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

Synthesizing Pd-based high entropy alloy nanoclusters for enhanced oxygen reduction

We report the synthesis of uniform Pd-based high-entropy alloy clusters via rapid Joule heating. The quinary PdMnFeCuNi clusters exhibit 4.95 times higher mass activity than the Commercial Pt/C for the oxygen reduction reaction, and outstanding stability with only 2 mV decay in the half-wave potential after 20 000 cycles of testing.

Insights of the efficient hydrogen evolution reaction performance in bimetallic Au4Cu2 nanoclusters

The design of efficient electrocatalysts for improving hydrogen evolution reaction (HER) performance using atomically precise metal nanoclusters (NCs) is an emerging area of research. Here, we have studied the HER electrocatalytic performance of monometallic Cu6 and Au6 nanoclusters and bimetallic Au4Cu2 nanoclusters. A bimetallic Au4Cu2/MoS2 composite exhibits excellent HER catalytic activity with an overpotential (η10) of 155 mV vs. reversible hydrogen electrode observed at 10 mA cm-2 current density. The improved HER performance in Au4Cu2 is due to the increased electrochemically active surface area (ECSA), and Au4Cu2 NCs exhibits better stability than Cu6 and Au6 systems and bare MoS2. This augmentation offers a greater number of active sites for the favorable adsorption of reaction intermediates. Furthermore, by employing X-ray photoelectron spectroscopy (XPS) and Raman analysis, the kinetics of HER in the Au4Cu2/MoS2 composite were elucidated, attributing the favorable performance to better electronic interactions occurring at the interface between Au4Cu2 NCs and the MoS2 substrate. Theoretical analysis reveals that the inherent catalytic enhancement in Au4Cu2/MoS2 is due to favorable H atom adsorption over it and the smallest ΔGH* value. The downshift in the d-band of the Au4Cu2/MoS2 composite influences the binding energy of intermediate catalytic species. This new catalyst sheds light on the structure-property relationship for improving electrocatalytic performance at the atomic level.

A universal strategy for green and surfactant-free synthesis of noble metal nanoparticles

We propose a universal, green, and surfactant-free strategy to synthesize noble metal particles with high monodispersity using gaseous H2 as a reducing agent in a solution at 60 °C. The prepared Pt nanoparticles have a 24 mV more positive half-wave potential than the commercially available Pt/C in the oxygen reduction reaction, while showing high durability with negligible half-wave potential decay after 10 000 cycles of testing.

In-situ synthesis of carbon-supported ultrafine trimetallic PdSnAg nanoparticles for highly efficient alcohols electrocatalysis

Designing functional and durable electrocatalysts for the oxidation of alcohols plays a significant role for the development of direct alcohol fuel cells (DAFCs). Herein, carbon-supported ultrafine PdSnAg nanoparticles with an average size of 3.27 nm (denoted as PdSnAg/C NPs) have been synthesized for alcohols electrocatalysis. The smaller particle size means a higher proportion of surface exposed atoms for catalyzing the reaction followed by high catalytic performance. The multimetallic nanoalloys have potential electronic structure adjustment and synergistic effect between different components. The incorporation of oxophilic metals Sn and Ag facilitates the removal of intermediates produced during the oxidation of alcohols. The PdSnAg/C NPs exhibit a remarkable electrocatalytic performance for ethylene glycol oxidation reaction (EGOR) with the mass activity of 12.3 A mgPd-1, which is 15.6, 2.50 and 2.60 times higher than those of commercial Pd/C (0.790 A mgPd-1), PdSn/C NPs (4.85 A mgPd-1) and PdAg/C NPs (4.69 A mgPd-1), respectively. Meanwhile, PdSnAg/C NPs show superior mass activities of 10.6 A mgPd-1 and 6.65 A mgPd-1 for ethanol oxidation reaction (EOR) and glycerol oxidation reaction (GOR), which are 14.3 and 8.30 times superior than the commercial Pd/C, respectively. The exceptional mass activity promises the PdSnAg/C NPs to be the potential Pd-based catalysts for alcohols electrocatalysis.

