Leveraging Pd(100)/SnO2 interfaces for highly efficient electrochemical formic acid oxidation†

The electrocatalytic formic acid oxidation (FAO) is the crucial anodic reaction of direct formic acid fuel cells (DFAFCs), but its activity remains to be largely improved in order to be practically viable. The rational development of enhanced catalysts requires thorough consideration of various contributing factors that are possibly integrated in composite systems. Here, we demonstrate that, Pd(100)/SnO2 interfaces, provided being efficiently exploited, can significantly boost FAO activity by a factor of ∼10, compared with pure Pd(100) facets, with the mass activity reaching a record of 14.55 A mgPd−1 at a 40 mV-lower peak potential. Unique Pd/SnO2 nanocomposites with a myriad of Pd(100)/SnO2 interfaces were obtained by a newly developed successive seeded growth strategy, wherein pre-formed SnO2 nanospheres are used as seeds for two-round overgrowth of multitudinous Pd nanocubes. Using electron microscopic, electrochemical, spectroscopic and computational analyses, we found that the Pd(100)/SnO2 interfaces induce lattice contraction and electron loss on Pd nanocubes, which optimize intermediate binding during FAO. Moreover, we showed that the good cubicity of the Pd nanocubes and the presence of SnO2 nearby further promote the activity by facilitating the potential-determining step and the elimination of the poisoning CO intermediate, respectively. As such, the combined high intrinsic activity and number density of Pd(100)/SnO2 interfaces enabled the superior activity of the Pd/SnO2 nanocomposites. The composite material presented here holds promise for application in DFAFCs, but equally importantly, the insights regarding the structure–performance relationship would be beneficial for designing efficient metal/oxide composite catalysts for diverse electro- and photo-catalytic reactions.