Targeted Grafting Metal-Organic Frameworks on Polyoxometalates for Efficient Water Oxidation

Abstract

In recent years, due to the diverse and tunable microenvironment of metal centers, Metal-organic framework materials (MOFs) have shown great advantages in heterogeneous catalysis.[1,2] Studies have found that in some oxidation scenarios, taking water oxidation as an example, the instability of is framework limits its practical application under severe conditions. Therefore, many efforts have focused on improving the catalytic stability of MOFs materials. [3-5]The MOFs-based electro-catalytic systems developed for oxygen evolution under alkaline conditions in our work are discussed in the following three sections. First, based on the loss of active sites faced by MOFs during OER and the high oxidation potential due to insufficient electrical conductivity, a kind of nanoscale inorganic materials with oxygen-enriched surfaces --polyoxometalates (POMs), was selected as a composite modifier. Subsequently, a two-dimensional nanomaterial (MOFs@POMs) with high catalytic activity and ultra-high stability was synthesized on the basis of MOFs using a facile solvothermal method to immobilize the active sites of MOFs through the M-O ionic bond between POM and MOFs. Furthermore, we found that the structure of POMs plays a key role in the formation of this unique superstructure, which leads to a catalytic active site that can be persistently maintained during the OER process. Based on this, a scheme for the immobilization of MOFs active sites by POMs is proposed to synthesize MOFs composites with ultra-high OER stability based on both POMs and MOFs materials. The assembly mechanism of the composites during the synthesis process is proposed, and the intrinsic reason for the modulation of the active site of MOFs by POMs and its long-lasting immobilization is demonstrated, which enables the MOFs materials to maintain excellent catalytic activity throughout the great OER catalytic process. This study successfully demonstrates that the stability challenges faced in the OER process of MOFs can be solved, which may provide a helpful solution for the application of MOFs-related OER catalysts.