Electrodeposition of Nickel Hydroxide Nanoparticles on 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