Water is thermochemically decomposed to produce hydrogen by the following sequence of reactions: KI, NH3, CO.sub. 2 and water in an organic solvent such as ethyl or propyl alcohol are reacted to produce KHCO 3 and NH4 I. The KHCO3 is thermally decomposed to K2 CO3, H2 O and CO2, while the NH4 I is reacted with Hg to produce HgI2, NH3 and H2.