Polyhedral Palladium-Silver Alloy Nanocrystals as Highly Active and Stable Electrocatalysts for the Formic Acid Oxidation Reaction

Unconventional Electrocatalytic CO Conversion to C2 Products on Single-Atomic Pd-Agn Sites

The electrochemical reduction of CO or CO2 into C2+ products has mostly been focused on Cu-based catalysts. Although Ag has also been predicted as a possible catalyst for the CO-to-C2+ conversion from the thermodynamic point of view, however, due to its weak CO binding strength, CO rapidly desorbs from the Ag surface rather than participates in deep reduction. In this work, we demonstrate that single-atomic Pd sites doped in Ag lattice can tune the CO adsorption behavior and promote the deep reduction of CO toward C2 products. The monodispersed Pd-Agn sites enable the CO adsorption with both Pd-atop (PdL) and Pd-Ag bridge (PdAgB) configurations, which can increase the CO coverage and reduce the C-C coupling energy barrier. Under room temperature and ambient pressure, the Pd1Ag10 alloy catalyst exhibited a total CO-to-C2 Faradaic efficiency of ~37 % at -0.83 V, with appreciable current densities and electrochemical stability, thus featuring unconventional non-Cu electrocatalytic CO-to-C2 conversion capability.

Sn-doped PdCu alloy nanosheet assemblies as an efficient electrocatalyst for formic acid oxidation

A ternary alloy catalyst has been confirmed to be an effective catalyst for anode catalysis in direct formic acid fuel cells, which can improve the electrocatalytic performance of the fuel cell by introducing commonly used metal elements to change the Pd electronic structure and can reduce the use of precious metals and the cost of catalyst production. In this study, PdCuSn Ns/C with a special 3D structure was synthesized by a simple two-step wet chemical method. The PdCuSn Ns/C catalyst prepared exhibits excellent catalytic activity and stability for the formic acid oxidation reaction (FAOR). The mass activity of 2420.1 mA mg-1Pd is 3.94 times that of the Pd/C catalyst. The improvement in the electrocatalytic performance stems from the introduction of Cu and Sn atoms and the unique 3D nanosheet structure, which changes the electronic structure of Pd to increase the reactive active site and accelerates the reaction mass transfer rate, and also reduces the content of precious metals, while improving the electrocatalytic performance. Therefore, the PdCuSn Ns/C catalyst has a promising future in the field of electrocatalysis.

Boosting Electrocatalytic Oxidation of Formic Acid on Ir(IV)-Doped PdAg Alloy Nanodendrites with Sub-5 nm Branches

The formic acid oxidation reaction (FAOR) represents an important class of small organic molecule oxidation and is central to the practical application of fuel cells. In this study, we report the fabrication of Ir(IV)-doped PdAg alloy nanodendrites with sub-5 nm branches via stepwise synthesis in which the precursors of Pd and Ag were co-reduced, followed by the addition of IrCl₃ to conduct an in situ galvanic replacement reaction. When serving as the electrocatalyst for the FAOR in an acidic medium, Ir(IV) doping unambiguously enhanced the activity of PdAg alloy nanodendrites and improved the reaction kinetics and long-term stability. In particular, the carbon-supported PdAgIr nanodendrites exhibited a prominent mass activity with a value of 1.09 A mg_Pd^-1, which is almost 2.0 times and 2.7 times that of their PdAg and Pd counterparts, and far superior to that of commercial Pt/C. As confirmed by the means of the DFT simulations, this improved electrocatalytic performance stems from the reduced overall barrier in the oxidation of formic acid into CO₂ during the FAOR and successful d-band tuning, together with the stabilization of Pd atoms. The current study opens a new avenue for engineering Pd-based trimetallic nanocrystals with versatile control over the morphology and composition, shedding light on the design of advanced fuel cell electrocatalysts.

Integration of plasmonic AgPd alloy nanoparticles with single-layer graphitic carbon nitride as Mott-Schottky junction toward photo-promoted H2 evolution

Plasmonic AgPd alloy nanoparticles (AgPdNPs) decorated on single-layer carbon nitride (AgPdNPs/SLCN) for the designing of the Mott-Schottky junction were constructed with the ultrasonically assisted hydrothermal method and used toward photo evolution H2 from formic acid (FA) at near room temperature (30 °C). The Pd atom contains active sites that are synergistically boosted by the localized surface plasmon resonance (LSPR) effect of Ag atoms, leading to considerably enhanced photocatalytic properties. The photoactive AgPdNPs/SLCN obtained supreme catalytic activity to produce 50 mL of gas (H2 + CO2) with the initial turnover frequency of 224 h-1 under light irradiation. The catalyst showed stable catalytic performance during successive cycles.

