The Reparation Of Electrode Modified By Poly-porphyrin And Study Of Catalytic Performance For Oxygen Reduction In Alkaline Medium

With the depletion of oil resources, the increasing of automobile exhaust emissions,worsening environmental pollution, the development of sustainability green energy andhigh utilization of energy is imminent! Fuel cell is a plant and conversion systemswhich the chemical reaction of fuel and oxidizer can be directly converted intoelectricity. Hydrogen fuel cell (FC) is attracting people’s widespread concern taking theadvantage of highly efficient pollution-free, accessible fuel and convenient to storageand carry. Platinum (Pt) is commonly used as cathode material of hydrogen fuel cell,however, its application is limitted for it is expensive and susceptible to carbonmonoxide (CO) poisoned. People are eager to find a new material to replace Pt. A largenumber of researches showed that metalloporphyrin not only have the uniqueconjugated structure and stability, but also exhibit good catalytic activity for the oxygenreduction both in acidic and in alkaline conditions, so the research on metalloporphyrinfor fuel cell is more and more deep.This paper described the preparation of poly-porphyrin modified electrode and itscatalytic performance for oxygen reduction in alkaline medium. Firstly,tetraphenylporphyrin (TPP), tetraphenyl cobalt porphyrin (CoTPP), tetraphenyl ironporphyrin (FeTPPCl), tetraphenyl manganese porphyrin (MnTPPCl), tetraphenyl nickelporphyrin morpholine (NiTPP) were synthesized by the method of Alder, andcharacterized by Uv-visible spectroscopy. Cyclic voltammetry (CV) were used as anadditional method to study the electrochemical properties of the five substances. All theresults showed that the synthesized products were target products.The electrode was modified with poly-porphyrin by electrochemicalpolymerization, and the catalytic properties of poly-porphyrin were tested for oxygenreduction in oxygen saturated1mol/L NaOH solution, the results indicated that the bestcatalytic performance for oxygen reduction was pCoTPP; Uv-vis spectroscopy resultsshowed that the film formed on the electrode surface was the correspondingpoly-porphyrin film generated by electrochemical polymerization, as compared with themetalloporphyrin monomer, the soret band of polymer emerged red shift and theabsorption peak broadened after electrochemical polymerization.The detailed study of pCoTPP modified electrode catalysis for oxygen reductionincluded the influencing factors of scan rate, pH value and electron transfer number. Scanning electron microscope (SEM) showed that the polymer pCoTPP had a sheet-likestructure of two-dimensional formed in the surface of the conductive glass ITO; theresearch of differrent scan rate influenceed on the peak current for oxygen reductionrevealed the process of pCoTPP modified electrode catalysis for oxygen reduction wasaffected by the diffusion of molecular oxygen; With the increasing of pH in the alkalinemedium, the potential of oxygen reduction was more and more negative, furthemore,pH value with the potential of oxygen reduction showed a good linear relationship;Oxygen reduction polarization curves formed by the test of rotating disc electrode(RDE), the electron transfer number in the process of oxygen reduction was3.6calculated according to Koutecky-Levich, which was very close to the theoreticalfour-electron; pCoTPP modified electrode cycled100laps in oxygen saturated1mol/LNaOH solution, the peak potential and peak current of oxygen reduction werebasically the same compared the first lap with the100th laps, showed that the stabilityof modified electrode was good.