Robust Copper-Based Nanosponge Architecture Decorated by Ruthenium with Enhanced Electrocatalytic Performance for Ambient Nitrogen Reduction to Ammonia

Electrochemical conversion of nitrogen to green ammonia is an attractive alternative to the Haber-Bosch process. However, it is currently bottlenecked by the lack of highly efficient electrocatalysts to drive the sluggish nitrogen reduction reaction (N₂RR). Herein, we strategically design a cost-effective bimetallic Ru-Cu mixture catalyst in a nanosponge (NS) architecture via a rapid and facile method. The porous NS mixture catalysts exhibit a large electrochemical active surface area and enhanced specific activity arising from the charge redistribution for improved activation and adsorption of the activated nitrogen species. Benefiting from the synergistic effect of the Cu constituent on morphology decoration and thermodynamic suppression of the competing hydrogen evolution reaction, the optimized Ru_0.15Cu_0.85 NS catalyst presents an impressive N₂RR performance with an ammonia yield rate of 26.25 μg h^-1 mg_cat.^-1 (corresponding to 10.5 μg h^-1 cm^-2) and Faradic efficiency of 4.39% as well as superior stability in alkaline medium, which was superior to that of monometallic Ru and Cu nanostructures. Additionally, this work develops a new bimetallic combination of Ru and Cu, which promotes the strategy to design efficient electrocatalysts for electrochemical ammonia production under ambient conditions.

Molecular dynamics study on the thermodynamic stability and structural evolution of crown-jewel structured PdCu nanoalloys

The novel crown-jewel (CJ) structured PdCu nanoalloys have attracted considerable interest in high-performance single-atom catalysis. The characteristics of demanding high-temperature calcination in the synthesis of these samples disable us from experimentally understanding the details of the thermal evolution behavior of PdCu nanoclusters during the heating process. In this work, by analyses of potential energy surface, bond order parameter, and radial distribution function, we have theoretically studied the thermodynamic stabilities and structural evolution of Pd-decorated Cu-based CJ nanoclusters with various compositions and sizes by molecular dynamics simulations. PdCu nanoclusters undergo a cuboctahedral (Cubo) to icosahedral (Ico) structural transformation before melting. This transformation is size- and Pd-composition dependent. The small size and high Pd-composition of PdCu nanoclusters facilitate this transformation. In addition, we find that the surface and interface effects of clusters have an important impact on the structural transformation and Cubo-Ico structural transformation is strongly related to the release of excess energy.

One-Pot Aqueous Synthesis of Porous Hollow PdCu Alloy Nanoparticles for Enhanced Ethanol Electrooxidation

Bimetallic PdCu porous hollow nanoparticles (PHNs) with hierarchical nanostructures and well-alloyed compositions were precisely synthesized through a one-pot aqueous synthetic route. Bimetallic PdCu PHNs exhibited multiple enhancement synergies and thus performed well in ethanol oxidation electrocatalysis with remarkable activity and stability. This work expedites rational design and synthesis of the high-hierarchy alloy electrocatalysts for fuel cell electrocatalysis.

Catalytic activity, thermal stability and structural evolution of PdCu single-atom alloy catalysts: the effects of size and morphology

Single-atom alloys (SAAs) have been emerging as an important field of research in electrocatalysis owing to extremely high atom utilization, unique structure and high catalytic activity. In this work, the catalytic properties and thermal stability of PdCu SAAs with a crown-jewel (CJ) structure are studied by density functional theory (DFT) calculations and the molecular dynamics (MD) simulation method. The DFT results reveal that CJ-structured PdCu SAAs show excellent HER and ORR catalytic performance, and can be regarded as a promising alternative to Pt catalysts towards the ORR or HER. Additionally, we attempt to explain the high catalytic activity of PdCu SAAs by electronic structure analysis. In addition, MD simulation results confirm the thermal stability of CJ-structured PdCu. More importantly, we found that CJ-structured PdCu clusters undergo a structural transformation from cuboctahedral (Cubo) to icosahedral (Ico) structure by heating or after the adsorption of reaction intermediate, which indicates that Cubo is less stable than the Ico structure. Besides, Cubo-Ico transformation is size-dependent and only found in small clusters. Furthermore, the effects of size and morphology on melting properties are discussed. The melting point increases as cluster size increases, which agrees well with Pawlow's law.

