Artificial Photosynthesis with Inorganic Particles
Water photoelectrolysis with particles is a special form of artificial photosynthesis that can offer substantial cost savings over established photovoltaic-electrolyzer and photoelectrochemical cells. Existing particle water splitting devices only reach a fraction of their theoretical solar to hydrogen conversion (STH) efficiency limit, which means that significant advances are still possible with such systems. In order to promote development of this technology, this chapter surveys particle-based water splitting photocatalysts and photoreactors and provides an introduction to their operational principles. The factors that control the generation of charge carriers by absorption of light, charge transport, separation, recombination, and electrochemical reactions at particle surfaces are described in detail. The use of solid–liquid and solid–solid junctions and Ohmic contacts to control carrier transport are discussed, as well as strategies to prevent electron/hole recombination and the oxygen reduction reaction (back reaction) in particle photocatalysts. The effects of pH and ions on the energetics and conversion efficiency will be examined, and recent developments in particle-based water splitting devices will be highlighted, including the discovery of photocatalyst sheets, studies on long term stability, and the application of new experimental techniques for the characterization of charge transport across particle junctions. Selected theoretical modeling efforts will be summarized and promising new materials for particle based water splitting systems will be discussed.