Nano-Folded Gold Electrocatalysts Enhance the Selectivity of Carbon Dioxide Reduction

Abstract

The local structure and geometry of catalytic interfaces can influence the selectivity of chemical reactions. Here, using a pre-strained polymer, we uniaxially compress a thin gold film to form a nano-folded catalyst. We observe two kinds of folds and can tune the ratio of loose to tight folds by varying the extent of pre-strain in the polymer. We characterize the nano-folded catalysts using x-ray diffraction, scanning, and transmission electron microscopy. We observe grain reorientation and coarsening in the nano-folded gold catalysts. Electroreduction of carbon dioxide with these nano-folded catalysts reveals an enhancement of Faradaic efficiency for carbon monoxide formation by a factor of about four. This result suggests that electrolyte mass transport limitations and an increase of the local pH in the tight folds of the catalyst outweigh the effects of alterations in grain characteristics. Together, our studies demonstrate that nano-folded geometries can significantly alter grain characteristics, mass transport, and catalytic selectivity.Electroreduction of carbon dioxide (CO2) to valuable carbon-rich products is a potential solution to end the anthropogenic carbon cycle. 1,2 However, slow kinetics and reduced control over product yield and selectivity have hindered widespread commercial viability. 3,4 Nanostructured catalysts offer the potential to address these limitations. 5 Indeed, a variety of nanoparticles, 6-9 thin films, 10-14 and nanoporous materials 15-18 have been explored, but there are still challenges with scalability, reproducibility, extreme reaction conditions, and cost. 6,10,12,15 Mechanical wrinkling of metallic thin films using pre-strained polystyrene (PS) substrates offers a reproducible strategy to create nanostructured interfaces. This approach is compatible with nanoparticles, 19 nanoporous, 20 thin films, 21,22 and twodimensional (2D) materials (e.g. graphene and MoS2), 23-28 and the morphology can be controlled using lithography. 24,25,29,30 Previous studies with wrinkled catalysts show improvement in different electrochemical reactions including hydrogen evolution reaction (HER), 25,27,28,30 glucose sensing, 31 and DNA detection. 32 For example, wrinkled platinum (Pt) arrays electrodes improved the performance of HER from ~70 mA/cm 2 to ~ 120 mA/cm 2 at 0.1 V as compared to conventional Pt on carbon. This improvement was attributed to weak adhesion of hydrogen (H2) gas bubbles, resulting in a lower overpotential.Here, for the first time, we present evidence that a nano-folded gold (Au) catalyst can improve the selectivity of CO2 reduction. We utilized a pre-strained PS substrate to uniaxially compress and create a novel Au catalyst with a combination of loose (>200