Single-Cluster Polyoxometalate Catalysts via Modular Electrostatic Assembly on Cationic Covalent Organic Framework for Furfural Electroreduction

Abstract

Single-cluster catalysts (SCCs) provide atomically precise active sites and model systems for mechanistic studies, but achieving uniform dispersion of clusters on supports remains challenging. Herein, a cationic porphyrin–viologen covalent organic framework (PV) is employed to immobilize diverse polyoxometalate (POM) clusters within its ordered channels via electrostatic assembly, thereby establishing a modular platform for fabricating well-defined SCCs. As a representative example, the sandwich-type Cu4(PW9)2 cluster was uniformly immobilized on PV, yielding Cu4(PW9)2@PV with high loading and stability. This catalyst exhibits remarkable catalytic activity in the electrocatalytic reduction of furfural to furfuryl alcohol, achieving 96.4% selectivity. The compositional tunability of POMs, together with the generality of this strategy, facilitates systematic mechanistic investigations. Combined experimental and theoretical analyses (control experiments, kinetic isotope studies, electrochemical and spectral analyses, and DFT calculations, etc.) reveal that Cu sites serve as the catalytic centers, while polyoxotungstate units act as electron–proton reservoirs, switching the reaction pathway from hydrogen atom transfer to proton-coupled electron transfer. This work not only establishes a modular platform for the rational design and synthesis of SCCs but also provides new insights into the catalytic process of biomass electroreduction.