The present invention is directed to a method of thermochemical forming H2, O2, or a combination thereof from water, said method comprising the steps of contacting a composition comprising a spinel-type transition metal oxide of formula M3O4 with an alkali metal carbonate bicarbonate, or mixture thereof in the presence of H2O to form H2, CO2, and an alkali metal ion-transition metal oxide; hydrolytically extracting at least a portion of alkali metal ions from the alkali metal ion-transition metal oxide by the reaction with CO2 and liquid H2O; and thermochemically reducing the resulting oxidized-transition metal oxide. The thermochemical reduction of CO2 based on analogous methods is also disclosed.