The "Bubble-Template"-Guided Construction of Pd₄Cu₁ Porous Nanocages for Efficient Formic Acid Electrooxidation

Direct formic acid fuel cells (DFAFCs) are promising candidates for portable energy conversion; however, their widespread application is limited by sluggish formic acid oxidation reaction (FAOR) kinetics and catalyst deactivation. Herein, we report a urea-assisted one-step hydrothermal strategy to synthesize hollow porous Pd₄Cu₁ nanocages (PNCs) with a well-defined morphology. Under alkaline conditions, the thermal decomposition of urea generates CO₂ and NH₃ gases, which act as dynamic soft templates to guide the formation of the hollow architecture via a gas-bubble-mediated mechanism. Simultaneously, urea coordinates with Pd²⁺ and Cu²⁺ ions, modulating the reduction kinetics and promoting homogeneous alloying. The resulting Pd₄Cu₁ PNCs feature a high surface area, abundant mesopores, and defect-rich surfaces, while Cu alloying effectively tunes the electronic structure of Pd, enhancing the CO tolerance and catalytic activity. The optimized catalyst delivers a peak current density of 2.23 mA cm^-2 and a mass activity of 943.1 mA mg_Pd^-1, outperforming commercial Pd black. This work highlights a facile, scalable, and bubble template-assisted synthesis route for engineering advanced Pd-based electrocatalysts toward efficient and durable DFAFCs.