A Top-Down Strategy to Realize Surface Reconstruction of Small-Sized Platinum-Based Nanoparticles for Selective Hydrogenation

Over the past decades, despite the substantial efforts that have been devoted to the modifications of Pt nanoparticles (NPs) to tailor their selectivities for hydrogenation reactions, there are still a lack of facile strategies for precisely regulation of the surface properties of NPs, especially for those with small sizes. In this work, we propose a top-down thermal annealing strategy for tuning the surface properties of Pt-based NPs (≈4 nm) without the occurrence of aggregation. Compared to conventional bottom-up methods, the present top-down strategy can precisely regulate the surface compositions of Pt-Cd NPs and other ternary Pt-Cd-M NPs (M=Fe, Ni, Co, Mn, and Sn). The optimized Pt-Cd NPs exhibit excellent selectivity toward phenylacetylene and 4-nitrostyrene hydrogenations with a styrene selectivity and 4-aminophenyl styrene selectivity of 95.2 % and 94.5 %, respectively. This work provides a general strategy for the surface reconstructions of Pt-based NPs, and promotes fundamental research on catalyst design for heterogeneous catalysis.

3D nitrogen-doped carbon nanofoam arrays embedded with PdCu alloy nanoparticles: Assembling on flexible microelectrode for electrochemical detection in cancer cells

In this work, we developed a novel and facile strategy for the synthesis of a highly active and stable electrocatalyst based on PdCu alloy nanoparticles (PdCu-ANPs) embedded in 3D nitrogen-doped carbon (NC) nanofoam arrays (NFAs), which were assembled on flexible carbon fiber (CF) microelectrode for in situ sensitive electrochemical detection of biomarker H₂O₂ in cancer cells. Our results showed that NC-NFAs support possessed a unique hierarchically porous architecture by integrating the macrospores in arrays scaffold within mesopores in individual NC nanofoam, which offered exceptionally large surface area for embedding high-density PdCu-ANPs in it as well as facilitated the mass transfer and molecular diffusion during the electrochemical reaction. Taking the advantages of the unique structural merit of NC-NFAs support and excellent electrocatalyitc properties of PdCu-ANPs that embedded in it, the resultant PdCu-ANPs/NC-NFAs modified CF microelectrode exhibited good electrochemical sensing performances towards H₂O₂ including a wide linear range from 2.0 μM to 3.44 mM, a low detection limit of 500 nM, as well as good reproducibility, stability and anti-interference ability. When used in real-time in situ tracking H₂O₂ secreted from different types of human colorectal cancer cells, i.e., HCT116, HT29, SW48 and LoVo, it can distinguish the types of cancer cells by measuring the number of extracellular H₂O₂ molecules released per cell, which demonstrates its great promise in cancer diagnose and management.

Applications of bimetallic PdCu catalysts

Bimetallic PdCu nanoparticles can be applied as catalysts in a wide range of chemical and electrochemical reactions.

Bromide Ions Triggered Synthesis of Noble Metal-Based Intermetallic Nanocrystals

Ordered intermetallic nanomaterials with a well-defined crystal structure and fixed stoichiometry facilitate the predictable control of their electronic structure and catalytic performance. To obtain the thermodynamically stable intermetallic structures, the conventional approaches with high-temperature annealing are still far from satisfactory, because of annealing-induced aggregation and sintering of nanomaterials. Herein, a general wet-chemical method is developed to synthesize a series of noble metal-based intermetallic nanocrystals, including hexagonal close-packed (hcp) PtBi nanoplates, face-centered cubic (fcc) Pd₃ Pb nanocubes, and hcp Pd_2.5 Bi_1.5 nanoparticles. During the synthetic process, Br^- ions play two important roles for the formation of ordered intermetallic structures: i) Br^- ions can coordinate with the metal ions to decrease their reduction potentials thus slowing down the reduction kinetics. ii) Br^- ions can combine with molecular oxygen to generate an oxidative etching effect, hence reconstructing the atom arrangement, which is beneficial for the formation of the intermetallic structure. As a proof-of-concept application, Pd₃ Pb nanocubes are used as electrocatalysts for ethanol and methanol oxidation reactions, which exhibit significantly improved electrochemical performance compared with the commercial Pd black catalyst.

