Preparation Of Novel Nitrogen Doped Carbon-based Electrocatalysts And Its Application

Fuel cell is a very promising energy utilization device and has received extensive attention.The cathode oxygen reduction reaction(ORR)of the fuel cell reaction process is relatively slow,and the electrochemical catalyst is used to improve the reaction efficiency and catalytic performance.The progress of the ORR catalyst is very necessary for the rapid development of the fuel cell.Our research goal is to synthesize catalysts for ORR catalytic reactions,mainly novel high-catalyzed nitrogen-doped carbon-based electrocatalysts,including nitrogen-doped carbon materials and metal nitrogen-doped carbon materials.The two-dimensional carbon material graphene with sp2 hybrid carbon atom is a kind of carbon material with unique morphology,large specific surface area,and functional functional groups,and has good stability and conductivity.Currently,research on graphene for ORR catalysts is also extensive.The modified H?ker method was used to synthesize GO,and GO was used as the carbon substrate.The nitrogen-doped modified Ppy/GO was synthesized and calcined to obtain Ppy/GO-600.Compared to the catalytic activity of GO,the catalytic activity of Ppy/GO was improved,with a Ppy/GO starting potential of-0.20 V(vs SCE)and a cathodic current potential of-0.38 V(vs SCE).The improved ORR catalytic activity of GO is illustrated,and N doping is an effective method.Ppy/GO was calcined at600 °C to obtain a two-dimensional lamellar Ppy/GO-600,and an onset potential and cathode potential of Ppy/GO-600 were-0.10 V(vs SCE)and-0.30 V(vs SCE),respectively.The results showed that the electrochemical catalytic performance of Ppy/GO-600 was improved after calcination at 600°C.It has been demonstrated that improving high-temperature pyrolysis of ORR properties is also an effective method.It is more conducive to the formation of active sites and promotes electron or charge transfer on the electrodes,making the ORR reaction easier to perform.As a typical metal-free catalyst material,carbon nitride(g-C3N4)has received great attention in recent years.We have chosen graphene as a nitrogen-doped carbon carrier,andthe surface area of ? ? g-C3N4 synthesized by thermal polymerization is high.In order to further improve the electro-catalytic performance,we used homogenous doping to modify the metal doping of g-C3N4 material,and further synthesized carbon materials Fe/g-C3N4 and Cu/g-C3N4.Among them,the initial potential and cathodic reduction potential of g-C3N4 were-0.30 V(vs SCE),-0.42 V(vs SCE),and the current density at-0.1 V was 0.85 m A cm-2 at1600 rpm.The number of electron transfer in ORR is 3.5 calculated using Koutecky-Levich Equation.The initial potentials of Fe/g-C3N4 and Cu/g-C3N4 obtained by metal organic synthesis were-0.20 V(vs SCE)and-0.28 V(vs SCE),and the cathode current potentials were-0.32 V(vs SCE)and at-0.38 V(vs SCE),the current densities at-0.1 V were 1.40 m A cm-2and 1.55 m A cm-2at 1600 rpm,respectively,and the electron transfer numbers were 2.5and 3.6.This shows that we have significantly improved the grafted metal g-C3N4 synthesized by metal organic synthesis.Reversible protonation of g-C3N4 can be conducted by using inorganic strong acids.Protonation can improve the solubility,dispersibility,electronic structure and specific surface area of ? ? g-C3N4.Therefore,we used protonation of g-C3N4 with strong oxidizing concentrated sulfuric acid to obtain nano-g-C3N4.We also modified nano-g-C3N4 by homogenous doping to synthesize Fe/nano-g-C3N4.Cu/nano-g-C3N4,in which the initial potential and cathodic current potential of nano-g-C3N4 are-0.30 V(vs SCE),-0.42 V(vs SCE),respectively,at a rotational speed of 1600 rpm,the current density at-0.1 V is 1.75 m A cm-2.The oneset potentials of Fe/nano-g-C3N4 and Cu/nano-g-C3N4 synthesized from metal organics were-0.28 V(vs SCE)and-0.28 V(vs SCE),respectively,and the cathode potentials were-0.38 V(vs SCE)and-0.35 V(vs SCE)with current densities of 2.55 m A cm-2 and 1.8 m A cm-2,respectively.It shows that we have significantly improved the grafted metal g-C3N4 synthesized by the synthesis of metal Fe organics.Ppy/g-C3N4 and Ppy/nano-g-C3N4 were prepared by hydrothermal reaction of the synthesized g-C3N4 and nano-g-C3N4 with increasing nitrogen content and a certain ratio of pyrrole/ethanol solution.Among them,the starting potential and cathodic current potential of Ppy/g-C3N4 were-0.28 V(vs SCE),-0.35 V(vs SCE),and the current density at-0.1 V was1.40 m A cm-2 at 1600 rpm;The oneset potential of Ppy/nano-g-C3N4 was-0.30 V(vs SCE)and-0.35 V(vs SCE),respectively,for the cathode potential,and the current density was 2.0m A cm-2,respectively.This shows that the ORR of Ppy/g-C3N4 and Ppy/nano-g-C3N4 synthesized by hydrothermal copolymerization has been significantly improved.After increasing the nitrogen content,the ORR performance has been improved.In summary,we used graphene and carbon nitride as carbon-based catalysts,doped with metals,and performed oxygen reduction catalytic studies to obtain cyclic voltammograms(CVs)and polarization at different rotational speeds.According to CVs and LSVs,their respective starting potentials and cathode current potentials,as well as the current density values at the same rotational speed and the same voltage,are obtained.In alkaline electrolytes,carbon-based catalysts have very good properties.