Filling in Nanoporous Gold with Silver via Bulk Deposition and Surface-Limited Redox Replacement Approaches

Abstract This work reports on the development of an all-electrochemical metal-filling of nanoporous structures via conformal deposition. The study focuses on the Ag-filling of nanoporous Au (np-Au) using both overpotential (bulk) deposition (OPD) and electrochemical atomic layer deposition by surface-limited redox replacement (SLRR). The SLRR protocol shows advantageous generation of uniform Ag filling by layer-by-layer deposition throughout the nanometer-sized porous substrate as opposed to OPD that features drawbacks including incomplete filling and clustered deposition outside of the pores. The np-Au structure to be filled with Ag is obtained by de-alloying of Cu from an electrodeposited Au-Cu precursor alloy. In both approaches, the Ag-filled np-Au composites feature an electrochemically active surface area that is comparable to that of the original precursor alloy, as monitored by cyclic voltammetry of Pb underpotential deposition (Pb UPD). Scanning electron microscopy (SEM) is also employed to characterize both the composites’ surface and cross-section morphology and the SEM findings generally corroborate the Pb UPD results. Finally, a secondary Ag de-alloying was performed to ascertain that Ag filling via SLRR is more uniform than that performed via OPD.