Treelike two-level PdxAgy nanocrystals tailored for bifunctional fuel cell electrocatalysis

Pd-based alloy catalysts have been extensively investigated as the anodic and cathodic catalysts of direct formic acid fuel cells (DFAFCs) by virtue of their unique synergistic effect, good stability and relatively low cost compared with Pt-based alloy catalysts. Controlling the structure and morphology of nanocatalysts is of great significance to tune and boost their electrocatalytic performance. Herein, we propose a simple, rapid and green approach to fabricate tree-like PdAg nanocrystals with tunable chemical composition (PdxAgy NTs) via mixing the metal precursors and 1-naphthol, and then aging for a mere 30 min at 60 degrees C. The obtained PdxAgy NTs feature a two-level structure of tiny Pd1Ag1 alloy nanodendrites and Pd1Ag2 alloy nanobranches with abundant active sites and enhanced structural stability. The formation mechanism of PdxAgy NTs has been investigated well via a series of control experiments, which is just like the germination and growth of a tree. To the best of our knowledge, treelike two-level PdxAgy nanostructures have never been reported before. Electrochemical measurements demonstrate that the Pd3Ag1 NTs outperform commercial Pd black and other compositional Pd1Ag1 and Pd1Ag3 NTs in the aspects of bifunctional activity and stability towards the anodic formic acid oxidation and cathodic oxygen reduction of the DFAFCs.