The holy grail in efficient and cost-effective conversion of solar energy into electrical and chemical energy is solar energy-driven water splitting using semi-conductor-based photo-catalysts. Overall conversion efficiencies of best systems so far are however far from the level needed for practical applications. Viable materials must exhibit good visible light absorption and carrier generation, good carrier transport, and good redox reactivity. This presentation will focus on investigating collective behavior of charge carrier transport in photocatalytic systems intended towards enhancing carrier separation such as facet-engineered nanocrystals and multiphase junctions. We employed multiscale modeling, combining DFT+U calculations of polaron hopping by Marcus/Holstein theory and kinetic Monte Carlo (KMC) modeling of mesoscale transport. We will highlight the approach first for stoichiometric bulk BiVO4 (BVO), the most promising anode material to date: simulations reveal that hole transport is bi-modal and confirm that charge carrier transport in BVO is gated by e- transport. For homo-junction of W/Mo gradient doped BVO, simulations indicate that e- favor higher doping regions and that the increase in carrier density upon doping overshadows the marginal decrease in intrinsic electron mobility in doped bulk BVO resulting in higher material conductivity. Lastly we plan to report on simulations of carrier dynamics in a TiO2 multiphase junction system, and of conversion efficiency in a model of finite size nano-particles while accounting for redox surface reactions.

Multiscale modeling of carrier transport in photocatalytic systems towards enhanced charge separation

2019 Fall National Meeting

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