Au-Doped intermetallic Pd3Pb wavy nanowires as highly efficient electrocatalysts toward the oxygen reduction reaction

Au-Doped intermetallic Pd₃Pb wavy nanowires were synthesized and exhibited substantially enhanced properties for the oxygen reduction reaction relative to commercial Pt/C.

Intermetallic Pd3Pb square nanoplates as highly efficient electrocatalysts for oxygen reduction reaction

Intermetallic Pd₃Pb square nanoplates were synthesized and exhibited excellent performance for the oxygen reduction reaction in alkaline solution.

Fabrication of palladium-copper nanoparticles with controllable size and chemical composition

A series of Pd_xCu_100-x (x = 20, 40, 60, 80) particles with the sizes of 7-9 nm were fabricated by a two-step polyol reduction process, which differentiated the nucleation and growth steps of the nanoparticles. The primary reduction of Pd²⁺ by ethylene glycol at 393 K formed appreciable amounts of Pd⁰ nuclei, while the subsequent reduction at 473 K fully reduced the Pd²⁺ and Cu²⁺ species with the aid of the initially formed Pd nuclei seeds. Meanwhile, the releasing oleylamine, previously coordinated with metal cations, acted as the capping agent to segregate the nanoparticles. Both parameters simultaneously controlled the assembly kinetics of the bimetallic nanoparticles and resulted in uniform sizes and designed chemical compositions. Among them, the Pd₈₀Cu₂₀ nanoparticles showed quite promising activity and selectivity for the hydrogenation of nitrobenzene under mild conditions.

Synthetically Tuned Atomic Ordering in PdCu Nanoparticles with Enhanced Catalytic Activity toward Solvent-Free Benzylamine Oxidation

Synthesis of ordered compounds with nano size is of particular interest for tuning the surface properties with enhanced activity and selectivity toward various important industrial catalytic processes. In this work, we synthesized ordered PdCu nanoparticles as highly efficient catalyst for the solvent-free aerobic oxidation of benzylamine. The Pd_xCu_1-x catalysts with different chemical compositions (x = 0, 0.25, 0.4, 0.5, 0.6, 0.75, 1) were prepared by polyol method using NaBH₄ as a reducing agent and were well-characterized by X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy (TEM) energy-dispersive analysis of X-rays, and X-ray absorption fine structure. The effect of different metal concentrations of Pd and Cu on the formation of Pd_xCu_1-x nanoparticles was investigated. The XRD and TEM confirmed the formation of ordered PdCu intermetallic phase with body-centered cubic (BCC) structure for the synthetic composition of Pd/Cu = 1:1. For compositions x = 0, 0.25, 0.75, and 1, Pd_xCu_1-x alloy with face-centered cubic (FCC) structure was observed, whereas mixed phase of BCC and FCC was observed for x = 0.4 and 0.6. The use of strong reducing agent (NaBH₄) was essential to synthesize PdCu ordered phase compared to weak reducing agents such as oleylamine and ascorbic acid. The PdCu nanocatalyst with ordered structure (BCC) showed excellent catalytic activity compared to Pd_xCu_1-x alloy nanoparticles with FCC structure. The atomic ordering in the PdCu intermetallic was the driving force for the enhancement in the catalytic activity with high benzylamine conversion of 94.0% and dibenzylimine selectivity of 92.2% compared to its monometallic and alloy counterparts. Moreover, ordered PdCu alloy showed good recyclability and activity toward the oxidation of different amines.

