Study On The Electrochemical Oxidation Of Formic Acid And Methanol On Pt Supported On Activated Carbon Doped Carbon Paste Electrode

Recently,with the rapid development of science and technology and the improvement of living standards,people's thirst for energy is increasing day by day.They are eager to find a new pollution-free energy with high energy conversion rate to replace the traditional fossil fuel energy.Hydrogen fuel cell is the cleanest energy source,but Hydrogen is not easy to be used due to its explosive nature,high cost,storage and transportation difficulties.Therefore,people focus on direct formic acid fuel cell?DFAFCs?and direct methanol fuel cell?DMFCs?.Because both formic acid and methanol are liquids at room temperature,they are easy to store and transport.In addition,formic acid and methanol are easy to obtain and have high energy density.These advantages accelerate the commercialization of direct formic acid fuel cell and direct methanol fuel cell.At present,pure Pt and Pt-based catalysts are the most studied catalysts in direct methanol fuel cell and direct formic acid fuel cell.However,Pt as a noble metal,has a low content in nature,which makes it expensive.Moreover,CO_ads,an intermediate,is generated when the formic acid and methanol are oxidized on the surface of Pt catalyst,which leads to the poisoning and deactivation of Pt.These problems restrict the development of DFAFCs and DMFCs.In order to reduce the amount of Pt catalyst and improve the utilization rate of Pt,carbon materials with better conductivity and larger specific surface area can be selected to be the supports of Pt catalyst,such as graphite and carbon nanotubes.In recent decades,conducting polymers,as a newly emerging organic semiconductor material,can also be used as support for Pt catalyst.In addition,Pt is combined with other metals?such as Pd,Cu,etc.?to improve the toxic resistance and electrocatalytic activity of Pt.In this work,Pt/CPE and Pt/CPEYBC?X%?composite electrodes with different contents of YBC carbon paste electrodes?CPE?were prepared and applied to the electrocatalytic oxidation of formic acid.Secondly,different Pt-Pd atomic ratios of Pt-Pd/CPEYBC composite electrodes were prepared and then their electrocatalytic oxidation activity toward formic acid was studied.At last,Polyo-aminophenol?POAP?,polyaniline?PANI?,polyo-methoxyaniline?POA?and polyo-methylaniline?POT?films were prepared on carbon paste bottom electrode(CPEYBC?12%?dopedwith12%YBCbycyclicvoltammetry?CV?.Pt/POAP/CPEYBC?12%?,Pt/PANI/CPEYBC?12%?,Pt/POA/CPEYBC?12%?and Pt/POA/CPEYBC?12%?were prepared by electrodeposition of Pt.Then the influence of the type and thickness of conducting polymer on the electrocatalytic oxidation of methanol was investigated.Finally,the effect of impurities on Pt electrocatalytic oxidation toward formic acid on Pt/CPEYBC?12%?electrode was investigated.The preliminary research contents of this experiment are as follows:?1?Distinctive electrocatalytic activity,impedance performance and stability of Pt on the activated carbon doped carbon paste electrode toward formic acid oxidationIn this work,a low cost and environmental friendly method has been prepared for YBC doped carbon paste electrode?CPEYBC?and carbon paste electrode?CPE?.Then,the electrodes of Pt/CPEYBC?X%?and Pt/CPE were prepared by electrodeposition of Pt on CPEYBC?X%?and CPE,respectively,in the presence of3.0 mM H₂PtCl₆ at a constant potential of-0.1 V.The prepared Pt particles are characterized by scanning electron microscopy?SEM?,electrochemical impedance spectra?EIS?and CV.The SEM images investigated that YBC influences morphology of the Pt particles,Pt was well dispersed on the bottom electrode CPEYBC?12%?.The EIS study indicates that Pt/CPEYBC?12%?has the minimum charge transfer resistance.In the process of electrochemical experiments,the ratio of YBC and graphite is crucial to achieve the best activity of electrocatalytic oxidation toward formic acid.The