Allen Bai

Effects of electroplating variables on the composition and morphology of nickel–cobalt deposits plated through means of cyclic voltammetry

Abstract The effects of temperature and pH of the plating baths as well as the potential range and cycle number of cyclic voltammetry on the composition and morphology of NiCo deposits were systematically investigated. A reaction scheme corresponding to the NiCo codeposition was proposed. Nickel–cobalt deposits with the composition approximately equal to their corresponding plating solutions (based on the metal content) were formed when pH of the plating bath was equal to 2.0 and the potential range of CV was between 0 and −1.2 V. This complete depression in the anomaly of NiCo codeposition was attributed to the anodic dissolution of the freshly deposited metal atoms resulting in the simultaneous dissolution of the adsorbed monohydroxide species occurring between −0.3 and 0 V. The effects of temperature and pH of the plating bath, the cycle number and potential range of CV on the morphology, loading, or crystalline structure of NiCo deposits were also compared.

Optimization of Hydrogen evolving activity on Nickel–Phosphorus Deposits using Experimental Strategies

The effects of electroplating variables on the hydrogen evolving activity of Ni–P deposits were systematically examined using fractional factorial design (FFD), path of steepest ascent, and central composite design (CCD) coupled with the response surface method (RSM). The FFD study indicates that the main and interactive effects of temperature, pH, and NaH2PO2·H2O concentration are the key preparation factors influencing the Ni–P cathode. Empirical models for apparent activity (i), specific activity (i/Ra), and phosphorus content (at %) are fitted against these three variables in the CCD study. These models, represented as contour diagrams, show that a Ni–P deposit with 7P at % exhibits the maximum electrocatalytic activity.

Composition control of electroplated nickel-phosphorus deposits

The influences of electroplating variables, such as temperature, current density, pH, NaH2PO2·H2O concentration and agitation rate, on the phosphorus content of Ni–P deposits electroplated from a Watts nickel bath modified with NaH2PO2·H2O are systematically compared using fractional factorial design (FFD). A very strong interactive effect on the Ni–P composition exists between the current density of deposition and pH of the modified Watts nickel bath. The effects of temperature and current density of electroplating on the phosphorus content of Ni–P deposits are further examined using the path of the steepest ascent and central composition design (CCD). On the basis of the results and discussion in the experimental design sections, various Ni–P deposits with approx. 0–28 at.% phosphorus can be galvanostatically electroplated by controlling the key variables.

Iron–cobalt and iron–cobalt–nickel nanowires deposited by means of cyclic voltammetry and pulse-reverse electroplating

Abstract Metal nanowires composed of Fe–Co and Fe–Co–Ni alloys were successfully prepared by means of cyclic voltammetry (CV) and pulse-reverse (PR) electroplating techniques from acidic metal chloride solutions. The anodic dissolution process in the CVs or in the reverse electroplating period was found to be the key factor influencing the formation of metal nanowires. The addition of nickel into the Fe–Co alloy was found to extend the diameter of these nanowires. The morphology and crystalline information of these alloy deposits prepared by CV and PR deposition techniques were obtained from the field-emission scanning electron microscopic (FE-SEM) photographs and X-ray diffraction (XRD) patterns, respectively.

The Inhibition of Anomalous Codeposition of Iron-Group Alloys Using Cyclic Voltammetry

Binary iron-group deposits, including Co-Ni, Fe-Co, Fe-Ni, Zn-Fe, and Zn-Ni alloys, with composition equal to that of the plating baths, were electroplated using cyclic voltammetry (CV) in suitable potential regions. Three processes, corresponding to cathodic deposition, double-layer response, and anodic dissolution, were found on the CV curves of deposition. The dissolution of newly deposited metal atoms caused the codissolution of an adsorbed monohydroxide layer in the anodic dissolution process, resulting in the inhibition of anomalous codeposition for these iron-group alloys. This proposal was further confirmed by an electrochemical impedance spectroscopic study. The anodic stripping of linear sweep voltammetry and the X-ray diffraction patterns demonstrated the poor-crystalline or amorphous nature of Zn-Ni alloys in different phases.

Composition control of ternary Fe/Co/Ni deposits using cyclic voltammetry

Ternary FeCoNi alloys were electroplated through mean of cyclic voltammetry in simple chloride baths with pH of 2.0. The anodic process in the voltammetric curves was found to completely depress the anomalous deposition of binary alloys while this anomaly was still obvious for the deposition of ternary FeCoNi alloys. From the energy-dispersive X-ray results, the Fe/Co ratio in the ternary FeCoNi deposits was equal to the Fe2+/Co2+ ratio in the deposition solutions when the Ni2+ content was continuously changed. The composition of ternary FeCoNi deposits could be precisely predicted and easily controlled by adjusting the Ni2+/(Fe2++Ni2++Co2+) ratio in the plating solutions although a synergistic effect in depressing the codeposition of Ni onto the FeCoNi matrix due to the coexistence of Co2+ and Fe2+ was clearly demonstrated in this work.

Cyclic voltammetric deposition of nanostructured iron-group alloys in high-aspect ratios without using templates

Abstract This work demonstrates the possibility in potentiodynamic deposition of nanostructured Fe–Co–Ni deposits (including nanoparticles, nanowires, nanonetworks, and nanowalls) without the employment of templates. The formation of whiskers on the deposit surface is promoted by the employment of the anodic process in the CV deposition. The high-aspect ratio deposition of nanowires, nanonetworks, nanowalls, and nanoplates can be achieved by changing the scan rates of CV and total concentrations of precursors in the plating bath. The formation and control of these nanostructures of Fe–Co–Ni deposits are attributable to a combined effect of the tip-discharge phenomenon and the diffusion of metal ions. The crystalline information of these nanostructured Fe–Co–Ni deposits is obtained from the grazing incident X-ray diffraction patterns.

Preparation of Iron-Group Nanoparticles by Means of Cyclic Voltammetry and Pulse-Reverse Plating

Nanostructures made of Co metal and Fe-Co-Ni alloys were successfully prepared by means of cyclic voltammetry (CV) and pulse-reverse (PR) plating techniques in simple chloride deposition solutions. Cobalt nanoparticles without whiskers or nanowires could be prepared by using CV plating without the anodic dissolution process under a scan rate of 50 mV/s. The diameter of each Co nanoparticle decreased as the scan rate of CV plating increased. The Co nanoparticles were found to homogeneously disperse on the electrode surface when a pre-deposited film composed of Co provided nucleation islands for the growth of these particles. The diameter of the Co particles ranged from 60 to 110 nm as the CV scan rate varied from 50 to 20 mV/s. The anodic dissolution process of PR and CV plating was found to be the key factor promoting the formation of Fe-Co nanowires on Fe-Co-Ni nanoparticles. The diameter of the Fe-Co-Ni nanowires varied between 20 and 40 nm, while the diameter of the Fe-Co-Ni nanoparticles varied from 110 to 130 nm. The morphologies and crystalline information of these iron-group deposits, prepared using CV and PR plating techniques, were examined through field-emission scanning electron microscopic (FE-SEM), atomic force microscopic (AFM), and X-ray diffraction (XRD) analyses.