Galvanic Displacement Across Single-Layer Graphene for The Deposition of Metal Nanoparticles

This work aims to advance the scientific and engineering understanding of galvanic displacement reactions as buffered by a monolayer of graphene, specifically by investigating palladium deposition on graphene on a copper foil substrate via galvanic displacement between the copper and palladium (II) ions in solution. To understand palladium nanoparticle deposition and determine how this process can be controlled, electrochemical thermodynamics and classical nucleation theory are first synthesized into a thermodynamic model of the system. Next, scanning electron microscopy is used to characterize palladium deposition on the graphene/copper surface after galvanic displacement. Copper etch pits are observed to form during the reaction, maintaining contact between the deposition solution and the copper and thereby ensuring that the reaction is not self-limiting under the conditions studied. Palladium is observed to preferentially deposit along atomic steps in the copper foil, at graphene defects where the copper is exposed to the deposition solution, and at etch pits. The effects of varying palladium concentration and graphene/copper surface treatments are characterized, and these results are synthesized to propose a mechanism of palladium deposition via galvanic displacement through graphene. Finally, galvanic displacement is investigated in a novel engineering application, as a method of sealing graphene defects for the synthesis of centimeter-scale nanoporous atomically thin membranes. Palladium nanoparticles deposited on the graphene surface are observed to largely survive graphene transfer to a support membrane substrate, as well as mounting and use in aqueous diffusion cell experiments. However, diffusion experiments show that graphene treated via galvanic displacement has higher leakage than untreated graphene, indicating that under the reaction conditions studied here, galvanic displacement has a net effect of graphene defect enhancement rather than defect sealing. This work contributes new insights regarding galvanic displacement as a method of modifying monolayer graphene, as well as exploring this method in the novel application of membrane separations. With further development, this simple, quick, and inexpensive technique for the fabrication of 2D material/nanoparticle composites may have a myriad of applications relevant to sustainability and beyond.