Storage Potential of Green Hydrogen

Green hydrogen can be stored and transported in several ways, including compressed hydrogen gas, liquid hydrogen, methanol, and ammonia. Liquid ammonia has a higher capacity for hydrogen storage by volume compared to liquid hydrogen, with a capacity of 121 kg H2/m3 for ammonia compared to 70.8 kg H2/ for liquid hydrogen. At room temperature, ammonia can be stored at a relatively low pressure (0.99 MPa), which is significantly lower than the pressure required for liquid hydrogen storage. However, ammonia has a lower energy density than hydrogen (18.6 MJ/kg compared to 142.8 MJ/kg for hydrogen gas at standard temperature and pressure) and a higher mass density (600 kg/m3 compared to 70.8 kg/m3 for liquid hydrogen), which can make it more challenging to store and transport. Methanol is another potential option for hydrogen storage, but it has a lower energy density compared to ammonia (20.1 MJ/kg), and utilization release CO2, which can be a concern from an environmental perspective. The decomposition of ammonia to release hydrogen requires a relatively large amount of energy (30.6 kJ/mol H2), while the regasification of liquid hydrogen only requires a small amount of energy (0.907 kJ/mol H2). This can make the utilization of ammonia as a hydrogen storage and transportation medium less energy efficient.