Synergistic effect of CoII, NiII and FeII/FeIII in trimetallic MOFs for enhancing electrocatalytic water oxidation†

Metal–organic frameworks (MOFs) can catalyze the oxygen evolution reaction (OER) process. Despite the established link between pristine MOFs and electrocatalysts, a number of limitations still hamper the understanding of the key factors that determine OER performance. In this paper, taking the ideal Co-MOF model as the structural basis (this MOF contains unsaturated coordinated metal centers and one-dimensional metal chains), nickel ions and/or iron ions are introduced to obtain isostructural bimetallic and trimetallic MOFs. Furthermore, the valence state of the iron element in the trimetallic MOF is regulated to improve the OER performance. The electrochemical performance test results confirm that the trimetallic (Co₁Ni₁)₂Fe₁(II)-MOF regulated by valence state shows excellent catalytic performance in the OER, which is superior to monometallic and bimetallic MOFs. Its enhanced catalytic performance can be attributed to the synergistic interactions between unsaturated Co, Ni and Fe sites as well as the faster charge transfer ability of the Fe^II/Fe^III mixed-phase system, which facilitates the optimization of the adsorption and activation processes of the reactants/intermediates. This exploration provides a new perspective for further studying the structure–performance relationship of metal–organic framework materials and developing more efficient OER catalysts.