of whether it is used in internal combustion engines or in electric fuel cells.  There are many reasons for this, most notably that hydrogen has a very low energy density by volume and poses extreme dangers of explosion.

H2 has a high energy density by weight or mass, but horrible energy density by volume.  Even in its densest, liquid form, pure hydrogen contains only about 1/4 the energy present in the same volume of gasoline.  In fact, gasoline actually contains 64% more hydrogen atoms by volume than is present in liquid hydrogen.  The bonding structure of hydrocarbons allows them to create more compact, energy-dense molecules than the light, "fluffy" molecules of H2.

Hydrogen being the smallest of all the elements, it is very difficult to make a container "hydrogen-tight".  While it is easy to seal a container well enough to hold water, the tiny molecules of H2 will literally pass through many materials.  Containment vessels designed for hydrogen must have thick, dense walls to prevent leakage, and sealing connections to and from the storage tank is difficult.

Liquid hydrogen, like that used in the space shuttle for the main thrusters, is completely impractical as a replacement for gaseous hydrogen in automotive applications.  To remain liquid, hydrogen must be stored at high pressure and extremely low temperatures (–252.882 °C or -423.188 °F).  Of course, no passenger vehicle could reasonably handle maintaining these conditions.

Pressurized H2 gas (as is currently used in most prototype fuel cell vehicles) is also very problematic.  To carry any reasonable amount of hydrogen on-board, the gas must be compressed to incredible pressures.  Even with the gas pressurized to 5,000-10,000 psi, a vehicle would need a tank many times larger and heavier than a conventional fuel tank.  In an accident, damage to a tank under such extreme pressure could potentially cause a catastrophic physical explosion of the tank. 

Even if the tank itself does not rupture and explode from the extreme pressures within, connecting lines are almost certain to rupture during a significant accident.  Hydrogen is extremely flammable, and will ignite easily when mixed with air.  Because it burns in the ultraviolet spectrum, its flames are very difficult to detect.  Accident victims and rescue workers could easily place themselves in the path of invisible jets of flame coming from leaking hydrogen lines, unable to see the danger.

One possibility for developing the safe transport and use of hydrogen in fuel cell vehicles is to bond the hydrogen atoms to other chemicals that can serve as carriers, then separating it within the system right before feeding it into the fuel cells.  This kind of process adds significantly to the complexity of a fuel system, however, and some efficiency will inevitably be lost in the process.

So, until science makes a huge leap forward in technology, don't get your hopes up about driving around in a hydrogen fuel cell car anytime soon.