Particle suspension reactors and materials for solar-driven water splitting

Reactors based on particle suspensions for the capture, conversion, storage, and use of solar energy as H 2 are projected to be cost-competitive with fossil fuels. In light of this, this review paper summarizes state-of-the-art particle light absorbers and cocatalysts as suspensions (photocatalysts) that demonstrate visible-light-driven water splitting on the laboratory scale. Also presented are reactor descriptions, theoretical considerations particular to particle suspension reactors, and efficiency and performance characterization metrics. Opportunities for targeted research, analysis, and development of reactor designs are highlighted. Global climate disruption fueled by anthropogenic greenhouse gas emissions is a major concern for humanity and life on Earth. The only way to significantly attenuate the rate of carbon dioxide emitted into the atmosphere is to reduce fossil fuel use for energy and industrial applications. Hydrogen produced by water splitting using renewable solar energy is a clean replacement for fossil fuels. Solar photoelectrochemical water splitting represents a ''Holy Grail'' technology, but faces challenges before solar hydrogen can compete with fossil fuels on a cost-per-energy basis. To make solar hydrogen feasible, particle suspension reactors projected to cost less than fixed-electrode designs must be coupled with low-cost, stable, and efficient materials. Should these proposed technologies become a reality, society will have an economic impetus to use clean hydrogen as a fuel source for important industrial processes such as transportation and production of chemicals including ethylene and ammonia.