Conductive Metal–Organic Frameworks with Extra Metallic Sites as an Efficient Electrocatalyst for the Hydrogen Evolution Reaction

Abstract

The 2D conductive metal-organic frameworks (MOFs) are expected to be an ideal electrocatalyst due to their high utilization of metal atoms. Exploring a new conjugated ligand with extra active metallic center can further boost the structural advantages of conductive MOFs. In this work, hexaiminohexaazatrinaphthalene (HAHATN) is employed as a conjugated ligand to construct bimetallic sited conductive MOFs (M2₃(M1₃∙HAHATN)₂) with an extra M-N₂ moiety. Density functional theory (DFT) calculations demonstrate that the 2D conjugated framework renders M2₃(M1₃∙HAHATN)₂ a high electric conductivity with narrow bandgap (0.19 eV) for electron transfer and a favorable in-plane porous structure (2.7 nm) for mass transfer. Moreover, the metal atom at the extra M-N₂ moiety has a higher unsaturation degree than that at M-N₄ linkage, resulting in a stronger ability to donate electrons for enhancing electroactivity. These characteristics endow the new conductive MOFs with an enhanced electroactivity for hydrogen evolution reaction (HER) electrocatalysis. Among the series of M2₃(M1₃∙HAHATN)₂ MOF, Ni₃(Ni₃∙HAHATN)₂ nanosheets with the optimal structure exhibit a small overpotential of 115 mV at 10 mA cm^-2, low Tafel slope of (45.6 mV dec^-1), and promising electrocatalytic stability for HER. This work provides an effective strategy for designing conductive MOFs with a favorable structure for electrocatalysis.