New study reveals critical carbon footprint of Japan’s future hydrogen imports

Japan’s ambitious plan to import vast quantities of low-carbon hydrogen could still exceed its own climate targets unless the entire supply chain—from overseas production to final delivery—is decarbonized, according to a peer-reviewed study published today in ENGINEERING Energy (formerly Frontiers in Energy).

Researchers at Japan’s National Institute of Advanced Industrial Science and Technology (AIST) modeled the life-cycle CO₂ emissions of hydrogen produced in Australia and the United Arab Emirates (UAE) and shipped to Japan via three emerging carriers: liquid hydrogen (LH), methylcyclohexane (MCH), and ammonia (NH₃). The findings show that electricity and heat sources used in liquefaction, dehydrogenation, and Haber-Bosch synthesis dominate the carbon footprint—often pushing total emissions well above Japan’s current 3.4 kg-CO₂e per kg-H₂ threshold for “low-carbon” hydrogen.

Key findings at a glance

• Liquid hydrogen pathways emit 4.5–13 kg-CO₂e kg⁻¹ when grid electricity is used for liquefaction; switching to 100 % renewable power cuts this to 0.75 kg-CO₂e kg⁻¹.
• MCH and NH₃ carriers emit 5–15 kg-CO₂e kg⁻¹ largely because dehydrogenation in Japan currently relies on city-gas combustion. Replacing that heat with renewable or carbon-free sources could reduce emissions by 60–80 %.
• Coal-gasification with CCS in Australia exceeds the 3.4 kg-CO₂e target if grid electricity is used, but drops below 1.2 kg-CO₂e kg⁻¹ when renewable electricity powers the plant and CCS operations.

“Japan’s hydrogen strategy rightly focuses on securing affordable, abundant supplies overseas,” said lead author Dr. Yuki Kudoh. “Our numbers show that the same attention must now be paid to how that hydrogen is liquefied, converted, and reconverted—otherwise the climate benefits evaporate.”

Policy implications The study recommends that Japan’s new Hydrogen Society Promotion Act and the forthcoming well-to-delivery gate emissions standard explicitly account for:

1. Renewable electricity for liquefaction and synthesis.
2. Low-carbon heat for MCH and NH₃ dehydrogenation.
3. Transparent certification that follows the IPHE and ISO/TS 19870 methodologies.

“Without these measures, imported hydrogen risks becoming a ‘hidden carbon loophole’ rather than a decarbonization tool,” Kudoh cautioned.

Next steps The AIST team is now expanding the analysis to include capital-goods emissions (solar farms, electrolyzers, tankers) and will release a companion cost–benefit study in 2026 to guide public and private investment decisions.

JOURNAL: ENGINEERING Energy (formerly Frontiers in Energy)

Read the full article for free: https://rdcu.be/feL7U

Cite this article

Kudoh, Y., Ozawa, A. Life cycle CO2 emissions of international hydrogen supply chains envisaged in Japan. Front. Energy 19, 1045–1053 (2025). https://doi.org/10.1007/s11708-025-0979-3