New Covalent Organic Square Lattice Based on Porphyrin and Tetraphenyl Ethylene Building Blocks toward High-Performance Supercapacitive Energy Storage
Bidhan Chandra Patra, Santanu Bhattacharya
Abstract
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.