Palladium nanoparticles and nanowires deposited electrochemically: AFM and electrochemical characterization

Abstract

Palladium nanoparticles and nanowires electrochemically deposited onto a carbon surface were studied using cyclic voltammetry, impedance spectroscopy and atomic force microscopy. The ex situ and in situ atomic force microscopy (AFM) topographic images showed that nanoparticles and nanowires of palladium were preferentially electrodeposited to surface defects on the highly oriented pyrolytic graphite surface and enabled the determination of the Pd nanostructure dimensions on the order of 50-150 nm. The palladium nanoparticles and nanowires electrochemically deposited onto a glassy carbon surface behave differently with respect to the pH of the electrolyte buffer solution. In acid or mild acid solutions under applied negative potential, hydrogen can be adsorbed/absorbed onto/into the palladium lattice. By controlling the applied negative potential, different quantities of hydrogen can be incorporated, and this process was followed, analysing the oxidation peak of hydrogen. It is also shown that the growth of the Pd oxide layer begins at negative potentials with the formation of a pre-monolayer oxide film, at a potential well before the hydrogen evolution region. At positive potentials, Pd(0) nanoparticles undergo oxidation, and the formation of a mixed oxide layer was observed, which can act as nucleation points for Pd metal growth, increasing the metal electrode surface coverage. Depending on thickness and composition, this oxide layer can be reversibly reduced. AFM images confirmed that the PdO and PdO 2 oxides formed on the surface may act as nucleation points for Pd metal growth, increasing the metal electrode surface coverage.

Linen fiber template-assisted preparation of TiO2 nanotubes: palladium nanoparticle coating and electrochemical applications

“…A similar behavior was reported earlier for Pd and Pd-Au alloys [38][39][40][41]. These effects are accompanied by changes in the current intensities, which may significantly increase or decrease after the hydrogen treatment, depending on the electrode composition.…”

Solid‐State Electrochemical Method for Determining Core and Shell Size in Pd@PdO Nanoparticles

“…As depicted in Figure 6a for Pd@PdO54, on initiating the potential scan at the open circuit potential (À 0.05 V vs. AgCl/Ag) in the cathodic direction, weak reduction peaks at À 0.28 and À 0.75 V are recorded while in the subsequent anodic scan, a prominent oxidation current at þ 0.45 V was recorded. This process is followed, in the second and successive cathodic scans, by a prominent reduction peak at À 0.48 V. This response can be interpreted on assuming that the PdO shell is first reduced to Pd metal via processes at À 0.28 and À 0.75 V (tentatively attributable to isolated and aggregated nanoparticles, respectively) to Pd metal and that the entire nanoparticles are oxidized to Pd 2þ (aq) at potentials above þ 0.45 V, consistently with data from Diculescu et al [55]. In the second and subsequent cathodic scans, the Pd 2þ ions in solution coming from the nanoparticle core, are massively reduced to Pd metal at À 0.45 V. The potential for the Pd to Pd 2þ oxidation in 0.10 M NaOH is close to that theoretically expected from thermochemical data, taking into account the pH of the media (E8(Pd 2þ /Pd) ¼ 0.62 V vs. AgCl/Ag at pH 0.0) [57].…”

In situ XAFS Study of Palladium Electrodeposition at the Liquid/Liquid Interface

“…In situ microscopic methods such as atomic force microscopy (AFM) or liquid-phase TEM can be utilised to follow the growth process [15][16][17][18]. The drawback of studying nucleation and growth through electrochemistry on a solid electrode is the presence of defects on the electrode surface which act as preferential nucleation sites causing heterogeneity within the reaction [19].…”