Broader contextAlthough sunlight provides by far the most abundant renewable energy resource, solar energy utilization at massive scale will require integrated storage and distribution, in addition to technologies that enable solar energy capture and conversion. Due to their very high energy density, far dwarfing that of batteries, compressed air energy storage systems, or pumped hydro systems, chemical fuels present an extraordinarily attractive option for enabling persistent, long term, high deliverability and high energy density, solar energy storage on a massive scale. Photovoltaics in series with electrolysis units accomplish this functionality, but require expensive electrical interconnections between the two separate (individually and collectively expensive) components of the energy system. Photosynthesis accomplishes the conversion of sunlight into chemical fuel (initially in the form of NADH and ultimately in the form of reduction of CO2to form sugars), albeit at very low (<1%) yearly averaged real energy efficiencies. Artificial photosynthesis has been shown to produce fuel from sunlight with much higher (>10%) overall energy conversion efficiency. However, photoelectrode materials for artificial photosynthesis that exhibit long-term stability in sunlight are relatively inefficient at fuel production, and conversely photoelectrode materials that exhibit high energy conversion efficiencies are relatively unstable. New materials that simultaneously possess both of these attributes are thus desirable. One approach to this problem, as described herein, is to explore a wide set of new photoelectrode materials in a combinatorial fashion, enabling screening of a wide variety of possibilities while compiling a structure–function database to guide yet further exploration and screening of promising new photoelectrodes. If a suitable material were successfully identified and developed, in principle it would underpin the development of a complete solar energy capture, conversion, and storage system that would be capable, if suitably widely deployed, of providing hundreds of exaJ per year of energy from sunlight in a storable, transportable, readily utilizable form,i.e.as chemical fuel.