Green and Gray Hydrogen Production Technologies: What You Need to Know

Hydrogen has been touted as a potential game-changer in the transition to a low-carbon economy. It is a clean, versatile energy carrier that can be used in a variety of applications, from transportation to industrial processes. However, the production of hydrogen is currently dominated by gray hydrogen, which is produced from fossil fuels and emits significant amounts of greenhouse gases. Green hydrogen, produced from renewable sources, is considered a more sustainable alternative but is still in the early stages of development. In this article, we’ll take a closer look at the two main hydrogen production technologies: green and gray hydrogen.

Gray Hydrogen Production Technologies

Gasification and Steam Reforming are the two main technologies used to produce gray hydrogen. Gasification involves the use of coal or biomass to create a mixture of carbon monoxide and hydrogen, known as syngas, which is then refined through additional steam and catalysts to yield pure hydrogen. Steam reforming is the process of heating natural gas or biogas to produce syngas, which is then further refined to yield pure hydrogen. Both of these processes emit significant amounts of greenhouse gases such as carbon dioxide and carbon monoxide.

Green Hydrogen Production Technologies

Electrolysis is the most common technology used to produce green hydrogen. It involves using an electric current to split water molecules into hydrogen and oxygen. The most mature electrolysis technology is proton-exchange membrane (PEM) electrolysis, which uses a membrane to separate the hydrogen and oxygen. Alkaline electrolysis is another type of electrolysis that uses an alkaline solution of sodium or potassium hydroxide to generate hydrogen in the presence of electricity. Solid oxide electrolysis, still in the research and development phase, uses a solid ceramic material as the electrolyte.

Other green hydrogen production technologies include photoelectrochemical splitting, which uses semiconductor materials to harness energy from light to split water molecules, and thermochemical splitting, which uses high temperatures to drive chemical reactions in a closed loop to split water into hydrogen and oxygen.

Storing and Using Hydrogen

Once produced, hydrogen can be stored as a gas, liquid, or on the porous surfaces of nanostructures of certain materials. However, due to hydrogen’s low density, storing it as a gas requires large, pressurized containers or very low temperatures, which can complicate transportation and increase storage costs. Storing hydrogen as a liquid decreases the overall storage volume required but may increase storage costs and decrease efficiency. Finally, hydrogen atoms can be stored within the spaces inside metal or alloy lattices or on the surface of carbon structures, such as carbon nanotubes.

When electricity is needed, hydrogen can either be combusted with oxygen to generate steam or electrochemically combined in fuel cells to produce water and electricity. Combining hydrogen and oxygen in fuel cells generates water and electricity through an electrochemical reaction, the reverse of electrolysis. While some forms of hydrogen production can see efficiencies as high as 80%, the round-trip electrons-to-electrons efficiency of hydrogen energy storage is relatively low, in the 40%–50% range.

Conclusion

Hydrogen is a promising energy carrier that can play a critical role in the transition to a low-carbon economy. However, its production is currently dominated by gray hydrogen, which emits significant amounts of greenhouse gases. Green hydrogen, produced from renewable sources, is still in the early stages of development but has the potential to be a more sustainable alternative. As technology continues to advance, we may see a shift towards more sustainable hydrogen production and usage, helping to reduce greenhouse gas emissions and combat climate change.