Some articles have revealed that the electrodeposition of calcium phosphate (CaP) coatings entails a precursor phase, similarly to biomineralization in vivo. The chemical composition of the initial layer and its thickness are, however, still arguable, to the best of our knowledge. Moreover, while CaP and electrodeposition of metal coatings have been studied utilizing atom-probe tomography (APT), the electrodeposition of CaP ceramics has not been heretofore studied. Herein, we present an investigation of the CaP deposition on a gold substrate. Using APT and transmission electron microscopy (TEM) it is found that a mixture of phases, which could serve as transient precursor phases to hydroxyapatite (HAp), can be detected. The thickness of these phases is tens of nanometers, and they consist of amorphous CaP (ACP), dibasic calcium phosphate dihydrate (DCPD), and octacalcium phosphate (OCP). This demonstrates the value of using atomic-resolved characterization techniques for identifying the precursor phases. It also indicates that the kinetics of their transformation into the more stable HAp is not too fast to enable their observation. The coating gradually displays higher Ca/P atomic ratios, a porous nature, and concomitantly a change in its density.
The activity of chiral self-assembled monolayers (SAMs) in electrochemistry is reviewed. Chiral SAMs have been used as a means of introducing stereoselectivity in electron transfer at the electrode/electrolyte interface. In most cases, a cysteine-based SAM was used on gold electrodes. Different attempts have involved the application of chiral thiolated molecules, e.g., cyclodextrin, imprinting of chiral objects and competitive complexation. More recently, spintronics in which magnetic fields applied next to chiral SAM induced chiral effects, were also reported. Yet, there is much room for additional and innovative ideas in this field of electrochemistry.
The formation and local deposition of well-shaped Au nanostructures on a nonconducting surface are described. Specifically, the local electroless deposition of Au in aqueous solutions in the presence of various n-alkylpyridinium surfactants is driven by electrochemically generating a flux of AuCl4- at a gold tip close to a 3-mercaptopropyltrimethoxysilane modified Si oxidized wafer. Two reducing agents, NaBH4 and ascorbic acid, were used for the reduction of the gold ions. We studied the effect of the solution temperature, the potential applied to the gold tip and its distance from the surface, the reductant, and the nature of the alkylpyridinium on the structure of the gold deposit. The chloride salts of methylpyridinium, butylpyridinium, cetylpyridinium, 4-carbamoyl-1-cetylpyridinium, and 4-methyl-l-cetylpyridinium were added separately and showed remarkable effect on the shape of the structures that were formed. We find that short chain n-alkylpyridinium salts do not adsorb preferentially on the gold facets, whereas the longer chain n-alkylpyridinium ions cause the formation of well-faceted Au structures, such as cubes, hexagons, and even multipods. Moreover, comparison between local and bulk deposition revealed a significant difference in Au structures that were formed, presumably due to the different concentration profile of the AuCl4-.
Chronoamperometry was used to study the dynamics of Pt nanoparticle (NP) collision with an inert ultramicroelectrode via electrocatalytic amplification (ECA) in the hydrogen evolution reaction. ECA and dynamic light scattering (DLS) results reveal that the NP colloid remains stable only at low proton concentrations (1.0mm) under a helium (He) atmosphere, ensuring that the collision events occur at genuinely single NP level. Amperometry of single NP collisions under a He atmosphere shows that each discrete current profile of the collision event evolves from spike to staircase at more negative potentials, while a staircase response is observed at all of the applied potentials under hydrogen-containing atmospheres. The particle size distribution estimated from the diffusion-controlled current in He agrees well with electron microscopy and DLS observations. These results shed light on the interfacial dynamics of the single nanoparticle collision electrochemistry.
The incorporation of spacers between graphene sheets has been investigated as an effective method to improve the electrochemical performance of graphene papers (GPs) for supercapacitors. Here, we report the design of free-standing GP@NiO and GP@Ni hybrid GPs in which NiO nanoclusters and Ni nanoparticles are encapsulated into graphene sheets through electrostatic assembly and subsequent vacuum filtration. The encapsulated NiO nanoclusters and Ni nanoparticles can mitigate the restacking of graphene sheets, providing sufficient spaces for high-speed ion diffusion and electron transport. In addition, the spacers strongly bind to graphene sheets, which can efficiently improve the electrochemical stability. Therefore, at a current density of 0.5 Ag-1, the GP@NiO and GP@Ni electrodes exhibit higher specific capacitances of 306.9 and 246.1 Fg(-1) than the GP electrode (185.7 Fg(-1)). The GP@NiO and GP@Ni electrodes exhibit capacitance retention of 98.7% and 95.6% after 10000 cycles, demonstrating an outstanding cycling stability. Additionally, the GP@NiO vertical bar GP@Ni delivers excellent cycling stability (93.7% after 10000 cycles) and high energy density. These free-standing encapsulated hybrid GPs have great potential as electrode for high-performance supercapacitors.