Introduction
The emission of greenhouse gases is a major cause of global warming and climate change, primarily due to the continuous burning of fossil fuels. [1] In line with the current European target of reducing net greenhouse gas emissions by at least 55% by 2030, EU nations are developing new laws to meet this goal and achieve climate-neutrality by 2050. [2] Promoting the development of renewable energy sources is one of the key solutions to this problem.
Reinforced by numerous studies, hydrogen technology has emerged as a clean and reliable alternative to traditional fossil fuels. [1] As highlighted in our Basics of Hydrogen blog, hydrogen is the most abundant element in the universe, but it is not readily available in large quantities on Earth. Consequently, various methods, as explained below, are required to produce hydrogen.
Production methods from renewable sources
Hydrogen can be produced through various processes, utilizing either fossil fuels or renewable energy sources. As we saw in this carousel, hydrogen is categorized by its production method and the associated emissions generated during the process, with green, blue and black hydrogen being the most popular categories.
While fossil fuel-based methods remain common, they are associated with significant greenhouse gas emissions. This article explores the renewable pathways, which are broadly categorized into biomass processes and water splitting technologies.
The biomass path
Biomass processes convert organic materials into hydrogen and hydrogen-rich gases. The main methods in this category include biological and thermochemical processes.
Biological processes
Research on biological hydrogen production has grown due to increased interest in sustainability and waste reduction, utilizing energy-efficient methods at normal temperatures and pressures. Key processes include bio-photolysis, photo fermentation, dark fermentation, and multi-stage fermentation, all of which use renewable resources and waste materials.
- Bio-photolysis: This process mimics photosynthesis to generate hydrogen gas. Algae, equipped with unique enzymes, can split water into hydrogen and oxygen when exposed to light.
- Dark fermentation: In this process, bacteria that thrive in the absence of oxygen break down carbohydrate-rich materials to produce hydrogen.
- Photo-fermentation: Photosynthetic bacteria use solar energy and organic acids in low-nitrogen conditions to produce hydrogen and carbon dioxide. [1]
Thermochemical processes
Thermochemical processes transform biomass into hydrogen and hydrogen-rich gases, offering ways to reduce greenhouse gas emissions. The main methods are:
- Pyrolysis: This process involves heating biomass to temperatures of 650–800 K under low pressure and in the absence of oxygen. The result is the production of liquid oils, solid charcoal, and gases.
- Gasification: This method converts biomass into syngas (a mixture of hydrogen, carbon monoxide, and carbon dioxide) using air, oxygen, or steam at high temperatures (500 to 1,400 °C) and pressures (up to 33 bar). [1]
- Combustion: Burning biomass materials like wood and agricultural residues in the presence of air at 800–1,000°C releases energy and produces hydrogen, but also emits pollutants such as CO₂, SOₓ, and NOₓ. [3]
The water splitting path
These types of processes work by splitting water into hydrogen and oxygen. To do this, two reactions are needed – one for each element, right now some catalysts are being developed to increase the efficiency of these reactions. [4]
- Electrolysis: Electrolysis consists in using electricity to split water molecules into hydrogen and oxygen. Recently, this method has been increasingly powered by the upswing of renewable energy sources. This is the most widely used technology for producing green hydrogen because it is currently the most efficient and has the scalability to meet the growing demand for green hydrogen. [5]
- Thermolysis: In thermolysis, water molecules break down into hydrogen and oxygen. For example, at 2,200°C, about 3% of water molecules split into different forms of hydrogen and oxygen, like H, H2, O, O2, and OH. At a very high temperature of 3,000°C, more than half of the water molecules break down, while at room temperature, only one in 100 trillion molecules splits due to heat.
- Photolysis: Photolytic or direct solar water splitting processes, though still in their early stages, show promising long-term potential for sustainable hydrogen production. These processes utilize light to separate water into hydrogen and oxygen, thus achieving hydrogen production with minimal environmental impact.
It is important to note that approximately 40% of planned low-emission hydrogen production projects are located in regions with limited water resources. Therefore, using various water sources and managing them sustainably will be crucial for the success of these projects. [6]
Producing green hydrogen requires methods that rely on renewable energy sources and sustainable feedstocks, avoiding fossil fuel inputs and minimizing emissions. While these methods vary in maturity and efficiency, ongoing advancements are essential to improve affordability, scalability, and effectiveness, making sustainable hydrogen more accessible.
Methodology in HYIELD
HYIELD employs a thermochemical approach to convert biogenic waste into high purity green hydrogen. Through a multi-stage gasification process, HYIELD produces green hydrogen without emitting any greenhouse gases and also repurposes waste, providing value from the waste generated by various populations.
This solution is expected to achieve a Levelized Cost of Hydrogen of 2.19€/kg at industrial scale (20,000t/year waste treated), significantly lower than current electrolyser pathways (>5.5€/kg).
Conclusion
Hydrogen technology is pivotal in reducing greenhouse gas emissions and achieving the EU’s climate neutrality goals. HYIELD’s innovative renewable hydrogen production methods, which integrate renewable energy and utilize waste, exemplify sustainable approaches essential for a low-carbon future. Continued investment and development in these technologies are crucial to drive progress toward a resilient and sustainable energy landscape.
Join us in supporting clean energy initiatives and stay informed about the latest advancements in hydrogen technology with HYIELD.
References
[1] https://www.sciencedirect.com/science/article/pii/S1364032116305366
[2] https://www.consilium.europa.eu/en/policies/green-deal/fit-for-55/
[3] https://onlinelibrary.wiley.com/doi/full/10.1002/aesr.202300273
[4] Scientists Have Developed The Most Efficient Water-Splitting Catalyst Yet: ScienceAlert
[5] Green hydrogen production pathways for sustainable future with net zero emissions – ScienceDirect
Writer: Zoe Cardell
Editorial: Lucía Salinas
November, 2024
