Nucleation and Aggregative Growth of Palladium Nanoparticles on Carbon Electrodes: Experiment and Kinetic Model

Abstract

The mechanism and kinetics of the electrochemical nucleation and growth of Pd nanoparticles (NPs) on carbon electrodes have been investigated using a microscale meniscus cell on both highly oriented pyrolytic graphite and a carbon coated transmission electron microscopy (TEM) grid. Using a microscale meniscus cell, it is possible to monitor the initial stage of electrodeposition electrochemically, while the ability to measure directly on a TEM grid allows subsequent high resolution microscopy characterization which provides detailed nanoscopic and kinetic information. TEM analysis clearly shows that Pd is electrodeposited in the form of NPs (approximately 1 − 2 nm diameter) that aggregate into extensive nanocrystaltype structures comprised of NPs. This gives rise to a high NP density. This mechanism is shown to be consistent with double potential step chronoamperometry measurements on HOPG, where a forward step generates electrodeposited Pd and the reverse step oxidizes the surface of the electrodeposited Pd to Pd oxide. The charge passed in these transients can be used to estimate the amounts of NPs electrodeposited and their size. Good agreement is found between the electrochemically determined parameters and the microscopy measurements. A model for electrodeposition based on the nucleation of NPs that aggregate to form stable structures isproposed that is used to analyze data and extract kinetics. This simple model reveals considerable information on the NP nucleation rate, the importance of aggregation in the deposition process and quantitative values for the aggregation rate.

Scanning electrochemical cell microscopy: New perspectives on electrode processes in action

“…By avoiding the need to fully immerse the substrate (as in SECM), SECCM opens up the possibility to work with a wide range of substrate materials, with electrodes ranging from polycrystalline metal foils (i.e., "pseudo single crystal" approach [15][16][17][18]), photoactive materials (e.g., semiconductors or polymers [19,20]) and other unusual substrates (e.g., transmission electron microscopy, TEM grids [21][22][23] or battery materials [6]). Beyond 5 electrode surfaces, it is worth noting that insulating materials can also be studied with this meniscus-based format, from the dissolution of crystals [10] to the titration of static charge [11].…”

“…A particularly exciting substrate on which to perform SECCM is a TEM grid (see Figure 2A), as this allows direct characterization of deposited nanomaterials (e.g., NPs) to resolve fully the relationship between structure and function. For example, using this approach, the initial stages of palladium electro-deposition was elucidated on a carbon TEM grid substrate, and a model for electrodeposition based on the nucleation of NPs that aggregate to form stable structures (aggregative growth mechanism) was proposed [21]. In a more recent study [23•], a chemical vapour deposition (CVD) grown graphene sheet was transferred by a polymer-free method to a TEM grid, and using SECCM, it was found that Cusupported graphene exhibited stronger wettability than suspended graphene, as exemplified in Figure 2B.…”

Tracking Metal Electrodeposition Dynamics from Nucleation and Growth of a Single Atom to a Crystalline Nanoparticle

“…[9][10][11] However, studies making use of advancements in microscopic analysis often show that these models are inappropriate descriptors for the early stages of nucleation and growth. 7,[12][13][14][15][16] Such work has led to factors such as electrochemically driven surface diffusion and aggregation being postulated as important pathways, 7,16 but to date such processes have yet to be dynamically visualized and thus confirmed. Furthermore, the resolution obtained using scanning probe techniques such as atomic force microscopy (AFM) and scanning electrochemical cell microscopy is typically limited to the nanoparticle (NP) level.…”

High-Throughput Correlative Electrochemistry–Microscopy at a Transmission Electron Microscopy Grid Electrode

“…Scanning electrochemical cell microscopy (SECCM) is a powerful tool in single-entity studies, in which the meniscus cell protruding from an electrolyte-filled micropipet (or nanopipet) probe is used to electrochemically interrogate a single or small population of supported NPs within an ensemble. ,− For example, in a recent study, SECCM was deployed as a high-throughput screening method to probe the heterogeneous response of individual LiMn 2 O 4 particles (a Li-ion battery cathode material), revealing a diverse library of responses within a family of superficially similar single-entities . The meniscus cell configuration of SECCM also enables local decoration (i.e., micro- or nanofabrication) at electrode surfaces, for example, with metal NPs, , polymer nanostructures, and graphene microwires . Here, we present a platform whereby PtNP “microensembles” are locally electrodeposited under a series of different (tunable) conditions and subsequently characterized ex situ with aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), allowing the relationship between the applied potential ( E app ) and the Pt deposit morphology (i.e., NP size, shape, and density) to be studied in a detailed high-throughput manner.…”