Study On The Electrochemical Performance Of Triazine Based Covalent Porous Framework Materials

The energy crisis and environmental pollution are becoming more and more serious.So the development of renewable energy is badly needed,among which the energy conversion and storage device is the most important part.Fuel cells and supercapacitors have a good application prospect in energy conversion and storage area for their high energy conversion efficiency and environment-friendly nature.However,the low cathodic oxygen reduction reaction rate of fuel cells and the low energy density of supercapacitors are still the bottleneck for their further development and application.Heteroatom-doped carbon materials have great application prospects in this field because of their own advantages,including relatively abundant raw materials,large specific surface area,high chemical stability and a wide operating temperature range.However,most traditional heteroatom-doped porous carbon materials have random structures and pore distributions with high uncertainty,which is harmful for a deep understanding of supercapacitors and the ORR mechanism.Based on a molecular design,we introduced the heteroatoms into the final products evenly and stable via covalent bond.These heteroatoms can not only improve the specific capacitance of the electrode material but also help to form active sites for oxygen reduction.The specific contents are as follows:(1).The monomer PYPZ containing cyanide groups was synthesized.Then the monomer was further polymerized with nano-silicon microsphere as template at the temperature of700°C,800°C,900°C.The samples were denoted as p-PYPZ-700,p-PYPZ-800,and p-PYPZ-900,used as supercapacitor electrodes and catalyst materials for oxygen reduction reaction.The results indicate that the p-PYPZs obtained at different temperatures have a hierarchical pore structure with both micropores and mesopores.As the polymerization temperature increased,the specific surface area increased from 697 m² g^-1 for p-PYPZ-700 to988 m² g^-1 for p-PYPZ-900.The p-PYPZ-700 owes the better specific capacitance than that of the others in 1 mol L^-1 H₂SO₄,three-electrode system.The specific capacitance of p-PYPZ-700was 257 F g^-1 at 0.1 A g^-1.Nitrogen and oxygen atoms introduced via covalent bond and the hierarchically porous structure endow the material with excellent cycling stability,and 96%capacitance retention after 35 000 cycles.The results also indicate a positive correlation between the N-Q content and the selectivity of the four-electron pathway in oxygen reduction reaction.(2).On the basis of previous work,in order to further improve the electrical conductivity of the electrode material,TNPZ was selected as monomer and polymerized with nano-silicon microsphere as template at the temperature of 700°C,800°C,900°C.The samples were denoted as p-TNPZ-700,p-TNPZ-800,and p-TNPZ-900.The p-TNPZ-700 owes the better specific capacitance than that of the others in 1 mol L^-1 H₂SO₄,three-electrode system.The specific capacitance of p-PYPZ-700 was 253 F g^-1 at the current density of 0.1 A g^-1.Nitrogen and oxygen atoms introduced via covalent bond and the hierarchically porous structure endow the material with excellent cycling stability,and 98%capacitance retention after 35 000 cycles.Electrochemical impedance spectroscopy results indicated that p-TNPZs series materials have better electrical conductivity than that of p-PYPZs.What's more,p-TNPZs have a better selectivity of four-electron pathway than that of p-PYPZs.This result indicating that a better electrical conductivity is beneficial to further improve the selectivity of four-electron pathway in oxygen reduction catalysis.