Lattice-Resolution, Dynamic Imaging of Hydrogen Absorption into Bimetallic AgPd Nanoparticles

Palladium's strong reactivity and absorption affinity to H₂ makes it a prime material for hydrogen-based technologies. Alloying of Pd has been used to tune its mechanical stability, catalytic activity, and absorption thermodynamics. However, atomistic mechanisms of hydrogen dissociation and intercalation are informed predominantly by theoretical calculations, owing to the difficulty in imaging dynamic metal-gas interactions at the atomic scale. Here, we use in situ environmental high resolution transmission electron microscopy to directly track the hydrogenation-induced lattice expansion within AgPd triangular nanoprisms. We investigate the thermodynamics of the system at the single particle level and show that, contrary to pure Pd nanoparticles, the AgPd system exhibits α/β coexistence within single crystalline nanoparticles in equilibrium; the nanoparticle system also moves to a solid-solution loading mechanism at lower Ag content than bulk. By tracking the lattice expansion in real time during a phase transition, we see surface-limited β phase growth, as well as rapid reorientation of the α/β interface within individual particles. This secondary rate corresponds to the speed with which the β phase can restructure and, according to our atomistic calculations, emerges from lattice strain minimization. We also observe no preferential nucleation at the sharpest nanoprism corners, contrary to classical nucleation theory. Our results achieve atomic lattice plane resolution─crucial for exploring the role of crystal defects and single atom sites on catalytic hydrogen splitting and absorption.

Recent Advances in Amino-Based Molecules Assisted Control of Noble-Metal Electrocatalysts

Morphology-control synthesis is an effective means to tailor surface structure of noble-metal nanocrystals, which offers a sensitive knob for tuning their electrocatalytic properties. The functional molecules are often indispensable in the morphology-control synthesis through preferential adsorption on specific crystal facets, or controlling certain crystal growth directions. In this review, the recent progress in morphology-control synthesis of noble-metal nanocrystals assisted by amino-based functional molecules for electrocatalytic applications are focused on. Although a mass of noble-metal nanocrystals with different morphologies have been reported, few review studies have been published related to amino-based molecules assisted control strategy. A full understanding for the key roles of amino-based molecules in the morphology-control synthesis is still necessary. As a result, the explicit roles and mechanisms of various types of amino-based molecules, including amino-based small molecules and amino-based polymers, in morphology-control of noble-metal nanocrystals are summarized and discussed in detail. Also presented in this progress are unique electrocatalytic properties of various shaped noble-metal nanocrystals. Particularly, the optimization of electrocatalytic selectivity induced by specific amino-based functional molecules (e.g., polyallylamine and polyethyleneimine) is highlighted. At the end, some critical prospects, and challenges in terms of amino-based molecules-controlled synthesis and electrocatalytic applications are proposed.

Nature-inspired electrocatalysts and devices for energy conversion

A NICE approach for the design of nature-inspired electrocatalysts and electrochemical devices for energy conversion.

Effect of Metal Substrate on Electrocatalytic Property of Palladium Nanowire Array for High Performance Ethanol Electro-Oxidation

In this research, a high performance, ionomer-free electrocatalyst based on vertically aligned palladium (Pd) nanowire array was developed as an anode electrode toward ethanol oxidation reaction (EOR) in an alkaline environment. Using a one-step electrodeposition method, the Pd nanowires with controlled length were obtained by varying the electrodeposition current density and the synthesis time. Scanning electron microcopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray powder diffraction (XRD) were employed to characterize the morphology, chemical composition, and crystal structure of the Pd nanowires. The length effects of the nanowires, in the range of 0.8-4.5 μm, and various metal substrates, such as Ag, Cu, Ni, and Ti, were investigated for their electrochemical activities. The results demonstrated that Ag was the most active substrate to facilitate the ethanol oxidation reaction of the Pd nanowire array (NWA) electrocatalyst, which could be related to its good electrical conductivity. The stability test of the Pd NWA/Ag over time for EOR was also carried out, and the catalytic activity was recovered after the electrode was replaced with a new ethanol solution. Electrochemical impedance spectroscopy (EIS) measurements were performed to provide insights in the electron transfer resistance between the electrode and analyte. Gas chromatography and UV-vis spectroscopy were employed to measure the concentration of chemical species, which helped elucidate the overall reaction mechanism on the electrode surfaces.

