Though hydrogen is often presented as a new solution in the developing energy crisis, this should not be taken to mean that hydrogen as a chemical and industrial gas is an any way a novel or poorly understood commodity (or raw material). In fact, hydrogen is used extensively in industry and the way it is produced, stored, transported and applied in different chemical reactions is very well known. Safety aspects are very well understood. Where significant R & D is needed is in trying to find highly efficient ways of making hydrogen by renewable means and then distributing huge quantities of the gas around the world as a consumer rather than industrial product.
In this page, some of the main uses of hydrogen are listed. Note that ammonia production (55%), methanol production (10%) and refinery use (25%) use the greatest fractions of total production and that energy uses at this stage only make up a tiny proportion.
There is no free hydrogen anywhere on earth and all hydrogen must be manufactured. This is done in bulk by splitting methane molecules (natural gas reforming), but the process releases carbon dioxide into the atmosphere. This is referred to as ‘blue hydrogen’ and its use is fully justified as a way of starting a fully green hydrogen economy, a transition fuel. Green hydrogen is made from renewable electricity by electrolysis. In addition, heat can also be used to split water molecules (thermolysis). Bacteria and other biological methods can also be used. Note all lesser methods such as water splitting by direct sunlight and ‘pink hydrogen’, hydrogen made from nuclear power.
In the diagram above, the yellow boxes indicate where the hydrogen molecules reside at each stage of the application. The first set of applications exploit the intrinsic properties of hydrogen and the gas is not changed in the process. For example, hydrogen is excellent for weather balloons at it is more buoyant and easier to obtain than helium. Hydrogen molecules are small and easy to detect, which makes it is easy to find leaks in pipelines using hydrogen. Hydrogen gas has an incredibly high specific heat, more than 10 times that of air, therefore it is a much more effective cooling gas within any closed system.
Nitrogen gas combines with hydrogen at high temperature to form ammonia, a basic building block for all fertilizer production. In the Haber process, the temperature is lowered and the reaction speeded up using an appropriate catalyst.
Many applications of hydrogen involve the gas reacting with oxygen to form water. One example is the production of tungsten metal; hydrogen is used to reduce the oxide. Electrolysis to produce electricity is another example. The electricity produced has many applications. Of course, the gas can be directly burnt for heating or cooking, either on its own mixed into the gas network. Hydrogen is also used as a rocket propellant and the high flame temperature makes it effective for some types of specialist welding.
There are a number of important industrial applications. Hydrogen is used to make hydrochloric acid and methanol, both important chemicals with a variety of applications. In an oil refinery, heavy fractions of crude oil are broken into the more commercially valuable shorter carbon chain alkanes by breaking long chains at a carbon-carbon bond and tying up the ends with hydrogen. Something similar happens in the manufacture of margarine. Hydrogen is supplied to break many of the double bonds in unsaturated fats or oils to produce an saturated product with a higher melting point (hydrogenation).
One speculative application is the combination of hydrogen nuclei by fusion to produce helium. This is potentially a clean energy source, but hard to do anywhere but inside a star.
The diagram above includes links to mostly academic papers which could act as an entry point for learning more about these processes - the link will open in a new webpage. Note that in some cases you will need your institution credentials to access the papers.
Investigations