PdCu alloy nanodendrites with tunable composition as highly active electrocatalysts for methanol oxidation

PdCu alloy nanodendrites were prepared and exhibited enhanced catalytic properties towards methanol oxidation relative to commercial Pd/C.

Size-Dependent Disorder-Order Transformation in the Synthesis of Monodisperse Intermetallic PdCu Nanocatalysts

The high performance of Pd-based intermetallic nanocatalysts has the potential to replace Pt-containing catalysts for fuel-cell reactions. Conventionally, intermetallic particles are obtained through the annealing of nanoparticles of a random alloy distribution. However, this method inevitably leads to sintering of the nanoparticles and generates polydisperse samples. Here, monodisperse PdCu nanoparticles with the ordered B2 phase were synthesized by seed-mediated co-reduction using PdCu nanoparticle seeds with a random alloy distribution (A1 phase). A time-evolution study suggests that the particles must overcome a size-dependent activation barrier for the ordering process to occur. Characterization of the as-prepared PdCu B2 nanoparticles by electron microscopy techniques revealed surface segregation of Pd as a thin shell over the PdCu core. The ordered nanoparticles exhibit superior activity and durability for the oxygen reduction reaction in comparison with PdCu A1 nanoparticles. This seed-mediated co-reduction strategy produced monodisperse nanoparticles ideally suited for structure-activity studies. Moreover, the study of their growth mechanism provides insights into the size dependence of disorder-order transformations of bimetallic alloys at the nanoscale, which should enable the design of synthetic strategies toward other intermetallic systems.

One-pot synthesis of lotus-shaped Pd–Cu hierarchical superstructure crystals for formic acid oxidation

Lotus-shaped Pd–Cu hierarchical superstructure crystals with enhanced electrocatalytic properties toward HCOOH oxidation were successfully synthesized through an aqueous solution method.

An ordered bcc CuPd nanoalloy synthesised via the thermal decomposition of Pd nanoparticles covered with a metal-organic framework under hydrogen gas

Presented here is the synthesis of an ordered bcc copper-palladium nanoalloy, via the decomposition of a Pd nanoparticle@metal-organic framework composite material. In situ XRD measurements were performed in order to understand the mechanism of the decomposition process. This result gives a further perspective into the synthesis of new nanomaterials via metal-organic framework decomposition.

Size and aspect ratio control of Pd₂Sn nanorods and their water denitration properties

Monodisperse Pd2Sn nanorods with tuned size and aspect ratio were prepared by co-reduction of metal salts in the presence of trioctylphosphine, amine, and chloride ions. Asymmetric Pd2Sn nanostructures were achieved by the selective desorption of a surfactant mediated by chlorine ions. A preliminary evaluation of the geometry influence on catalytic properties evidenced Pd2Sn nanorods to have improved catalytic performance. In view of these results, Pd2Sn nanorods were also evaluated for water denitration.

Component-controlled synthesis and assembly of Cu-Pd nanocrystals on graphene for oxygen reduction reaction

Exploring low-cost, high-activity, and long-durability hybrid electrocatalysts for cathodic oxygen reduction reaction (ORR) is vital to advance fuel cells technologies. In this paper, a series of graphene (G)-CuxPdy (Cu4Pd, Cu3Pd, CuPd, CuPd3, CuPd4) nanocomposites (G-CuxPdy NCPs) is obtained by assembly of CuxPdy alloy nanocrystals (NCs) with controlled component ratios on G nanosheets using the "dispersing-mixing-vaporizing solvent" strategy and used as electrocatalysts for ORR. Compared with pure CuxPdy NCs, greatly enhanced interfacial electron transfer dynamics are observed in G-CuxPdy NCPs, which show a strong correlation with the alloy compositions of the NCPs. The electrocatalytic experiments in alkaline solution reveal that the ORR activities of those G-CuxPdy NCPs are also strongly dependent on alloy components and exhibit a double-volcano feature with variations of alloy components. Among them, G-Cu3Pd NCPs possess the highest electrocatalytic activity, which is much better than some reported electrocatalysts and commercial Pd/C catalyst and close to Pt/C catalyst. By correlating the Pd 3d binding energies and the sizes of CuxPdy NCs with the mass-specific activities of G-CuxPdy NCPs and considering the interfacial electron transfer dynamics, the best catalytic activity of G-Cu3Pd NCPs may result from the unique electronic structure and the smallest size of Cu3Pd NCs as well as the strong synergistic effect between G and Cu3Pd NCs. Moreover, the durability of G-Cu3Pd NCPs is superior to that of Pt/C catalyst, indicating that they are promising cathodic electrocatalysts for using in alkaline fuel cells.

