Development of low cost, highly stable and active water splitting photocatalysts for hydrogen production
Goh, Simon Chun Kiat
Date of Issue2014
School of Chemical and Biomedical Engineering
Rapid increase in carbon dioxide build up in the atmosphere hastens the process of global warming. The release of carbon dioxide is often the consequence of burning of fossil fuel for energy harvesting. Therefore, alternative energy should be rapidly studied and made available globally before the situation spin out of control. To date, the safest source of energy derives from the sun in the form of solar energy. Solar energy is captured by a light absorbing semiconductor to catalyze the splitting of water to form hydrogen and oxygen gases. Rose Bengal photosensitizer dye and hydrothermally synthesized carbon sphere supported 1 wt% Pt co-catalyst reduce water to form hydrogen gas under visible light irradiation. By altering pH of the synthesis solvents, varying sizes of carbon spheres (200 nm and 5 J.tm) can be obtained. It was purported that dark coloured carbon sphere supported photocatalytic system was found to confer remarkable increase in hydrogen gas production over 24 hours period than systems using other supports such as layered double hydroxide and silica or without support. When 1 wt>/o Pt was loaded onto carbon spheres, the system reveals 48 times increase in activity than unsupported Pt system. Dark coloured carbon spheres disperse Pt nanoparticles and protect Rose Bengal from rapid photodegradation. The photocatalyst system was stable for more than 5 cycles ofharvest-redispersion recycling test. Highly efficient CdS quantum dots (CdSQD) - MoS2 catalyst-co-catalyst system affords high hydrogen gas output. Synthesized MoS2nanoflower are highly dispersible in water while providing good anchor for CdSQD (3 nm diameter). Photoexcited CdSQDs inject electrons into the conduction band of MoS 2 • Active sites on MoS 2 then allow protons reduction to hydrogen. The system affords stable H2 production in excess of 600 J.Lmol per hour in lactic acid. Photoluminesence (PI) studies showed MoS 2-CdSQD composite have low recombination rate than bare CdSQD. Electrochemical Impedance Spectroscopy (EIS) provides evidence of low impedance on MoS2 which enable efficient electron transport from CdSQD to MoS 2 edge active sites.