Bimetallic Cage-Based Metal-Organic Frameworks for Electrochemical Hydrogen Evolution Reaction with Enhanced Activity

A cage-based metal-organic framework (Ni-NKU-101) with biphenyl-3,3',5,5'-tetracarboxylic acid was synthesized via solvothermal method. Ni-NKU-101 contains two types of cages based on trinuclear and octa-nuclear nickel-clusters that are connected with each other by the 4-connected ligands, to form a 3D framework with a new topology. A mixed-metal strategy was used to synthesize isostructural bimetallic MOFs of M_x Ni_1-x -NKU-101 (M=Mn, Co, Cu, Zn). The electrocatalytic studies showed that the hydrogen evolution reaction (HER) activity of Cu_x Ni_1-x -NKU-101 is much higher than that of other M_x Ni_1-x -NKU-101 catalysts in acidic aqueous solution, owing to the synergistic effect of the bimetallic centers. The optimized Cu_0.19 Ni_0.81 -NKU-101 has an overpotential of 324 mV at 10 mA cm^-2 and a Tafel slope of 131 mV dec^-1 . The mechanism of HER activity over these bimetallic MOF-based electrocatalysts are discussed in detail.