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Pt-based core–shell nanocrystals are a fantastic catalyst to enhance the catalytic performance for the oxygen reduction reaction (ORR). Pursuing further enhancement in ORR properties requires an unconventional interaction between the components of a catalyst. Here Pb is selected to alloy with Pd cores and Pt shells for generating Pd3Pb@PtmPb (m = 3 and 4) nanocubes. Both nanocubes are much more active and stable for the ORR relative to commercial Pt/C, with Pd3Pb@Pt3Pb nanocubes being the better one. Specifically, Pd3Pb@Pt3Pb nanocubes achieved record-breaking mass (4.69 A mgPt−1) and specific (6.69 mA cm−2) activities in alkaline media, which are ∼40.4 and 25.3 times as high as those of commercial Pt/C, respectively. Furthermore, these nanocubes are highly stable with only 9.3% loss in mass activity after 10 000 cycles, as compared to a big decrease of 59.9% for commercial Pt/C. From geometrical phase analysis (GPA) combined with theoretical calculation data, the strain effect in such nanocubes contributes only ∼4% enhancement in ORR activity and the ligand effect is prominent due to the negligible lattice mismatch between Pd3Pb and PtmPb. Besides electronic coupling between Pt and Pd, density functional theory (DFT) calculations show that the strong p–d orbital hybridization between Pt and Pb is critical to downshift the d-band center of Pt and dramatically boost the ORR activity.

Electrocatalytic CO2 reduction to formate is considered as a perfect route for efficient conversion of the greenhouse gas CO2 to value-added chemicals. However, it still remains a huge challenge to design a catalyst with both high catalytic activity and selectivity for target products. Here we report a unique Sn-doped Bi2O3 nanosheet (NS) electrocatalyst with different atomic percentages of Sn (1.2, 2.5, and 3.8%) prepared by a simple solvothermal method for highly efficient electrochemical reduction of CO2 to formate. Of them, the 2.5% Sn-doped Bi2O3 NSs exhibited the highest faradaic efficiency (FE) of 93.4% with a current density of 24.3 mA cm-2 for formate at -0.97 V in the H-cell and a maximum current density of nearly 50 mA cm-2 was achieved at -1.27 V. The formate FE is stable maintained at over 90% in a wide potential range from -0.87 V to -1.17 V. Electrochemical and density functional theory (DFT) analyses of undoped and Sn doped Bi2O3 NSs indicated that the strong synergistic effect between Sn and Bi is responsible for the enhancement in the adsorption capacity of the OCHO* intermediate, and thus the activity for formate production. In addition, we coupled 2.5% Sn-doped Bi2O3 NSs with a dimensionally stable anode (DSA) to realize battery-driven highly active CO2RR and OER with decent activity and efficiency.

Nanoscale Kirkendall effect has been widely used for rationally fabricating high-quality hollow nanocrystals, but often requires the intrinsic diffusion coefficient of out-diffusion materials higher than that of in-diffusion components. Here we demonstrate an unexpected Kirkendall effect that occurs in diffusing intrinsically faster Cu atoms into Pd icosahedra, leading to the formation of PdCu alloyed hollow nanocrystals. The control experiment with Pd octahedra replacing icosahedra indicates the critical role of twin boundaries in facilitating such unexpected Kirkendall effect. In addition, geometric phase analysis and density functional theory calculation show that out-diffusion of Pd atoms in the icosahedra is faster than in-diffusion of Cu atoms, particularly through the twin boundaries, upon the strain gradient with an inward distribution from tensile to compressive strains. The unexpected Kirkendall effect is also found in the interdiffusion of Ag and Pd atoms in Pd icosahedra. Our finds break the limitation of the intrinsic diffusion coefficient for the synthesis of hollow nanocrystals through Kirkendall effect and are expected to enormously enrich the family of hollow nanocrystals which have shown great potential in broad areas, such as fine chemical production, energy storage and conversion, and environmental protection. This work also provides a deep understanding in the diffusion behavior of atoms upon the strain gradient.

Developing high-performance non-Pt electrocatalysts toward the oxygen reduction reaction (ORR) is highly desirable but still challenging for industrial application in fuel cells. Here, we report a facile approach for the synthesis of Au-doped Pd3Pb wavy nanowires (WNWs) with different amounts of Au. We found that the oriented attachment dictated the formation of the WNWs. Such WNWs with several attractive features including a high density of defects, anisotropic one-dimensional nanostructures, ordered intermetallic structures, and Au doping exhibited substantially enhanced catalytic properties in terms of activity and durability towards the ORR in alkaline media compared to commercial Pt/C. Interestingly, the Au doped Pd3Pb WNWs showed a volcano-like relationship in ORR activity as a function of the amount of Au with the 2% Au-doped Pd3Pb WNWs being the best ORR electrocatalysts. Specifically, the 2% Au doped Pd3Pb WNWs achieved the highest mass activity (0.75 mA μg−1) at 0.9 V, which was 1.25 and 7.5 times higher than that of the Pd3Pb WNWs and commercial Pt/C, respectively. More importantly, the 2% Au-doped Pd3Pb WNWs displayed higher durability with only 22.7% loss in mass activity after 10 000 cycles compared to the commercial Pt/C (38% loss in mass activity) due to their chemically stable intermetallic structures and the effect of Au doping.

