Chemistry at the Interface: Polymer-Functionalized GaP Semiconductors for Solar Hydrogen Production

New opportunities for organizing and controlling molecular components arise with the use of a stabilizing organic layer composed of grafted polymer chains at a semiconductor surface. We highlight recent advances in our research efforts to use polymer brush coatings containing pendent ligands that direct and assemble molecular catalysts for fuel production to visible-light-absorbing substrates. We illustrate how the polymeric interface can be varied to control the structure and photoelectrochemical response of gallium phosphide (100) electrodes containing surface-immobilized pyridyl or imidazole ligands with attached cobaloximes for hydrogen production. Surface sensitive spectroscopic methods, including X-ray photoelectron spectroscopy, grazing angle total reflectance Fourier transform infrared spectroscopy, and ellipsometry provide structural information regarding the nanoscale molecular connectivity and mesoscale dimensions of the cobaloxime-containing polymer grafts. At the macroscale, three electrode photoelectrochemical testing of the cobaloxime-modified electrodes under simulated solar lighting conditions in pH neutral aqueous solutions show up to a 3-fold increase of hydrogen production as compared to results obtained using polymer-grafted electrodes without attached cobaloximes tested under nearly identical conditions.