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, Co-MOF-1D 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 Co (where @2 denotes template-directed synthesis of MOF-74). Its electrocatalytic performance is superior to that of the conventional one-step-synthesized Co (where @1 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 Co were further regulated to obtain the electrocatalytic materials Co and Co. The electrochemical performance test results confirm that Co regulated by valence state has a better catalytic performance than Co in the oxygen evolution reaction (OER) process. This phenomenon is related to the gradual increase in the valence state of Fe ions in Co, 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.