Micro-sized conductive metal–organic framework nanosheets for the electrochemical hydrogen evolution reaction in acidic media

Abstract

Electrically conductive metal–organic frameworks (MOFs) have emerged as promising platforms for the electrochemical hydrogen evolution reaction (HER) owing to their tunable active centers; however, their bulky three-dimensional architectures limit active-site accessibility. Here, we present a reconstruction strategy for 2,3,6,7,10,11-hexaaminotriphenylene (HITP)-based MOFs, enabling the fabrication of micro-sized nanosheets. The method involves sonication of M-HITP nanoparticles in aqueous tetramethylammonium hydroxide, proceeding through a rearrangement–reconstruction pathway. This approach yields nanosheets with a thickness of ∼30 nm and an efficiency of ∼30 wt%. In an acidic electrolyte, the HER overpotential at 10 mA cm⁻² over Ni-HITP decreases markedly from 253 mV (nanoparticles) to 105 mV (nanosheets). Bimetallic engineering further boosts activity and CoNi-HITP nanosheets achieve an overpotential of only 151 mV at 100 mA cm⁻², substantially lower than that of Ni-HITP nanosheets (453 mV). Density functional theory calculations identify Co as the primary active site, with stronger H* binding than Ni. Moreover, incorporation of Ni shifts the d-band center of Co upward, enhancing H* adsorption. Consequently, the free-energy change for the HER on CoNi-HITP is reduced to 0.258 eV, compared with 0.942 eV for pristine Ni-HITP, consistent with the experimentally observed superior performance of CoNi-HITP nanosheets.