Layered and Heterostructured Pd/PdWCr Sheet-Assembled Nanoflowers as Highly Active and Stable Electrocatalysts for Formic Acid Oxidation

Unique layered and heterostructured Pd/PdWCr nanosheet-assembled flowers (L-Pd/PdWCr) are successfully synthesized, resulting in the most negative onset potential (up to -0.174 V vs SCE) for formic acid oxidation among all reported Pd-based electrocatalysts. It has 4.3-times higher catalytic peak current density and better stability than that of the commercial Pd/C. The catalytic enhancement mechanism is mainly due to the synergetic effect of the layered and heterostructures of the Pd/PdWCr nanosheet. The W- and Cr-tailored Pd/PdWCr heterostructures optimize the electronic structure of Pd with suitable binding energy to reduce the charge-transfer resistance. Moreover, the layered nanosheet-assembled flowers provide easily accessible large surface area and rapid mass transport path. The great stability can be attributed to the reduced total free energy resulting from the layered structure and the highly stable structure formed by the cross-linked flower skeleton and suppressed Pd dissolution with W and Cr. This work provides an inexpensive, highly active, and stable anode electrocatalyst for direct formic acid fuel cells while demonstrating a method to synthesize layer-structured metal alloy catalysts.