Synthesis Of Non-Metal Heteroatoms Co-doped Carbon Aerogels And Their Electroccatalytic Performance For Oxygen Reduction Reaction

Fuel cells become more and more popular because of their high energy conversion efficiency,environmental friendliness and small noise.Oxygen reduction reaction(ORR)is the foremost step in fuel cells.However,the kinetics of ORR in fuel cells is very slow without catalyst.Therefore,the development of high active electrocatalysts for ORR is an urgent and significant.Until now,platinum materials have been regarded as the most excellent catalysts for ORR,but they are costly and rare,suffer from low tolerance to methanol and limited stability.Therefore,it is significant to develop efficient and inexpensive ORR catalyst for replacing Pt.A large amount of researches reveal that transition metal or heteroatoms doped carbon-based catalyst has tempted growing concerns because of their high catalytic activity and good tolerance to methanol poisoning effects,which is regarded to a new ORR catalyst to replace Pt.In this paper,on the basis of many researches about carbon aerogel in both at home and abroad,extensive research of carbon aerogels as ORR materials is mainly focused on graphene aerogels,formaldehyde resin aerogels,polymer hydrogels and so on.However,these carbon aerogels suffer from a great deal of issues,for example,graphene carbon aerogels were synthesized by hydrothermal reaction at 180? for 12h,which is tremendous waste energy.Synthetic time of formaldehyde resin aerogels is too long,at least a day,to more than a week,meanwhile,formaldehyde is a toxic volatile material,which could cause pollution of the environment.The polymer hydrogels were synthesized by initiator,crosslinking agent,and oxidizer due to the complicated preparation process.Although these carbon aerogels exhibit better properties in ORR,these shortcomings largely limit its large-scale application.So we hope to design a simple,fast and greet method to synthesize transition metal or heteroatoms doped carbon aerogel.The primary exploits of this paper can be summarized as follows:(1)A boron and nitrogen dual-doped porous carbon material catalyst(BN-CA-900)was successfully synthesized by a simple hydrothermal process and a pyrolysis procedure(at 900?,under NH3 atmosphere)using glucose and borax.BN-CA-900 has a huge specific surface area(1032 m2g-1)and high nitrogen content(4.04%,atomic ratio).The same onset potential,half-wave potential and reduction current density of BN-CA-900 for ORR are really close to commercial Pt/C,indicating that BN-CA-900 has an identical catalytic activity campared to the commercial Pt/C in the alkaline media.The number of electron transfer is 3.98?3.99 and the yield of hydrogen peroxide is less than 3.14%at the potential range from-0.8 V to-0.2 V(vs.Hg/HgO).Under acidic condition(at-0.2 vs.Ag/AgCl),the current density of BN-CA-900(5.55 mA cm-2)is the equal of commercial 20%Pt/C(5.55 mA cm-2).More importantly,whether in acid or in alkaline conditions,BN-CA-900 all shows excellent methanol resistance and excellent stability.(2)A sulfur and nitrogen dual-doped porous carbon material catalyst(SN-GA-1000)was successfully fabricated by a pyrolysis procedure(at 1000?,under NH3 atmosphere)using carbon nanotubes aerogels and graphene.Under alkaline condition,the limiting diffusion current of SN-GA-1000(5.72 mA cm-2)is very close to the commercial Pt/C(5.75 mA cm-2)at the potential of-0.8(vs.Hg/HgO).Meanwhile,the same onset potential and half-wave potential of SN-GA-1000 are also consistent with Pt/C at the same condition,indicating that SN-GA-1000 exhibited the excellent catalytic performance for ORR.The RRED show that number of electron transfer is 3.94-3.99 and the yield of hydrogen peroxide is 0.056?3.13%at the potential range from-0.8 V to-0.2 V(vs.Hg/HgO).The catalyst exhibited excellent ORR activity via a dominated 4e reduction pathway.We suggest that the catalyst is high activity performance many be attributed to:(1)a coordination effect of the doping of sulfur and nitrogen,(2)carbon nanotube aerogels can obstruct the aggregation of graphene,which is conducive to increasing the surface area.(3)A cobalt and nitrogen dual-doped porous carbon material catalyst(CoN-CA-900)was successfully fabricated by a pyrolysis procedure(at 900?,under Ar atmosphere)using polyacrylamide and ZIF-67.CoN-CA-900 has a huge specific surface area(1568.4 m2g-1)and porous structure.Under alkaline condition,The RDE test results display the limiting diffusion current density of CoN-CA-900(at-0.8 V vs.Hg/HgO)is 5.66 mA/cm2,which is very close to the Pt/C(5.75 mA/cm2).In the potential range from-0.8 V to-0.2 V(vs.Hg/HgO),the number of electron transfer is 3.92-3.95 and the yield of hydrogen peroxide is 2.6?3.94%.Even more important,the catalyst exhibited excellent ORR activity via a dominated four-electron(4e)reduction pathway,as well as tolerance to methanol poisoning effects.