Electrochemical investigation of surface-bound and encapsulated molecular wires

CO2 electrocatalytic reduction has been proposed as a potential method to store energy from a renewable source in the form of hydrocarbon fuels. However, the activity, selectivity, and durability of contemporary catalysts still need to be improved to make a significant impact. The electrode electronic structure seems to be the key to an effective catalyst, but it is a difficult property to tune. In this study, we address this difficulty by examining a new semiconductor-insulator-metal structure with a buried conjugated molecular wire (CMs), which we adapt to be a cathode for CO2 electrocatalytic reduction. This structure enables modifying the catalyst (metal nanoparticle) electronic properties through tuning the substrate (semiconductor-CMs-insulator) properties. For this purpose, we fabricated a ZnO/CMs@Al2O3 electrode. Here we examine its structural and electrochemical properties.

A silane linker molecule was covalently attached to the ZnO surface as an anchoring group. CMs were connected to the linker by a peptide bond, and the molecular compound was encapsulated in a stiff, ultrathin insulating layer, by atomic layer deposition (ALD). FTIR spectroscopy, XPS and ellipsometry were used to characterize each step. Cycle voltammetry with a water-soluble redox couple was used for pinholes testing and charge transfer characterization.

The use of a silane linker molecule and peptide coupling chemistry between the ZnO and the organic CMs proved as a more selective and reproducible method for CMs attachment, compared to the unsuccessful direct electrostatic attachment of the CMs to the ZnO surface. We built suitable and pinholes-free ALD procedures for the ZnO and Al2O3 layers at 125ºC and 80ºC respectively that maintain the integrity of the CMs in the ALD encapsulation process. By creating this new catalyst support structure, we aim to achieve a platform to modify the catalyst electronic properties and influence its activity, selectivity, and durability during CO2 electrocatalytic reduction.