Production

There are several ways to produce hydrogen.

These include from natural gas, coal, biomass and water. However, nearly all of the hydrogen currently produced comes from fossil fuels with high associated carbon emissions. In 2021, the total global production of hydrogen was 94 million tonnes. Of this, 62% came from natural gas, 19% came from coal and 18% was produced as a by-product from refineries.

It is also possible to produce hydrogen from renewable, low-carbon sources or reduce the carbon emissions by other methods, such as carbon capture, utilisation and storage (CCUS). In 2021, however, these forms of production only accounted for 0.04% (35,000 tonnes) and 0.7% (1 million tonnes) respectively¹.

^{1 Global Hydrogen Review 2022 (IEA)}

Steam Methane Reforming

Currently, the most common method for hydrogen production is steam methane reforming (SMR). In this process, methane (CH₄), which is the main component of natural gas, is reacted with steam (H₂O) to produce hydrogen (H₂) and carbon monoxide (CO).

The carbon monoxide is then further reacted with steam to produce hydrogen and carbon dioxide (CO₂). The SMR process occurs in a reactor at high temperatures (around 700 – 1000 °C) and pressures (around 3 – 25 bar) and in the presence of a catalyst (such as the metal nickel). As CO₂ is also produced, SMR is a significant source of greenhouse gas emissions.

Gasification

Gasification is the other main process to produce hydrogen. In this process, carbon-based feedstock materials (such as coal, biomass, or waste materials) are converted into a mixture of gases, including hydrogen, carbon monoxide, and carbon dioxide. Gasification occurs in a reactor at high temperatures (above 700°C) in the presence of a gasifying agent such as air, oxygen, or steam. The produced gas is then purified and the hydrogen separated out and collected. Gasification is less efficient than SMR and, as CO₂ is again produced, is also a source of greenhouse gas emissions.

Electrolysis

Another method for hydrogen production is via the electrolysis of water, whereby an electrical current is used to split water molecules (H₂O) into hydrogen (H₂) and oxygen (O₂). Water is first purified and then fed into an electrolyser, a cell which contains two electrodes (an anode and a cathode) separated by an electrolyte. When an electrical current is applied to the cell, the electrolyte conducts the current and separates the hydrogen and oxygen gases.

There are various types of electrolysers which are distinguished by the type of electrolyte that is used. The two main types are alkaline electrolysers (AE), which use a liquid electrolyte such as potassium hydroxide, and proton exchange membrane (PEM) electrolysers, which use a solid polymer membrane such as Nafion. This method does not produce greenhouse gases directly, however it still requires electrical energy.

The source of this electricity determines whether it is a viable and sustainable option. Only if the electricity is generated from renewable sources (such as wind or solar) is this a clean and sustainable option for hydrogen production.

Your task

Which method of hydrogen production do you see being used most prominently in the future? Share your thoughts below.

References

_{Geoscience Australia (n.d.) What is CCS?, Australian Government}

_{IEA (2022), Global Hydrogen Review 2022, IEA, Paris, License: CC BY 4.0}