Comparative life-cycle assessment of electrolyzer-integrated and air separation unit-based biomass conversion for net-negative emissions hydrogen production

• Compares oxy-BECCS H₂ pathways with electrolyzer and ASU oxygen supply. • Low-CI grids yield net-negative H₂; ASU-O₂ doubles CO₂ removal per kg H₂. • Feedstock-specific CFbio shows harvested trees, residues weaken net removal. • Grid carbon intensity and O₂-supply energy dominate life-cycle GHG results. • TEA–LCA integration shows credit levels where ASU-O₂ undercuts electrolyzers. Four cradle-to-gate life-cycle assessments are performed for biomass-to-hydrogen pathways with integrated carbon capture and storage. The pathways comprise oxy-combustion and oxy-gasification at 2 and 27 bar(a), with oxygen supplied either from electrolyzer-integrated oxygen or, for selected gasification cases, a cryogenic air-separation unit. The functional unit is 1 kilogram hydrogen compressed to 71 bar(a). Low-carbon intensity (hydro/nuclear-dominated) and high-carbon intensity (fossil-dominated) Canadian grids are modelled in openLCA. Biogenic carbon is quantified using a feedstock-specific biomass-regrowth global warming potential factor and compared with a climate-neutral baseline. Under a low-carbon intensity grid, all electrolyzer-integrated systems are net-negative, with gasification removing ≈21–23 % more carbon dioxide equivalent than combustion. Substituting air separation unit oxygen roughly doubles total carbon removal: similar carbon dioxide is captured from about half the hydrogen output, doubling carbon dioxide per kilogram of hydrogen and cutting oxygen-supply electricity use by nearly an order of magnitude. On high-carbon intensity grids, electrolyzer configurations become net-positive, whereas air separation unit systems remain net-negative (≈ –3 to –5 kilogram carbon dioxide equivalent per kilogram of hydrogen) due to lower electricity use and higher carbon dioxide captured per kilogram of hydrogen. Under low-carbon supply, the biomass-regrowth global warming potential factor values govern outcomes: harvested trees cut net removal by ∼58 % versus climate-neutral, while forest residues cut it by ∼82 %. Additional sensitivities (process pressure, biomass and carbon dioxide transport, future grid decarbonization) exert a secondary influence relative to grid intensity, oxygen-supply route, and feedstock type. Techno-economic integration shows that, without carbon dioxide credits, electrolyzer-oxygen yields lower levelized cost of hydrogen than air separation unit-oxygen in Québec- and Ontario-like grids, while increasing carbon dioxide credits favour air separation unit-oxygen due to greater per-kilogram carbon dioxide removal and stronger levelized cost of carbon mitigation response.