Uncertainty analysis of factors affecting coating thickness distribution during nickel electrodeposition

Co-deposition of Co-Ni alloy catalysts from an ethylene glycol system for the hydrogen evolution reaction

The preparation of active, stable and low-cost non-noble electrocatalysts for the hydrogen evolution reaction (HER) using the electrochemical water splitting process is crucial for the promotion of sustainable energy. In this study, Co-Ni alloys with various Co contents are prepared using a galvanostatic method and the co-deposition behavior of Co²⁺ and Ni²⁺ in ethylene glycol (EG) is reported. These results indicate that the presence of additional Ni²⁺ species can accelerate the Co-Ni co-deposition process and Co²⁺ species in the system can inhibit the reduction of Ni²⁺. Moreover, the two effects are improved with an increase in Ni²⁺ or Co²⁺ species concentration in the EG system, respectively. Chronoamperometry records show that the Co-Ni electro-crystallization mechanism is one of 3D instantaneous nucleation and growth. Moreover, the Co-Ni alloy with 59.46 wt% Co exhibits high electrocatalytic activity for HER with an overpotential of 133 mV at 10 mA cm^-2 in 1 M KOH due to a high value of electrochemical active surface area (ECSA) (955.0 cm²). Therefore, the Co-Ni alloy electrocatalyst obtained from the EG system could be a promising candidate for practical hydrogen production.

Numerical and Experimental Investigation of the Effect of Current Density on the Anomalous Codeposition of Ternary Fe-Co-Ni Alloy Coatings

Gradient-structured ternary Fe-Co-Ni alloy coatings electrodeposited on steel substrates at various current densities from chloride baths were numerically and experimentally investigated. The electrodeposition process, considering hydrogen evolution and hydrolysis reaction, was modelled using the finite element method (FEM) and was based on the tertiary current distribution. The experimentally tested coating thickness and elemental contents were used to verify the simulation model. Although there was a deviation between the simulation and experiments, the numerical model was still able to predict the variation trend of the coating thickness and elemental contents. The influence of the current density on the coating characterization was experimentally studied. Due to hydrogen evolution, the coating surface exhibited microcracks. The crack density on the coating surface appeared smaller with increasing applied current density. The XRD patterns showed that the deposited coatings consisted of solid-solution phases α-Fe and γ (Fe, Ni) and the metallic compound Co₃Fe₇; the current density in the present studied range had a small influence on the phase composition. The grain sizes on the coating surface varied from 15 nm to 20 nm. The microhardness of the deposited coatings ranged from 625 HV to 655 HV. Meanwhile, the average microhardness increased slightly as the current density increased from 5 A/dm² to 10 A/dm² and then decreased as the current density further increased. Finally, the degree of anomaly along with the metal ion and hydrogen atom concentrations in the vicinity of the cathodic surface were calculated to investigate the anomalous codeposition behaviour.