Introduction to Hydrogen as an Energy Source

What is hydrogen gas (H₂)? 

In its non-naturally occurring gaseous form, hydrogen exists as H2, which has the highest specific energy (expressed in kilowatt hours per kilogram) of all combustible fuels (approximately three times that of gasoline). 

What are the drawbacks of hydrogen? 

1. Hydrogen is the lightest of all gases, making it extremely buoyant and diffusive. This presents two main challenges, namely poor energy density and difficulty to compress and store. 

2. Hydrogen is able to insert itself into the crystalline structures of metals commonly used for storage vessels and pipework, leading to hydrogen embrittlement which causes degradation in the mechanical strength of these metals.

Between embrittlement and its propensity to leak, the latter presents the more practical day-to-day challenge in designing robust hydrogen-fuelled systems. 

What are the practical applications for hydrogen? 

Hydrogen is already a significant industrial chemical, consumed by the oil and gas industry in processes to remove sulphur from natural gas and refined petroleum products, in the production of ammonia for fertilisers and refrigeration, for refining metals, and the production of hydrogenated vegetable oils for human consumption among many others. 

What is the current global demand for hydrogen? 

Global demand for hydrogen was approximately 90 million tons in 2020, with around 95% of that amount used in petroleum refining and chemical production. Nearly all of that demand was filled by fossil fuel-derived hydrogen, and was responsible for the emission of 900 million tons of carbon dioxide. 

What is the hydrogen colour spectrum?

• Black hydrogen. The use of black coal to produce hydrogen.
• Brown hydrogen. The use of lignite (brown coal) to produce hydrogen.
• Blue hydrogen. The use of natural gas and heated water to produce hydrogen. This method uses carbon capture and storage (CCS) to store the carbon produced.
• Grey hydrogen. The use of natural gas and heated water to produce hydrogen. Unlike blue hydrogen, this method does not store the carbon produced.
• Green hydrogen. The use of renewable energy to produce hydrogen. This method does not create carbon dioxide.
• Pink hydrogen. The use of nuclear energy to produce hydrogen. 

What is the difference between fuel cells and electrolysers? 

Fuel cells take hydrogen and oxygen, and make electricity. Electrolysers do the reverse, making hydrogen and oxygen from electricity. 

What is hydrogen’s potential as a transport fuel? 

The hydrogen user experience is similar to that of petrol and diesel today. You drive up to the pump, or dispenser, open the filling door of your vehicle, and bring the nozzle up to the filler port. Although this sounds futuristic, hydrogen powered buses have been used in routes across the UK and Europe. 

Road transport in the EU consumed 270 million tons of oil equivalent energy in 2019 which approximates to about 3140 terawatt hours. By comparison, the lower heating value of 90 million tons of hydrogen (the total global demand in 2020), approximates to around 3000 terawatt hours. There are potential future opportunities in developing dual-purpose hydrogen production where surpluses in supply to industrial customers could be diverted to transport.