The strain effect is a critical knob to tune the catalytic performance and has received unprecedented research interest recently. However, it is difficult to distinguish the strain effect from the synergistic effect, especially in alloyed catalysts. Here we have synthesized Pd@PdAg icosahedra and {111} truncated bi-pyramids with only different surface strains between them as electrocatalysts for the ethanol oxidation reaction (EOR). Due to the same exposed facets and compositions of the two electrocatalysts, their EOR performances are mainly determined by the surface strains of PdAg alloys. These two electrocatalysts provide a perfect model to investigate the role of the strain effect in tuning the EOR performance. It is indicated that Pd@PdAg {111} truncated bi-pyramids with a surface strain of 0.3% show better catalytic activity and durability than Pd@PdAg icosahedra with a surface strain of 2.1% including commercial Pd/C. Density functional theory (DFT) calculations reveal that the lowered d-band center of 0.3% strained PdAg alloys relative to 2.1% strained ones reduced the adsorption energy of the acetate-evolution key intermediate *CH

Although tremendous efforts have been devoted to exploring non-Pt based electrocatalysts toward the oxygen reduction reaction (ORR), achievements in both catalytic activity and durability are still far from satisfactory. Here, we report a facile approach for the synthesis of intermetallic Pd3Pb ultrathin nanoplate-constructed flowers. Such highly opened hierarchical nanostructures with an ordered phase and low-coordinated edge sites exhibited a substantially enhanced activity toward the ORR. Especially, the intermetallic Pd3Pb nanoflowers achieved a record-breaking mass activity (1.14 mA μgPd−1) in an alkaline solution at 0.9 V vs. a reversible hydrogen electrode among the reported Pd-based ORR electrocatalysts to date, which was 1.8, 3.9 and 11.4 times higher than those of intermetallic Pd3Pb nanocubes, Pd3Pb dendrites and commercial Pt/C, respectively. More importantly, the intermetallic Pd3Pb nanoflowers also showed a higher durability with only 23.7% loss in mass activity after 10 000 cycles compared to the commercial Pt/C (35% loss in mass activity) due to their chemically stable intermetallic structures.

Pd is generally regarded as an alternative catalyst material to Pt for the oxygen reduction reaction (ORR). However, its catalytic activity and durability are much lower than those of Pt. Here, we report a facile approach for the synthesis of intermetallic Pd3Pb square nanoplates enclosed by {100} facets. The use of oleylamine (OAm), oleic acid (OA), and 1-octadecene (ODE) played important roles in the formation of the Pd3Pb intermetallic square nanoplates in high-quality. The Pd3Pb square nanoplates exhibited substantially enhanced ORR properties in terms of activity and durability. In particular, such nanoplates showed higher mass activity (0.62 mA μgPd−1) and specific activity (3.59 mA cm−2), which were 10.3 and 32.6 times higher than those of the commercial Pt/C, respectively, due to ligand and geometry effects. Significantly, the Pd3Pb square nanoplates/C were highly stable with 23% loss in specific activity and 21% loss in mass activity after 10 000 cycles compared to the Pd3Pb alloy dendritic nanocrystals/C (over 50% loss in specific and mass activities) due to their unique intermetallic structure with high chemical stability.

Hydrolysis of ammonia borane (AB) is a safe and convenient means of H2 production when efficient catalysts are used. Here we report a facile one-pot solvothermal method to synthesize Rh/WO3−x hybrid nanowires. Ultra-small Rh nanoparticles with an average size of ∼1.7 nm were tightly anchored on WO3−x nanowires. Rh/WO3−x catalysts exhibited substantially enhanced activity for hydrolytic dehydrogenation of AB under both dark and visible light irradiation conditions relative to mixed Rh nanoparticles and WO3−x nanowires (Rh + WO3−x), and Rh/C and WO3−x nanowires. X-ray photoelectron spectroscopy (XPS) analysis indicated that the synergistic effect between Rh nanoparticles and WO3−x nanowires was responsible for such an enhancement in activity. Specifically, Rh/WO3−x achieved the highest turnover frequency (TOF) with a value of 805.0 molH2 molRh−1 min−1 at room temperature under visible light irradiation. The H2 release rate as a function of reaction time exhibited a volcano plot under visible light irradiation, indicating that a self-activation process occurred in the hydrolytic dehydrogenation of AB due to additional oxygen vacancies arising from in situ reduction of WO3−x nanowires by AB, and thus an enhanced localized surface plasmon resonance (LSPR). Such a self-activation process was responsible for the enhanced catalytic activity under visible light irradiation relative to that under dark conditions, which was supported by the lower activation energy (45.2 vs. 50.5 kJ mol−1). In addition, Rh/WO3−x catalysts were relatively stable with only little loss in activity after five cycles due to the tight attachment between two components.

