Recently hydrogen has gained popularity and is dubbed as the future fuel. This popularity has been fueled by sources such as incentive initiatives, changes in policies due to devastating climate change effects. There are primarily three types of hydrogen production which are named based on their greenhouse gas (GHG) emissions: Grey, Blue, and Green hydrogen.
Grey hydrogen is the mainstream type of hydrogen production that comes from steam methane reforming (SMR) in natural gas . More than 96% of global hydrogen production supplies come from grey hydrogen technology . The primary drawback of grey hydrogen is high CO2 emissions. Then, proponents of blue hydrogen put it forward as an alternative solution in line with green hydrogen to reach a carbon neutrality future. Although blue hydrogen has low CO2 emissions, it releases another GHG, that is methane [1,3].
Blue hydrogen is produced with fossil fuels, such as coal or gas, based on SMR or the gasification of coal. However, during the production process CO2 captures and stores in tanks which is known as carbon capture and storage (CCS) . The total CO2 emissions from blue hydrogen are only 9-12% less than for grey hydrogen. While fugitive methane emissions, as another GHG for blue hydrogen, are higher than for grey hydrogen because of the increased use of natural gas to power the carbon capture system .
According to new joint research by Stanford University and Cornell University, the GHG emissions of blue hydrogen is 20% greater than burning natural gas or coal for heat and some 60% greater than burning diesel oil for heat, based on an assumption that there is indefinite potential to CCS .
Another type of hydrogen production is green hydrogen. In this regard, hydrogen is made from the electrolysis of water. When the electricity demand of this technology supplies from renewable ones, the hydro, wind, or solar power, for instance, is termed as green hydrogen. Since it does not release any GHG, CO2, or fugitive methane, over its production. Therefore, blue hydrogen is not suitable for meeting the goals of carbon neutrality in the future. Hydrogen is generally proposed as the future fuel in order for the energy transition. While it is relatively expensive compared to fossil fuels imposes a hurdle to its massive extension [1,4].
 Howarth, R. W., & Jacobson, M. Z. (2021). How green is blue hydrogen?. Energy Science & Engineering.
 Kotze, R., Brent, A. C., Musango, J., de Kock, I., & Malczynski, L. A. (2021). Investigating the Investments Required to Transition New Zealand’s Heavy-Duty Vehicles to Hydrogen. Energies, 14(6), 1646.
 PV-Magazine, “Blue is not the new green“, August 13, 2021, Emiliano Bellini, available here
 Bartlett, J., & Krupnick, A. (2020). Decarbonized Hydrogen in the US Power and Industrial Sectors: Identifying and Incentivizing Opportunities to Lower Emissions.