Ni-Doped Ti₃CNT_x-Coated Nanoporous Covalent Organic Frameworks to Accelerate Hydrogen Diffusion for Enhanced Hydrogen Evolution

One of the reasons for the slowness of the hydrogen evolution reaction (HER) is that the accumulation of hydrogen generated near the active site hinders the efficient HER. In this work, Ni-doped Ti3CNTx-coated nanoporous covalent organic frameworks (Ni-Ti3CNTx/COFs, abbreviated as NMXC) were prepared to improve the diffusion concentration gradient of hydrogen due to the nanoscale structure design. The doped Ni nanoparticles can improve the catalytic activity of the conductive Ti3CNTx MXene. The results show that in a 0.5 M H2SO4 solution, the Tafel slope of Ni-Ti3CNTx/COF (the concentration of Ni in Ti3CNTx is 0.3%, abbreviated as N0.3MXC) is only 46.2 mV dec–1. The current density only decreased by 7.8% after 18 h in the long-term stability test under simulated sunlight. First-principles calculations show that the introduction of Ni significantly improves the catalytic activity (|ΔGH*| can be as low as 0.06 eV). At the same time, the calculation of hydrogen adsorption energy and molecular dynamics simulations show that the gradient of hydrogen concentration on the surface of the NMXC composite is significantly different, which is beneficial to the diffusion of generated hydrogen molecules. This kind of structural engineering can shed some light for studying gas/catalyst interfaces on the nano/microscale.