Experimental investigation of a catalyst under various solar light conditions for hydrogen production.

Abstract

The light absorption characteristics of the photocatalyst {[Ru(bpy)2(dpp)]2RhBr2}5+ and the photochemical Ru(bpy)2(dpp)2+ is investigated. Extinction coefficient versus wavelength is determined for both a low intensity broad spectrum LED light source and one sun intensity simulated sunlight. Variation in the absorption characteristics from both the previously published monochromatic values and from each other is observed. absorption characteristics are dependent upon the type of light used and that specific testing for the design wavelength range should be conducted so that the actual absorption characteristics are then used to establish an optimum light absorbing configuration for photocatalyst use. This technique is used to create a simulation model that is analyses the distribution of hydrogen production rates in the existing test cell and demonstrates that most of the hydrogen production occurs in a relatively small volume within the existing test configuration. The absorption spectroscopy of the photocatalyst is found to change after extended exposure to light. Two possibilities exist, transformation of the photocatalyst to a different configuration and breakdown of the photocatalyst into component parts. Degradation would explain observed changes in photocatalyst quantum efficiency with time. A chemical model for water photocatalysis is proposed. In addition to identifying several of the isomers that occur and explaining the changes in absorption spectroscopy; it also addresses the impact of changing solution solvent on quantum efficiency. It also addresses the apparent contradiction between photon supply rate and molecular excited state lifetimes on photocatalytic ability.