Electrochemical nucleation and growth of Cu onto Au nanoparticles supported on a Si (111) wafer electrode

Mechanism and Kinetics of Palladium Nanoparticles Electrochemical Formation onto Glassy Carbon, from a Deep Eutectic Solvent (Reline)

From electrochemical potentiodynamic and potentiostatic techniques, the electrodeposition mechanism and kinetics of palladium nanoparticles (PdNPs) onto a glassy carbon electrode (GCE), from Pd(II) ions dissolved in the choline chloride-urea deep eutectic solvent (reline) at 343 K, are reported for the first time. From the analysis of the potentiostatic current density transients, using the model developed by Palomar-Pardavé et al. [ Electrochim. Acta, 2005, 50, 4736-4745], it shows that the PdNPs electrodeposition occurs by multiple 3D nucleation and diffusion controlled-growth with the simultaneous reduction of residual water on the PdNPs growing surfaces. This model renders not just the quantification of the palladium nucleation kinetics parameters, but it effectively allows deconvolving the individual contributions to the total current and, thus, from the integration of the j-t plots of these contributions. It was demonstrated that the charge amount of each process depends on the deposition time and applied overpotential. From SEM images, it was possible to verify that the palladium deposits were constituted by PdNPs and from XPS measurements that these PdNPs were formed by a metallic palladium (core) and Pd(OH)₂ (shell).

Combined Experimental and Theoretical Study of the Structure of AuPt Nanoparticles Prepared by Galvanic Exchange

In this article, experiment and theory are combined to analyze Pb and Cu underpotential deposition (UPD) on ∼1.7 nm Au nanoparticles (NPs) and the AuPt structures that result after galvanic exchange (GE) of the UPD layer for Pt. Experimental Pb (0.49 ML) and Pt (0.50 ML) coverages are close to values predicted by density functional theory-molecular dynamics (DFT-MD, 0.59 ML). DFT-MD reveals that the AuNPs spontaneously reconstruct from cuboctahedral to a (111)-like structure prior to UPD. In the case of Pb, this results in the random electrodeposition of Pb onto the Au surface. This mechanism is a consequence of opposing trends in Pb-Pb and Pb-Au coordination numbers as a function of Pb coverage. Cu UPD is more complex, and agreement between theory and experiment takes into account ligand effects (e.g., SO₄^2- present as the electrolyte) and the electric double layer. Importantly, AuPt structures formed upon Pt GE are found to differ markedly depending on the UPD metal. Specifically, cyclic voltammetry indicates that the Pt coverage is ∼0.20 ML greater for Cu UPD/Pt GE (0.70 ML) than for Pb UPD/Pt GE (0.50 ML). This difference is corroborated by DFT-MD theoretical predictions. Finally, DFT-MD calculations predict the formation of surface alloy and core@shell structures for Pb UPD/Pt GE and Cu UPD/Pt GE, respectively.