Electrodeposition of nickel hydroxide nanoparticles onto carbon nanotube electrodes: correlation of particle crystallography with electrocatalytic properties

The use of two different electrodeposition approaches to form nickel hydroxide, Ni(OH)2, nanoparticles (NPs) of different crystallographic orientations on single-walled carbon nanotubes is demonstrated via: (i) the electrochemical generation of OH– (∼mM), in the presence of Ni2+, resulting in the formation of disordered α-phase Ni(OH)2 NPs by precipitation (direct approach); (ii) the electrodeposition of Ni NPs that are converted to Ni(OH)2 through potential cycling in alkaline media to form the more thermodynamically favorable, ordered β-phase Ni(OH)2 NPs (indirect approach). NPs produced by the direct approach exhibit remarkable electrocatalytic activity toward both methanol and ethanol oxidation, with excellent specific activities (SAs) of ∼2.8 kA g–1 for 0.5 M methanol and ∼3.7 kA g–1 for 0.5 M ethanol. In contrast, NPs produced by the indirect approach show SA values about an order of magnitude lower. This study demonstrates the capability of electrochemistry for the tailored synthesis of Ni(OH)2 nanostructures for electrocatalytic applications and a powerful, but simple, combinatorial approach for quick activity screening.