Exploring the Effects of Saturated and Transition-Metal-Substituted Dawson Doping on Electrocatalytic CO2 Reduction Activity in P2W18@PCN-222 and P2W17M@PCN-222 (M = Co, Mn, Ni) Composites.

To exploit the electron-sponge properties of polyoxometalates (POMs) and elucidate the mechanistic impact of doping with saturated versus metal-substituted Dawson-type POMs on electrocatalytic CO2 reduction, P2W18@PCN-222 and P2W17M@PCN-222 (M = Co, Mn, Ni) composites were prepared using an impregnation method. Electrochemical analyses, in situ infrared spectroscopy, and DFT calculations reveal that substituted P2W17M clusters lower the free energy barriers for *COOH and *CO formation, promoting CO evolution. Specifically, P2W17Co acts as an electron donor, facilitating the directional transfer of electrons from the POM to the porphyrin active centers of the PCN-222. Consequently, P2W17Co@PCN-222 exhibits superior CO2 reduction reaction (CO2RR) performance, achieving a Faradaic efficiency for CO (FECO) of 82% and a partial current density (jCO) of 3.4 mA cm-2 at -0.80 V vs RHE, an 11.9-fold and 34.1-fold enhancement over pristine PCN-222 (FECO = 6.9%, jCO = 0.1 mA cm-2), respectively. In contrast, the saturated P2W18 cluster failed to establish an effective electron transfer pathway with the porphyrin centers and did not reduce the energy barrier associated with the rate-determining step (*COOH formation), thus conferring no promotional effect on the CO2RR.