Ni(II)-Pyrazolate Framework Bearing a Metalated Schiff-Base Moiety for Electrocatalytic Hydrogen Evolution

A robust and porous Ni-based metal-organic framework (MOF), NiL1, was assembled from Ni(II) ions and a dipyrazolate linker (L1^2-). A Ni(II)-anchored MOF catalyst Ni@NiL1-Sal has been successfully prepared by post-synthetic modification (PSM) condensation between NiL1 with salicylaldehyde, followed by chelation of Ni(II) ions by salicylaldimine as a secondary active site. Ni@NiL1-Sal with carbon black was found to exhibit enhanced electrocatalytic hydrogen evolution reaction (HER) performance (the smallest overpotential, 384 mV, and Tafel slope, 87 mV dec^-1) when compared with primitive NiL1 and NiL1-Sal. Such improvement in HER highlights the creation of unambiguous secondary active sites as an avenue to the rational design of a functional MOF-based electrocatalyst.