Preparation Of Electroless Ni-P-TiO2Composite Coating And Its Application To Electrocatalytic-oxidation Methanol And Ethanol

In this paper, Ni-P-TiO2composite coatings were prepared by electroless technique from Ni-P plating bath containing TiO2powder on brass, technological parameter and electrocatalytic oxidation methanol and ethanol properties of Ni-P-TiO2composite coatings were discussed.In term of technological process, effect of main salt concentration, TiO2recruitment, surfactant, stabilizer and technological conditions such as stirring speed, bath pH, bath temperature and plating time are studied to obtain suitable process parameters by single-factor experiment. Results show that the optimum process parameters are as follows: stirring speed200-250r/min, bath pH=5.0, bath temperature85～90℃and plating time60min. Methods to obtain the best bath composition of Ni-P-TiO2electroless plating with the orthogonal test of four factors that is nickel satl(NiSO4·6H2O), reducing agent(NaH2PO4· H2O), complexing agent(C6HgO7) and buffering agent(NaOOCCH2CH2COONa) at three different levels. According to deposition rate and Ti content in the coatings, the optimum bath composition is as follows:30g/L NiSO4·6H2O,30g/L NaH2PO2·H2O,8ml/L C3H6O3,3g/L C6H8O7-H2O,4.5g/L CH3COONa,7g/L NaOOCH2CH2COONa,2mg/L CH4N2S,0.15g/L C18H29SO3Na.The microstrcuture, morphology, composition, corrosion resistance, bonding force and specific surface area of the Ni-P-TiO2composite coating were studied by XRD、SEM、EDS and electrochemical workstation ect.The experiment results show:TiO2particles are embedded in the deposit to form the Ni-P-TiO2composite coating, TiO2particles contained in the coating distributes evenly throughout the coating. The incorporation of TiO2in the coating resulted in increased specific surface area of the composite coatings. XRD spectrum of the Ni-P-TiO2composite coating indicates that characteristic absorption bands which belong to TiO2, this is to say that TiO2particles exist in the coating surface. In respect of bonding force, using thermal shock test and bending stress experiment show that the Ni-P coating and Ni-P-TiO2composite coatings have well bonding force. In respect of corrosion resistance, the corrosion resistances were tested with Tafel experiment in5%H2SO4, analysis of Tafel curves demonstrate that Ni-P coating has the better function of corrosion resistance than Ni-P-TiO2composite coating, and the more Ti content in composite coating, the better corrosion resistance of composite coating.Cyclic voltammetry, linear sweep voltammetry (LSV), chronoamperometry and electrochemical impedance spectroscopy (EIS) were used to test the electrocatalytic oxidation performance of Ni-P-TiO2electrodes. It was shown that:the electrocatalytic oxidation process of Ni-P-TiO2electrode b3(W(Ti content of coating surface)=19.35%) in1mol/L KOH solution was a reversible process and electrode reactions were carried on Ni(OH)2/NiOOH. Ni-P-TiO2electrode b3has excellent electrocatalytic activities for the oxidation methanol and ethanol. The kinetic parameters of Ni-P-TiO2electrode b3electrocatalytic oxidation methanol and ethanol were determined by the steady polarization curves. The onset potential and peak potential of Ni(II) oxidation on the Ni-P-TiO2electrodes were lower than those on the Ni-P electrode. It showed that the electrocatalytic oxidation activity of the Ni-P-TiO2electrodes were superior to Ni-P electrode. The electrocatalytic oxidation activity of the Ni-P-TiO2electrodes depended on the content of TiO2in the coating. Ni-P-TiO2electrode b3has most excellent electrocatalytic capacity.