Preparation and characterization of Grafoil/Ni and polyaniline/Ni composites from the controlled electrochemical reduction of NiCl4 2

The controlled reduction of a nickel metal anion, NiCl₄²⁻, at a carbon (Grafoil) and Polyaniline (PANI) electrode is explored. The incremental increase of Ni deposits is achieved from the reduction of the metal precursor at both electrodes. The normal oxidation/reduction was used to facilitate the uptake and dispersion of the precursor using electrostatic interactions with the positively charged PANI. The controlled in-situ reduction of the dispersed Ni precursor in the polymer was utilized to produce PANI/Ni composites with variable metal content. Scanning electron microscope (SEM) analysis and energy dispersive x-ray (EDX) spectroscopy of both substrates confirm the reduction of the Ni metal precursor at both electrodes. The chemical reactivity of the Ni metal deposited was also confirmed for both substrates using surface specific electrochemical reactions including the formation/reduction of oxidized nickel species and the catalytic oxidation of methanol in alkaline solutions (pH ≈ 14). The electrochemistry associated with NiOOH/Ni(OH)₂ and the catalytic oxidation of methanol is resolved in alkaline solution for both electrodes. Furthermore, the electrochemical activity of PANI/Ni composite materials is maintained without acid doping the polymer. Finally, an alternative pathway for the inclusion of anionic transition metal species in PANI that eliminates the competitive uptake of proton and metal cation precursors commonly used in traditional acidic environments is demonstrated.