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Encapsulating active electrocatalysts with permeable oxide overlayers offers additional “control knobs” for tuning electrocatalyst selectivity and/or activity in ways that are not possible with conventional electrocatalysts.[1] In particular, nanoscopic oxide overlayers can possess selective transport characteristics that allow them to behave as ultrathin membranes that can block impurities and undesirable reactants while still permitting desired reactants and products to pass between the bulk electrolyte and active sites at the overlayer/catalyst buried interface.[1,2] In this presentation, I will describe recent investigations of silicon and titanium oxide-encapsulated thin film electrodes that allow for quantification of species permeabilities and to establish general design principles that govern the structure-property-performance relationships for nanoscopic oxide overlayers. First, I will show how the porosity and chemical composition of silicon oxide overlayers can be systematically tuned to control the relative permeabilities of protons and molecular oxygen, both of which are of great importance for water splitting.[3] Next, the selective transport properties of these coatings are reported in the presence of redox mediator species that are of interest for photocatalytic H2 production from Z-scheme water splitting.[4] Both silicon and titanium oxide overlayers are shown to be capable of selectively facilitating the desirable oxygen and hydrogen evolution reactions with selectivities of > 80% in the presence of a reversible redox mediator. Importantly, this work highlights the ability of ultrathin oxide overlayers to dramatically alter reaction selectivities, and presents design rules for overlayers that can be extended to many other (photo)electrocatalytic materials and reactions of interest to the solar fuels community. References [1] D.V. Esposito, ACS Catalysis, 2018, vol. 8, 457–465. [2] N. Y. Labrador, et al. , ACS Catalysis, 2018, vol. 8, 1767–1778. [3] M.E. Beatty, et al., ACS Applied Energy Materials, (Articles ASAP), doi.org/10.1021/acsaem.0c02359 [4] Bala Chadran, et al., Energy & Environmental Science, 2018. vol. 1, 115-135 |
