Electrocatalytic and Optical Properties of Cobaloxime Catalysts Immobilized at a Surface-Grafted Polymer Interface

We report on the electrocatalytic and optical properties of cobaloxime hydrogen production catalysts assembled on a polymer-modified nanostructured indium tin oxide (nanoITO) electrode. The hybrid construct is assembled using built-in ligand sites (pyridyl groups) of the surface-attached polymer to direct, template, and assemble cobaloxime units. The conductive nature of the nanoITO substrate allows direct electrochemical measurements of the Co^III/Co^II and Co^II/Co^I redox couples of the cobaloxime-polyvinylpyridine assembly recorded in organic electrolyte solutions, confirming the polymer interface used in this work does not preclude formation of reduced cobalt species. Electrochemical measurements using modified and nonmodified nanoITO electrodes in buffered aqueous solutions indicate the immobilized cobaloxime units remain catalytically active. The relatively large surface area of the nanostructured support, coupled with its visual transparency, also permits optical characterization of the modified electrodes. In general, the cobaloxime-polymer assembly possesses optical and electronic properties similar to those of the non-surface-attached counterpart, albeit with enhanced chemical reversibility. We propose that the unique encapsulating environments of surface-grafted polymeric architectures can provide a molecular strategy for improving the chemical stability of surface-immobilized catalysts. The modular nature of the attachment chemistry used in this work should allow application to a range of catalysts, polymers, and transparent conducting oxide surfaces. Thus, the construct sets the stage for an improved understanding of structure-function relationships governing the optoelectronic and catalytic properties of surface-immobilized catalyst-polymer assemblies. (Chemical Equation Presented).