Gasification investigations of coal and biomass blends for high purity H2 production with carbon capture potential

•Gasification conversion to high-purity H2 of coal/seaweed with carbon capture were revealed.•Gas formation kinetics were online observed by GC and mass balance was evaluated.•The H2 production is 486.91–801.5ml/g in the alkaline gasification with 80.1%–93.2% purity.•Synergistic effect is approved while gasification of coal/seaweed has low-carbon potential.