Mixed-Metal-Cluster Strategy for Boosting Electrocatalytic Oxygen Evolution Reaction of Robust Metal-Organic Frameworks

Rational construction of mixed metal-organic frameworks (MOFs) has been proved to be an effective way to heighten the electrocatalytic performance for MOFs, while the function of mixed metal clusters in MOFs to the electrocatalytic activity has not been known. For the first time, we present a mixed-metal-cluster strategy to boost electrocatalytic oxygen evolution reaction (OER) performance for MOFs. Heterometal clusters (Fe₂M(μ₃-O) (CH₃COO)₆(H₂O)₃, denoted as Fe₂M (M: Co or Ni)), were chosen as the metal source to construct two bimetal PCN-250-Fe₂M. Then, we further mixed Fe₂Co and Fe₂Ni clusters to construct mixed-metal-cluster PCN-Fe₂Co-Fe₂Ni by the in situ solvothermal reaction. Consequently, the OER activity of PCN-Fe₂Co-Fe₂Ni shows a dramatic enhancement compared with that of the parent bimetal MOFs. The PCN-Fe₂Co-Fe₂Ni displays a lower overpotential of 271 mV (η₁₀), small Tafel slope (67.7 mV dec^-1), and good linear sweep voltammetry cycle stability for the OER. Combination of DFT calculation and experiment results show that the improved electrocatalytic activity of PCN-Fe₂Co-Fe₂Ni is ascribed to the increased electron density of Co and Ni active centers and electrochemically active areas.