Carbon-loaded ultrafine fully crystalline phase palladium-based nanoalloy PdCoNi/C: facile synthesis and high activity for formic acid oxidation

Recent studies have found surface engineering to be an effective strategy to improve the catalytic performance of noble-metal based catalysts. Herein, the successful synthesis of a fully crystalline PdCoNi alloy supported on carbon is reported. The as-synthesized catalyst has an ultrafine nanoparticle size distribution with low-coordination active sites distributed on the surface which was clearly captured by scanning transmission electron microscopy. The fully crystalline PdCoNi/C shows a significant enlarged electrochemical surface area (ECSA) and improved Pd-based mass activity and specific activity compared with bimetallic PdCo/C, PdNi/C and partly crystalline PdCoNi/C. An enhancement of the formic acid oxidation reaction activity can be explained by: (1) ultrafine size distribution from the greatly enlarged ECSA; (2) enhancement of the synergistic effect of the ternary PdCoNi alloy; (3) easier formation of a possible Pd intermediate state, PdH_x, due to the regular atom arrangement being fully crystalline. This approach provides a strategy to design noble-metal-based catalysts for improved electrochemical performance.

Cu5Pt Dodecahedra with Low-Pt Content: Facile Synthesis and Outstanding Formic Acid Electrooxidation

Tailoring composition and structure are significantly important to improve the utilization and optimize the performance of the precious Pt catalyst toward various reactions, which greatly relies on the feasible synthesis approach. Herein, we demonstrate that Cu-rich Cu₅Pt alloys with unique excavated dodecahedral frame-like structure (Cu₅Pt nanoframes) can be synthesized via simply adjusting the amounts of salt precursors and surfactants under hydrothermal conditions. It is established that the presence of hexamethylenetetramine and cetyltrimethylammonium bromide, as well as the selection of a proper Pt/Cu ratio are key for the acquisition of the target product. The immediate appeal of this material stems from frame-like architecture and ultralow Pt content involved, which can be used to greatly improve the utilization efficiency of Pt atoms. When benchmarked against commercial catalysts, the developed Cu₅Pt nanostructures display superior electrocatalytic performance toward formic acid oxidation, owing to unique electronic effect and ensemble effect. This work elucidates a promising methodology for the synthesis of Pt-based nanostructures while highlights the significance of composition and structure in electrocatalysis.

In situ high-potential-driven surface restructuring of ternary AgPd-Ptdilute aerogels with record-high performance improvement for formate oxidation electrocatalysis

Engineering nanoparticle surfaces driven by various gas atmospheres has attracted intensive attention in the design of efficient electrocatalysts for sustainable energy applications. However, the development of a more facile and efficient in situ engineering strategy under electrochemical testing conditions to achieve surface-reconstruction-induced high performance is significantly lacking. Herein, for the first time, we report in situ high-potential-driven restructuring in ternary AgPdPt aerogels with dilute Pt (AgPd-Ptdilute) during the electrochemical cyclic voltammetry testing for the alkaline formate oxidation reaction (FOR), in which the upper potential limit is ingeniously extended to the Ag redox region. Impressively, the resulting AgPd-Ptdilute aerogel displayed remarkable structural and compositional reconstruction in an alkaline environment. Our comprehensive results revealed that the high-potential cycling induces unique Ag outward diffusion to form an enriched PdPt metallic surface atomically coupled with amorphous Ag2O, which provides more opportunities to expose abundant active sites and induce robust electronic structure modulation. Notably, the surface-restructured AgPd-Ptdilute aerogel achieved record-high activity for FOR when the upper potential limit was extended to 1.3 V, exhibiting an unprecedented 5-fold improvement in activity compared to that of the commercial Pd/C. Moreover, it also offered greatly enhanced electrochemical stability with negligible activity decay after 500 cycles. This work gives a good understanding of surface reconstruction during such a novel high-potential-driven cycling process and opens a new door to designing more efficient electrocatalysts for FOR and beyond.

Facile Synthesis of Porous Pd3 Pt Half-Shells with Rich "Active Sites" as Efficient Catalysts for Formic Acid Oxidation

Exploring highly efficient electrocatalysts is greatly important for the widespread uptake of the fuel cells. However, many newly generated nanocrystals with attractive nanostructures often have extremely limited surface area or large particle-size, which leads them to display limited electrocatalytic performance. Herein, a novel anode catalyst of hollow and porous Pd₃ Pt half-shells with rich "active sites" is synthesized by using urea as a guiding surfactant. It is identified that the formation of Pd₃ Pt half-shells involves the combination of bubble guiding, in situ deposition of particles and bubble burst. The obtained Pd₃ Pt half-shells demonstrate a rich edge area with abundant exposed active sites and surface defects, indicating great potential for the electrocatalysis. When used as an electrocatalyst, the Pd₃ Pt half-shells exhibit remarkably improved electrocatalytic performance for formic acid oxidation (FAO), where it promotes the dehydrogenation process of FAO by suppressing the formation of poisonous species CO_ads via the electronic effect and ensemble effect.

