[Show abstract][Hide abstract] ABSTRACT: Sustainable hydrogen production is a key target in the development of alternative energy systems of the future for providing a clean and affordable energy supply. The conversion of solar energy into hydrogen via a water-splitting process assisted by photosemiconductor catalysts is one of the most promising technologies for the future because large quantities of hydrogen can potentially be generated in a clean and sustainable manner. Undoubtedly, the conversion of solar energy into a clean fuel (H2) under ambient conditions is the greatest challenge facing scientists in the twenty-first century.This chapter provides an overview of the principles, experimental designs, and research progress on solar-hydrogen production via the water-splitting reaction on photocatalyst surfaces. The concept of using solar energy to drive the conversion of water into hydrogen and oxygen is examined from the standpoint of both energy requirements and factors that determine the activity of photocatalysts. A survey is presented of the advances made in the development of catalysts for photochemical water splitting under visible light since the pioneering work by Fujishima and Honda in 1972. Photocatalysts for water splitting under ultraviolet light have made remarkable progress in recent years, but there are many technical challenges, mainly the low efficiency in light-to-hydrogen conversion, still facing photocatalysts under visible light. There are still major challenges in the development of photocatalysts with improved efficiencies for hydrogen production from water using solar energy. An overview is provided in this chapter about research strategies and approaches adopted in the search for photocatalysts for water splitting under visible light (new photocatalyst materials and the control of the synthesis of materials for customizing the crystallinity, electronic structure, and morphology of catalysts at nanometric scale).
[Show abstract][Hide abstract] ABSTRACT: Sustainable hydrogen production is a key target for the development of alternative, future energy systems that will provide a clean and affordable energy supply. The Sun is a source of silent and precious energy that is distributed fairly all over the Earth daily. However, its tremendous potential as a clean, safe, and economical energy source cannot be exploited unless the energy is accumulated or converted into more useful forms. The conversion of solar energy into hydrogen via the water-splitting process, assisted by photo-semiconductor catalysts, is one of the most promising technologies for the future because large quantities of hydrogen can potentially be generated in a clean and sustainable manner. This Minireview provides an overview of the principles, approaches, and research progress on solar hydrogen production via the water-splitting reaction on photo-semiconductor catalysts. It presents a survey of the advances made over the last decades in the development of catalysts for photochemical water splitting under visible-light irradiation. The Minireview also analyzes the energy requirements and main factors that determine the activity of photocatalysts in the conversion of water into hydrogen and oxygen using sunlight. Remarkable progress has been made since the pioneering work by Fujishima and Honda in 1972, but he development of photocatalysts with improved efficiencies for hydrogen production from water using solar energy still faces major challenges. Research strategies and approaches adopted in the search for active and efficient photocatalysts, for example through new materials and synthesis methods, are presented and analyzed.
[Show abstract][Hide abstract] ABSTRACT: Solid solutions Cd1−xZnxS with different Zn concentration (0.2 < x < 0.35) are investigated in the production of hydrogen from aqueous solutions containing SO32−/S2− as sacrificial reagents under visible light. Textural, structural and surface catalyst properties are determined by N2 adsorption isotherms, UV–vis spectroscopy, SEM and XRD and related to the activity results in hydrogen production from water splitting under visible light irradiation. It is found that the crystallinity and energy band structure of the Cd1−xZnxS solid solutions depend on their Zn atomic concentration. The hydrogen production rate is found to increase gradually when the Zn concentration on photocatalysts increases from 0.2 to 0.3. Subsequent increase in the Zn fraction up to 0.35 leads to lower hydrogen production. Variation in photoactivity is analyzed in terms of changes in crystallinity, level of conduction band and light absorption ability of Cd1−xZnxS solid solutions derived from their Zn atomic concentration.
[Show abstract][Hide abstract] ABSTRACT: The demand for hydrogen over the coming decade is expected to grow for both traditional uses (ammonia, methanol, refinery) and running fuelcells. At least in the near future, this thirst for hydrogen will be quenched primarily through the reforming of fossil fuels. However, reformingfossil fuels emits huge amounts of carbon dioxide. One approach to reduce carbon dioxide emissions, which is considered first in this review, is to apply reforming methods to alternative renewable materials. Such materials might be derived from plant crops, agricultural residues, woody biomass, etc. Clean biomass is a proven source of renewable energy that is already used for generating heat, electricity, and liquid transportation fuels. Clean biomass and biomass-derived precursors such as ethanol and sugars are appropriate precursors for producing hydrogen through different conversion strategies. Virtually no net greenhouse gas emissions result because a natural cycle is maintained, in which carbon is extracted from the atmosphere during plant growth and released during hydrogen production. The second option explored here is hydrogen production from water splitting by means of the photons in the visible spectrum. The sun provides silent and precious energy that is distributed fairly evenly all over the earth. However, its tremendous potential as a clean, safe and economical energy source cannot be exploited unless it is accumulated or converted into more useful forms of energy. Finally, this review discusses the use of semiconductors, more specifically CdS and CdS-based semiconductors, which are able to absorb photons in the visible region of the spectrum. The energy stored within a semiconductor as electronic energy (electrons and holes) can be used to split water molecules by simultaneous reactions into H2 and O2. This conversion of solar energy into a clean fuel (H2) is perhaps the greatest challenge for scientists in the 21st century.
No preview · Article · Jan 2009 · Energy & Environmental Science
[Show abstract][Hide abstract] ABSTRACT: A CdS–CdO–ZnO mixture annealed at different temperatures and loaded with Ru or Pt cocatalysts has been investigated in the production of hydrogen from aqueous solutions containing SO32− + S2− as sacrificial reagents under visible light. The physicochemical characterization of the CdS–CdO–ZnO catalyst revealed significant changes in the crystalline structure and visible light absorption capacity as a result of thermal treatments. Catalytic activity was found to be strongly dependent on physicochemical changes associated with thermal annealing. Hydrogen evolution over the CdS–CdO–ZnO catalyst was enhanced in the sample annealed at 773 K by the better contact between the CdS and CdO–ZnO phases, which improved physical charge separation. CdS–CdO–ZnO catalyst activity was significantly improved by the addition of Pt or Ru cocatalysts. Among the noble metals studied, activity promotion was higher for the sample loaded with Ru. The enhancement of activity associated with Ru loading is linked to a good interaction between Ru oxide particles and CdS, which reduces the possibility of electron–hole recombination, thus resulting in more efficient water splitting.
No preview · Article · Aug 2008 · International Journal of Hydrogen Energy