Research On Electrosynthesis And Corrosion Protection Property For Conducting Polythiophene And Polypyrrole

The conducting Polythiophene?PTh?and polypyrrole?PPy?have the advantages of good conductivity,environmental stability,easy synthesis and flexiblity by electrochemical synthesis,there are widely researched in supercapacitors,photoelectronic devices,sensor,biomedicine and metal anticorrosion etc.In this article,PTh and PPy were prepared on stainless steel.The surface morphology of PTh and PPy films were observed by scanning electron microscope?SEM?.The anticorrosion properties of PTh and PPy were investigated by methods such as circuit voltage curves,open-circuit potential-time curves,potentiodynamic polarization curves and electrochemistry impedance spectrum.The results of electrosynthesis for PTh showed that the increase of the content of nitromethane in boron trifluoride et herate?BFEE?was helpful to increase the synthesis current density and reaction rate,whereas the overhigh nitromethane content would lead the increase of non-conjugated structure of PTh and the destruction of the membrane.The PTh prepared in BFEE contain 10%?v/v,the following except for especially marking,the rest are all the same?nitromethane had kept the higher self-corrosion potential and the lower co rrosion current density than synthesis on other nitromethane content during the time of being immersed in0.1mol/L HCl.The results showed that the PTh electrosynthesized in BFEE electrolyte containing 10%nitromethane was anodic polarized to 1.5V?vs SCE?in0.1mol/L HCl+0.1mol/L H₂SO₄ solution,which still protected the stainless steel from corrosion,neither BFEE without nitromethane nor BFEE containing 50%nitromethane would have the behavior of anticorrosion and the anode dissolution current density to decrease.The PTh synthesized in electrolyte containing 10%nitromethane had been maintaining the higher charge transfer impedance on the surface of stainless steel and prevent ing the corrosion substance from premeating it for long time in 3.5wt%Na Cl.Above the experiment results turned out that the PTh synthesized in electrolyte containing 10%nitromethane had protected continuously the stainless steel substrate from corrosion.The reasons might that the PTh could have better mechanical prevention from cor rosion substance and the film doped with a certain amount of Cl O₄^-could passivate the stainless steel.PPy films doped with different passivator ions synthesized on the surface of stainless steel by electrosynthesis method.The PPy film prepared by citric acid was more completed and uniform than oxalic acid and nitric acid by SEM.Cyclic voltammetry of stainless/PPy in the 0.1 mol/L Na Cl showed that PPy films doped with the ions of citric acid and oxalic acid hardly dedoped.The PPy film synthesized by citric acid had beening maintaining a high open-circuit potential and a low corrosion current density for a long time,to play a very good anode protection effect.Neither synthesis by oxalic acid nor nitric acid did it.The results of electrochemistry impedance spectrum showed that the PPy synthesized by citric acid had a high membrane impedance and no the time constant corresponding to the membrane micropore for stainless steel when immersed in 0.2mol/L Na Cl for a long time.This illustrated that PPy doped citric acid as a passivator of stainless steel had a very good protective effect.ThePPypreparedonstainlesssteelbygalvanostatic in pyrrole+P-toluensulfonic acid solution with 0.15mol/L glutamic acid solution or not.The behaviors of the anticorrosio n to the stainless steel from PPy had been studied.The PPy doped with glutamate ions as well as not doped that could maintain the higher self-corrosion potentials during the intial of immersi on in solution of3.5wt%Na Cl.With the immersion time going on,the PPy doped with glutamate ions had been slowly decreasing the self-corrosion potentials and released glutamate ions to the surface of substrate of the stainless steel to form an anticorrosion film,which formed few of corrosion holes,but the undoped glutamate ions could cause the majority of corrosion holes on the stainless steel.The results of potentiodynamic polarization curves also demonstrated that the PPy doped with glutamate ions decreased the corrosion currents density of the the stainless steel rapidly during the soaking process.In the 0.3mol/L HCl solution,the electrochemistry impedance spectrum of the PPy undoped glutamate ions immersed for 1h,which showed the time constant with surface micropores,but the PPy doped with glutamate ions film appeared for 1.5h.It turned out that PPy doped with glutamate ions had a better protective effect on stainless steel.