Tensile-Strained Holey Pd Metallene toward Efficient and Stable Electrocatalysis

Noble metal-based metallenes are attracting intensive attention in energy catalysis, but it is still very challenging to precisely control the surface structures of metallenes for higher catalytic properties on account of their intrinsic thermodynamic instability. Herein, the synthesis of tensile-strained holey Pd metallene by oxidative etching is reported using hydrogen peroxide, which exhibits highly enhanced catalytic activity and stability in comparison with normal Pd metallene toward both oxygen reduction reaction and formic acid oxidation. The pre-prepared Pd metallene functions as a catalyst to decompose hydrogen peroxide, and the Pd atoms in amorphous regions of Pd metallene are preferentially removed by the introduced hydrogen peroxide during the etching process. The greatly enhanced ORR activity is mainly determined by the strong electrostatic repulsion between intermediate O* and the dopant O, which balances the adsorption strength of O* on Pd sites, ultimately endowing a weakened adsorption energy of O* on TH-Pd metallene. This work creates a facile and economical strategy to precisely shape metallene-based nanoarchitectures with broad applications for energy systems and sensing devices.

Selective edge etching of Pd metallene for enhanced formic acid electrooxidation

We develop a facile, selective edge etching strategy to create edge sites in Pd metallene using acetic acid. The created edge sites remarkably increase the electrochemically active surface area but reduce the charge transfer resistance, resulting in significant enhancement of catalytic activity and stability toward formic acid oxidation.

A 2D/2D heterojunction of ultrathin Pd nanosheet/MXene towards highly efficient methanol oxidation reaction: the significance of 2D material nanoarchitectonics

Two-dimensional (2D) Pd nanosheet-based catalysts have recently garnered widespread attention due to their high atom utilization efficiency. However, their catalytic ability and structural stability still require significant enhancement before they can be widely applied. In this study, we presented the rational design and controllable fabrication of a novel 2D/2D heterojunction, which consists of ultrathin Pd nanosheets (NSs) grown on the Ti3C2Tx MXene surface (Pd NSs/MXene). This heterostructure was achieved through a robust and convenient stereo-assembly strategy. The newly developed Pd NSs/MXene heterojunction not only provides numerous exposed active Pd atoms with an optimized electronic structure but also enables an intimate Pd/MXene interfacial interaction, ensuring a stable hybrid configuration. Consequently, the resulting Pd NSs/MXene heterojunction exhibits exceptional methanol oxidation properties. It possesses a large electrochemically active surface area, high mass and specific activities, and a long operating life, which are significantly superior to those of traditional Pd nanoparticle/carbon and Pd nanosheet/carbon catalysts. Theoretical simulations further reveal strong electronic interactions between the Pd nanosheet and MXene, which dramatically enhance the adsorption energy of the Pd component and simultaneously lower its d-band center. As a result, the Pd NSs/MXene heterojunction is less susceptible to CO poisoning. This work introduces a new 2D/2D heterojunction based on MXene and noble metallic materials and holds significance for the development of other novel heterojunctions, particularly within the realm of 2D material nanoarchitectonics.

Assembly of Alloyed PdM (Ag, Cu, and Sn) Nanosheets and Their Electrocatalytic Oxidation of Ethanol and Methanol

Direct alcohol fuel cells are popular due to their high energy density, abundant sources, and ease of transportation and storage. Palladium-based nanosheet self-assembled materials have emerged as an effective catalyst for alcohol oxidation reactions. In this work, nanosheets were synthesized with the same feeding ratio assembly of alloyed PdM (M = Ag, Cu, and Sn). The introduction of the second element was able to enhance the catalytic response of the catalysts to alcohol electrooxidation. Among them, the PdCu alloy exhibited the best performance in terms of catalytic activity, toxicity resistance, and stability to ethanol oxidation reaction (EOR) and methanol oxidation reaction (MOR). The catalytic current densities for EOR can reach 2226, 2518, and 1598 mA mg-1 for PdAg, PdCu, and PdSn nanosheet assemblies, respectively. These are mainly attributed to better electronic effects, altered atomic distances within the cell for the d-band centers of Pd, and a larger electrochemical active surface area (ECSA). The optimized d-band center is beneficial to promote the catalytic performance of EOR and MOR. Experimental data also demonstrated that higher electrocatalytic temperature, higher pH, and higher alcohol concentration can accelerate the rate of alcohol electrooxidation. These results have the potential to be extended to Pd-M (M = other metals) nanosheets and help for a wider range of catalytic applications.

