Exploring the spectrum: an environmental examination of hydrogen's diverse colors

Abstract

Hydrogen is emerging as an immense source of energy having the potential to at least partly replace fossil fuels. It is an abundant element on earth, but does not mainly exist in free form. Hydrogen can be produced through different technologies and feedstocks, and based on these, it can be categorized into colors with different environmental impacts. This work aimed to review the environmental impacts of the production of gray (from natural gas without carbon capture and storage), brown (from coal gasification), blue (from fossil fuels with carbon capture and storage), green (from renewable energy or biological process), and turquoise (pyrolysis of natural gas) hydrogen and to identify sustainable hydrogen production pathways that minimize environmental impacts. Global warming, acidification, eutrophication, and resource depletion were considered as indicators to assess the environmental impacts. The results showed that brown hydrogen produced via coal gasification had the highest global warming, acidification, and resource depletion impacts among all the options considered. On the other hand, green hydrogen from electrolysis through wind energy had the lowest environmental impacts. However, adopting these hydrogen colors presents different challenges and opportunities. Success depends on effective policy frameworks, international cooperation, and technological readiness to ensure positive contributions to global sustainability goals.