Pd–Ag decorated g-C3N4 as an efficient photocatalyst for hydrogen production from water under direct solar light irradiation

Pd–Ag bimetallic and monometallic nanoparticles were decorated on g-C₃N₄ and evaluated for their ability to produce H₂ through water splitting reactions.

Synthesis of Ultrathin PdCu Alloy Nanosheets Used as a Highly Efficient Electrocatalyst for Formic Acid Oxidation

Inspired by the unique properties of ultrathin 2D nanomaterials and excellent catalytic activities of noble metal nanostructures for renewable fuel cells, a facile method is reported for the high-yield synthesis of ultrathin 2D PdCu alloy nanosheets under mild conditions. Impressively, the obtained PdCu alloy nanosheet after being treated with ethylenediamine can be used as a highly efficient electrocatalyst for formic acid oxidation. The study implicates that the rational design and controlled synthesis of an ultrathin 2D noble metal alloy may open up new opportunities for enhancing catalytic activities of noble metal nanostructures.

Weight prediction in complex networks based on neighbor set

Link weights are essential to network functionality, so weight prediction is important for understanding weighted networks given incomplete real-world data. In this work, we develop a novel method for weight prediction based on the local network structure, namely, the set of neighbors of each node. The performance of this method is validated in two cases. In the first case, some links are missing altogether along with their weights, while in the second case all links are known and weight information is missing for some links. Empirical experiments on real-world networks indicate that our method can provide accurate predictions of link weights in both cases.

PdCo/Pd-Hexacyanocobaltate Hybrid Nanoflowers: Cyanogel-Bridged One-Pot Synthesis and Their Enhanced Catalytic Performance

Elaborate architectural manipulation of nanohybrids with multi-components into controllable 3D hierarchical structures is of great significance for both fundamental scientific interest and realization of various functionalities, yet remains a great challenge because different materials with distinct physical/chemical properties could hardly be incorporated simultaneously into the synthesis process. Here, we develop a novel one-pot cyanogel-bridged synthetic approach for the generation of 3D flower-like metal/Prussian blue analogue nanohybrids, namely PdCo/Pd-hexacyanocobaltate for the first time. The judicious introduction of polyethylene glycol (PEG) and the formation of cyanogel are prerequisite for the successful fabrication of such fascinating hierarchical nanostructures. Due to the unique 3D hierarchical structure and the synergistic effect between hybrid components, the as-prepared hybrid nanoflowers exhibit a remarkable catalytic activity and durability toward the reduction of Rhodamine B (RhB) by NaBH₄. We expect that the obtained hybrid nanoflowers may hold great promises in water remediation field and beyond. Furthermore, the facile synthetic strategy presented here for synthesizing functional hybrid materials can be extendable for the synthesis of various functional hybrid nanomaterials owing to its versatility and feasibility.

Insights into the geometries, electronic and magnetic properties of neutral and charged palladium clusters

We performed an unbiased structure search for low-lying energetic minima of neutral and charged palladium Pd_n^Q (n = 2–20, Q = 0, + 1 and –1) clusters using CALYPSO method in combination with density functional theory (DFT) calculations. The main candidates for the lowest energy neutral, cationic and anionic clusters are identified, and several new candidate structures for the cationic and anionic ground states are obtained. It is found that the ground state structures of small palladium clusters are more sensitive to the charge states. For the medium size Pd_n^0/+/– (n = 16–20) clusters, a fcc-like growth behavior is found. The structural transition from bilayer-like structures to cage-like structures is likely to occur at n = 14 for the neutral and cationic clusters. In contrast, for the anionic counterparts, the structural transition occurs at Pd₁₃^–. The photoelectron spectra (PES) of palladium clusters are simulated based on the time-dependent density functional theory (TD-DFT) method and compared with the experimental data. The good agreement between the experimental PES and simulated spectra provides us unequivocal structural information to fully solve the global minimum structures, allowing for new molecular insights into the chemical interactions in the Pd cages.

Bimetallic Ag–Cu alloy nanoparticles as a highly active catalyst for the enamination of 1,3-dicarbonyl compounds

Bimetallic Ag–Cu alloy nanoparticles were obtained via a simple co-reduction method, which exhibited significantly improved activity for the synthesis of β-enaminones and β-enaminoesters compared with their monometallic counterparts.

Nanostructured platinum-free electrocatalysts in alkaline direct alcohol fuel cells: catalyst design, principles and applications

A review of the fundamental principles that allow for the intelligent design and synthesis of non-precious metal nanostructured electrocatalysts for ADAFCs.