Controllable Preparation Of Two-dimensional Porous Carbons For Energy Conversion

Two-dimensional（2D）porous carbon nanosheets（2DPCs）have attracted great attention in energy conversion field for its good porosity as well as unusual physical,chemical and electronic properties.However,the performance of pure 2DPCs was normal by its few active sites,so scientists began to dope 2DPCs with various heteroatoms such as N,P,S and metal atoms,and achieved ideal results.In this work,based on existing research achievements and aiming at solving problems of poor control over the morphology,size,diversity and uniform dispersion of2DPCs,an efficient strategy was proposed by choosing the appropriate template,carbon precursor,metal source and activation method.And the as-prepared materials exhibited excellent electrocatalytic performance.The main contents and details are list as follows:At first,an ionic polyimide with both sp²-and sp³-hybridized nitrogen was prepared as a precursor for fabricating N-doped hexagonal porous carbon nanosheets through a hard-template approach.Because of large surface area and efficient charge–mass transport,the resulting 2D porous carbons displayed promising electrocatalytic activity for oxygen reduction reaction（ORR）in alkaline and acidic media,such as ultralow half-wave potential（0.83 vs 0.84 V of Pt/C）and superior limiting current density(5.42 vs 5.14 m A cm^-2 of Pt/C).As air cathode in Zn–air batteries,the as-developed 2DPCs exhibited long stability and high capacity(up to614 m A h g^-1)—both higher than those of commercial Pt/C.This work provided a convenient method for controllable and scalable 2DPCs fabrication as well as new opportunities to develop high-efficiency electrocatalysts for ORR and Zn–air batteries.Based on the work above,an ion-exchanging process towards facile and scalable fabrication of metal complex embedded freestanding hexagonal porous carbon nanosheets（2DPC-M,M=Mo,Ru,RuMo）was introduced with Mg Al-layered double hydroxide（Mg Al-LDH）as the sacrificial template and viologen based polyimide as the graphitic carbon source.Due to the isolated Mo atoms in ruthenium lattice as revealed by aberration-corrected high-resolution transmission electron microscopy and X-ray absorption fine structure measurement,the 2DPC-RuMo showed a superior catalytic performance towards hydrogen evolution reaction with an extremely low overpotential of 18 m V at 10 m A cm^-2 in alkaline media,an ultralow Tafel slope of 25 m V dec^-1 and high turnover frequencies（TOF）of 3.57 H₂ s^-1,which exhibit top-level catalytic activity among state-of-art Ru-based electrocatalysts.This work also provides a convenient methodology towards controllable and scalable fabrication of active components-doped carbon nanosheets for a broad range electrocatalytic performance.