Controllable Preparation Of Heteroatom Doped Defective Carbon Materials And Synergistic Effect In Electrocatalysis

It is believed that the fuel cell is one of the cleanest technologies to be used in the future portable electronic products and transportation systems.However,the sluggish cathodic oxygen reduction reaction（ORR）greatly restricts the overall cell performance of the fuel cell.Therefore,to develop the low-cost,effective and durable ORR catalysts is still one of the effective ways to break through the bottleneck of the large-scale commercialization of fuel cells.Defect-rich metal-free carbon nanomaterials are often used as cathodic ORR catalysts due to their low cost,high conductivity and strong stability.The previous reports have conducted extensive research on metal-free heteroatom-doped defect carbon materials.However,up to now in the most of the carbon catalysts,the active sites such as heteroatoms and defect sites were introduced through a one-step method;thus,it was hardly to analyze the synergistic effect between co-doped active sites quantitatively.This greatly limits the rational design of high-activity catalysts and hinders the further improvement of the catalytic performance.To this end,we proposed a new preparation method by gradual introduced or removed different active sites,to control the type and quantity of active sites in the material.Then gradually improve the catalytic performance of the material,and study its synergistic effect.Herein,we chose and designed two precursors MAF-6 and Zn O@MAF-6.then pyrolyzed the two precursors at 1000℃to obtain N-C and N-DC materials.Then N/S-C and N/S-DC were obtained by vulcanizing N-C and N-DC After removing part of N active site of N-DC and N/S-DC at high temperature,DC and S-DC were obtained.According to the Raman spectroscopy,the I_D/I_G of N-C and N/S-C were 0.99,while N-DC and N/S-DC increase to 1.06,indicated that the introduction of Zn O into MAF-6 can produce more defect sites.The electrochemical test shown that the E_1/2 of N-C,N/S-C,N-DC,N/S-DC,DC and S-DC in 0.1 M KOH were 0.82 V,0.82V,0.88 V,0.90 V,0.84 V and 0.85 V,respectively.In 0.1 M HCl O₄ the E_1/2 were 0.58V,0.55 V,0.7 V,0.77 V,0.63 V and 0.68 V,respectively.The experimental results demonstrated that the N modified defective carbon exhibited excellent alkaline medium,while synergistic effect of the S,N and defect was vital in achieving high performance in acidic condition.And the S,N co-doped defect carbon（N/S-DC）showed E_1/2 0.77 V in 0.1 M HCl O₄ which was superior to most metal-free electrocatalysts reported to date.The E_1/2 in 0.1M KOH is 0.90 V,which has exceeded the commercial Pt/C catalyst.At the same time,the N/S-DC material showed excellent methanol tolerance and long-term stability.In 0.1 M HCl O₄,N/S-DC can maintain 93%of the initial current after50000s measurement,and after 50000 s in 0.1 M KOH was even as high as 97.3%.This work showed that catalysts with different types and numbers of active sites were synthesized successfully.At the same time,it provided an ideal model for the study of the synergistic effect between different active sites in the ORR.