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.

The synthesis of metal nanometer electrocatalysts with a two-dimensional (2D) structure or rich active sites has become a research hotspot in electrocatalysis. In this work, surfactant hexadecyltrimethylammonium bromide (CTAB) was used to assist the synthesis and assembly of Pd ultrathin nanosheet with the help of Mo­(CO)6 in the start system. Pd nanochain composed of nanoparticles is obtained under the same condition, replacing CTAB with carrageenan only. Electrochemical measurements showed that the catalytic peak current density for the electrooxidation of ethanol can reach 2145 mA mg–1 for the Pd nanosheet assembly (NSA) and 1696 mA mg–1 for Pd nanochains. Pd nanosheet assembly also has a lower electron-transfer barrier, better catalytic stability, and antipoisoning performance than that of Pd nanochains. The mechanism of Pd nanosheets and nanochains catalysts the enhanced electrocatalytic activity toward ethanol oxidation has been discussed based on the experimental data.

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.

Two-dimensional (2D) nanostructured catalysts have attracted great attention in many important fields, including energy applications and chemical industry. In this study, PdCu nanosheet assemblies (NSAs) have been synthesized and investigated as electrocatalysts for direct ethanol fuel cells in an alkaline medium. A great number of active sites on the nanosheets of PdCu NSAs for ethanol electrooxidation are exposed, where the electron structures are optimized combined with the second element copper. Electrochemical measurements show that PdCu NSA1 exhibits excellent catalytic activity (2536 mA mg −1 ) and cyclic stability compared to PdCu NSA2 (1700 mA mg −1 ) and PdCu NSA3 (1436 mA mg −1 ), much higher than commercial Pd/C. Kinetics studies on the electrolysis of ethanol suggest that PdCu NSAs should be more favorable at higher catalytic temperatures, higher concentrations of ethanol, and low pH value environments. The unique composition and structures PdCu NSA1 would result in the lowest energy barrier in the rate-controlling step of the ethanol oxidation reaction (EOR), confirmed by density functional theory (DFT). The formation mechanism of PdCu NSAs and their excellent electrocatalytic activity toward EOR have been discussed and analyzed.