Photoelectrochemistry of Redox-Active Self-Assembled Monolayers Formed on n-Si/Au Nanoparticle Photoelectrodes

Controlling the chemistry of the electrode-solution interface is critically important for applications in sensing, energy storage, corrosion prevention, molecular electronics, and surface patterning. While numerous methods of chemically modifying electrodes exist, self-assembled monolayers (SAMs) containing redox-active moieties are particularly important because they are easy to prepare, have well-defined interfaces, and can exhibit textbook photoelectrochemistry. Here, we investigate the photoelectrochemistry of redox-active SAMs on semiconductor/metal interfaces, where the SAM is attached to the metal site instead of the semiconductor. n-Si/Au photoelectrodes were fabricated using a benchtop electrodeposition procedure and subsequently modified by immersion in aqueous solutions of (ferrocenyl)hexanethiol and mercaptohexanol. We explored the relevant preparation conditions, finding that after optimization, we were able to obtain canonical cyclic voltammetry for a surface-bound redox molecule that could be turned on and off using light. We then characterized the optimized electrodes under varying illumination intensities, finding that the heterogeneous electron transfer kinetics improved under higher illumination intensities. These results lay the foundation for future studies of semiconductor/metal/molecule interfaces relevant to sensing and electrocatalysis.