Hydrogen is produced in many colors of the rainbow according to the feedstock and process used in its manufacture. The implications of these multihued choices for contributing to climate change were the focus of a comparative lifecycle analysis conducted by researchers from LUT University in Finland.

Grey hydrogen is produced by steam methane reforming (SMR), a high-temperature process in which steam reacts with a hydrocarbon to produce hydrogen with carbon dioxide (CO2) as a by-product. Similarly, blue hydrogen is produced by SMR in a process that also incorporates carbon capture and storage to reduce emissions. Thermal decomposition of methane yields hydrogen and solid carbon to form turquoise hydrogen.

Grey, blue and turquoise hydrogen are produced using natural gas while green hydrogen is derived from water and renewable electricity sources. The life cycle assessment is based on sourcing natural gas feedstock from the pipeline route connected to Russia and through the liquefied natural gas (LNG) route from the U.S.

The highest emissions were associated with grey hydrogen, with the LNG route showing higher emissions of 13.9 kg of CO2 equivalent (CO2 eq)/kg hydrogen compared to the pipeline route, which generates 12.3 kg CO2 eq/kg hydrogen. The implementation of carbon capture technology reduced the impact of blue hydrogen to 7.6 kg CO2 eq/kg hydrogen for the pipeline route and 9.3 kg CO2 eq/kg hydrogen for the LNG route.

The lowest emissions were determined for green hydrogen produced using wind energy — 0.6 kg CO2 eq/kg hydrogen. Use of solar energy resulted in higher emissions of 2.5 kg CO2 eq/kg hydrogen.

As reported in Green Chemistry, the climate change impact showed a 12% to 25% increase for a 20-year horizon global warming potential compared to a 100-year global warming potential for grey, blue and turquoise hydrogen.

To contact the author of this article, email shimmelstein@globalspec.com