Photoelectrochemical reduction of Carbon dioxide by metal-complexes-membrane electrodes

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Object : Phtochemical reduction of CO_2 is considered to be one of the most pro-mising approaches to photochemical conversion and storage of solar energy. An aqucous system of Ruthenium (II) -bipyridine complexes-methylviologen (MV^<2+>) -triethanolamine is one of homogeneous photosinsitized reductions of CO_2. In thissystem tricthanolamine is exhausted as sacrificial electron donor. With a view to search a cyclic system, we study on photoelectrochemical CO_2 reduction using coated membrane electrodes containing complexes and MV^<2+> without sacrificial clectron donor. Additionally photocatalytic reduction of CO_2 was studied using TiO_2 in suspension in liquid CO_2 and supercritical CO_2.Results :1.The electrode covered by the membranes containing Ru (bpy)_3^<2+> and MV^<2+> formed the largest photocurrent in the potential below -0.2 V.This indicates that Ru (bpy)_3^<2+> and MV^<2+> system in the membrane was most effective in generating photoc-urrent.2.In the Ru (bpy)_3^<2+> and MV^<2+> membrane system, exclusively II_2 was found as the reduction product. The electrode electrodeposited Pt or Ru reduced photoelectro-chemically CO_2 to produce malonic acid, acetic acid and formic acid as reduction products.3.We found that CO_2 was reduced by two stage reactions, that is, CO_2 fluid was photoc-atalytically reduced with TiO_2 in suspension and then protonated to formic acid by water addition.