Role of Sulfites in the Water Splitting Reaction

Photolysis of Na2SO3-Na2S sacrificial agent under irradiation with a high-pressure Hg lamp was analyzed to gain insight into the reaction steps for hydrogen formation and the function of in the photochemical reaction. This sacrificial agent leads to the formation of thiosulfate, disulfide, tetrasulfide, free sulfur and hydroxyl radical intermediates during the reactions. The collected total volume of evolved hydrogen versus photolysis time data suggest that Na2SO3 and Na2S concentrations have different but pronounced effects on the hydrogen evolution rate: a low and stable concentrations of Na2SO3 or high concentration of Na2S facilitates hydrogen formation. In comparison with Na2S solutions, two competing reaction paths have been postulated in solutions with Na2SO3-Na2S sacrificial agent, the dominant reaction path being determined by the Na2SO3 concentration in the sacrificial agent.