Assembly and Valence Modulation of Ordered Bimetallic MOFs for Highly Efficient Electrocatalytic Water Oxidation

Metal synergy can enhance the catalytic performance, and a prefabricated solid precursor can guide the ordered embedding, of secondary metal source ions for the rapid synthesis of bimetallic organic frameworks (MM'-MOFs) with a stoichiometric ratio of 1:1. In this paper, <b>Co-MOF-1D</b> containing well-defined binding sites was synthesized by mechanical ball milling, which was used as a template for the induced introduction of Fe ions to successfully assemble the ordered bimetallic <b>Co₁Fe₁-MOF-74@2</b> (where <b>@2</b> denotes template-directed synthesis of MOF-74). Its electrocatalytic performance is superior to that of the conventional one-step-synthesized <b>Co₁Fe₁-MOF-74@1</b> (where <b>@1</b> denotes one-step synthesis of MOF-74), and the ratio of the two metal sources, Co and Fe, is close to 1:1. Meanwhile, the iron valence states (Fe^II and Fe^III) in <b>Co₁Fe₁-MOF-74@2</b> were further regulated to obtain the electrocatalytic materials <b>Co₁Fe₁(II)-MOF-74@2</b> and <b>Co₁Fe₁(III)-MOF-74@2</b>. The electrochemical performance test results confirm that <b>Co₁Fe₁(II)-MOF-74@2</b> regulated by valence state has a better catalytic performance than <b>Co₁Fe₁(III)-MOF-74@2</b> in the oxygen evolution reaction (OER) process. This phenomenon is related to the gradual increase in the valence state of Fe ions in <b>Co₁Fe₁(II)-MOF-74@2</b>, which promotes the continuous improvement in the performance of the MOF before reaching the optimal steady state and makes the OER performance reach the optimum when the Fe^II/Fe^III mixed-valence state reaches a certain proportion. This provides a new idea for the directed synthesis and optimization of highly efficient catalysts.