Improved understanding of selectivity and transport mechanisms in multicomponent photocatalytic materials for H2 evolution is essential for optimizing activity. In this work, we performed atomistic molecular dynamics simulations and enhanced free energy sampling to understand selectivity and transport mechanism of water, redox ion pair Fe3+/Fe2+, H2 and O2 in contact with liquid water permeating through ultrathin oxide coatings, and elucidate the effects of chemistry and porosity of the coating. Our simulations demonstrate that water and O2 can easily transport through the porous coatings to enable H2 evolution at the underneath interface. Transport of Fe3+ and Fe2+ ions through the pores is limited due to high energy barriers, supporting the experimental findings showing that coatings severely limit Fe3+/Fe2+ redox by blocking its access to the underneath interface. The simulations suggest possible mechanisms that explain different kinetic energy barriers experienced by water, O2, H2, Fe3+ and Fe2+ions. Our findings can be used to fine tune coatings for improved desirable chemical reactivity in hydrogen evolution.

Unraveling selectivity and transport mechanism in photocatalytic materials coated with porous selective coatings

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ACS Fall 2022

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