Study On The Preparation Of Ni/Transition Metal Composite Oxide Electrode And Its Structure And Performance Toward Oxygen Evolution Reaction

Hydrogen is a clean and efficient energy. It involves the preparation andutilization of hydrogen energy, such as water electrolysis, fuel cells, and so on. Inalkaline medium, the over-potential of the oxygen evolution reaction is too high, sothe greater energy consumption in the production and the electrode un-stability aremajor problems which limit the hydrogen development at present. A series ofresearch about the anode electrode preparation and properties toward the oxygenevolution reaction（OER）were carried out to solve this problems.For a wider application prospect, perovskite oxide LaNiO₃and spinel oxideNiCo₂O₄were mainly studied. LaNiO₃and NiCo₂O₄powders were prepared bysol-gel method and co-precipitation method, respectively. Their surfacemorphology and structure were characterized. As a result, the prepared LaNiO₃powder was narrow size distribution and nano-particles, the structure was theperovskite crystal; the diameter of the NiCo₂O₄power was micron level, and itsstructure was perfect spinel. The Ni/composite oxide electrodes was prepared bycomposite electro-deposition using nickel anode in a watt plating nickel solution byadding the composite oxide powders. The LaNiO₃content of the Ni/LaNiO₃composite coating is highest value （about60wt%） at the best plating conditions，which are the bath pH of5.8, the cathodic current density of90mA/cm²and a slowmagnetic stirring speed. The best preparation conditions of the Ni/NiCo₂O₄composite coating were as follows: the bath pH of6.2, the cathode current densityof100mA/cm²and slowly magnetic stirring. Weight percent of NiCo₂O₄in thecomposite coating was up to30.6wt%. The Ni/NiCo₂O₄porous compositeelectrode was prepared to increase the electrode specific surface area, so as toimprove the electro-catalytic activity toward OER. The NiCo₂O₄content （8.31wt%）and Al content （1.28wt%） of the Ni/NiCo₂O₄porous composite electrode wasobtained at the best plating conditions，which are the bath pH of6.4, the cathodecurrent density j_kof80mA/cm², the concentration of NiCo₂O₄in plating bath of60 g/L, the concentration of Al in plating bath of50g/L, the temperature of45°C, themagnetic stirring speed of400r/min.In a5mol/L KOH solution, the electro-catalytic properties toward OER of theelectrodes were studied using cyclic voltammetry, anodic steady-state polarization,chronoamperometry and electrochemical impendence spectroscopy （EIS）. Theresults showed that the initial oxygen evolution potential sequence from negative topositive followed as: the porous Ni/NiCo₂O₄composite electrode (0.250V（vs.HgO/Hg,0.1mol/LOH-，the same as follows）, the Ni/NiCo₂O₄compositeelectrode （0.320V）, the Ni/LaNiO₃composite electrode （0.410V）. The specificsurface area from larg to small order is as follow: the porous Ni/NiCo₂O₄compositeelectrode, the Ni/LaNiO₃composite electrode, the Ni/NiCo₂O₄composite electrode,the nickel electrode. The OER mechanism was studied by EIS. As a result, themechanism on these three electrodes is basically the same, but differentrate-determining step. The porous electrode is controlled by the adsorption and theelectrochemical reaction together. The long constant potential electrolysisexperiment was employed to study the electrodes stability of OER. In a5mol/LKOH and at electrolysis time over20h, the stability of the three compositeelectrodes is good, and the apparent current density of the porous electrode was thehighest. Thus, the Ni/NiCo₂O₄porous composite electrode toward OER possessesbest electro-catalytic activity and stability.