Tuning the Hydroxyl Density of MXene to Regulate the Electrochemical Performance of Anchored Cobalt Phthalocyanine for CO₂ Reduction

Precise electronic state regulation through coordinationenvironmentoptimization by metal-support interaction is a promising strategyto facilitate catalysis reaction, while the limited density of functionalgroups in the bulk substrate restricts the regulation degree. Herein,different sizes of Ti3C2T x MXene with hydroxyl (-OH) terminal including the MXenelayer (ML-OH, 3 mu m), the MXene nanosheet (MNS-OH, 600 nm), andthe MXene quantum dot (MQD-OH, 8 nm) were prepared to anchor CoPc,and the effect of -OH density on the performance of electrochemicalCO(2) reduction was systematically investigated. Notably,a linear relationship was established by plotting reactivity vs hydroxyldensity. With the highest -OH density, CoPc/MQD-OH exhibitsa superior Faradaic efficiency for CO formation (FECO)of similar to 100% at -0.9 to -1.0 V vs RHE and a highFE(CO) of >90% over a wide potential window from -0.8to -1.4 V. The mechanism exploration shows that the axial coordinationinteraction of the -OH terminal with Co increases the electrondensity of the Co site, thus promoting the adsorption and activationof CO2. This work provides a new insight into designingof molecular catalysts with high efficiency and tunable structurefor other electrochemical conversions.