| An artificial photocatalyst can achieve quantum efficiency up to 93% in photocatalytic H2 production from Na2S–Na2SO3 aqueous solution under visible light irradiation. Yan et al. Click to enlarge. |
Researchers at the Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences have developed a new three-component photocatalyst that produces hydrogen with a quantum efficiency (QE) of up to 93% in the presence of sacrificial reagents under visible light irradiation, and is very stable under the photocatalytic reaction conditions.
The catalyst—cadmium sulfide doped with palladium sulfide and platinum (Pt–PdS/Cd)—can achieve its extremely high QE with loadings as low as 0.30 wt% of Pt and 0.13 wt% of PdS as co-catalysts on CdS. Quantum efficiency can be expressed as the number of product molecules to incident photons.
A report on their work is in press in the Journal of Catalysis; a corrected proof was published online 3 August.
For synthetic photocatalysts using visible light, the highest QE achieved up to now has been about 65%. Natural photosynthetic systems can reach a QE of about 95%.
The catalyst does not split water into hydrogen and oxygen. Rather, it evolves hydrogen alone and does so only from aqueous solutions containing sulfur-based sacrificial reagents that consume oxygen.
The research team, led by Can Li (the director of the institute’s catalysis laboratory), observed that pure cadmium sulfide evolves hydrogen from water very slowly. The found that co-doping CdS with PdS and platinum resulted in a material 380 times more active than pure CdS.
The group suggest the palladium sulfide serves as an oxidation co-catalyst, and that the role of platinum is to facilitate reduction. Further work is already under way to establish the roles of each of the components.
Quoted in a review of the DICP work in Chemical and Engineering News, Kazunari Domen, a photocatalysis expert at the University of Tokyo, said that the most significant aspect of the work is the novel combination of cocatalysts, which will likely motivate other researchers to explore that strategy in the search for better performing catalysts.
Resources
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Hongjian Yan, Jinhui Yanga, Guijun Ma, Guopeng Wu, Xu Zong, b, Zhibin Lei, Jingying Shi and Can Li (2009) Visible-light-driven hydrogen production with extremely high quantum efficiency on Pt–PdS/CdS photocatalyst. Journal of Catalysis, in press doi: 10.1016/j.jcat.2009.06.024
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“Hydrogen from Sulfur and Water”, Mitch Jacoby, Chemical and Engineering News, 10 August 2009, Vo. 87, No. 32, p 7