Surfactant-Assisted Synthesis of Palladium Nanosheets and Nanochains for the Electrooxidation of Ethanol

Recent advances of H-intercalated Pd-based nanocatalysts for electrocatalytic reactions

The intercalation of H into Pd-based nanocatalysts plays a crucial role in optimizing the catalytic performance by tailoring the structural and electronic properties. We herein present a comprehensive review about the recent progress of interstitial hydrogen atom modified Pd-based nanocatalysts for various energy-related electrocatalytic reactions. Before systematically manifesting the great potential of Pd-based hydrides for electrocatalytic applications, we have briefly illustrated the synthesis strategies and corresponding mechanisms for the Pd-based hydrides. This is followed by a comprehensive discussion about the fundamentals and functions of H intercalation in tailoring their physicochemical and electrochemical properties. Subsequently, we focus on the widespread application of Pd-based hydrides for electrocatalytic reactions, with the emphasis on the role of H intercalation played in determining electrocatalytic performance. Finally, the future direction and perspectives regarding the development of more efficient Pd-based hydrides are also manifested.

Low-Dimensional High-Entropy Alloys for Advanced Electrocatalytic Reactions

Low-dimensional high-entropy alloy (HEA) nanomaterials are widely employed as electrocatalysts for energy conversion reactions, due to their inherent advantages, including high electron mobility, rich catalytically active site, optimal electronic structure. Moreover, the high-entropy, lattice distortion, and sluggish diffusion effects also enable them to be promising electrocatalysts. A thorough understanding on the structure-activity relationships of low-dimensional HEA catalyst play a huge role in the future pursuit of more efficient electrocatalysts. In this review, we summarize the recent progress of low-dimensional HEA nanomaterials for efficient catalytic energy conversion. By systematically discussing the fundamentals of HEA and properties of low-dimensional nanostructures, we highlight the advantages of low-dimensional HEAs. Subsequently, we also present many low-dimensional HEA catalysts for electrocatalytic reactions, aiming to gain a better understanding on the structure-activity relationship. Finally, a series of upcoming challenges and issues are also thoroughly proposed as well as their future directions.

Two-Dimensional Metal Nanostructures: From Theoretical Understanding to Experiment

This paper reviews recent studies on the preparation of two-dimensional (2D) metal nanostructures, particularly nanosheets. As metal often exists in the high-symmetry crystal phase, such as face centered cubic structures, reducing the symmetry is often needed for the formation of low-dimensional nanostructures. Recent advances in characterization and theory allow for a deeper understanding of the formation of 2D nanostructures. This Review firstly describes the relevant theoretical framework to help the experimentalists understand chemical driving forces for the synthesis of 2D metal nanostructures, followed by examples on the shape control of different metals. Recent applications of 2D metal nanostructures, including catalysis, bioimaging, plasmonics, and sensing, are discussed. We end the Review with a summary and outlook of the challenges and opportunities in the design, synthesis, and application of 2D metal nanostructures.

Pd-Based Metallenes for Fuel Cell Reactions

Pd-based metallenes, atomically thin layers composed primarily of under-coordinated Pd atoms, have emerged as the newest members in the family of two-dimensional (2D) nanomaterials. Moreover, the unique physiochemical properties, high intrinsic activity associated with metallenes coupled with the ease of applying chemical modifications result in great potential in catalyst engineering for fuel cell reactions. Especially in recent years, interest in Pd-based metallenes is growing, as evidenced by surge in available literatures. Herein, we have reviewed the recent findings achieved in Pd-based metallenes in fuel cells by highlighting the technologies available for deriving metallenes and manifesting the modification strategies for designing them to better suit the application demand. Moreover, we also discuss the perspective insights of Pd-based metallenes for fuel cells regarding the surfactant-free synthesis method, strain engineering, constructing high-entropy alloy, and so on.

