The study investigates the pyrolysis of algae in alkaline molten NaOH-Na2CO3 (AMS) to produce hydrogen. The transformation of pyrolysis products, particularly the heavy bio-oil fraction, is crucial for improving hydrogen yield and purity. The research reveals that molten salt promotes the cyclization and aromatization of linear alkenes, increasing aromatic compound content and hydrogen production. However, decarbonation of Na2CO3 and deoxygenation of NaOH lead to methane release, reducing hydrogen production. Heavy compounds tend to polymerize at higher temperatures, forming compounds with higher molecular weights and unsaturation, while generating hydrogen. Char reacts with molten salt to form hydrogen and disappears at 650 °C, while aromatics in light compounds condense into heavy compounds, growing to form soot-like at 600 °C, accompanied by hydrogen release. The study proposes strategies to improve hydrogen yield and purity, such as ex-situ steam reforming using Ni-based catalysts.The study investigates the pyrolysis of algae in alkaline molten NaOH-Na2CO3 (AMS) to produce hydrogen. The transformation of pyrolysis products, particularly the heavy bio-oil fraction, is crucial for improving hydrogen yield and purity. The research reveals that molten salt promotes the cyclization and aromatization of linear alkenes, increasing aromatic compound content and hydrogen production. However, decarbonation of Na2CO3 and deoxygenation of NaOH lead to methane release, reducing hydrogen production. Heavy compounds tend to polymerize at higher temperatures, forming compounds with higher molecular weights and unsaturation, while generating hydrogen. Char reacts with molten salt to form hydrogen and disappears at 650 °C, while aromatics in light compounds condense into heavy compounds, growing to form soot-like at 600 °C, accompanied by hydrogen release. The study proposes strategies to improve hydrogen yield and purity, such as ex-situ steam reforming using Ni-based catalysts.