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Storage and Utilisation

How can hydrogen be stored?

Theoretically hydrogen can be stored as a liquid, gas or solid. Liquid hydrogen is typically kept at temperatures bordering on -253°C in highly insulated tanks. Hydrogen can also be stored as a compressed gas underground at up to 150bar, and as a solid within the chemical structure of hydrides or porous carbon-based materials.


Gaseous hydrogen storage is the simplest route and is extensively employed around the world for both large and small scale storage. The two main methods currently used for large-scale hydrogen gas production are: cavities created by dissociation in salt formations and deep aquifer layers[2]. Some examples of gaseous hydrogen caverns are given below:

  • Teesside, UK, by Sabic Petrochemicals (3 × 70,000 m3 storage capacity)
  • Clemens Dome, lake Jackson, Texas, U.S., by ConocoPhillips (580,000 m3)
  • Moss Bluff salt dome, Liberty County, Texas, U.S., by Praxair (566,000 m3 maximum permitted capacity)

At the other end of the spectrum, small scale hydrogen storage, such as that required on board road vehicles, is commonly in conventional steel cylinders or special composite material tanks capable of holding the gas at 700bar. There are, however, a few drawbacks associated with the different methods for storing hydrogen at this very high pressure. These include:

  • The high cost of materials required to store hydrogen as a gas at 700bar
  • The high amount of energy required to liquefy hydrogen and the need to minimise evaporation of the liquid
  • The challenge to develop a solid hydrogen store lightweight enough to achieve at least 7 wt% of hydrogen[3].

Distributing hydrogen is another key element to its use. Pipeline transportation is traditionally done within large petrochemical complexes when the hydrogen produced is to be used directly. Long distance hydrogen pipelines do exist, with the longest in Europe being between France and Belgium at 400km[4]. At present, the UK only has about 25m of hydrogen pipeline.

How can hydrogen be utilised?

Hydrogen is a raw material used extensively in industry, particularly in the chemical industry (for ammonia and methanol synthesis) and the refining industry (for hydro-treatments by hydrogenation of unsaturated hydrocarbons and hydro-sulphuration). Other areas include the aerospace industry, food and semiconductor industries.

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utilisation


UK hydrogen consumption by industry sector in 1996[5] and the global hydrogen consumers by industry in 2007[6]
Hydrogen can be used to provide electricity and heat through its use in fuel cells or through combustion in an internal combustion engine (ICE). Fuel cells generate electricity from an electrochemical reaction where oxygen and hydrogen combine to form water. The electricity produced from the reaction can be used in many portable, stationary and transport applications, and the heat produced as a by-product can also be used for heating and cooling purposes[7].

How does a fuel cell work?

A fuel cell unit consists of a stack - a unit composed of a number of individual cells. Each cell within the stack has two electrodes - one positive and one negative - called the cathode and the anode. The reactions that produce electricity take place at the electrodes.

Every fuel cell also has a solid or liquid electrolyte (facilitates movement of ions from one electrode to another) and a catalyst (accelerates the reactions at the electrodes). The electrolyte's role is key as it must only permit the appropriate ions to pass between the electrodes. If free electrons or other substances travel through the electrolyte, the chemical reaction will be disrupted.


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How the hydrogen fuel cell works


As a transport fuel, hydrogen can be used in hydrogen internal combustion engine vehicles (HICEVs) and hydrogen fuel cell electric vehicles (HFCEVs). Hydrogen's use in internal combustion engines is much the same as the petrol-powered engines we have in our cars today, but with slight modifications. However, hydrogen fuel cells in vehicles are likely to be the more popular utilization technology for transport mainly because the fuel cells generate electricity on-board the vehicle.
Most major car manufacturers have fuel cell electric vehicles prototypes in development, and others already lease out vehicles to end-users in different parts of the world e.g. Honda, Toyota, Hyundai, Ford, Chrysler, Mercedes-Benz, Nissan, General Motors.

Current Hydrogen Activities

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