Study On Porphyrin-based Covalent Organic Framework Materials In Electrochemical Energy Conversion

COF is a new crystalline porous polymer,which is connected by stable covalent bond,and the covalent bond between organic module units endows COF with high chemical durability.COF has a periodic skeleton and ordered pore extension structure,and its adjustable skeleton and pore structure provide abundant docking sites as catalytic active substances,as well as a relatively large surface area for reactant adsorption and product desorption.In the past decade,many porphyrin based MOFs and COFs have been prepared.Porphyrin molecules can be used as both organic linkers for MOFs and component monomers for COFs.Due to the different functional groups of porphyrin molecules,porphyrin based COFs have been constructed with different topological structures and tunable porous structures.COF provides a suitable platform for porphyrin molecules to realize heterogeneous catalysis.At present,porphyrin based frameworks have become one of the most widely studied porous structures.The main research directions of this paper include the following parts:（1）Design of high friction electrification materials is an effective way to improve the output performance of friction nanogenerator.Here,we synthesized a series of covalent organic frameworks（COFs）with similar skeletons but different functional groups,ranging from electron donating to electron withdrawing.These COFs form an ideal platform for elucidating the contribution of each group to TENG performance,as the pore walls are perturbed in a pre designed manner.Kelvin probe force microscopy and computational data indicate that introducing electron donating or electron withdrawing groups can increase the surface potential and electron affinity of COF,with fluorine COF having the highest surface potential and electron affinity.The output voltage and current of TENG containing fluorinated COF are 420V and 64μA,respectively,which are comparable to other reported materials.This strategy can be used to efficiently screen suitable skeleton materials as TENG materials.（2）DPP-H₂Por COF and DPP-Co Por-COF were synthesized by porphyrin and monomer with diketopyrrolopyrrole（DPP）structure unit.Various characterizations proved that the prepared COF has good crystallinity,high specific surface area,excellent chemical stability and outstanding electron transport ability.In order to gain a deeper understanding of the role of diketopyrrolopyrrole（DPP）units in catalytic processes,we synthesized COF without DPP units in their structure as a control.The results show that the catalytic activity of ORR can be effectively improved by introducing the redox active unit DPP and change the catalytic center Co（II）.The starting potential of DPP-Co-Por COF in ORR is 0.87 V（vs RHE）,the half wave potential is 0.79 V,the limiting Diffusion current density(J_lim)is 4.33 m A·cm^-2,the Tafel slope is 80.1 m Vdec^-1,and the smaller resistance value indicates its faster kinetic reaction.at 0.4 V（vs RHE）,the electron transfer number（n）of DPP-Co Por-COF is 3.72,and it can still maintain90%stability after continuous operation for 20000 seconds.Based on the excellent ORR performance of DPP-Co Por COF,we applied the DPP-Co-Por-COF catalyst to rechargeable zinc air batteries（ZAB）to evaluate its practical application.The results demonstrate that the open circuit voltage is 1.367 V,the maximum peak power density is 94.65 m W·cm^-2,and the specific capacity is 736 m Ah·g _Zn^-1.Not only can it stably power the light-emitting diode（LED）panel,but it can also maintain high stability when discharged again at a current density of 2m A·cm^-2 after discharge at 2、5、8、and 10 m A·cm^-2 current densities.