Cunping Huang

Hydrogen production via photolytic oxidation of aqueous sodium sulfite solutions.

Sulfur dioxide (SO(2)) emission from coal-burning power plants and refinery operations has been implicated as a cause of acid rain and other air pollution related problems. The conventional treatment of SO(2)-contaminated air consists of two steps: SO(2) absorption using an aqueous sodium hydroxide solution, forming aqueous sodium sulfite (Na(2)SO(3)), and Na(2)SO(3) oxidation via air purging to produce sodium sulfate (Na(2)SO(4)). In this process, the potential energy of SO(2) is lost. This paper presents a novel ultraviolet (UV) photolytic process for production of hydrogen from aqueous Na(2)SO(3) solutions. The results show that the quantum efficiency of hydrogen production can reach 14.4% under illumination from a low pressure mercury lamp. The mechanism occurs via two competing reaction pathways that involve oxidation of SO(3)(2-) to SO(4)(2-) directly and through the dithionate (S(2)O(6)(2-)) ion intermediate. The first route becomes dominant once a photostationary state for S(2)O(6)(2-) is established. The initial pH of Na(2)SO(3) solution plays an important role in determining both the hydrogen production rate and the final products of the photolytic oxidation. At initial solution pH of 9.80 Na(2)SO(3) photo-oxidation generates Na(2)SO(4) as the final reaction product, while Na(2)S(2)O(6) is merely a reaction intermediate. The highest hydrogen production rate occurs when the initial solution pH is 7.55. Reduction in the initial solution pH to 5.93 results in disproportionation of HSO(3)(-) to elemental sulfur and SO(4)(2-) but no hydrogen production.

Preparation of high efficiency visible light activated Pt/CdS photocatalyst for solar hydrogen production

Production of hydrogen by water splitting using solar energy is one of the long sought goals of hydrogen economy. Approximately 33% of solar radiation is emitted as high energy photons while the remaining 67% consists of primarily thermal energy. Utilization of both thermal and photonic energies within the solar spectrum is essential for achieving water splitting at high efficiency. At FSEC, we have developed a solar-thermochemical water splitting cycle for the production of hydrogen. In this cycle, the photonic portion of solar irradiance is diverted and used to drive the hydrogen production step, while solar thermal portion drives the oxygen generation step of the cycle. The photocatalytic hydrogen production step of the cycle employs aqueous ammonium sulfite solution that is oxidized to ammonium sulfate in the presence of nanosized photocatalysts. We have developed a technique for the preparation of polymer encapsulated nanosize photocatalysts that show high activity toward oxidation of ammonium sulfite aqueous solution. The use of nano-scale and defect free photocatalysts hinder the recombination of photo-generated electron-hole pairs, thereby increasing solar to hydrogen energy conversion efficiency.