Covalent attachment of molecular redox mediators to photoelectrode surfaces is a promising approach to designing integrated, freestanding photoelectrochemical devices capable of carrying out selective electrochemical reactions. As a photoelectrode material, microstructured silicon offers high surface area and orthogonal paths for light absorption and minority charge carrier diffusion, along with other advantages over planar silicon. However, while the surface chemistry of planar silicon is a relatively mature field, integration of even the archetypal redox reporter ferrocene onto high-aspect ratio silicon microwires presents challenges with respect to stability, characterization, and mass transport. This presentation will detail a method for the covalent attachment of vinylferrocene to chlorine-terminated silicon microwires. Using X-ray photoelectron spectroscopy (XPS) and electrochemistry, coverages of up to 30% of a monolayer of ferrocenyl groups were observed. Backfill of unreacted Si–Cl sites with methyl groups was used to generate ferrocenyl-terminated surfaces with stable cyclic electrochemical properties over extended periods in air and repeated electrochemical cycling. Electrodes constructed from ferrocenyl-decorated microwire arrays were applied in the (photo)electrocatalytic oxygen reduction reaction (ORR) of dioxygen to hydrogen peroxide.