Pd-based catalysts exhibit higher catalytic activity and durability in many electrochemical reactions. However, the electrochemical performance can be further enhanced by fine-tune of the alloy composition. Although binary alloys have been fully studied, the multicomponent alloys are far beyond understanding, which leaves cocktail effect a compromised explanation for the high-entropy alloy. Herein Pd nanosheet-seeded growth was used to synthesize a Pd-Zn-Cd ternary alloy by accurately controlling the Pd-Zn-Cd molar ratio through adjusting the amount of introduced Cd precursor. Through analysis of the crystal phase structure of PdCdZn_x and PdZn_xCd_1−x, the competitive relationship of Zn and Cd in the alloying process with Pd was unveiled: Pd₁Cd₁ intermetallics (IMC) is thermodynamically favored over Pd₁Zn₁ IMC in the ternary system. However, the increased structure stability of PdCd over PdZn does not bring about increased durability in the catalytic ethanol oxidation reaction. The morphology selection of Pd seeds is also crucial for the study, as Pd cubes, Pd tetrahedrons, and Pd octahedrons do not form PdZn in the same protocol. The successful alloying through the seeded growth depends on the maximum diffusion depth of foreign atoms into the seed.

Ultrathin Pd nanosheets (NSs) have great advantages in catalysis due to their large specific surface area and high percentage of under-coordinated atoms. However, the electrochemical performance still can be improved via composition-controllable growth of their solid solution. Herein, seeded alloying strategy was proposed to synthesize Pd-Cu solid solution from Pd NSs and Pd-Cu nanostructures with tunable molar ratios obtained by changing the amount of Cu precursor. As compared to the pristine Pd NSs, the Pd-Cu solid solution shows significantly enhanced methanol oxidation reaction (MOR) performance over those of Pd NSs and homemade Pd/C as the incorporation of Cu weakens the adsorption of CO intermediate on Pd in the MOR process. The choice of template is pivotal to the growth, as a shape-dependent behavior could be identified in the alloying of Cu with Pd nanosheets enclosed by {111} and {100} facets, Pd nanocubes enclosed by {100} facet, and Pd nano-tetrahedrons enclosed by {111} facet. The Pd-Cu solid solution with tunable composition can only be obtained from Pd NSs and the shape-dependent alloying process is mainly determined by the diffusion barrier and the minimum diffusion depth of the different facets.

Bimetallic alloys could form three typical structures including solid solution, heterostructure, and intermetallic compound, depending on the interactions between identical and different atoms. Although the trend can be predicted by the types of binary phase diagram, different synthetic protocols will trap the system in various kinetic intermediates among the three typical structures. Herein, we studied the phase evolution and elemental segregation in the alloy nanoparticles of immiscible Pd-Ru before and after thermal annealing. By developing an analysis method of local element segregation (LES) based on the energy dispersive spectroscopy (EDS) mapping signals, we were able to quantify the mixing of Pd and Ru atoms during the gradual phase transition from face-centered cubic (fcc) to hexagonal close packed (hcp). Density functional theory was also applied to calculate the energies of all possible PdRu₄ structures (93 fcc models and 267 hcp models), which helps to rationalize the phase transition and element segregation. The annealing process also leads to the change of the electronic structure, which further influences the performance in the electrocatalytic hydrogen evolution reaction. The highest activity of PdRu₄-400 was largely attributed to the proper interface between the Pd-rich fcc phase and Ru-rich hcp phase, as revolved by the above methods.

Developing efficient catalysts with high activity and durability via alloying strategy is essential to the energy conversion in various electro-catalytic reactions. Among the different alloy structures, intermetallic compounds (IMCs) have received much attention recently due to the special geometric and electronic effects and outstanding activity and durability, endowed by their ordered structure. Herein, A series of hollow-structured nanocrystals of Pd-Sn alloy, including face-centered cubic solid solution of Pd(Sn), IMCs of Pd₂Sn, and IMCs of Pd₃Sn₂, are fabricated via a solvothermal strategy by varying the precursor ratio of Pd and Sn. The structure difference of the nanocrystals has been investigated via combined electron microscopy and spectroscopy, assisted by local elemental separation analysis and X-ray spectroscopy. Among all, Pd₃Sn₂ IMCs show outstanding methanol oxidation reaction (MOR) activity in terms of mass activity (1.3 A·mg_Pd⁻¹) and specific activity (5.03 mA·cm⁻²). Through density functional theory (DFT) simulation calculations on three different Pd-Sn alloy models, the performance has been well understood. As compared with Pd(Sn) and Pd₂Sn, the high MOR kinetics on Pd₃Sn₂ is featured by its weaker CO adsorption and favorable CO–OH co-adsorption.

Metal catalysts play an important role in the catalytic electrochemical processes and optimization of their performance is usually achieved through alloying with other metal atoms. Doping with interstitial hydrogen atoms is a special but effective way to regulate the electronic structure of host catalysts. Herein we demonstrate the intermixing of Pd and Rh atoms during the hydrogen-doping process of Pd@Rh core-shell nanocubes, forming an alloyed surface in Pd@Rh-H. The catalysts show enhanced performance in electrocatalytic methanol oxidation, as compared to commercial Pt/C and are even better than PdH@Rh core-shell nanocubes. The small structural differences between the two hydride catalysts are revealed by X-ray electron spectroscopy and pair distribution function analysis of electron diffraction. The theoretical calculation results show that Rh in Pd@Rh-H contains more negative charges than Rh in PdH@Rh, indicating more effective charge transfer in Pd@Rh-H. The d-band center (ε_d) of the Rh site in Pd@Rh-H shifts up, and the synergy between Rh and Pd optimizes the binding energy of CO and OH, inducing preferential catalytic activity. Our work provides guidance for the synthesis of high-performance catalysts by doping with interstitial atoms, which may provide a new strategy to fine-tune the electronic structure of other bimetallic nanoparticles.

Two-dimensional (2D) oxide can be continuously produced by bubbling oxygen into liquid metals and the harvesting of these oxide relies on the proper choice of dispersion solvents. The mass-production of ligand-free 2D materials from high melting-point metals will not be possible if the limited stability of the traditional dispersion solvents is not circumvented. Herein, liquid tin was used for the first time in the bubbling protocol and 2D tin oxide was obtained in molten salts. The nanosheets were studied with combined microscopic and spectroscopic techniques, and high-density grain boundaries was identified between the sub-5-nm nano-crystallites in the nanosheets. It gives rise to the high performance in electrocatalytic CO₂ reduction reaction. Density-functional-theory based calculation was applied to achieve a deeper understanding of the relationship between the activity, selectivity, and the grain- boundary features. The molten-salt based protocol could be explored for the synthesis of a library of functional 2D oxides.

A series of carbon-based binary single-atom catalysts of Fe and Ni coordinated by nitrogen are fabricated using a glucose-chelating method. Depending on the Ni/Fe content, they exhibit a wide-range of controllable CO/H₂ ratio from 0.14 to 10.86, which is meaningful to specific chemical processes. The durability of the catalyst is evaluated over an 8-hour period with no significant degradation of activity. The variation of the faradaic efficiency with Ni/Fe content is justified by density-functional-theory based calculation of the reaction barrier in both hydrogen evolution and CO₂ reduction reactions.