New sensitizing relay compounds for H2 production

Abstract

Abstract Hydrogen producing systems, which consist of a photosensitizer (like Ru(bipy)3Cl2), an electron relay (e.g. methyl viologen), a colloidal catalyst (platinum) and a sacrificial electron donor (EDTA) are well known. We have investigated new electron relay substances (1,1″, 1′″-trialkyl [4,2′;4′,4″;6′,4″′] quaterpyridinium trichloride and related compounds), which combine the features of the sensitizer and the electron relay. The maxima of light absorption of these compounds were in the u.v. range, at about 320 nm. The fluorescence of the relay compounds decreased with increasing relay concentration (self-quenching). We have determined the quantum yields of the systems (containing the electron relay, EDTA, platinum catalyst and acetate buffer) by exciting these solutions with near-u.v. light (high-pressure Hg lamp, λ > 280 nm, for the calculations the number of incident photons with λ > 280 nm, but only hydrogen in the gas phase ( 1 2 H 2 ) was taken into account). The quantum yields were in the region of about 2%. Furthermore, we found that only electron relay compounds which have a pyridinium ring with a free electron pair were capable of producing hydrogen without dye stuff. The reaction mechanism is discussed in detail.