Invited Talk: Photocatalytic Particle-Suspension Reactors for Solar Water Splitting

Sunlight driven water splitting to produce hydrogen and oxygen provides a pathway to store available solar energy in the form of stable, energy-dense chemical bonds. Here, we investigate a tandem, particle-suspension reactor design for solar water splitting comprising micron-scale semiconductor particles (photocatalysts) suspended in an aqueous solution with soluble redox shuttles. Redox shuttles mediate electrons between the oxygen and hydrogen evolution reaction compartments. A porous separator facilitates redox species transport while averting gas crossover between the two reaction compartments. Numerical models have been developed to evaluate the transport of charged and neutral species, and reaction kinetics for the proposed reactor design at varying lengthscales ranging from that of a single photocatalyst particle to a suspension of photocatalyst particles in the reactor. At the lengthscale of a single particle, model results illustrate the impacts of particle size and the electrochemical potential of the redox shuttle on the rate of charge-carrier transport across the semiconductor-electrolyte interface. Using a transient reactor model, we demonstrate that a 1% solar-to-hydrogen conversion efficiency can be sustained by diffusion-driven mass transport in 1 cm tall reaction compartments using BiVO4 and SrTiO3:Rh photocatalysts for oxygen and hydrogen evolution, and with proton-coupled electron transfer redox shuttles. This talk will also highlight recent developments in my research group on designing and developing solar-powered wastewater treatment devices for energy and nutrient recovery.