The Synthesis Of Polyaniline-Based Porous Carbon And Their Electrocatalytic Properties

Polymer-based porous carbon materials can carry high-density active sites due to their rich pore structure and high specific surface area,and polymers as precursors have the advantages of batch preparation,controllable composition,and these materials have been developed to preferred material for the catalyst of oxygen reduction reactions.In this paper,a series of highly active carbon-based oxygen reduction catalysts were prepared using polyaniline nanotubes as precursors.Firstly,nitrogen-doped carbon nanotubes were prepared by ammonia activation method.Nitrogen-doped porous carbon nanotubes with rich nitrogen atoms(4.82at%)and microporous-mesoporous ordered distribution were obtained at a pyrolysis temperature of 900? for 2h.This carbon material has a specific surface area of up to 1609 m2/g and a pore volume of 0.899 cm3/g.The nitrogen-doped carbon material as an oxygen reduction catalyst is more durable than commercial Pt/C,but the half-wave potential is 40 mV less negative than commercial Pt/C.using metal chloride as metal source,the active sites of TM-N-C(TM=Fe,Co,Cu)were introduced into the nitrogen-doped carbon nanotubes by co-pyrolysis method.These TM-N-CNTs catalysts showed enhanced electrocatalytic activity,and the half-wave potential of Fe-N-CNTs reached 0.87 V(vs RHE),which is 30mV more positive than commercial Pt/C.The reaction pathway was an ideal four-electron reaction with good stability and methanol resistance over commercial platinum carbon.The analysis of the origin of the activity found that the metal atom does not act as a direct active site,but indirectly regulates the electronic structure of the N-C.After the transition metal connected to the N-C,the C atom shows a higher positive charge,which promotes the adsorption of oxygen on C atoms and facilitate electron transfer during reduction.Comparing the promoting effect of different transition metals,it was found that the order of activity enhancement was Fe>Co>Cu.According to the d-band center theory,the d-band center value of Fe is the highest,which could enhance the ability to adsorb electrons,and the adsorption capacity of Co and Cu are weakened in turn.Therefore,the enhancement effect has declined.This conclusion can guide the design and preparation of high active transition metal-nitrogen-carbon catalysts.This article also explored the oxygen reduction performance of carbon-based catalysts that are rich in defects.Using ZnC12 as a pore-forming agent,a catalyst rich in carbon intrinsic defects is obtained by pyrolysis in an ammonia atmosphere.When the amount of ZnC12 is 0.05mM,the specific surface area of the sample is 1892 m2/g,and the pore volume is 0.973 cm3/g.The high contents of edge defects are observed in the HRTEM images.The catalyst showed significantly high Oxygen reduction catalytic performance with a half-wave potential of 0.88V(vs RHE),more than commercial Pt/C 40mV,and occurring four-electron reaction.In addition,a heterogeneous carbon-based catalyst was also designed and prepared.Graphitized carbon black/polyaniline and carbon nanotube/polyaniline composite catalysts were prepared by in-situ growth and pyrolysis.The perfect combination of nitrogen-doped layer and conductive layer made these catalyst exhibited enhanced oxygen reduction catalytic activity.