| In recent years, according to the scholars’the research progress about the preparation of nano-precious metals and the main problems.The nanomaterials that load on the other materials have a better catalytic performance,but their electrochemical catalytic performances are not very stable when the nanomaterials as electrodes.Unsupported nanoporous gold metal materials have high roughness and good electron transport capacity,so they have a high electrochemical catalytic activity and thermal conductivity,they are performance stability.We use the electrochemical alloying/dealloying method for the nanoporous precious metal preparation in this paper. We choose silver that the most commonly used in precious metals to research.Using the process of the electrochemical alloying,polarizing the smooth silver sample in the self-regulating battery at0mV voltage25hours for Ag-Li alloying compound.Making Ag-Li alloy samples to react with H2O for removing Li on the surface of the samples for nanoporous silver. Using X-ray diffraction (XRD),scanning electron microscopy (SEM) and lithium voltammetry tester and etc,to test every stages of the sample in the process about nanoporous silver’s preparation,analysing the pictogram and morphology changes of the various stages of sample preparation of nanoporous silver and the interrelated mechanism about the nanoporous silver. Studying electro-catalytic activity of nanoporous silver to HCHO.It was proved that using the electrochemical alloying method to execute the Ag-Li alloying compound by cyclic voltammetry experiments. It was found that lithium ion in the LiPF6restore to lithium atom at the smooth silver electrode surface in the electrochemical alloying process.The lithium atom reacted with smooth silver electrode, there were four new generation silver-lithium alloy compounds that were produced, LiAg, Li12Ag, Li10Ag3, Li9Ag4.The reaction was irreversible electrochemical reaction.It was counted that the rate of diffusion of lithium ions in metallic silver was2.03x10-12cm2S-1by results of potential step experiments in the self-assembly of the battery.It would happen that Li atom to enter the silver electrode internal in electrochemical alloying process.And it could reach a certain depth.It indicated that the electrochemical alloying reaction of Ag-Li alloy had a certain thickness.It was found the polarization of Ag-Li alloy sample surface with a layer of underpotential deposition through the analysis of Li atom after25hours at OmV.Under this layer of Li atoms with a certain thickness of the Ag-Li alloy compounds; Ag-Li alloy samples reacted with H2O, the Li atom on the sample surface was successfully removed completely through chemical corrosion dealloying process. Only Ag elemental existed, the sample was a nanoporous silver.The SEM images showed the Ag-Li alloy samples with rough surface, there were a large number of particles on it, and distribution of small cavities between the particles, the aperture was about0.5～1μm.The surface of the nanoporous silver samples also became rough after chemical etching dealloying process,the diameter of the particles was about200nm, the aperture was about30-70nm. This layer of silver nano-porous structure attached to the basal surface of the silver strip, It had a certain thickness, It was about15-17μm.According to the results of Cyclic voltammetry that the silver electrode in1.0M NaOH solution, it was calculated that anodic oxidation charge and the cathode to restore power of smooth silver electrode were111mA· S,119mA· S,and the anodic oxidation power of the nanoporous silver electrode and cathode restore power were1010mA· S,1019mA· S. The ratio of the anode oxidation power and the cathode restore power of the two electrodes were both about10.According to oxidation and reduction of power consumption and electrode micro proportional to the area. Comparing with the smooth silver electrode,the nanoporous silver electrode was prepared by using the electrochemical alloying/dealloying method, the microscopic surface area of the nanoporous silver was increased by10times at least. It was reached the requirement that to increase the specific surface area of the material.It was showed that the cyclic voltammetry results of the silver electrode in1M NaOH+0.1M HCHO mixed solution,to nanoporous silver electrode,the the oxidation potential of HCHO was-900mV,it’s oxidation potential was lower200mV than the smooth silver electrode’s.It was found that the oxidation current density of nanoporous silver is smooth electrode’s8times in the-500mV potential.At range of-900mV～-500mV, it was found that the oxidation current density of nanoporous silver was smooth electrode’s9times. The oxidation current density of nanoporous silver was5.7times than the smooth electrode’s in the-310mV.At range of-900mV ～310mV, it was found that the oxidation current density of nanoporous silver was smooth electrode’s7.5times.lt showed that compared with the smooth silver, nanoporous silver electrode for the electrochemical catalytic oxidation of HCHO has been greatly improved.The potential step experiment results of silver electrode in the1.0M NaOH+0.1M HCHO mixed solution when the open circuit direct transformed to-500mV, it showed that the current density of nanoporous silver electrode was19.6mA· cm-2at the polarization moment,it was6times than the smooth silver electrode’s.Current declined in, the current density of nanoporous silver electrode was12.6mA·cm-2after600s,it was more12times than the smooth silver electrode’s in the same time.。The potential step experiment results of silver electrode in the1.0M NaOH+0.1M HCHO mixed solution when the open circuit direct transformed to-300mV,it showed that the current density of nanoporous silver electrode was27.1mA· cm-2at the polarization moment,the current density became14.5mA· cm-2after37s,then the current density increased,it was21.3mA· cm-2after160s and kept stable,it was about22.7mA· cm-2after600s.It showed that the nanoporous silver electrode had greatly electrochemical activity at-300mV. |
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