The Synthesis And Study On Catalytic Performance Of Nitrogen-doped Carbon Electrode

Metal-air flow battery has been widely concerned for its low cost,high energy density and good reliability.As for ORR and OER suffer from sluggish kinetics resulting in low energy conversion efficiency.Non-metal nitrogen doped carbon material has the characteristics of high catalytic activity and low cost,which has a good prospect in the field of catalytic oxygen reduction and oxygen precipitation.However,the current air positive electrode based on non-metal nitrogen doped carbon still has many problems such as low density of active sites,poor mass transfer,and powder catalyst is easy to fall off from the electrode.In view of the problems above,a nitrogen-doped carbon electrode with multistage pore structure was designed and prepared in this paper,and its physicochemical properties,electrocatalytic performance and application performance in batteries were systematically studied.The specific research contents and achievements are as follows:(1)Developed a method for preparing multistage porous nitrogen doped integrated electrode.The content of polypyrrole was regulated by controlling the number of cyclic voltammetry cycles,and then the composition and structure of the carbon layer were regulated.The results showed that:with the electropolymerization of 75 cycles,the prepared nitrogen-doped carbon electrode(CC@NCL-75)had abundant macropores and mesoporous pores(126 m2 g-1),and the polymerization amount was too little(50 cycles)or too much(100 cycles),resulting in a dense carbon layer with few mesoporous and macropores(CC@NCL-50:67 m2 g-1,CC@NCL-100:76 m2 g-1),which was not conducive to the material transport.(2)Investigated the effect of pore structure on the utilization rate of active center and electrocatalytic performance.We measured the adsorption capacity and oxygen transfer rate of nitrogen doped carbon electrode with multistage structure with the designed experimental apparatus,and evaluated the catalytic oxygen reduction and oxygen precipitation reactivity and stability of the electrode.Study showed that compared with CC@NCL-50 and CC@NCL-100,CC@NCL-75 with rich mesoporous and large pores exposes more active sites,and can absorb 7.6×10-8 mol of oxygen per unit area(1 cm2).The diffusion coefficient of oxygen on its surface is the largest,reaching 4.97×10-3 cm2·s-1.The half-wave potential of CC@NCL-75 can reach 0.855 V,and the over-potential of 10 mA cm-2 current generated by catalytic oxygen precipitation is only 0.35 V.The catalytic performance of ORR and OER remained at 89%and 63%after the 20,000 seconds i-t test,better than commercial platinum carbon and iridium dioxide.Investigated the application performance of integrated multistage porous nitrogen doped carbon electrode in zinc air flow battery.As an integrated electrode,the nitrogen-doped carbon electrode is directly applied to the positive electrode of the zinc air flow battery,avoiding the degradation of performance and stability caused by the catalyst falling off.Study showed that CC@NCL-75 can significantly reduce the polarization of the battery during charging and discharging compared with the air electrode(Pt/C+IrO2)/CC coated on the carbon cloth.The energy efficiency of Zn air flow battery with CC@NCL-75 can reach 56%and the battery exhibits neglectable performance decay within 1380 minutes...