Pt-based multimetallic nanorings with a hollow structure are attractive as advanced catalysts due to their fantastic structure feature. However, the general method for the synthesis of such unique nanostructures is still lack. Here we report the synthesis of Pd@PtM (M = Rh, Ni, Pd, Cu) multimetallic nanorings by selective epitaxial growth of Pt alloyed shells on the periphery of Pd nanoplates in combination with oxidative etching of partial Pd in the interior. In situ generation of CO and benzoic acid arising from interfacial catalytic reactions between Pd nanoplates and benzaldehyde are critical to achieve high-quality Pt-based multimetallic nanorings. Specifically, the in-situ generated CO promotes the formation of Pt alloyed shells and their epitaxial growth on Pd nanoplates. In addition, the as-formed benzoic acid and residual oxygen are responsible for selective oxidative etching of partial Pd in the interior. When evaluated as electrocatalysts, the Pd@PtRh nanorings exhibit remarkably enhanced activity and stability for ethanol oxidation reaction (EOR) compared to the Pd@PtRh nanoplates and commercial Pt/C due to their hollow nanostructures.

Pd@Pt core–shell nanocrystals with ultrathin Pt layers have received great attention as active and low Pt loading catalysts for oxygen reduction reaction (ORR). However, the reduction of Pd loading without compromising the catalytic performance is also highly desired since Pd is an expensive and scarce noble-metal. Here we report the epitaxial growth of ultrathin Pt shells on PdxCu truncated octahedra by a seed-mediated approach. The Pd/Cu atomic ratio (x) of the truncated octahedral seeds was tuned from 2, 1 to 0.5 by varying the feeding molar ratio of Pd to Cu precursors. When used as catalysts for ORR, these three PdxCu@Pt core–shell truncated octahedra exhibited substantially enhanced catalytic activities compared to commercial Pt/C. Specifically, Pd2Cu@Pt catalysts achieved the highest area-specific activity (0.46 mA cm−2) and mass activity (0.59 mA μgPt−1) at 0.9 V, which were 2.7 and 4.5 times higher than those of the commercial Pt/C. In addition, these PdxCu@Pt core–shell catalysts showed a similar durability with the commercial Pt/C after 10 000 cycles due to the dissolution of active Cu and Pd in the cores.

Developing an efficient Pt‐based electrocatalyst with well‐defined structures for the methanol oxidation reaction (MOR) is critical, however, still remains a challenge. Here, a one‐pot approach is reported for the synthesis of Pd3Pb/PtnPb nanocubes with tunable Pt composition varying from 3.50 to 2.37 and 2.07, serving as electrocatalysts toward MOR. Their MOR activities increase in a sequence of Pd3Pb/Pt3.50Pb << Pd3Pb/Pt2.07Pb < Pd3Pb/Pt2.37Pb, which are substantially higher than that of commercial Pt/C. Specifically, Pd3Pb/Pt2.37Pb electrocatalysts achieve the highest specific (13.68 mA cm−2) and mass (8.40 A mgPt −1) activities, which are ≈8.8 and 6.8 times higher than those of commercial Pt/C, respectively. Structure characterizations show that Pd3Pb/Pt2.37Pb and Pd3Pb/Pt2.07Pb are dominated by hexagonal‐structured PtPb intermetallic phase on the surface, while the surface of Pd3Pb/Pt3.50Pb is mainly composed of face‐centered cubic (fcc)‐structured PtxPb phase. As such, hexagonal‐structured PtPb phase is much more active than the fcc‐structured PtxPb one toward MOR. This demonstration is supported by density functional theory calculations, where the hexagonal‐structured PtPb phase shows the lowest adsorption energy of CO. The decrease in CO adsorption energy and structural stability also endows Pd3Pb/PtnPb electrocatalysts with superior durability relative to commercial Pt/C., Pd3Pb/PtnPb nanocubes with tunable surface composition and structure are synthesized by a one‐pot approach. Hexagonal‐structured PtPb intermetallics on the surface and the incorporation of Pd3Pb cores endow Pd3Pb/Pt2.37Pb electrocatalysts with remarkably enhanced activity and durability toward the methanol oxidation reaction relative to commercial Pt/C due to the lower CO absorption energy.

Developing an efficient electrocatalyst for the hydrogen evolution reaction (HER) working in both acidic and alkaline solutions is highly desirable, but still remains challenging. Here, Ptx Ni ultrathin nanowires (NWs) with tunable compositions (x = 1.42, 3.21, 5.67) are in situ grown on MXenes (Ti3 C2 nanosheets), serving as electrocatalysts toward HER. Such Ptx Ni@Ti3 C2 electrocatalysts exhibit excellent HER performance in both acidic and alkaline solutions, with the Pt3.21 Ni@Ti3 C2 being the best one. Specifically, Pt3.21 Ni@Ti3 C2 achieves record-breaking performance in terms of lowest overpotential (18.55 mV) and smallest Tafel slope (13.37 mV dec-1 ) for HER in acidic media to date. Theory calculations and X-ray photoelectron spectroscopy analyses demonstrate that the coupling of MXenes with the NWs not only approaches the Gibbs free energy for hydrogen adsorption close to zero through the electron transfer between them in acidic media, but also provides additional active sites for water dissociation in alkaline solution, both of them being beneficial to the HER performance.