Comparative Life Cycle Greenhouse Gas Analysis of Clean Hydrogen Pathways: Assessing Domestic Production and Overseas Import in South Korea

The development of a Clean Hydrogen Standard based on life-cycle greenhouse gas (GHG) emissions is gaining prominence on the international agenda. Thus, a framework for assessing life-cycle GHG emissions for clean hydrogen pathways is necessary. In this study, the comprehensive datasets and effects of various scenarios encompassing hydrogen production, carriers (liquid hydrogen, ammonia, methylcyclohexane), carbon capture and storage (CCS), target analysis year (2021, 2030) to reflect trends of greening grid electricity and potential import countries on aggregated life-cycle GHG emissions were presented. South Korea was chosen as a case study region, and the low-carbon alternatives were suggested for reducing aggregated emissions to meet the Korean standard (5 kgCO2e/kgH2). First, capturing and storing nearly entire (>90%) CO2 from fossil- and waste-based production pathways is deemed essential. Second, when repurposing the use of hydrogen that was otherwise used internally, applying a penalty for substitution is appropriate, leading to results notably exceeding the standard. Third, for electrolysis-based hydrogen, using renewable or nuclear electricity is essential. Lastly, when hydrogen is imported, in a well-to-point-of-delivery (WtP) perspective, using renewable electricity during hydrogen conversion into a carrier and reusing the produced hydrogen for endothermic reconversion reaction are recommended. By implementing the developed calculation framework to other countries' cases, it was observed that importing hydrogen to regions having scope of WtP or above (e.g., well-to-wheel) might not meet the threshold due to additional emissions from importation processes. Additionally, for hydrogen carriers undergoing the endothermic reconversion, the approach to reduce WtP emissions (reusing produced hydrogen) may conflict with the approach to reduce well-to-gate (WtG) emission (using external fossilbased fuel). The discrepancy highlights the need to set a broader scope of emissions assessment to effectively promote the life-cycle emission reduction efforts of hydrogen importers. This study contributes to the field of clean hydrogen GHG emission assessment, offering a robust database and calculation framework while addressing the effects of greening grid electricity and CCS implementation, proposing low-carbon alternatives and GHG assessment scope to achieve global GHG reduction.