Design and Realization of Ni Clusters in MoS2@Ni/RGO Catalysts for Alkaline Efficient Hydrogen Evolution Reaction

Due to their almost zero relative hydrogen atom adsorption-free energy, MoS2-based materials have received substantial study. However, their poor electronic conductivity and limited number of catalytic active sites hinder their widespread use in hydrogen evolution reactions. On the other hand, metal clusters offer numerous active sites. In this study, by loading Ni metal clusters on MoS2 and combining them with the better electrical conductivity of graphene, the overpotential of the hydrogen evolution reaction was reduced from 165 mV to 92 mV at 10 mA·cm-2. This demonstrates that a successful method for effectively designing water decomposition is the use of synergistic interactions resulting from interfacial electron transfer between MoS2 and Ni metal clusters.

Modulate the metallic Sb state on ultrathin PdSb-based nanosheets for efficient formic acid electrooxidation

Incorporation of oxophilic metals into Pd-based nanostructures has shown great potential in small molecule electrooxidation owing to their superior anti-poisoning capability. However, engineering the electronic structure of oxophilic dopants in Pd-based catalysts remains challenging and their impact on electrooxidation reactions is rarely demonstrated. Herein, we have developed a method for synthesizing PdSb-based nanosheets, enabling the incorporation of the Sb element in a predominantly metallic state despite its high oxophilic nature. Moreover, the Pd₉₀Sb₇W₃ nanosheet serves as an efficient electrocatalyst for the formic acid oxidation reaction (FAOR), and the underlying promotion mechanism is investigated. Among the as-prepared PdSb-based nanosheets, the Pd₉₀Sb₇W₃ nanosheet exhibits a remarkable 69.03% metallic state of Sb, surpassing the values observed for the Pd₈₆Sb₁₂W₂ (33.01%) and Pd₈₃Sb₁₄W₃ (25.41%) nanosheets. X-ray photoelectron spectroscopy (XPS) and CO stripping experiments confirm that the Sb metallic state contributes the synergistic effect of their electronic and oxophilic effect, thus leading to an effective electrooxidation removal of CO and significantly enhanced FAOR electrocatalytic activity (1.47 A mg^-1; 2.32 mA cm^-1) compared with the oxidated state of Sb. This work highlights the importance of modulating the chemical valence state of oxophilic metals to enhance electrocatalytic performance, offering valuable insights for the design of high-performance electrocatalysts for electrooxidation of small molecules.

2D Materials Boost Advanced Zn Anodes: Principles, Advances, and Challenges

Aqueous zinc-ion battery (ZIB) featuring with high safety, low cost, environmentally friendly, and high energy density is one of the most promising systems for large-scale energy storage application. Despite extensive research progress made in developing high-performance cathodes, the Zn anode issues, such as Zn dendrites, corrosion, and hydrogen evolution, have been observed to shorten ZIB's lifespan seriously, thus restricting their practical application. Engineering advanced Zn anodes based on two-dimensional (2D) materials are widely investigated to address these issues. With atomic thickness, 2D materials possess ultrahigh specific surface area, much exposed active sites, superior mechanical strength and flexibility, and unique electrical properties, which confirm to be a promising alternative anode material for ZIBs. This review aims to boost rational design strategies of 2D materials for practical application of ZIB by combining the fundamental principle and research progress. Firstly, the fundamental principles of 2D materials against the drawbacks of Zn anode are introduced. Then, the designed strategies of several typical 2D materials for stable Zn anodes are comprehensively summarized. Finally, perspectives on the future development of advanced Zn anodes by taking advantage of these unique properties of 2D materials are proposed.

