Research trends in life cycle assessment of hydrogen production: Methodological review on thermochemical conversion processes

The methodology and processes used in conducting life cycle assessment (LCA) can significantly alternate the environmental impacts of hydrogen production processes, which demands more critical reviews. To address this, a bibliometric analysis of 518 research works cataloged in Scopus and Web of Science was conducted to assess the research trend of LCA on hydrogen production. In addition, the methodology of LCA used in the thermochemical conversion process, which is the most technically feasible pathway, was critically reviewed by selecting the 40 most relevant articles. The bibliometric analysis showed that the number of publications has rapidly increased, at 30% annually over the past decade. Biomass and residue are found to be the feedstock that is studied the most, and the research focusing on utilizing renewable energy sources to reduce associated impact has gained momentum in recent years. The methodological review showed that cradle-to-gate system boundaries with one kg of hydrogen as a functional unit are the most common, and the SimaPro, Ecoinvent, and CML are found to be the most common impact assessment tools, databases, and methods, respectively. The study highlighted that meticulous attention is required to select feedstock, process, and energy source to minimize the impact, as these are the most influential parameters. Further, the study suggests careful consideration while choosing the system boundary, as the impact can significantly vary.