(Invited) Mathematical Modeling of Novel Artificial-Photosynthesis Devices

An artificial-photosynthesis device is a multicomponent system composed of various components including perhaps light absorbers, electrocatalysts, membranes or separators, and electrolytes in a specific system geometry. The overall solar-to-fuel conversion efficiency of such a system depends on the performance and materials properties of the individual components as well as the design of the system. In this talk, we will cover recent modeling of various motifs of such artificial-synthesis systems. In particular, we will examine modeling and experimental results for particle-based devices for solar-hydrogen production as well as vapor-feed devices for solar water splitting and electrochemical carbon-dioxide reduction. Mathematical modeling is ideally suited to examine the various tradeoffs and determine design targets and feasibility. Z-scheme particle-suspension reactor designs consisting of freely suspended semiconductor particles in an electrolyte to drive solar water splitting could be cost-effective alternatives to produce renewable hydrogen. In this work, we develop a device-scale model to evaluate the effects of coupled light absorption, electrolyte species transport, and reaction kinetics on overall reactor performance and ability to sustain rector operation via diffusion. We also extend this work by numerically investigating particle-scale and -size effects on colloidal stability, light absorption and scattering, and charge-carrier transport across the semiconductor/cocatalyst/electrolyte interface. Within the Joint Center for Artificial Photosynthesis (JCAP), we utilize continuum-scale modeling of the various components in order to determine design tradeoffs of vapor-feed or gas-diffusion electrode systems. Such systems can provide routes towards optimizing local reaction conditions and overcoming inherent liquid-phase transport limitations for carbon-dioxide reduction as well as solar water splitting to produce hydrogen. For the latter, integrated architectures can be used that are more stable than those in liquid environments. Overall, the functioning of both vapor feed and particle systems will be explored.