Boosting efficient electrocatalytic CO2 reduction by two-dimensional polyoxometalate@metal-organic framework composites with asymmetric sites

Abstract

To address environmental challenges associated with CO₂ emissions, the electrocatalytic reduction of CO₂ to CO has emerged as a promising strategy. Silver-based catalysts exhibit high selectivity for CO, yet their performance is limited by the high energy barrier of the proton-coupled electron transfer step. Enhancing ∗H generation is therefore key to lowering this barrier and improving catalytic efficiency. Herein, a rational design integrating polyoxometalates (POMs) with controlled solvent ratios is reported to induce asymmetric active sites, enabling the synthesis of two types of two-dimensional silver-based polyoxometalate@metal-organic framework (POM@MOF) composites (Ag-TPT-SiW₁₂-1 and Ag-TPT-SiW₁₂-2, TPT = 2,4,6-tris(4-pyridyl)-1,3,5-triazine). Ag-TPT-SiW₁₂-2 contains asymmetric bifunctional sites (Ag–N₂O₁ and Ag–N₃) that operate synergistically: Ag–N₂O₁ activates CO₂, while Ag–N₃ promotes ∗H generation, thereby accelerating the formation of the ∗COOH intermediate and enhancing overall catalytic activity, compared with Ag-TPT-SiW₁₂-1. Ag-TPT-SiW₁₂-2 achieves a CO Faradaic efficiency exceeding 90% over a wide potential range (−0.7 V to −1.2 V vs. RHE), maximum at 94.2% at −1.0 V, which is 120% of that of Ag-TPT-SiW₁₂-1. Theoretical calculations combined with experiments indicate that POMs donate electrons to catalytic centers, while cooperative interaction between the asymmetric bifunctional sites lowers the hydrogenation activation energy barrier. This work presents a new paradigm for designing high-performance electrocatalysts through precise electronic modulation and reaction pathway optimization.