Facile Synthesis of the TiO₂-Supported Ultrathin Palladium Facet Composite Catalyst with Superior Metal Dispersion and Enhanced Catalytic Performance in Formic Acid Electro-Oxidation

Abstract

Supported metal catalysts are widely applied in electrocatalysis and heterogeneous catalysis. However, the agglomeration and/or sintering of metal nanoparticles is still a big problem, which usually causes the deactivation of these catalysts. Moreover, the inhomogeneity of the exposed facets of metal nanoparticles hinders the establishment of the structure–activity relationship of catalysts. Thus, it is crucial to develop new strategies to prepare supported metal catalysts with exposed specific metal facets that remarkably decrease the agglomeration of metal nanoparticles and achieve superior metal dispersion, especially in situations of high metal loading. In this manuscript, an ultrathin palladium layer exposed to a Pd{111} facet with an average thickness of 0.9 nm is grown on {001}-faceted anatase TiO2 nanosheets to form the TiO2(001)@Pd­(111) facet composite catalyst by precise control of the reduction of palladium precursors in the presence of CO at ambient temperature under mild conditions. On one hand, well-dispersed ultrathin Pd metal with a high metal loading of ∼31 wt % is achieved, which leads to a much larger active surface area and improved atom utilization efficiency as compared to the supported Pd nanoparticle catalyst, Pd/TiO2(001), prepared by the conventional impregnation method. On the other hand, the maximized interface contact between the ultrathin Pd layer and the TiO2 nanosheet improves the stability of the ultrathin palladium layer and downshifts the Pd d-band center. Therefore, the TiO2(001)@Pd­(111) catalyst shows much higher activity, stability, and CO tolerance as compared to Pd/TiO2(001) and commercial Pd/C­(Aldrich) catalysts with similar palladium loadings in the formic acid electro-oxidation reaction. This work opens up an effective strategy to synthesize highly stable and active supported ultrathin metal catalysts with exposed specific facets, which also sheds light on enhancing the stability and activity of Pd anodic catalysts in formic acid electro-oxidation.