composite electrode Pt/CPEYBC?12%?doped with 12%content of YBC has better activity of electrocatalytic oxidation toward formic acid.What's more,the effects of scan rate,formic acid?HCOOH?concentrations towards HCOOH oxidation as well as long-term stability of the electrocatalyst have been investigated.?2?Different Pt-Pd atomic ratio catalysts were constructed and the electrocatalytic oxidation activity toward formic acid was investigated.The effects of different Pt-Pd atomic ratio catalysts on the electrocatalytic oxidation activity and stability of formic acid were studied.The prepared Pt-Pd were characterized by SEM,EIS and CV.Calculation of electrochemical activity specific surface area?EASA?of composite electrode using hydrogen absorption and dehydrogenation peak in CV.The SEM results showed that Pt-Pd3 were evenly distributed on the bottom electrode of CPEYBC?12%?.The EIS study showed that the Pt-Pd3/CPEYBC?12%?composite electrode had a small charge transfer resistance.Finally,the influence of Pt-Pd atomic ratios on the electrocatalytic oxidation activity toward formic acid was investigated,and the CVs of formic acid catalyzed by Pt-Pd catalyst were analyzed,the peak current of direct and indirect catalytic oxidation of formic acid was quantitatively analyzed.The experimental results showed that Pt-Pd atomic ratio was very important to achieve the best electrocatalytic oxidation activity toward formic acid.The composite electrode with higher electrocatalytic oxidation activity toward formic acid was Pt-Pd3/CPEYBC?12%?.?3?The effect of conducting polymer modified carbon material with Pt on the electrocatalytic oxidation toward methanol.Polyo-aminophenol?POAP?,polyaniline?PANI?,polyo-methoxyaniline?POA?and polyo-methylaniline?POT?with different film thickness were prepared by CV,Then,theelectrodesofPt/PAOP/CPEYBC?12%?,Pt/PANI/CPEYBC?12%?,Pt/POA/CPEYBC?12%?andPt/POT/CPEYBC?12%?werepreparedby electrodepositionofPtonPAOP/CPEYBC?12%?,PANI/CPEYBC?12%?,POA/CPEYBC?12%?and POT/CPEYBC?12%?,respectively,in the presence of 3.0mM H₂PtCl₆ at a constant potential of-0.1 V.The morphology of Pt/PAOP/CPEYBC?12%?,Pt/PANI/CPEYBC?12%?,Pt/POA/CPEYBC?12%?and Pt/POT/CPEYBC?12%?were characterized by SEM.The results showed that Pt particles were evenly distributed on POAP/CPEYBC?12%?bottom electrode.Meanwhile,the effects of POAP,PANI,POA and POT with the same number of preparation cycles on the electrocatalytic oxidation activity toward methanol were studied.These experimental results showed that the electrocatalytic oxidation activity toward methanol first increased with the increase of the number of preparation cycles of conducting polymers film,and when the number of preparation cycles of the polymer film reaches 6,the electrocatalytic oxidation activity toward methanol reached the maximum,then they decreased with the increase of the number of preparation cycles of the polymer film.When the number of preparation cycles was the same,different conducting polymers also had an effect on the electrocatalytic oxidation activity toward methanol,in which Pt/POAP/CPEYBC?12%?had the highest electrocatalytic oxidation activity toward methanol.?4?Effect of impurities on Pt/CPEYBC?12%?electrocatalytic oxidation toward formic acidThe effects of potential scan rate on the electrooxidation of formic acid was inverstigated at Pt/CPEYBC?12%?composite electrode.The adsorption of impurities on Pt surface and the effect of impurities on Pt electrocatalytic oxidation of formic acid were investigated by CV.The charge transfer resistance of working electrode in0.5 M H₂SO₄+0.3 M HCOOH system with different impurities was investigated by EIS.These results showed that the chloride ion?Cl^-?on the surface of Pt catalyst behaves like the intermediate CO_ads,adsorption on the surface of platinum catalyst,poisoned Pt,while,aniline and acetonitrile adsorbed on the surface of Pt catalyst,impeded the adsorption of intermediate CO_ads,and did not deactivate the Pt catalyst.