Nanoscale design of an ethylene tetraaniline-bipyridine-based crystalline covalent organic framework for enhanced hydrogen evolution reaction

In this work, a two-dimensional covalent organic framework (ETTA-Bpy-COF) with an sql topology was synthesized via Schiff-base condensation of 4,4',4'',4‴-(ethene-1,1,2,2-tetrayl)tetraaniline (ETTA) and [3,3'-bipyridine]-6,6'-dicarbaldehyde (Bpy) under solvothermal conditions, followed by post-synthetic Ni incorporation. The layered porous architecture of the COF facilitates charge transport and provides accessible catalytic sites for the hydrogen evolution reaction (HER). In 0.5 M H₂SO₄, the pristine ETTA-Bpy-COF exhibits an overpotential of 247 mV at 10 mA cm^-2, a charge-transfer resistance of 70.3 Ω and a Tafel slope of 88 mV dec^-1. Upon Ni incorporation (0.647 wt%), the overpotential decreases to 214 mV, accompanied by a reduced charge-transfer resistance (48.4 Ω) and a lower Tafel slope (61 mV dec^-1), indicating enhanced HER kinetics. Density functional theory (DFT) calculations reveal favourable electronic modulation after Ni incorporation, consistent with the experimentally observed improvement in catalytic activity. The catalyst also demonstrates good durability after 1000 cycles and maintains stable current density for 15 h under chronoamperometric conditions. These results highlight the effectiveness of Ni incorporation in enhancing the HER performance of ETTA-Bpy-COF.