This presentation will describe unconventional electrocatalysts for which the active electrocatalyst component is encapsulated by ultrathin overlayers made of permeable oxides. In this work, 1-20 nm thick silicon oxide layers are synthesized with a room photochemical temperature process and deposited as uniform and continuous layers onto electrocatalytic Pt thin films. Through various electroanalytical measurements, we show that these oxide overlayers can be permeable to certain electroactive species such that electrocatalytic reactions occur at the buried interface between the overlayer and the active catalyst. For reactants having different permeabilities within the overlayer, selective transport from the bulk electrolyte to the buried interface greatly alters the concentration of the reactive species at the active sites, leading to significant changes to the reaction selectivity compared to an unencapsulated electrocatalyst. Because these overlayers exhibit selective transport properties, the electrocatalysts that are encapsulated by them may be referred to as membrane-coated electrocatalysts (MCECs). By varying the thickness and hydrophobicity of silicon oxide overlayers in MCECs, we analyze the influence of mass transport on the performance of thin film Pt electrocatalysts for the hydrogen evolution and methanol oxidation reactions. A reaction-diffusion model is described that is validated by hydrogen evolution experiments and used to predict maximum overlayer thicknesses for a given operating current density and species permeability. Importantly, this work highlights the potential for MCECs to be highly tunable electrocatalysts that should be of interest for a wide range of industrially-relevant electrochemical applications.

Ultrathin oxide overlayers for tunable electrocatalysis

2019 Fall National Meeting

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