Nucleation and growth mechanism of a nanosheet-structured NiCoSe layer prepared by electrodeposition.

Ni-Co-Se layers have attracted a great deal of attention in the field of solar cells, electrocatalyst water splitting and supercapacitors. Electrodeposition is a simple, convenient and low-cost way to obtain Ni-Co-Se layers. However, until now, the electrochemical kinetics of the Ni-Co-Se system, including its growth and nucleation mechanisms, are still unclear. In present work a NiCoSe layer with a nanosheet structure was electrodeposited in a chloride bath. The electrochemical mechanisms of the Ni-Co-Se system were also studied. It is noted that the electrochemical kinetics of Ni-Co-Se electrodeposition can be influenced by both temperature and electrode material; however, temperature does not change the progressive nucleation process and mixed controlled growth mechanism of Ni-Co-Se. The diffusion coefficient D and charge-transfer coefficient α of the Ni-Co-Se system were calculated. The values of D obtained by cyclic voltammogram and chromoamperometry are close to each other at both 20 and 50 °C, respectively, and increase with the increase of temperature. Moreover, the activation energy E was also calculated. Specially, a uniform 3D network-structure NiCoSe layer was electrodeposited on ITO glass at -0.9 V and 40 ∼ 60 °C. The increased overpotential during deposition makes the NiCoSe layer more easily gather together; however, there is no significant effect on the surface morphology of the NiCoSe layer when the temperature is between 40 and 60 °C.