The Catalyzed Photodissociation of Water

Chemical interactions between molecules in excited electronic, vibrational, or rotational states and surfaces is a new field of catalytic science. Photoassisted thermodynamically uphill reactions such as the photodissociation of water to hydrogen and oxygen are one class of these excited state reactions. Water photodissociation may also be observed when the platinum cathode is substituted with a p-type semiconductor such as gallium phosphide. Carrier generation and electron transfer at the semiconductor surface are the first of several elementary steps in the photodissociation of water. The difficulty with strontium titanate for the photodissociation of water is the necessity for ultraviolet radiation. The iron-oxide-based assembly has a photoresponse more closely matched to the solar spectrum than SrTiO3. The efficiency of the iron oxide p/n assembly is low, approximately 0.1%. This efficiency is lower than strontium titanate under ultraviolet illumination, but the iron oxide assembly operates with visible light in the solar range.