Why does the low energy density of hydrogen create challenges for fuel cell vehicles?
The proton exchange membrane is one of the most advanced fuel cell designs. Hydrogen gas under pressure is forced through a catalyst, typically made of platinum, on the anode (negative) side of the fuel cell. At this catalyst, electrons are stripped from the hydrogen atoms and carried by an external electric circuit to the cathode (positive) side. The positively charged hydrogen ions (protons) then pass through the proton exchange membrane to the catalyst on the cathode side, where they react with oxygen and the electrons from the electric circuit to form water vapour (H2O) and heat. The electric circuit is used to do work, such as power a motor.
The relatively low energy density of hydrogen presents a significant challenge for fuel cell vehicles because it necessitates larger storage systems to achieve a driving range comparable to that of conventional vehicles.
In the context of automotive design, energy density is a critical factor for vehicle utility. When a fuel has a lower energy density, a greater volume of it is required to provide the same amount of energy as a more dense fuel. Consequently, to maintain an equivalent driving range, fuel cell vehicles must be equipped with larger fuel storage containers, which can compromise the vehicle's cargo capacity and overall design efficiency.12
While hydrogen fuel cell technology is functional and offers high efficiency in converting chemical energy into electricity, these storage requirements—alongside concerns regarding the cost of platinum catalysts and the handling of hydrogen—have hindered the technology's ability to become fully commercially competitive with traditional internal-combustion systems.13