(Invited) Needed Research Focus for Achieving Cost-Effective and Reliable Solar-Thermal Water Splitting

Solar thermal water splitting (STWS) is a method for producing renewable hydrogen from water and concentrated sunlight using energy from the entire solar spectrum to directly drive the splitting reactions and, therefore, providing the opportunity for high theoretical solar to hydrogen efficiencies. In two-step STWS, a metal oxide is heated to high temperatures using concentrated sunlight until it reduces, forming a reduced product and O₂. In a second step, H₂O re-oxidizes the material to its original state, forming H₂. Various aspects of the operation of this process have been investigated since the 1970’s including the chemistry of the active redox material which is reducing and oxidizing, the effects of redox operating conditions, and the solarthermal reactors in which the reactions occur. A perspective will be presented for important future research directions that will allow the opportunity to be realized.