Climate change performance of hydrogen production and utilization in power-to-X technologies

Abstract

With global mean temperatures expected to rise more than 2 °C above pre-industrial levels, the world is will face multiple climate change impacts. This has driven industries and companies to transition toward low-carbon energy systems. Hydrogen and hydrogen-derived power-to-X (PtX) fuels can replace fossil-based fuels and support carbon neutrality and net-zero targets, making hydrogen a promising transition fuel. This dissertation assesses the climate change performance of hydrogen production and hydrogen utilization pathways within PtX systems using a life cycle assessment (LCA) methodology. The primary objective is to compare the climate change impacts of green hydrogen production with fossil-based hydrogen value chains and to identify the conditions under which hydrogen can deliver substantial emission reductions. The research is structured around three sub-objectives covering hydrogen production, biogas upgrading, and hydrogen-based PtX value chains at regional and international levels.

First, green hydrogen production is compared with grey, blue, and turquoise hydrogen pathways. The results confirm that green hydrogen has the lowest carbon footprint among the assessed options. Even in a worst-case scenario based entirely on solar electricity, green hydrogen results in emissions of 2.5 kgCO2eq/kgH2, which is lower than the emissions from natural gas extraction alone for fossil-based hydrogen pathways (2.6–4.0 kgCO2eq/kgH2). Upstream emissions from natural gas and liquefied natural gas supply chains, including extraction, liquefaction, transport, and regasification, are shown to be significant and can exceed the total climate change impact of green hydrogen. Turquoise hydrogen performs better than grey and blue hydrogen, with further mitigation potential through solid carbon utilization and renewable methane sourcing.

Second, the climate change performance of green hydrogen use in membrane separation, ex-situ biomethanation, and in-situ biomethanation of biogas is evaluated. All scenarios achieve emission reductions of 43–54% compared with fossil natural gas, assuming renewable electricity-based hydrogen production, with negligible differences between proton exchange membrane (PEM) and alkaline electrolysis.

Third, six hydrogen-based PtX value chains are compared with fossil alternatives. Green steel production yields the highest emission savings, followed by direct hydrogen use and e-ammonia. Among the carbon capture and utilization pathways e-methanol performs best, while e-fuels show the lowest savings. The results highlight strong regional effects, with export-oriented production shifting emission savings to end-use regions. Overall, the dissertation demonstrates that green hydrogen-based PtX pathways offer significant decarbonization potential when upstream emissions and regional contexts are fully accounted for.