How green is hydrogen production? A unified life cycle carbon accounting framework and dynamic standard optimization...

The rapid expansion of hydrogen production calls for robust life cycle carbon accounting and adaptive emission standards. However, most existing assessments remain static and do not capture the interaction between technological change and regulatory design. This study develops a unified life cycle carbon accounting framework to evaluate major hydrogen production pathways across China, the United States, the European Union, and Japan. It further builds a dynamic coordination model to examine the co-evolution of hydrogen production structures and carbon emission standards from 2025 to 2060, while accounting for technological learning, power system decarbonization, and international hydrogen trade. The results show substantial cross-country differences in life cycle carbon intensity. Wind-based electrolysis has the lowest emissions, whereas photovoltaic-based pathways remain more sensitive to local grid carbon intensity. Coordinated optimization can significantly accelerate decarbonization by aligning standard tightening with production system evolution. In China, hydrogen carbon intensity falls from about 16 kg CO₂e per kg H₂ in 2025 to about 3 kg CO₂e per kg H₂ in 2060, compared with about 7 kg CO₂e per kg H₂ under the baseline scenario. Clean shipping is also critical for preserving the carbon competitiveness of hydrogen exports under stringent international thresholds. Overall, the findings highlight the importance of integrating life cycle accounting, dynamic standard adjustment, and clean logistics to support long-term hydrogen decarbonization.