Plasma-induced implanting of active species in metal–organic frameworks for efficient hydrogen evolution reaction

Abstract

With the merits of high surface area and plentiful metal sites, metal–organic frameworks (MOFs) are promising catalysts for the hydrogen evolution reaction (HER). However, the HER activity of MOFs is not satisfactory due to their poor electrical conductivity and fewer HER active sites. Herein, taking a nickel-terephthalic acid-based MOF (Ni MOF) as an example, a low-temperature, environmentally friendly, and time-efficient N₂/H₂ plasma activation strategy is developed to implant multiple HER active species (Ni, Ni₃N and MoNi₄) in molybdenum-based polyoxometalate (POM)-encapsulated Ni MOF nanosheet arrays (Ni MOF/POM). Endowed with enhanced conductivity and increased active sites, the plasma-activated Ni MOF/POM (P-Ni MOF/POM) exhibits a splendid HER activity (35 mV at 10 mA cm⁻²) and a long stability (up to 120 h) in alkaline solution. Excellent HER performance is also demonstrated by P-Ni MOF/POM in alkaline seawater. During the HER process, it is interesting to observe that the Ni MOF in P-Ni MOF/POM undergoes reconstruction into β-Ni(OH)₂, while the HER active species (Ni, Ni₃N and MoNi₄) are largely maintained. The dynamic contact angle, in situ electrochemical impedance spectroscopy (EIS), and kinetic isotope effect (KIE) characterization studies suggest that plasma activation plays an important role in enhancing water adsorption and accelerating the kinetics of water dissociation, thus ensuring enhanced HER activity.