Cr(OH)3nanosheets@ZIF67 electrocatalysts prepared by electrodeposition method for efficient oxygen evolution reaction

In this paper, a Cr(OH)₃NSs@ZIF67 (NSs = nanosheets) electrocatalyst is prepared on foam Ni via a simple and rapid electrochemical deposition method. Excellent electrocatalytic activity of Cr(OH)₃NSs@ZIF67 is demonstrated. It can use the overpotential of 281 mV and 390 mV respectively to drive 10 mA cm^-2and 50 mA cm^-2. It is observed that the Cr(OH)₃NSs@ZIF67 electrode has the highest initial current density at 1.57 V compared with the other two monomer electrodes and shows excellent stability at the end of 60 000 s. It has the largest electrochemical activity specific surface and lowest charge-transfer resistance, and M-O bonds (M = Co, Cr) and shifting of binding energy peaks at the interface lead to more active sites and more efficient electron transfer for oxygen evolution reaction. This work highlights the construction of highly efficient composite electrocatalysts composted of low-dimensional non-precious transition metal compounds and metalorganic frameworks, promoting the development of low-cost non-noble metal composites in energy chemistry.

Pd3Co1 Alloy Nanocluster on the MWCNT Catalyst for Efficient Formic Acid Electro-Oxidation

In this study, the Pd₃Co₁ alloy nanocluster from a multiwalled carbon nanotube (MWCTN) catalyst was fabricated in deep eutectic solvents (DESs) (referred to Pd₃Co₁/CNTs). The catalyst shows a better mass activity towards the formic acid oxidation reaction (FAOR) (2410.1 mA mg_Pd^-1), a better anti-CO toxicity (0.36 V) than Pd/CNTs and commercial Pd/C. The improved performance of Pd₃Co₁/CNTs is attributed to appropriate Co doping, which changed the electronic state around the Pd atom, lowered the d-band of Pd, formed a new Pd-Co bond act at the active sites, affected the adsorption of the toxic intermediates and weakened the dissolution of Pd; moreover, with the assistance of DES, the obtained ultrafine Pd₃Co₁ nanoalloy exposes more active sites to enhance the dehydrogenation process of the FAOR. The study shows a new way to construct a high-performance Pd-alloy catalyst for the direct formic acid fuel cell.

Quaternary PdCuNiP Porous Nanosheets with Enhanced Electrochemical Performance in the Ethanol Oxidation Reaction

The ability to manipulate metal electrocatalysts with satisfactory performance for the ethanol oxidation reaction (EOR) is promising but still unsatisfactory for practical application in direct ethanol fuel cells. Beyond traditional metal-metal alloys, we herein report a novel metal-nonmetal alloy electrocatalyst that takes advantage of quaternary PdCuNiP alloy composition and the ultrathin/porous nanosheet (NS) structure. The optimized PdCuNiP porous NSs feature more undercoordinated active sites and modified electron/function structures, enabling better antipoisoning ability. Under alkaline conditions, this electrocatalyst shows excellent electrochemical EOR performance with a high EOR activity of 4.05 A mg_Pd^-1 and a low activation energy of 21.2 kJ mol^-1, comparable to the state-of-the-art electrocatalysts reported in the literature. Meanwhile, PdCuNiP porous NSs are electrocatalytically active for electrochemical oxidation of other fuels (methanol, glycerol, and glucose), highlighting their great potential for various direct alcohol fuel cells. The findings reported here may put forward some insights into designing new functional electrocatalysts for various fuel cell electrocatalysis and beyond.

