Pyrolysis Products Of Co Doped C/N Composites As Electrocatalysts For Oxygen Reduction Reaction

Fuel cell is an environmentally friendly,efficient and sustainable power generation device.,The commercial application of the fuel cell is seriously limited due to the high cost of the non-noble metal catalysts,so development of new nitrogen-doped non-precious catalysts has become the research focus.Much attention has been paid to the study on metal macromolecules containing nitrogen used as lelctrocatalysts for oxygen reduction reaction(ORR)since 1964.In this thesis,a series of cobalt-doped carbon-nitrogen composite catalysts have been synthesized by the pyrolysis method.The prepared catalysts have been characterized by XRD,XPS,SEM techniques and their electrochemical activities for ORR have been also investigated.Results show that addition of polyvinylpyrrolidone results in a better dispersion effect on the catalyst particle distribution.On the basis of this,the catalysts with the addition of m-nitroaniline have been prepared because more nitrogen contents in catalysts have higher electrocatalytic activity for ORR in alkaline environment,.The prepared catalysts have been also applied to membrane-less direct alcohol(or hydrazine)fuel cells as the cathodes.The main research contents are as follows:(1)The catalysts were prepared by high-temperature pyrolysis method.We firstly synthesized the precursors containing MWCNT,polyvinylpyrrolidone,pyrrole,carbon black and Co salt,and then the precursors were heated at 800? under N2 to obtain the Co-C-PY/CNT catalysts.The catalysts were characterized by SEM,XRD and XPS.The characterization results show that the Co-PVP-PY/CNT catalyst exhibits a smaller particle size and a better dispersity of Co nanoaprticles compared to the Co-C-PY/CNT and Co-CNT-PY/CNT catalysts.The electrochemical activity of the catalysts towards ORR was examined by cyclic voltammetry(CV)and linear sweep voltammetry(LSV).The ORR current density of catalyst Co-PVP-PY/CNT is120 mA·cm-2@-0.8 V in alkaline solution and 158 mA·cm-2@-0.8 V in acidic solution,and the onset potential of ORR is-0.08 V in alkaline solution and 0.2 V in acidic solution.(2)Through the high-temperature pyrolysis method,we firstly synthesized the precursor containing MWCNT,polyvinylpyrrolidone,m-nitroaniline,carbon black and Co salt,and then the precursor was heated at 800? under CO2 to obtain the Co-C-N and Co-C-N/CNT catalysts.The catalysts were characterized by SEM,XRD and XPS.The characterization results show that with the increase of m-nitroaniline,the catalyst exhibits a smaller particle size.The cyclic voltammetry(CV)and linear sweep voltammetry(LSV)test indicates that the catalysts containing carbon nanotubes have better electrocatalytic activity for ORR.The maximum current density of ORR on the Co-C-N(2)/CNT catalyst is 160 mA·cm-2@0.8 V in alkaline solution and 65 m A·cm-2@0.2 V in acidic solution;The onset potential of ORR is0.15 V in alkaline solution and 0.4 V in acidic solution.Catalysts present good tolerance ability of alcohols.(3)A membrane-less direct alcohol fuel cell was assembled using Co-C-N and Co-C-N/CNT as cathode catalysts and PdSn/beta-CD-CNT as anode catalyst.The methanol,ethanol,propanol,n-butyl alcohol were used as fuels.The discharge tests show that the prepared Co-C-N/CNT catalysts have better discharge performance,and these cells exhibit stable discharge performance.For the discharge test of the membrane-less direct propanol fuel cell,the maximum discharge current density is108 mA?cm-2?mg-1 and the maximum discharge power density is 11 mW?cm-2?mg-1 in alkaline solution.(4)A membrane-less direct hydrazine fuel cell was assembled using Co-C-N and Co-C-N/CNT as cathode catalysts and AgCo/CNT as anode catalyst.Hydrazine hydrate with different concentrations was used as fuels.The discharge tests show that the prepared Co-C-N/CNT catalysts have better discharge performance,and these cells exhibit stable discharge performance.Result shows that the membrane-less direct hydrazine fuel cell with 0.5 mol?L-1hydrazine hydrate as the fuel has the maximum discharge power density of 4.4 mW?cm-2?mg-1 and the maximum discharge current density of 76 mA?cm-2?mg-1in alkaline solution.With the increase of hydrazine concentration,the cell performance decreases gradually.