A metal-free perylene–porphyrin based covalent organic framework for electrocatalytic hydrogen evolution

Abstract

A crystalline perylene–porphyrin based covalent organic framework is synthesized via Schiff base [2 + 2] type condensation between 4,4′,4′′,4′′′-(perylene-2,5,8,11-tetrayl) tetrabenzaldehyde (PETA) and 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (PAM) under solvothermal conditions. The porphyrin and perylene units occupy the vertex of a three-dimensional triclinic crystal in an alternate manner. PETA-PAM-COF exhibits permanent microporosity, a reasonably high surface area (about 1400 m² g⁻¹), and promising chemical stability. A conducting perylene bridged channel is created by AA stacking. PETA-PAM-COF has been utilized for the metal-free hydrogen evolution reaction with a low charge-transfer resistance (R_ct) value of 62.22 Ω and a Tafel slope of 122 mV dec⁻¹, demonstrating its potential for practical utilization. PETA-PAM COF showed a current density of 10 mA cm⁻² at an overpotential of 261 mV. Remarkable HER activities are demonstrated by the PETA-PAM-COF catalyst as indicated by its faradaic efficiency (96%) and durability (which retained 93% of its original current density after 1000 cycles). We anticipate that the imine-based COF will not only enhance the structural variety but also the electrochemical behavior of these classes of materials.