In electrodeposition the key challenge is to obtain better control over nanostructure morphology. Currently, a lack of understanding exists concerning the initial stages of nucleation and growth, which ultimately impact the physicochemical properties of the resulting entities. Using identical location scanning transmission electron microscopy (STEM), with boron-doped diamond (BDD) serving as both an electron-transparent TEM substrate and electrode, we follow this process, from the formation of an individual metal atom through to a crystalline metal nanoparticle, under potential pulsed conditions. In doing so, we reveal the importance of electrochemically driven atom transport, atom cluster formation, cluster progression to a nanoparticle, and the mechanism by which neighboring particles interact during growth. Such information will help formulate improved nucleation and growth models and promote wider uptake of electrodeposited structures in a wide range of societally important applications. This type of measurement is possible in the TEM because the BDD possesses inherent stability, has an extremely high thermal conductivity, is electron beam transparent, is free from contamination, and is robust enough for multiple deposition and imaging cycles. Moreover, the platform can be operated under conditions such that we have confidence that the dynamic atom events we image are truly due to electrochemically driven deposition and no other factors, such as electron-beam-induced movement.

Nanoporous platinum nanoparticles (NPs) have been proposed as promising electrocatalytic materials. Routes to produce them typically consist of chemical synthesis or selective dissolution of one component of a two-component mix. Here we show that by employing a pulsed laser heating approach during electrodeposition, whereby the electrode/ electrolyte interface is continually heated and cooled, NPs with a nanoporous structure can be grown directly on the electrode (boron-doped diamond) surface. Transmission electron microscopy shows the NPs to be composed of loosely packed aggregates of much smaller crystalline particles of size 2−5 nm, with the porosity increasing with increasing deposition overpotential. In contrast, electrodeposition at room temperature (RT) results in particles which show a considerably more compact morphology and fewer higher index crystal facets, as revealed by electron diffraction techniques. Pulsed heating also offers a route toward controlling the monodispersity of the electrodeposited NPs. When applied to the oxidation of methanol, the laser-heated NPs show considerably higher catalytic current densities in comparison to RT-deposited particles. The highest catalytic activity is observed for the most porous NPs produced at the highest overpotential. Interestingly, the ratio of the forward oxidative current to the backward current is highest for those particles deposited under laser-heated conditions but with the smallest overpotential. This suggests that the most catalytically active NPs may also encourage binding of residual adsorbed carbon monoxide and that a compromise must be reached.

By changing the mole fraction of water (χwater) in the solvent acetonitrile (MeCN), we report a simple procedure to control nanostructure morphology during electrodeposition. We focus on the electrodeposition of...