Generation of covalent organic framework-derived porous N-doped carbon nanosheets for highly efficient electrocatalytic hydrogen evolution

Abstract

Hydrogen production by electrochemical water splitting is a promising green and renewable hydrogen energy route due to zero pollution, high purity, and abundant water resources. In this context, completely metal-free electrocatalysis is an emerging research area for clean energy production due to its low cost, eco-friendliness, high stability, and high resistance to a wide pH range. However, only a few electrocatalysts like g-C₃N₄, CNTs, and heteroatom-doped graphene have been reported to date that exhibit robust metal-free hydrogen evolution reaction (HER) performances. Herein, we have developed a triazine-containing polyimide-based covalent organic framework (TP-COF) by a one-pot condensation reaction between pyromellitic dianhydride and melamine under reflux condensation. The polymeric framework exhibited a unique two-dimensional nanosheet morphology with a moderate surface area of 312.6 m² g⁻¹ and abundant pores of 1.8 nm. The synthesized TP-COF displayed a reasonable electrocatalytic HER performance with excellent long-term stability. Furthermore, the HER performance was further enhanced by pyrolyzing the TP-COF at 700 °C to prepare the N-doped porous carbon nanosheet, TP-COF-C700. The high surface area (672.2 m² g⁻¹) with uniform mesopores (∼1.98 nm), amplified electrical conductivity of TP-COF-C700, and presence of enriching N as the dopants for improving active sites made the TP-COF-C700 a promising HER electrocatalyst. The TP-COF-C700 showed the HER overpotential of 94 mV@10 mA cm⁻² current density with 60 h long-range durability and 98% faradaic efficiency for hydrogen evolution. This report highlights a unique paradigm for preparing highly efficient metal-free electrocatalysts for HER.