The direct ethanol fuel cells in an alkaline medium have a broad vision of applications because of their large energy density, reasonable power density, and environmentally friendly features. Herein, we present a facile one-step method to synthesize PdAg nanosheet assemblies (NSAs) in a mixed solution of N,Ndimethylformamide and water with the addition of molybdenum hexacarbonyl and cetyltrimethylammonium bromide. Pure Pd NSA shows an irregular shape while PdAg NSAs gradually undergo a process from solid assembly to a hollow structure with the Pd/Ag molar ratio changing from 3:1 to 2:1 to 1:1. The formation of alloy nanosheets in the assemblies combined with the introduction of Ag in the Pd catalyst enhances the catalytic activity toward ethanol electrooxidation from 1524 mA mg −1 of pure Pd NSA to 1866 mA mg −1 of PdAg NSA with a Pd/Ag molar ratio of 2:1. On the basis of the experimental data, compared with pure Pd structures, both the nature of a thin nanosheet of PdAg NSAs and the structural changes in the alloy assemblies play key roles in determining the electrocatalytic activity of these Pd-based catalysts.

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Synthesizing alloyed bimetallic electrocatalysts with a three-dimensional (3D) structure assembly have arouse great interests in electrocatalysis. We synthesized a class of alloyed Pd3Pb/Pd nanosheet assemblies (NSAs) composed of a two-dimensional (2D) sheet structure with adjustable compositions via an oil bath approach at a low temperature. Both the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images reveal the successful formation of the nanosheet structure, where the morphology of Pd3Pb/Pd NSAs can be regulated by adjusting the atomic mole ratio of Pb and Pb metal precursors. The power X-ray diffraction (XRD) pattern shows that Pd3Pb/Pd NSA catalysts are homogeneously alloyed. Electrochemical analysis and the density functional theory (DFT) method demonstrate that the electrocatalytic activity of the alloyed Pd3Pb/Pd NSAs can be improved by the doping of the Pb element. As a result of the addition of element Pb and change of the electron structure, the electrocatalytic activity toward ethanol oxidation of alloyed Pd3Pb/Pd-15 NSA can reach up to 2886 mA mg–1, which is approximately 2.8 times that of the pure Pd NSA counterpart (1020 mA mg–1). The Pd3Pb/Pd NSAs are favorable in a high catalytic temperature, high KOH concentration, and high ethanol concentration.

Direct alcohol fuel cells are considered as promising and sustainable power sources to address global climate change as well as energy and environmental problems. However, designing efficient catalysts for the oxidation of alcohol molecules remains challenging. This study reports the synthesis of monodisperse PdAg nanoparticles (NPs) with face-centered cubic structures with controllable alloying degrees and particle diameters for improving oxidation of ethanol and methanol. Interestingly, the lattice enlargement of the silver-rich core leads to the lattice expansion of the palladium-rich sheath. The lattice expansion of the interface of the NPs leads to the upshifting of the d-band center of Pd toward the Fermi level followed by the stronger binding of a small molecule. The PdAg NPs exhibit "volcano-type" behavior, where the maximum electrocatalytic activity is governed by the balance of the adsorption energies of OH* (reactive intermediates) and CO* (blocking species). The Pd 5 Ag 1 NPs exhibit electrocatalytic activities of 2402 and 1541 mA mg Pd −1 for ethanol oxidation reaction and methanol oxidation reaction in alkaline solution, respectively, about four and three times those of the commercial Pd/C catalysts. The enhanced mass activities of the catalysts can be further analyzed by density functional theory calculations, indicating that the lattice expansion after including silver would lead to the upshifting of the d-band center followed by the strengthened OH* binding. This work discloses a promising way to build novel nanocatalysts with controllable alloying degrees as efficient fuel cell catalysts.

Alloyed Pd-based nanocatalysts are considered as highly active fuel cell anodes toward the ethanol oxidation reaction (EOR). However, challenges remain in synthesizing free-standing monodisperse nanoparticles (NPs) with outstanding mass activity and long-term stability. In this work, PdBi NPs are synthesized by a one-step oil bath method with controllable sizes and compositions. The doping of Bi displays a positive effect on the oxidation of ethanol. The Pd 8 Bi NPs with an average size of 9.0 nm are found to possess an exceptional electrocatalytic mass activity with superior antitoxic ability and outstanding long-term stability toward EOR. These are mainly attributed to the change in the electronic structure and the d-band center of Pd, increase of the interatomic distance within a unit cell, and large electrochemically active surface area values, with lots of reaction sites provided by the morphology-optimized NPs. Higher electrocatalytic temperatures, higher pH values, and higher concentrations of C 2 H 5 OH accelerate each step of electro-oxidation on EOR. The density functional theory calculations demonstrate that the energy barrier of PdBi NPs can be reduced by adjusting the Bi content, resulting in excellent electrocatalytic activity toward EOR. This work provides a promising strategy to prepare monodisperse PdM alloys as efficient catalysts for fuel electro-oxidation.