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surfaces and lower Ostwald ripening/ aggregation ability, thus endowing them with outstanding catalytic performance. [26] Huang et al. reported that the prepared freestanding hexagonal Pd NSs show 2.5 times higher peak current density than Pd black catalyst in formic acid oxidation reaction (FAOR). [14] Our group developed a facile approach to synthesize ultrathin Pd NSs using methanol as solvent, CO as a reducing and structure-directing agent, and they show highly enhanced catalytic activity and stability toward FAOR compared with Commercial Pd/C. [17,18] Both Pd-Mo bimetallene [19] and defect-rich porous Pd metallene [20] were also demonstrated as advanced catalysts for the oxygen reduction reaction. Therefore, it is highly desirable to synthesize Pd-based nano structures with the merits combination of 2D NSs and 1D nano wires for dramatically improving catalytic activity and stability.Apart from the effect of shape and atomic rough surface, alloying Pd with other transitional metals is another effective strategy to reduce the usage of Pd while achieving high catalytic performance. [27,28] Since the electronic structure of Pd would be significantly modulated after the introduction of the second metal, the adsorption property of CO-like poisoning species on the electrode is weakened consequently. [29,30] It is worth noting that both small-sized nanoparticle and single atomic site catalyst could also effectively improve the atom utilization efficiency of Pd. [31] Unfortunately, the surface free energy of nanocrystals increases with the decrease of their size, which usually leads to severe aggregation. While a major challenge for single atomic site catalysts is low metal-loading, which inevitably reduces the overall catalytic properties. [32] Among the Pd-based alloy catalysts, the PdCu system is considered as an efficient one in the electrooxidation of small organic molecules such as methanol and ethanol in alkaline media in comparison to other Pd-based alloy catalysts, including PdNi, PdCo, PdAg, and PdFe, because its d-band center downshifts to a very suitable position, resulting in a weaker adsorption energy of CO-like poisoning species. [33][34][35][36][37][38][39] Sheng et al. reported the synthesis of porous octahedral PdCu nanocages by templating against Cu 2 O combining with the disproportionation and displacement reactions. [40] Our group synthesized twisted PdCu nanochains via a staged thermal treatment route, showing greatly enhanced catalytic activity toward FAOR than Pd/C. [41] Zheng and co-workers prepared wrinkle-free PdCu NSs using n-butylamine as a bifunctional agent. [42] In this work, we report the preparation of web-footed PdCu NSs (WF-PdCu NSs) via a facile surfactant-free method, using Morphological control of noble-metal-based nanocrystals has attracted enormous attention because their catalytic behaviors can be optimized well by adjusting the size and shape. Herein, the controllable synthesis of web-footed PdCu nanosheets via a facile surfactant-free method is reported. It is discovered th...

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