| The electrochemical oxidation of methanol and other small organic molecules is widely involved in fuel cell research.At present,extensive investigations are being carried out on Pt,Pd and other related electrode materials,which are commonly used as catalyst in the electrochemical oxidation of methanol.However,the application is restricted in the lab scale due to its poisonous characteristics and high cost.Nickel and its related compounds have many advantages,such as low cost and wide sources. Besides,most of them have some catalytic activity to the oxidation of methanol and other alcohol molecules.Since 1970s,oxidation of small organic molecule compounds such as methanol and ethanol at various forms of nickel electrode in alkaline medium has drawn considerable attention.The research found that only Ni dispersed on graphite showed a catalytic activity on methanol oxidation while massive Ni did not.It also suggested that the catalytic activity of the Ni/C electrodes towards methanol oxidation varied with the amount of electro-deposited Ni.In the methanol oxidation catalytic reaction,Ni3+was the only effective catalyst.So we synthesized Ni(OH)2 directly,avoiding the transition process from single nickel to Ni2+.Pure Ni(OH)2 and Ni(OH)2 doped with different additives were synthesized by solid-state reaction at room temperature.The crystal structures of samples were tested by XRD.The electro-catalysis to the methanol oxidation was investigated. Also the effects of coating proportion,concentration of methanol,crystal structure of Ni(OH)2,species and content of additives were studied.The following results were obtained:1.Pure Ni(OH)2 without any additives were synthesized by the solid state reaction of NiSO4·6H2O and NaOH at room temperature.The XRD results revealed that the pure Ni(OH)2 wasβtype.The substituted Ni(OH)2 samples such as aluminum,zinc,cobalt,manganese substituted were also prepared by solid-state reaction at room temperature.The XRD results revealed that Ni(OH)2 substituted with 20%aluminum wasαform,while other samples were allβform.2.The reversibility of the electrode with different coated proportion was investigated.The experiments showed that the best reversibility was obtained at the mass ratio of 55:40:5(active substance:carbon powder:PTFE).3.The effect of the methanol concentration was also investigated.As the methanol concentration raised from 0.1mol/L to 0.5mol/L,the steady-state current trends showed a gradual increase with a gradually decreased rate.Finally,a solution with 0.1mol/L CH3OH +1 mol/L KOH was selected as the electrolyte solution for all the experiments.4.Regardless of their crystal structure,Ni(OH)2 had some catalytic effect towards the oxidation of methanol in alkaline media.According to the results of cyclic voltammetry and chronoamperometric experiments,the catalytic effect ofβ-Ni(OH)2 was better thanα-Ni(OH)2,the reason might be the oxidation potential ofβ-Ni(OH)2 was relatively lower.5.In order to find out a more suitableβ-Ni(OH)2 as methanol oxidation catalyst,we synthesized samples with different proportion and different elements such as zinc,cobalt,manganese.The tests of cyclic voltammetry and chronoamperometric revealed the electro-catalysis performances of different electrodes.In comparison with pure Ni(OH)2,the catalytic effect of substituted samples showed certain improvement.Among all samples,15%zine,5%cobalt and 10%manganese showed the best catalytic effect respectively,while the sample with 10%manganese was the best among all.This demonstrated that the doping metal ions could increase the catalyst efficiency of nickel hydroxide. |
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