Dihydrogen as a Fuel

Hydrogen's Potential as a Fuel

Burning dihydrogen releases a large quantity of heat, and comparing fuels on a mole, mass and volume basis (Table 9.5) shows just how energy-dense it is.

Table 9.5 — Energy Released by Combustion of Various Fuels

On a mass basis, dihydrogen releases roughly three times as much energy as petrol, and its combustion produces far fewer pollutants — essentially only oxides of nitrogen, arising from atmospheric $N_2$ mixed in with the hydrogen. Even this can be minimised by injecting a little water into the combustion chamber, which lowers the peak temperature enough to suppress the $N_2$–$O_2$ reaction.

Practical obstacles: what holds dihydrogen back as a mainstream fuel is largely the challenge of storing and transporting it. A cylinder of compressed dihydrogen weighs roughly 30 times as much as a petrol tank storing the same amount of usable energy. Liquefying it requires cooling to 20 K, which demands expensive, well-insulated tanks. Metal-alloy storage systems — $NaNi_5$, $Ti$–$TiH_2$, $Mg$–$MgH_2$ — are used for smaller-scale storage instead. …