Synthesis Of Doped Porous Nano-carbon Materials For Electrochemical Energy Storage

Porous carbon materials have a rich pore structure and a large specific surface area,and have been widely applied in energy storage and conversion devices such as fuel cells,zinc-air batteries,lithium ion batteries,lithium sulfur batteries,and sodium ion batteries.In this paper,a series of porous nano-carbon materials were designed and synthesized using cheap biomass as the carbon source,and their electrochemical performance in zinc-air batteries and lithium-ion batteries was invesitgated.The following is the main contents.?1?Nitrogen and phosphorus co-doped porous carbon?NPC-SiO₂?was successfully synthesized via a simple pyrolysis route by using chitosan as the carbon and nitrogen source,phytic acid as the phosphorus source and SiO₂ as the template.The as-prepared material has high specific surface area(1355 m² g^-1),abundant pore structure and defects,which can provide sufficient Li⁺storage sites and fast charge transport kinetics.Benefiting from its unique structural feature,it shows excellent cycle stability and rate performance as lithium-ion batteries anode.It delivers a high reversible capacity of 1588 mAh g^-1 at 0.1A g^-11 after 100 cycles.When the current density increases to 5 A g^-1,the specific discharge capacity remains at 561 mAh g^-1after 1000 cycles,which is higher than that of most reported heteroatom-doped carbon anode materials.?2?3D N,P-codoped carbon networks?3D-NPC?composed of interwoven porous nanosheets were converted from ubiquitous biomass chitosan and phytic acid via a facile NaCl-assisted pyrolysis route.NaCl was found to be indispensable for bestowing 3D-NPC with hierarchical porosity?micro-/meso-pores on the nanosheets and interconnected macropores between the nanosheets?,large surface area(967 m²g^-1),high doping level of N?2.97 at.%?and P?1.54 at.%?,abundant catalytically active sites?such as pyridinic-N,graphitic-N,P-C and edge defects?and high conductivity.3D-NPC exhibits excellent ORR catalytic activity and strong methanol tolerance in both alkaline and acidic media,especially exceeding Pt/C under alkaline conditions.Furthermore,the performance of the Zn-air batteries using 3D-NPC as the cathodic electrocatalyst outperformed Pt/C with higher open circuit voltage,larger power density,better stability,higher specific capacity and energy density.?3?Fe,N co-doped hierarchical porous carbon?Fe-N-HPC?was synthesized via a self-template method by using biomass sodium carboxymethyl cellulose?CMC?as the carbon source,FeCl₃·6H₂O as the Fe source,and urea as the nitrogen source.In the process of preparing the precursor,a Fe³⁺-CMC complex hydrogel was first formed,in which urea was evenly dispersed.During pyrolysis,CMC was converted into carbon and Na₂CO₃,which served as a template and pore-forming agent.Fe³⁺was reduced through a carbothermal reduction reaction into Fe,which was evenly distributed in the carbon network.Ammonia gas released from decomposition of urea acted as a nitrogen source to fulfill N-doping.As a result,Fe-N-HPC has a three-dimensional porous structure with large specific surface area,high conductivity,and abundant catalytic active sites.The as-prepared Fe-N-HPC showed excellent ORR and OER bifunctional catalytic activity(E_j=10?OER?-E_1/2?ORR??0.71 V)in alkaline media.The performance of the Fe-N-HPC-based rechargeable zinc-air batteries was better than that of the commercial Pt/C-based one.