Facile synthesis of Cu-Pd bimetallic multipods for application in cyclohexane oxidation

The synergy between Cu and Pd makes Cu-Pd bimetallic nanocrystals interesting materials for investigation. The scarcity of shapes of Cu-Pd bimetallic nanocrystals motivated us to explore highly branched structures, which may promote a wide range of applications. In this communication, we report a facile synthesis of Cu-Pd bimetallic multipods (19.2 ± 1.2 nm), on branches of which some high-index facets were exposed. Modification of reaction parameters concerning capping agents and reductant led to the formation of other shapes, including sphere-like nanocrystals (SNCs). When loaded onto TiO2, the as-prepared Cu-Pd bimetallic multipods exhibited excellent catalytic activity for the oxidation of cyclohexane by hydrogen peroxide and higher selectivity towards cyclohexanone than monometallic catalysts and SNCs/TiO2.

One-step synthesis and shape-control of CuPd nanowire networks

An effective one-step method has been developed to synthesize CuPd bimetallic nanowire networks. Investigation of the growth process revealed that the nanowires were formed by attachment of spherical particles and strongly influenced by interactions between surface ligands and metals. The morphology of CuPd nanoparticles is tuned via changing the molecular weight of polyvinylpyrrolidone (PVP) and solvents. The versatility of this method was further demonstrated by preparation of AgPd nanowires. An electrochemical study of CuPd nanowire networks shows morphology dependent activity in oxygen reduction reaction (ORR), which is comparable to that of platinum.

PdNi hollow nanoparticles for improved electrocatalytic oxygen reduction in alkaline environments

Palladium-nickel (PdNi) hollow nanoparticles were synthesized via a modified galvanic replacement method using Ni nanoparticles as sacrificial templates in an aqueous medium. X-ray diffraction and transmission electron microscopy show that the as-synthesized nanoparticles are alloyed nanostructures and have hollow interiors with an average particle size of 30 nm and shell thickness of 5 nm. Compared with the commercially available Pt/C or Pd/C catalysts, the synthesized PdNi/C has superior electrocatalytic performance towards the oxygen reduction reaction, which makes it a promising electrocatalyst for alkaline anion exchange membrane fuel cells and alkali-based air-batteries. The electrocatalyst is finally examined in a H2/O2 alkaline anion exchange membrane fuel cell; the results show that such electrocatalysts could work in a real fuel cell application as a more efficient catalyst than state-of-the-art commercially available Pt/C.

Facile synthesis of Pd-based bimetallic nanocrystals and their application as catalysts for methanol oxidation reaction

We employed an efficient and facile route to synthesise monodisperse Pd-based bimetallic nanocrystals (MPd: M = Cu, Co and Ni) via a controlled co-reduction of Pd(ii) chloride and M(ii) nitrate at 200-230 °C in the presence of oleylamine (OAm). These monodisperse Pd-based nanocrystals have small dimensions, unique structures and homogeneous morphology, thus exhibit efficient catalytic activities for methanol oxidation in alkaline solution, which is much better than commercial Pd/C with same amount of palladium. The catalytic activities of these nanocrystals followed the order of NiPd/C > CoPd/C > CuPd/C > commercial Pd/C, due to the different synergistic effects. Our results show that these Pd-based bimetallic nanocrystals can be promising as practical catalysts for methanol oxidation reactions and other catalytic reactions in further investigations.