Types of Hydrogen

• Grey Hydrogen:

The generation of hydrogen by using fossil fuels falls under the category of grey hydrogen [1]. Currently, most hydrogen production relies on fossil fuels and doesn't include any carbon dioxide capture [2]. Grey hydrogen is obtained through processes that result in greenhouse gas emissions exceeding 36.4 grams of carbon dioxide per megajoule (MJ) [3,4]. In the present scenario, the primary sources of hydrogen production are primarily based on the use of natural gas and coal [5].

• Blue Hydrogen:

The result of this procedure is known as blue hydrogen, which is derived from the use of fossil fuels combined with processes that involve capturing and storing carbon [6]. Blue hydrogen is typically produced from natural gas, often using steam reforming methods alongside carbon capture and storage. It's worth mentioning that although some blue hydrogen production methods include carbon capture, this approach doesn't completely eliminate carbon emissions [7]. The best expected efficiency for carbon dioxide capture falls in the range of 85% to 95%, which means there may still be a leakage of approximately 5% to 15% of the total carbon emissions [8].

• Green Hydrogen:

Hydrogen obtained from sustainable and renewable sources is categorized as green hydrogen, indicating that it originates from environmentally friendly processes that harness resources such as solar, wind, or hydropower [9]. However, achieving significant cost reductions requires scaling up production, focused research, and comprehensive development initiatives. In line with this trend, there has been a rapid growth in the number and scale of projects recently. With its current technical feasibility and the imminent potential to become a significant player in the global economy, hydrogen produced from renewable sources has the potential to greatly boost renewable energy production [10].

References:

1. Shafiqah, Mohd-Nasir Nor, et al. "Advanced catalysts and effect of operating parameters in ethanol dry reforming for hydrogen generation. A review." Environmental Chemistry Letters 20.3 (2022): 1695-1718.
2. Park, Changeun, et al. "Economic valuation of green hydrogen charging compared to gray hydrogen charging: The case of South Korea." International Journal of Hydrogen Energy 47.32 (2022): 14393-14403.
3. Hirscher, Michael, et al. "Materials for hydrogen-based energy storage–past, recent progress and future outlook." Journal of Alloys and Compounds 827 (2020): 153548.
4. Qureshi, Fazil, et al. "Current trends in hydrogen production, storage and applications in India: A review." Sustainable Energy Technologies and Assessments 53 (2022): 102677.
5. Liu, Tianxia, Kaicheng Yang, and Zhiliang Jin. "Promotion of the excited electron transfer over MoO3@ Cu3P pn heterojunction for photocatalytic hydrogen production under visible light irradiation." Molecular Catalysis 510 (2021): 111691.
6. Noussan, M., et al., The role of green and blue hydrogen in the energy transition—A technological and geopolitical perspective. Sustainability, 2021. 13(1).
7. Antzaras, A.N. and A.A. Lemonidou, Recent advances on materials and processes for intensified production of blue hydrogen. Renewable and Sustainable Energy Reviews, 2022. 155: p. 111917.
8. Bauer, C., et al., On the climate impacts of blue hydrogen production. Sustainable Energy & Fuels, 2022. 6(1): p. 66-75.
9. Su, W., et al., Hydrogen production and heavy metal immobilization using hyperaccumulators in supercritical water gasification. Journal of Hazardous Materials, 2021. 402: p. 123541.
10. Zhao, H., et al., Raw biomass electroreforming coupled to green hydrogen generation. Nature Communications, 2021. 12(1).