Confined Palladium Nanocrystals within Covalent Organic Framework-Intercalated MXene Nanoarchitectures toward Highly Efficient Methanol Electrooxidation

Abstract

The rational design of high-performance electrocatalysts toward the methanol oxidation reaction plays a noticeable role in the progress of stimulating the industrial development of direct methanol fuel cells. In this study, ultrafine palladium nanocrystals are in situ confined within the hydrazone-linked covalent organic framework (COF-42)-intercalated Ti₃C₂T_x MXene nanoarchitectures (Pd/COF-MX) through a facile and robust stereoconstruction strategy. The existence of hydrangea-shaped COF-42 with abundant N species makes it possible to optimize the coordination environments for Pd nanocrystals to facilitate their size confinement and homogeneous dispersion, while the MXene nanosheets afford strong electronic interactions and contemporaneously reduce the overall charge-transfer resistance of the hybrid catalyst. As a result, the emerging Pd/COF-MX nanoarchitectures demonstrate a preferable catalytic methanol electrooxidation performance with an extensive electrochemically active surface area, superior mass activity, and dependable long-term stability, significantly outperforming the conventional Pd/carbon black, Pd/carbon nanotube, Pd/reduced graphene oxide, and Pd/MXene catalysts. Density functional theory simulation additionally discloses that the functionalization of COF-42 enables a stronger atomic interaction with the Pd component, which induces an obvious left shift of its d-band center and leads to a weaker adsorption ability toward the CO molecule.