Combining surface chemical functionalization with introducing reactive oxygen species boosts ethanol electrooxidation

The introduction of functional groups or oxygen vacancies into Pd-based electrocatalysts is a powerful strategy for enhancing the electrocatalytic performances for many electrocatalytic reactions. Herein, an amorphous ceria-modified Pd nanocomposite anchored on D-4-amino-phenylalanine (DAP)-functionalized graphene nanosheets (Pd-CeO_2-x/FGS) was prepared by a facile and effective one-pot synthetic strategy and further used as an electrocatalyst for the ethanol oxidation reaction (EOR) in alkaline electrolytes. The obtained Pd-CeO_2-x/FGS exhibits relatively high electrocatalytic activity, fast kinetics and excellent antipoisoning ability as well as robust durability for EOR, outperforming the comparable electrocatalysts as well as commercial Pd/C. The experimental results show that the enhanced EOR properties of Pd-CeO_2-x/FGS can be attributed to the DAP-functionalization and CeO_2-x-modification. Adequate functional groups (amino and carboxyl groups) and abundant oxygen vacancies were introduced in Pd-CeO_2-x/FGS by DAP-functionalization and CeO_2-x-modification. The functional groups facilitate the anchoring of small nanoparticles onto the substrate as well as modulate the electron density of Pd. The oxygen vacancies boost the adsorption ability of the reactive oxygen species (OH_ads) and accelerate the kinetics of the potential-limiting step for EOR. This study proposes a new strategy for the rational design of highly efficient catalysts for the electro-oxidation reaction.

Unveiling the Synergistic Effects of Monodisperse Sea Urchin-like PdPb Alloy Nanodendrites as Stable Electrocatalysts for Ethylene Glycol and Glycerol Oxidation Reactions

In recent times, the fabrication of noble metal-based catalysts with controllable morphologies has become a research hotspot. Electrocatalytic devices with excellent catalytic performance and enhanced durability for the ethylene glycol oxidation reaction (EGOR) and the glycerol oxidation reaction (GOR) are significant for commercial direct fuel cells. Herein, a series of PdPb sea urchin-like nanodendrite (ND) structures with controllable molar ratios were synthesized as EGOR and GOR electrocatalysts of high efficiency. The optimized structurally regular Pd₃Pb NDs exhibit the best electrocatalytic activity and outstanding stability compared to other samples and commercial Pt/C. In addition, the integrated Pb on Pd₃Pb NDs can mitigate the bond energy the intermediates generate and further boost the electrooxidation of the intermediates by supplying enough active sites without considering its intrinsic structure, which is beneficial to the enhanced EGOR and GOR activity and stability. With the assistance of electrochemical measurement, the mechanism of the enhanced alloy was further investigated. This paper presents a promising strategy to fabricate catalysts with stable structures, which will elucidate a very promising approach for developing Pd-based catalysts for further applications in fuel cells.

Assembly of Alloyed PdCu Nanosheets and Their Electrocatalytic Oxidation of Ethanol

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 electro-oxidation 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.

Surfactant-Assisted Synthesis of Praseodymium Orthovanadate Nanofiber-Supported NiFe-Layered Double Hydroxide Bifunctional Catalyst: The Electrochemical Detection and Degradation of Diphenylamine

Physiological storage disorders are caused by ineffective post-harvest handling of horticultural crops, particularly fruits. To address these post-harvest concerns, diphenylamine (DPAH^•+) is widely used as a preservative to prevent fruit degradation and surface scald during storage around the world. Humans are negatively affected by the use of high concentrations of DPAH^•+ because of the various health complications related to its exposure. As a result, accurate detection and quantification of DPAH^•+ residues in treated fruits are critical. Rare earth metal orthovanadates, which have excellent physical and chemical properties, are potential materials for electrochemical sensors in this area. Herein, we present a simple and direct ultrasonication technique for the surfactant-assisted synthesis of praseodymium orthovanadate (PrVO₄ or PrV) loaded on nickel iron layered double hydroxide (NiFe-LDH) synthesized with deep eutectic solvent assistance, as well as its application as an effective catalyst in the detection and degradation of DPAH^•+ in fruits and water samples. The current work presents supreme electrochemical features of a PrV@NiFe-LDH-modified screen-printed carbon electrode (SPCE) where cetyltrimethylammonium bromide (CTAB) surfactant-driven fabrication of PrV directs the formation of highly qualified engineered structures and the deep eutectic solvent based green synthesis of NiFe-LDH creates hierarchical lamellar structures following the principles of green chemistry. PrV and NiFe-LDH combine to produce a synergistic effect that improves the number of active sites, charge transfer kinetics, and electronic conductivity. Differential pulse voltammetry analysis of PrV@NiFe-LDH/SPCE reveals a dynamic working range (0.005-226.26 μM), increased sensitivity (133.13 μA μM^-1 cm^-2), enhanced photocatalytic activity, and low detection limit (0.001 μM), which are considered significant when compared with the former reported electrodes in the literature for the determination of DPAḢ⁺ for its real-time applications.

