New Covalent Organic Square Lattice Based on Porphyrin and Tetraphenyl Ethylene Building Blocks toward High-Performance Supercapacitive Energy Storage

Covalent organic frameworks (COFs) are of increasing interest in the field of materials science. Polymerizations of the topologically fitted monomers into two-dimensional (2D) structures with a periodic order often make them crystalline. The existence of this structural periodicity and regular pores makes them effective for facile ion transport and storage applications. We report herein a new porphyrin-based 2D COF using Schiff base condensation reaction between 5,10,15,20-tetrakis(para-amino phenyl) porphyrin (TAPP) and 1,1,2,2-tetrakis(4-formyl-(1,1′-biphenyl))-ethane (TFBE) under solvothermal conditions. The as-prepared porphyrin-tetraphenyl ethylene COF (PT-COF) possesses high crystallinity along with a large surface area of 1998 m2 g–1. The PT-COF electrode was used as a supercapacitive energy storage system with the combination of an electrochemical double-layer capacitor and pseudocapacitor. This COF showed a maximum specific capacitance of 1443 F g–1 at a current density of 1 A g–1 in 0.5 M H2SO4 with 91% capacity retention after 3000 cycles. The presence of the porphyrin unit inside the framework causes good redox activity in the acidic media. During the cathodic scan, the porphyrin unit [H2P] got protonated, followed by 2e– reduction to form a 20π-electronic system [H4P]. Thus, the reversible proton accepting capability of the redox-active porphyrin-decorated PT-COF could allow for use as an energy storage material as a supercapacitor under acidic conditions. A high power density of 7.3 kW kg–1 was observed at a high scan rate, which outperforms most of the other COF-based electrode materials used for high storage performance.