B, P-co-doped PdCu nanothorn assemblies for enhanced oxygen reduction electrolysis

Nonmetal doping is a promising strategy to improve electrocatalytic performance of noble metal based catalysts for oxygen reduction reaction (ORR). Herein, we report a facile method to fabricate PdCuBP nanothorn assemblies (PdCuBP NTAs) by co-doping B and P into pre-synthesized PdCu NTAs using NaBH₄and NaH₂PO₂as B source and P source, respectively. The metal-nonmetal structure and multi-branched morphology can optimize oxygen adsorption energy and avoid catalyst migration, agglomeration and Ostwald ripening. As such, the obtained PdCuBP NTAs exhibit efficient activity and excellent long-term stability for ORR. This research offers an excellent strategy for co-doping nonmetal elements into metal nanocrystals with controllable composition and structure to improve electrocatalytic ORR performance.

Controllable engineering magnetite nanoparticles dispersed in a hierarchical amylose derived carbon and reduced graphene oxide framework for lithium-ion storage

A straightforward and eco-friendly method is demonstrated to engineer magnetite (Fe₃O₄) nanoparticles well dispersed by an amorphous amylose-derived carbon (AMC) and reduced graphene oxide (RGO) framework. Naturally available amylose (AM) serves as both reducing agent for few-layered graphene oxide (GO) in the first mild redox coprecipitation system and precursor for small-sized pyrolytic AMC in the following thermal treatment. In particular, the presence of the AM molecules effectively limits the crystal growth kinetics for the akaganeite (FeOOH) in the intermediate FeOOH@AM/RGO sample, which contributes to the transformation to Fe₃O₄ nanoparticles with significantly controlled size in the final Fe₃O₄@AMC/RGO composite. As a result, both Fe₃O₄ nanoparticles and AMC domains are adjacently anchored on the larger sized RGO sheets, and a unique hierarchical structure has been engineered in the Fe₃O₄@AMC/RGO sample. Compared with the controlled Fe₃O₄@RGO sample, the Fe₃O₄@AMC/RGO composite exhibits remarkably enhanced initial coulombic efficiency, superior cycling stability and rate performance for lithium-ion storage. The mechanisms of the interaction between GO sheets and AM molecules as well as the inspiring electrochemical behaviors of the Fe₃O₄@AMC/RGO electrode have been revealed. The Fe₃O₄@AMC/RGO sample possesses good potential for scaling-up and finding applications in wider fields.

Laser-scribed Graphene Electrodes Functionalized with Nafion/Fe3O4 Nanohybrids for the Ultrasensitive Detection of Neurotoxin Drug Clioquinol

The analysis of pharmaceutical active ingredients plays an important role in quality control and clinical trials because they have a significant physiological effect on the human body even at low concentrations. Herein, a flexible three-electrode system using laser-scribed graphene (LSG) technology, which consists of Nafion/Fe₃O₄ nanohybrids immobilized on LSG as the working electrode and LSG counter and reference electrodes on a single polyimide film, is presented. A Nafion/Fe₃O₄/LSG electrode is constructed by drop coating a solution of Nafion/Fe₃O₄, which is electrostatically self-assembled between positively charged Fe₃O₄ and negatively charged Nafion on the LSG electrode and is used for the first time to determine a neurotoxicity drug (clioquinol; CQL) in biological samples. Owing to their porous 3D structure, an enriched surface area at the active edges and polar groups (OH, COOH, and -SO₃H) in Nafion/Fe₃O₄/LSG electrodes resulted in excellent wettability to facilitate electrolyte diffusion, which gave ∼twofold enhancement in electrocatalytic activity over LSG electrodes. The experimental parameters affecting the analytical performance were investigated. The quantification of clioquinol on the Nafion/Fe₃O₄/LSG electrode surface was examined using differential pulse voltammetry and chronoamperometry techniques. The fabricated sensor displays preferable sensitivity (17.4 μA μM^-1 cm^-2), a wide linear range (1 nM to 100 μM), a very low detection limit (0.73 nM), and acceptable selectivity toward quantitative analysis of CQL. Furthermore, the reliability of the sensor was checked by CQL detection in spiked human blood serum and urine samples, and satisfactory recoveries were obtained.