The reaction mechanism of H-2 production with the ZnO/Fe3O4/H2O system at 973-1073 K was studied from the view point of solid-state chemistry. This reaction proceeds with nearly 100% yield via metal zinc the vaporization/deposition process between ZnO particles and Fe3O4 particles. The vaporized metal zinc from ZnO by ZnO = Zn(g) + 1/2O(2) seems to deposit on the surface of the Fe3O4 particle, and to form Zn2+ by the reaction with Fe3+ ions in Fe3O4. The Fe3+ ions will be immediately changed to Fe2+ ions by charge-hopping in the spinel structure. This causes the successive transportation of zinc atoms to Fe3O4 and the successive accumulation of Fe2+ and Zn2+ ions in the spinel structure. The accumulation of the Fe2+ ions gives a higher potential to react with O-2, which is generated in the metal zinc vaporization process, and the total reaction equation can be written as: xZn+1/2XO(2)+Fe3O4 = (3+x)/3(Znx/(3+x)Fe3/(3+x))(3)O4-delta); delta = x/(3+x). This indicates that the oxygen-deficient spinel-type compound is formed. The value of delta will increase, and the OD spinel-type compound will have a potential to decompose H2O to generate H-2 gas. (C) 2004 Elsevier B.V. All rights reserved.