Ni Microspheres as Electrocatalysts for Ethanol Oxidation in an Alkaline Medium

摘要

We report the synthesis of nickel microspheres and their structural and electrochemicalcharacterization. The materials were prepared by the microemulsion technique from NiSO4?6H2O andNaOH, and using NaH2PO2?H2O as a reducing agent. Sodium dodecyl sulfate (SDS) was used as asurfactant. The following ternary formulations were used for their synthesis: N1 (90%H2O-7.5%SDS-2.5%Pentanol), N2 (92.5%H2O-5%SDS-2.5%Pentanol), N3 (95%H2O-3.75%SDS-1.25%Pentanol)and N4 (99%H2O-0.75%SDS-0.25%Pentanol). The catalysts were characterized by scanning electronmicroscopy (SEM) and X-ray diffraction (XRD). The catalytic activity for ethanol oxidation in analkaline medium was evaluated by cyclic voltammetry (CV) and electrochemical impedancespectroscopy (EIS). The average diameters of the nickel microspheres ranged from 0.375 to 1.476 ?m.On subjecting the materials to heat treatment in a nitrogen atmosphere at 300 °C for 4 h, mixtures ofpolycrystalline Ni and nickel phosphide (Ni3P) were obtained. The best performance for the ethanoloxidation reaction (EOR) in an alkaline medium was recorded with non-heat-treated nickelmicrospheres, presenting a maximum peak potential at approximately 0.7 V vs. Hg/HgO withnormalized currents between 10.774 and 18.198 mA(mgcat)-1. These results indicate that nickelmicrospheres are potential candidates for use as anodes in alkaline direct alcohol fuel cells (ADAFCs).