GENERATION OF HYDROGEN AND OXYGEN FROM WATER AND STORAGE THEREOF WITH SILICIDES

摘要

The invention relates to a method for the photo- and thermochemical generation of hydrogen and/or oxygen from water in the presence of silicides, silicide-like compositions, metallosilicides and non-metallic silicides such as borosilicides, carbosilicides and nitrosilicides, i.e. all compositions containing silicon and being of the molecular formula RSi_x and/or RSi_xO_y wherein R represents an organic, metallic, organometallic and/or inorganic residue and/or oxides thereof, and Si being silicon and specifically a silicide moiety with X > zero and O representing oxygen with Y zero. The silicide moieties in these compositions exhibit characteristically a high electron density on silicon all of which can also be oxidized. The silicides and silicide-like compositions and/or oxides thereof can react catalytically in these aforementioned processes proceeding with or without light. However, upon irradiation of the reactions an increase of gas evolution is observed, this notably applying to artificial light as well as sunlight. Higher reaction temperatures are often favourable for these processes. Silicides and silicide-like compositions and/or oxides thereof are mostly semiconductor-type materials. Furthermore, these compositions are able to absorb/desorb hydrogen and oxygen reversibly wherein oxygen absorption/desorption is favourable but can occur simultaneously with hydrogen absorption and desorption. The desorption of hydrogen and oxygen can occur at ambient or higher temperatures, especially the processes concerning hydrogen, depending on the nature of the silicides and silicide-like compositions and/or oxides thereof employed. Furthermore, it was found that coupling or complexing a dye such as perylenes, perylene dyes and perylene congeners or analogs to silicides and silicide-like compositions and/or oxides thereof is favourable for the light absorption and hence for the reactivity of the silicides and silicide-like compositions. Further, it was found that the reactions using silicides and silicide-like compositions and/or oxides thereof for the purpose of water reduction and/or oxidation to yield hydrogen and/or oxygen, respectively, can be carried out by employing the silicides and silicide-like compositions and/or oxides thereof in immobilized form, i.e. when these compositions are attached onto or fixed in a polymeric material, as well as onto or in a glass or glass-like material, especially when these materials are electrically conducting. The same applies to the storage and release processes of the aforementioned gases. Furthermore a process is found wherein oxygen is transformed to polyoxygen of the formula O_n (n > 3) and/or hydogenpolyperoxides of the formula H₂O_n (n > 2) including the back reactions to form oxygen.