A Ni/Fe complex incorporated into a covalent organic framework as a single-site heterogeneous catalyst for efficient oxygen evolution reaction

Abstract

A molecular NiFe complex (Cyclen@Ni_0.5Fe_0.5) was incorporated into the framework of COF (NH₄@COF-SO₃) by a one-pot post-synthesis method. The use of cyclen that can strongly chelate metal ions enables the formation of completely isolated metal sits uniformly distributed on the framework of COF. The resulting single-site heterogeneous catalyst ((Cyclen@Ni_0.5Fe_0.5)@COF-SO₃) exhibits outstanding oxygen evolution reaction (OER) activity because of the maximum atom-utilization efficiency and significant bimetallic synergy effect. The TOF value at the overpotential of 300 mV reaches as high as 0.69 s⁻¹, which is superior to most of the recently reported efficient OER electrocatalysts. Moreover, the catalyst is stable and reusable without the loss of current density during a 25 h long-term test. The combination of advantages of molecular catalysts (metal complex) similar to homogeneous catalysts and solid COF materials for the fabrication of single-site heterogeneous catalysts first reported in this work can bring new avenues to develop highly efficient and stable COF-based catalysts in different catalytic fields.