Research on the Construction of a Series of Transition Metal-Substituted Keggin-Type TMSPOMs@PCN-224 Composites...

In order to take advantage of the distinct reversible multielectron transfer properties of polyoxometalates (POMs) and increase the electron density at the active sites during the electrochemical reduction of CO₂ (CO₂RR), a range of transition metal-doped polyoxometalates (TMSPOMs) was entrapped within the porphyrin-based framework of PCN-224 via an encapsulation method, known as TMSPOMs@PCN-224 (TMSPOMs = [XW₁₁O₃₉M^II(H₂O)]^n-, [XW₁₁O₄₀V^IV]^n-, M = Co^II, Mn^II; X = Si, n = 6; X = P, n = 5). The central elements (Si, P) and the incorporated transition metals (V^IV, Co^II, and Mn^II) both play a role in adjusting the electronic structure and electron transfer during the CO₂RR process. Remarkably, the composite material with cobalt substitution displayed significantly improved performance. Through fine-tuning the POM loading, the electrocatalytic activity was optimized, leading to an impressive Faradaic efficiency for CO production (FE_CO) of 89.9% for SiW₁₁Co@PCN-224, a significant improvement compared to the 12.1% FE_CO of PCN-224. Furthermore, the electrochemical stability of this catalyst was demonstrated over 20 h. Comparative analyses involving six composite materials indicated a relationship between the negative charge of the polyanions and their ability to facilitate effective electron transfer, ultimately enhancing the catalyst's performance. Meanwhile, these findings were supported by density functional theory (DFT) calculations.