Hydrogen photoproduction by Nafion/cadmium sulfide/platinum films in water/sulfide ion solutions

We report the construction, characterization, and evaluation of a novel system for photocatalytic hydrogen generation that comprises semiconductor (CdS) crystallites embedded in a polymer (Nafion) matrix that also contains a hydrogen-evolution catalyst (Pt). Hydrogen-production efficiencies from water containing a sacrificial electron donor (sulfide ion) were greater than those commonly obtained with unsupported colloidal or powdered semiconductors under similar conditions. Several factors dramatically influence performance: the crystalline form and surface composition of the semiconductor and the extent of catalyst dispersion throughout the film. Photocatalytic and photosynthetic reactions at semiconductor particles provide the possibility of the utilization of solar energy for the promotion of useful chemical reactions.'V2 Photoreactions at these particles are based on the production of electrons and holes (e-h+) upon absorption of light; these can react with species in solution to produce oxidized and reduced forms. These particulate systems are of interest because they are generally easy to fabricate, are potentially inexpensive, and have a large surface area which facilitates efficient light absorption and heterogeneous charge (eand h+) transfer to solution species. CdS is an interesting semiconductor material that has been studied as an electrode material; many studies of particulate systems involving CdS have also been r e p ~ r t e d . ~ ' ~ Particle systems have several disadvantages, however. Since they are dispersed in the solvent system, they are inconvenient to use in continuous-flow systems. They may also tend to flocculate and settle out with time. A previous brief comm~nication'~ Permanent address: Division of Applied Organic Chemistry, CSIRO, P.O. Box 4331, Melbourne 3001, Australia. described the production and immobilization of CdS in a polymer (Nafion) matrix and its use for the photocatalyzed reduction of (1) (a) Bard, A. J. J . Photochem. 1979, 10, 59. (b) Bard, A. J. J . Phys. Chem. 1982, 86, 172 and references therein. (2) Gratzel, M. Acc. Chem. Res. 1981, 14, 376. (3) Krasnovsky, A. A.; Brin, G. P.; Luganskaya, A. N.; Nikandrov, V. V. Dokl. Akad. Nauk. SSSR 1979, 249, 896. (4) Frank, S. N.; Bard, A. J. J . Phys. Chem. 1977, 81, 1484. (5) (a) Darwent, J. R.; Porter, G. J. Chem. SOC., Chem. Commun. 1981, 145. (b) Darwent, J. R. J . Chem. SOC., Faraday Trans. 2 1981, 77, 1703. (6) (a) Kalyanasundaram, K.; Borgarello, E.; Gratzel, M. Helu. Chim. Acra 1981,64, 362. (b) Borgarello, E.; Kalyanasundaram, K.; Pelizetti, E.; Gratzel, M. Ibid. 1982, 65, 243. (c) Duonghong, D.; Ramsden, J.; Gratzel, M. J . Am. Chem. SOC. 1982, 104, 2977. (7) (a) Harbour, J. R.; Hair, M. L. J . Phys. Chem. 1977,81, 1791. (b) Harbour, J. R.; Wolkow, R.; Hair, M. L. Ibid. 1981, 85, 4026. (8) (a) Kuczynski, J.; Thomas, J. K. J. Phys. Chem. 1983.87, 5498. (b) Kuczynski, J.; Thomas, J. K. Chem. Phys. Lett. 1982,88,445. (c) Kuczynski, J. P.; Milosavlejvic, B. H.; Thomas, J. K. J . Phys. Chem. 1984, 88, 980. (9) (a) Matsumura, M.; Hiramoto, M.; Iehara, T.; Tsubomura, H. J. Phys. Chem. 1984, 88, 248. (b) Matsumura, M.; Saho, Y.; Tsubomura, H. Ibid. 1983, 87, 3807. 0002-7863/84/1506-6537$01.50/0