| Covalent organic frameswork(COF)are a class of crystalline porous organic polymers with permanent porosity and highly ordered structure.Unlike other polymers,an important feature of COF is that they are structurally pre-engineered,integratively controlled,and functionally modified.Since the pioneering work of Yaghi and colleagues in 2005,the rapid development of this research field has attracted strong interest from researchers with varying expertise.So far,COF can be divided into 2D COF and 3D COF,where 2D COF is predominant in COF and the number of 3D COF is relatively small.Compared with 3D COF,2 D COF is easier to synthesize and is used in more extensive fields such as separation,catalysis,sensing,adsorption and other fields.Although 2D COF has many applications in photocatalysis,it remains to be studied in the application of electrocatalytic oxygen evolution,especially in metal-free COF catalysts for electrocatalytic oxygen evolution.With the development of society and the progress of science and technology,the demand for energy surges,and the burning of many fossil fuels and carbon emissions lead to increased environmental pollution.Considering the needs of renewable energy and clean energy production,electrochemical water cracking can be considered as a green and promising technology and plays a crucial role in advanced energy technologies,such as solar fuel production,supercapacitors,metal air batteries,etc.Because water electrolysis requires high energy to maintain,it is urgent to explore a stable,low-cost and environmentally friendly catalyst.COF as a porous material with high specific surface area,high porosity,and good chemical stability,it has potential advantages in the field of catalysis.In this paper,different 2D COF are synthesized and compared by designing construction units with different heteroatom doping and different structures.The study content is divided into the following three parts.1)Most metal-free covalent organic frameworks(COF)have poor electrical conductivity and is unfavorable to the OER reaction.Tetrathiofuvalene(TTF)is a superior electron donor with rapid electron transfer capability,and the integration of TTF into the covalent organic framework framework facilitates electron transfer.Therefore,we selected the four-node tetrathifuvalene and tetraaminobenzene monomer to react with 4,4 ′-(thiadiazole-4,7-digroup)benzophenyl 4,[1,2,5] to synthesize 2 D JUC-630 and Etta-Td COF with mesopore.The OER catalytic properties of two COF were tested in 1 M KOH solution,and the OER overpotential of the novel JUC-630 was found to be 400 m V,which was significantly lower than Etta-Td COF(450 m V),proving that the introduction of a tetrathiofuvalene building unit with strong electron supply can improve the catalytic performance of COF.2)Unlike other carbon materials,COF has a precisely tunable structure and to increase the number of active sites,we selected thienene S with different number of active sites as the building unit and synthesized JUC-631 and TT-Por-COF.We tested the OER performance of two COF in 1 M KOH solution and found that JUC-631 has lower overpotential,tafel slope as well as impedance values than TT-Por-COF.Demonstrated that the precise regulation of the number of active sites can improve the catalytic performance.3)On the basis of the first two works,to further investigate the factors affecting the performance of electrocatalytic OER,we synthesized three COF with the same twodimensional layered structure by selecting three monomers with electroactive benzo[1,2-b: 3,4-b ′: 5,6-b ′]-2,5,8-triformaldehyde(BTT)reaction,namely BTT-TPB COF,BTT-TPA COF,and BTT-TZT COF.The OER performance of the three COF in 1 M KOH solution showed that the COF synthesized by triazine monomer with planarity was 350 m V,overpotential 380 m V of BTT-TPB COF,and overpotential 410 m V of BTT-TPA COF.This indicates that the different degree of monomer planarity not only affects the crystallinity and porosity of COF,but also its catalytic properties. |
PDF Full Text Request