Study On Anodic Materials Of Graphene-based For Direct Methanolfuel Cell

Direct methanol fuel cells(DMFC)have been used in portable electronic devices because of their high energy density,high methanol utilization,low battery temperature,and easy operation.Compared with hydrogen energy,methanol is a cheaper liquid fuel,easy to store,easy to transport,and has a higher theoretical energy density.Therefore,methanol fuel cells have potential applications in new energy vehicles and other fields.However,methanol fuel cells also have short-board catalysts that restrict their commercialization.At present,the catalysts of methanol fuel cells are mainly prepared by using platinum nano materials,but the traditional platinum nanomaterials are prone to poisoning and precipitation during use,which makes the effective active area and catalytic activity of platinum nanocatalysts gradually decrease,which seriously affects methanol.In addition,the metal platinum required for the preparation of platinum nano materials has low storage capacity,high cost,and high cost,which is not conducive to the commercial application of direct methanol fuel cells.Therefore,the preparation of a catalyst with high activity and good stability is of great significance for further large-scale application of a methanol fuel cell.In this paper,basic research work is carried out to improve the activity,stability and cost reduction of DMFC anode catalysts.The main research contents are as follows:(1)The improved Hummers method was used to prepare graphite oxide,and urea was used as the N source to prepare different content of nitrogen-doped graphene(N-rGO)by hydrothermal method.Graphene-supported platinum(Pt/N-rGO)catalyst was prepared by one-step reduction of graphite oxide and noble metal salt by immersion reduction method.Scanning electron microscopy(SEM),Fourier transform infrared(FT-IR)spectroscopy,X-ray diffraction(XRD),nitrogen adsorption desorption analysis(BET),electrochemical testing of the morphology,structure,composition and electricity of the sample Characterization by chemical properties.The results show that N-rGO has been successfully prepared by hydrothermal method.By controlling the quality of graphite oxide and urea,graphene with different nitrogen content can be obtained.Among them,the specific surface area of Pt/3N-rGO reached 236.5m2/g.Among the series of catalysts prepared,the electrochemical performance of Pt/3N-rGO is also optimal,and its electrochemical active area is 73.75m2/g.In the CV curve,the peak current density of the methanol sweep peak reaches 16.63 mA/cm2,which is more than three times higher than the current density of the undoped nitrogen catalyst.Its AC impedance value is a minimum of 19.00 Ω.(2)Nitrogen-doped graphene(N-rGO)was prepared by hydrothermal method using graphite oxide and urea as raw materials.A catalyst with different Pt and CeO2 ratios was prepared by using N-rGO as a carrier and NaBH4 as a reducing agent.The prepared catalysts were characterized by XRD,SEM and FT-IR.The electrochemical properties of the prepared catalysts were investigated by electrochemical methods such as cyclic voltammetry,chronoamperometry and alternating current impedance.The results show that the hydrothermal method successfully introduces N atoms into graphene,and Pt and CeO2 are evenly loaded on the surface of N-rGO.The electrochemical activity area of 1:4Pt-CeO2/N-rGO is 5 times that of Pt/N-rGO,and the oxidation rate of methanol is more than three times that of Pt/N-rGO.The catalyst is determined by cyclic voltammetry and chronoamperometry.The electrocatalytic oxidation process for methanol is primarily controlled by the diffusion process.At the same time,with the addition of CeO2,the long-term cycle stability of the catalyst is gradually improved.The catalyst with the molar ratio of Pt:CeO2=1:4 is the most stable,indicating that the synergistic effect of the catalyst is best when the ratio of Pt and CeO2 is 1:4.It also has the smallest impedance value,only 10Ω.(3)Using graphene as carrier and TiO2 as cocatalyst,a series of catalysts with different Pt and Co ratios were prepared by impregnation one-step reduction method.The catalysts were characterized by XRD,SEM and FT-IR techniques.The electrocatalytic performance of the catalyst was investigated by electrochemical methods such as cyclic voltammetry,chronoamperometry,and alternating current impedance.The results show that the one-step reduction method successfully reduces the nanoparticles to the surface of graphene,and the nanoparticles are uniformly dispersed on the surface of graphene,and the particle size distribution is narrow.Among them,the 5PCTG catalyst has the smallest particle size and the best dispersion.Cyclic voltammetry results showed that the electrochemical active areas of PQ PTG,1PCTG,3PCTG,5PCTG,7PCTG were 24.65m2/g,82.35m2/g,122.93m2/g,156.36 m2/g,243.26 m2/g and 126.39 m2/g respectively.The active area of the 5PCTG catalyst is 5 times that of PG and more than twice that of PTG The methanol peak current density of PG is 6.349mA/cm2,and the peak oxidation current of 5PCTG is 10 times that of PG is 64.01 mA/cm2.After 500 cycles of cyclic voltammetry,PG,PTG,1PCTG,3PCTG,5PCTG and 7PCTG catalysts were reduced by 90.48%,47.95%,39.28%,29.76%,15.26%and 40.05%,respectively,compared to the initial current density.The chronoamperometry results show that after 1000 s,the remaining currents of PG,PTG,1PCTG,3PCTG,5PCTG,and 7PCTG are 0.6393mA/cm2,3.945mA/cm2,12.18 mA/cm2,14.58 mA/cm2,16.74mA/cm2 and 9.415mA/cm2,respectively.The RCT of 5 PCTG catalyst is only 8 2.The above results indicate that the 5PCTG catalyst has better methanol oxidation performance and electrochemical cycle stability.