Controllable Synthesis of Web-Footed PdCu Nanosheets and Their Electrocatalytic Applications

Morphological control of noble-metal-based nanocrystals has attracted enormous attention because their catalytic behaviors can be optimized well by adjusting the size and shape. Herein, the controllable synthesis of web-footed PdCu nanosheets via a facile surfactant-free method is reported. It is discovered that the Cu(II) precursor in this synthetic system displays a critical role in growing branches along the lateral of nanosheets. This work demonstrates a Pd-based alloy nanoarchitecture for efficient and stable electrocatalysis of both ethanal and formic acid oxidation reactions.

Electronic structure optimization boosts Pd nanocrystals for ethanol electrooxidation realized by Te doping

Te doping greatly modifies the electronic structure of Pd and promotes the electrocatalytic performance towards EOR.

Alloyed Palladium-Lead Nanosheet Assemblies for Electrocatalytic Ethanol Oxidation

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.

Mxene coupled over nitrogen-doped graphene anchoring palladium nanocrystals as an advanced electrocatalyst for the ethanol electrooxidation

Development of good support materials is widely adopted as a valid strategy to fabricate high performance electrocatalysts for the ethanol oxidation reaction (EOR). In this study, the small diameter Ti₃C₂T_x MXene thin nanosheets inserted into three-dimensional nitrogen-doped grapheme (NG) was constructed via a facile hydrothermal method and employed as support materials for anchoring Pd nanocrystals (Pd/Ti₃C₂T_x@NG). The obtained-Pd/Ti₃C₂T_x@NG as EOR electrocatalyst in alkaline media outperforms the commercial Pd/C with better electrocatalytic activity, enhanced long-term stability and high CO tolerance. The Ti₃C₂T_x inserted into NG probably plays a key role for enhancing the properties of the synthesized-catalyst. Inserting Ti₃C₂T_x into NG allows the electrocatalysts to have high porosity, surface hydrophilicity, sufficient number of anchor sites for Pd nanocrystals and modifies its electronic properties, which can promote the electrocatalytic activity and durability. The enhanced EOR performance endows Pd/Ti₃C₂T_x@NG with great application potential in fuel cells as an anode catalyst. Furthermore, the prepared Ti₃C₂T_x@NG is also suitable in various desired applications, especially other oxidation reactions.

Enhanced Electrocatalytic Activity of Alloyed Palladium-Lead Nanoparticles toward Electrooxidation of Ethanol

Although many researchers have made great efforts to pursue promising high-efficiency electrocatalysts, a formidable challenge remains for designing excellent palladium-based electrocatalysts for commercializing direct liquid fuel cells. This study reports the synthesis of bimetallic PdPb nanoparticles (NPs) via a mixed solution containing cetyl trimethyl ammonium bromide as the capping agent. Alloyed PdPb NPs are formed, where the size of the NPs increases as Pb atoms are introduced gradually. However, Pd₃Pb NPs are obtained with the same molar ratio of Pd and Pb in the raw systems. Among all of the as-made NPs, Pd₉Pb₁ NPs exhibit superior catalytic activity (2620 mA mg^-1) toward ethanol electrooxidation, 4.3 times higher than commercial Pd/C catalysts (613 mA mg^-1). The overall rate of the EOR for PdPb NPs is determined, demonstrating that the electrocatalytic activity of the PdPb NPs increases at high catalytic temperatures, in high pH environments, and/or at high ethanol concentrations.