Production and colour of hydrogen

From grey to green: How the production of hydrogen works

The potential ways of using hydrogen in the various sectors in order to decarbonise them is an important aspect of ensuring that we achieve climate neutrality – but the means of producing hydrogen is also critically important.


The different colours used to describe hydrogen provide information about how climate-friendly the substance is and usually also indicate the method used to produce it. In order to reach the Paris Climate Agreement targets, we should be aiming to only use green hydrogen. This is generally produced by electrolysis using electricity from renewable sources, such as wind and solar power. This is the only way to achieve the required reductions in emissions.

Grey hydrogen

Current demand for hydrogen is predominantly met by steam reforming. Under this process, fossil fuels such as natural gas or crude oil and steam react to produce syngas, a mixture of hydrogen and carbon monoxide, producing the greenhouse gas carbon dioxide as a by-product. The hydrogen obtained in this way is also known as “grey” hydrogen. In view of the carbon dioxide emissions produced, it cannot be described as a climate-neutral fuel, even if no CO2 emissions occur when it is subsequently used. We should also bear in mind that this process is frequently associated with considerable emissions in the upstream supply chain due to the transport and production of natural gas.

Blue hydrogen

Like “grey” hydrogen, “blue” hydrogen is mainly produced using natural gas. The CO2 that arises, however, is separated out and either used in other branches of industry or stored underground (Carbon Capture and Storage: CCS, Carbon Capture and Utilisation: CCU). In this way, no carbon emissions occur in the production process itself. Provided that the energy needed for the steam reforming process is supplied from renewable sources, this represents a more climate-friendly option than grey hydrogen. The process chain for blue hydrogen still gives rise to significant greenhouse gas emissions however, particularly in terms of the production and supply of natural gas.

Turquoise hydrogen

This “colour” hydrogen has recently been the focus of intense debate in specialist circles: what is known as “turquoise” hydrogen is produced using methane pyrolysis (simply put, pyrolysis means heating without oxygen), producing solid carbon instead of carbon dioxide, which, in contrast to CO2, can be stored easily or even utilised in many applications. This process is not yet viable on a large industrial scale, however. Although it avoids the obstacles associated with CCU/CCS processes (low acceptance, storage risks, additional energy demand, etc.), it does not overcome the familiar problem of blue hydrogen – greenhouse gas emissions that are extremely harmful to the climate being released in the upstream chain to produce natural gas. The possibility of using biomethane produced from biogas, which could replace fossil resources to a limited extent, is currently being considered.

Green hydrogen

“Green” hydrogen is obtained from water using electrolysis powered by electricity from renewable sources. An electric current is applied to water, breaking it down into its component elements of oxygen and hydrogen. The electrical charge splits the chemical compound. Under this process, oxygen is produced at the positively charged electrode (anode) and hydrogen at the negatively charged electrode (cathode). In order to avoid mixing the two products, the two electrode chambers are separated by a membrane thatis permeable to charge carriers.


So-called alkaline electrolysis has been an established industrial procedure for decades. Alternative electrolysis methods, such as PEM electrolysis and high temperature electrolysis (SOEL), are already being scaled up or tested for use on an industrial scale (for instance PEM electrolysis in the REFHYNE project at the Shell Energy and Chemicals Park).

The choice of location for producing hydrogen depends on renewable energy sources

The origin of the electricity used is crucial in terms of producing hydrogen by electrolysis in a way that is greenhouse gas-neutral. The enormous demand for electricity from renewable sources will determine the choice of location for electrolysers in the future. It is therefore likely that green hydrogen will be produced predominantly in the vicinity of renewable power plants. The areas in Northern Germany and neighbouring European countries are relevant in this respect, for example, as they offer good conditions for producing power from renewable sources (the Netherlands in particular, but also the UK, Denmark, Spain and Portugal). It can be assumed that a world market for green hydrogen will emerge in the future and that hydrogen will also be imported to Germany from regions further afield with very good production conditions (e.g. from the MENA region and Chile).


Plant construction offers economic opportunities for NRW

The hydrogen economy and the associated plant construction offer North Rhine-Westphalia economic opportunities, sustainable jobs and the prospect of added economic value. Ranging from electrolysers that produce hydrogen using renewable energy, to fuel cells and hydrogen burners that make it possible to use the substance, right up to essential components such as hydrogen compatible pressure tanks, compressors, gas turbines and pipelines: new markets and export opportunities are developing in this field for the economy of NRW.

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