Preparation Of 2D/3D Doped Graphene Catalysts And Applications In Metal-air Batteries

As an efficient and clean new energy storage device,fuel cell is one of the most potential new energy sources due to its high energy conversion efficiency,high specific energy and environmental friendliness.However,the high overpotential of the cathode seriously affects the performance of the fuel cell.Therefore,the development of cathode catalysts with low cost,high efficiency and strong stability have attracted people’s attention.Nitrogen-rich poly 2,5-benzimidazole（ABPBI）was prepared from 3,4-diaminobenzoic acid as carbon and nitrogen sources.The semi-enclosed,hydrophobic,cationic modified layered montmorillonite（CMMT）is the template.After the experimental steps of heating and vacuuming,ABPBI was inserted layer by layer into the CMMT template,followed by high-temperature pyrolysis,removal of the template and other operations,to obtain a 2D nitrogen-doped graphene catalyst（2D NG）.The onset potential of the catalytic ORR was0.973 V vs.RHE,the half-wave potential was 0.825 V vs.RHE,and the Tafel slope was 65.9m V dec^-1.The potential of catalytic OER at 10 m A cm^-2 was 1.633 V vs.RHE Catalytic oxygen activity of ORR/OER isΔE=E_j=10-E_1/2=0.808 V vs.RHE.The 2D NG was applied to ZAB,its discharge peak power density reached 197.3 m W cm^-2,and it had good charge-discharge performance.In order to further study the catalytic performance of nitrogen-doped graphene by introducing transition metals,ABPBI was also used as the carbon and nitrogen source,and Fe Cl₃?6H₂O as the metal precursor,and the optimal scheme of Fe³⁺insertion into the layered template was discussed.Cationic surfactant on CMMT raw material inserted by ABPBI was divided at 350 ^oC,Fe³⁺was inserted,and iron and nitrogen co-doped graphene（2D Fe-NG）catalyst was prepared by high temperature pyrolysis.And studied how to insert Fe³⁺into the layered template well.The prepared 2D Fe-NG possesses the structure of graphene and has a large specific surface area.Fe precursors coordinate with N in ABPBI and form Fe-N_xactive site.OER catalytic performance of 2D Fe-NG in the 0.1 M KOH electrolyte is E_j=10=1.633 V vs.RHE.2D Fe-NG has excellent ORR catalytic performance(E_1/2=0.86 V vs.RHE).In addition,the 2D Fe-NG possesses lower over potential difference(ΔE=E_j=10-E_1/2=0.76 V vs.RHE)and stability performance of catalytic ORR/OER.The application of 2D Fe-NG to the homemade Zn-air battery showed high discharge peak power density(235.2 m W cm^-2)and excellent charge-discharge performance.In order to simplify the treatment of template in the preparation of iron and nitrogen co-doped graphene,PANI was synthesized by in-situ oxidation polymerization of AN monomer in the H-MMT layer.Bifunctional Fe/N-doped graphene（Fe/N-G）was prepared by pyrolysis of PANI and Fe Cl₃?6H₂O compounds in H-MMT.The Fe/N-G catalyst has a thin,folded,multi-layered graphene structure.Fe-N_x bond exists and plays a major role in catalytic ORR performance.In terms of catalytic ORR,the half-wave potential of Fe/N-G in the oxygen saturated 0.1 M KOH electrolyte was 0.877 V vs.RHE.In terms of catalytic OER,the overpotential of Fe/N-G in the 0.1 M KOH electrolyte at 10 m A cm^-2 is 400 m V.Fe/N-G was applied to ZAB with high discharge power density(156.8 m W cm^-2)and stable charge-discharge performance.In order to solve the problems of two-dimensional graphene（2D G）,such as easy stacking and agglomeration,loss of active sites,poor mass transfer effect and reduced catalytic performance,a three-dimensional graphene with interpenetrating,multi-mesoporous,large specific surface area and abundant active sites was prepared to replace2D G.Polyacrylamide（PAM）was used as carbon and nitrogen source,Na Cl as template,Fe Cl₃?6H₂O as metal precursor.The 3D Fe/N-G#4 catalyst prepared by controlling the mass ratio of PAM and Na Cl to 1:4 had the highest bifunctional catalytic activity.It was proved that Fe element and N element formed Fe-N_x coordination bond,which played a major role in catalytic ORR performance.For ORR,the half-wave potential of the 3D Fe/N-G#4catalyst in the oxygen saturated 0.1 M KOH electrolyte was 0.852 V vs.RHE.For OER,the overpotential of 3D Fe/N-G#4 catalyst is 393 m V at the current density of 10 m A cm^-2.The3D Fe/N-G#4 catalyst was applied to the air cathode of the homemade ZABs,showing high peak power density(168.2 m W cm^-2)and good charge-discharge stability.In order to study the catalytic properties of transition metal and diheteroatomic co-doped graphene,preparing the N,P and Fe atoms co-doped 3D Fe-N/P-G catalyst with high ORR catalytic performance by using non-toxic and harmless KCl template through a new and simple synthesis method.The optimum preparation scheme was obtained by adjusting the ratio of different precursors to the template.The half-wave potential of the P-doped 3D3D Fe-N/P-G catalyst in the oxygen saturated 0.1 M KOH electrolyte was 0.858 V vs.RHE.After 50000 s of i-t test,the current of 3D Fe-N/P-G decreased by 10%.In the ADT test,the half-wave potential of 3D Fe-N/P-G shifted only 11 m V vs RHE.N,P and Fe atoms co-doped 3D Fe-N/P-G catalysts with have high ORR catalytic performance.