Electrodeposition of Nickel Hydroxide Nanoparticles on Boron-Doped Diamond Electrodes for Oxidative Electrocatalysis

Abstract

We demonstrate, for the first time, the electrosynthesis of uniformly dispersed nickel hydroxide nanoparticles (NPs) on polycrystalline boron-doped diamond (pBDD). This has been achieved by electrogenerating OH− at the pBDD surface in the presence of Ni2+ to create local conditions near the electrode where highly supersaturated (relative saturation ratio > 105) nickel hydroxide solutions are generated for short periods of time (approximately seconds). This results in the deposition of nickel hydroxide NPs directly on the electrode surface, as confirmed by X-ray photoelectron spectroscopy. The NPs have a reasonably homogeneous size distribution and are deposited uniformly across the heterogeneous pBDD surface. We show that by simply increasing the electrogeneration time and, hence, increasing both the local concentration of OH− and extent of the precipitation reaction, it is possible to increase the size of the NPs. For example, after 1 s, NPs with dimensions of 12 ± 3 nm form, whereas after 15 s, NPs of size ∼39 ± 9 nm result. Longer times result in larger particles, which form aggregated structures. The effect of nickel hydroxide NP size on electrocatalytic activity was investigated by measuring the steady-state current for the oxidation of glucose in alkaline media. For NPs ≥ 25 nm in size, glucose oxidation is close to diffusion-controlled. However, for the smallest NPs produced (∼12 nm) the currents passed suggest kinetic limitations. For glucose at an effective surface coverage of nickel hydroxide of ∼20 nmol cm−2, equivalent to 15 ng of nickel hydroxide, this functionalized electrode showed a sensitivity of 330 μA mM−1 cm−2 and a limit of detection of 400 nM. The latter represents one of the lowest limits of detection for glucose for nickel hydroxide-based electrodes. The electrocatalytic oxidation properties of this electrode toward methanol and ethanol was also found to be very efficient, yielding very high density currents of ∼1010 A g−1 for 0.5 M ethanol and 990 A g−1 for 0.47 M methanol.