Facile and Rapid Electrochemical Conversion of Ni into Ni(OH) 2 Thin Film as the Catalyst for Direct Growth of Carbon Nanotubes on Ni Foam for Supercapacitors.

In this paper, a facile and rapid aqueous-based electrochemical technique was used for the phase conversion of Ni into Ni(OH) 2 thin film. The Ni(OH) 2 thin film was directly converted and coated onto the network surface of Ni foam (NF) via the self-hydroxylation process under alkaline conditions using a simple cyclic voltammetry (CV) strategy. The as-formed and coated Ni(OH) 2 thin film on the NF was used as the catalyst layer for the direct growth of carbon nanotubes (CNTs). The self-converted Ni(OH) 2 thin film is a good catalytic layer for the growth of CNTs due to the fact that the OH - of the Ni(OH) 2 can be reduced to H 2 O to promote the growth of CNTs during the CVD process, and therefore enabling the dense and uniform CNTs growth on the NF substrate. This binder-free CNTs/NF electrode displayed outstanding behavior as an electric double-layer capacitor (EDLC) due to the large surface area of the CNTs, showing excellent specific capacitance values of 737.4 mF cm -2 in the three-electrode configuration and 319.1 mF cm -2 in the two-electrode configuration, at the current density of 1 mA cm -2 in a 6 M KOH electrolyte. The CNTs/NF electrode also displayed good cycling stability, with a capacitance retention of 96.41% after 10,000 cycles, and this the excellent cycling performance can be attributed to the stable structure of the direct growth of CNTs with a strong attachment to the NF current collector, ensuring a good mechanical and electrical connection between the NF collector and the CNTs.