AbstractHydrogen gas (H₂) is the primary storable fuel for pollution‐free energy production, with over 90 million tonnes used globally per year. More than 95% of H₂ is synthesized through metal‐catalyzed steam methane reforming that produces 11 tonnes of CO₂ per tonne H₂. “Green H₂” from water electrolysis using renewable energy evolves no CO₂, but costs 2–3x more, making it presently economically unviable. Here we report catalyst‐free conversion of waste plastic into clean H₂ along with high purity graphene. The scalable procedure evolves no CO₂ when deconstructing polyolefins and produces H₂ in purities up to 94% at high mass yields. Sale of graphene byproduct at just 5% of its current value yields H₂ production at negative cost. Life‐cycle assessment demonstrates a 39–84% reduction in emissions compared to other H₂ production methods, suggesting the flash H₂ process to be an economically viable, clean H₂ production route.This article is protected by copyright. All rights reserved