Synthesis of octopus-tentacle-like Cu nanowire-Ag nanocrystals heterostructures and their enhanced electrocatalytic performance for oxygen reduction reaction

Recent progresses in the synthesis of MnO2 nanowire and its application in environmental catalysis

Nanostructured MnO2 with various morphologies exhibits excellent performance in environmental catalysis owing to its large specific surface area, low density, and adjustable chemical properties. The one-dimensional MnO2 nanowire has been proved to be the dominant morphology among various nanostructures, such as nanorods, nanofibers, nanoflowers, etc. The syntheses and applications of MnO2-based nanowires also have become a research hotspot in environmental catalytic materials over the last two decades. With the continuous deepening of the research, the control of morphology and crystal facet exposure in the synthesis of MnO2 nanowire materials have gradually matured, and the catalytic performance also has been greatly improved. Differences in the crystalline phase structure, preferably exposed crystal facets, and even the length of the MnO2 nanowires will evidently affect the final catalytic performances. Besides, the modifications by doping or loading will also significantly affect their catalytic performances. This review carefully summarizes the synthesis strategies of MnO2 nanowires developed in recent years as well as the influences of the phase structure, crystal facet, morphology, dopant, and loading amount on the catalytic performance. Besides, the cutting-edge applications of MnO2 nanowires in the field of environmental catalysis, such as CO oxidation, the removal of VOCs, denitrification, etc., have been also summarized. The application of MnO2 nanowire in environmental catalysis is still in the early exploratory stage. The gigantic gap between theoretical investigation and industrial application is still a great challenge. Compared with noble metal based traditional environmental catalytic materials, the lower cost of MnO2 has injected new momentum and promising potential into this research field.

A reusable catalyst based on CuO hexapods and a CuO-Ag composite for the highly efficient reduction of nitrophenols

The enormous and urgent need to explore cost-effective catalysts with high efficiency has always been at the forefront of environmental protection and remediation research. This work develops a novel strategy for the fabrication of reusable CuO-based non-noble metal nanomaterials as high-efficiency catalysts. We report a facile and eco-friendly synthesis of CuO hexapods and CuO–Ag composite using uric acid as a reductant and protectant. Both exhibited high catalytic activity in the hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by sodium borohydride (NaBH₄), with the CuO–Ag composite showing superior catalytic performance. Notably, the highest turnover frequency of CuO–Ag reached 7.97 × 10⁻² s⁻¹, which was much higher than numerous noble-metal nanomaterials. In addition, CuO hexapods and CuO–Ag composite were also shown to act as highly efficient and recyclable catalysts in the degeneration of 4-NP. Both CuO hexapods and the CuO–Ag composite exhibited outstanding catalytic durability, with no significant loss of activity over more than 10 cycles in the hydrogenation of 4-NP.

Schematic illustration for the process of preparing CuO hexapods and CuO–Ag composite, and their application in catalytically reducing 4-NP and K₃(Fe(CN)₆).

Advancements in Copper Nanowires: Synthesis, Purification, Assemblies, Surface Modification, and Applications

Copper nanowires (CuNWs) are attracting a myriad of attention due to their preponderant electric conductivity, optoelectronic and mechanical properties, high electrocatalytic efficiency, and large abundance. Recently, great endeavors are undertaken to develop controllable and facile approaches to synthesize CuNWs with high dispersibility, oxidation resistance, and zero defects for future large-scale nano-enabled materials. Herein, this work provides a comprehensive review of current remarkable advancements in CuNWs. The Review starts with a thorough overview of recently developed synthetic strategies and growth mechanisms to achieve single-crystalline CuNWs and fivefold twinned CuNWs by the reduction of Cu(I) and Cu(II) ions, respectively. Following is a discussion of CuNW purification and multidimensional assemblies comprising films, aerogels, and arrays. Next, several effective approaches to protect CuNWs from oxidation are highlighted. The emerging applications of CuNWs in diverse fields are then focused on, with particular emphasis on optoelectronics, energy storage/conversion, catalysis, wearable electronics, and thermal management, followed by a brief comment on the current challenges and future research directions. The central theme of the Review is to provide an intimate correlation among the synthesis, structure, properties, and applications of CuNWs.

CuAg@Ag Core-Shell Nanostructure Encapsulated by N-Doped Graphene as a High-Performance Catalyst for Oxygen Reduction Reaction

Development of a robust, cost-effective, and efficient catalyst is extremely necessary for oxygen reduction reaction (ORR) in fuel cell applications. Herein, we reported a well-defined nanostructured catalyst of highly dispersed CuAg@Ag core-shell nanoparticle (NP)-encapsulated nitrogen-doped graphene nanosheets (CuAg@Ag/N-GNS) exhibiting a superior catalytic activity toward ORR in alkaline medium. The synergistic effects produced from the unique properties of CuAg@Ag core-shell NPs and N-GNS made such a novel nanohybrid display a catalytic behavior comparable to that of the commercial Pt/C product. In particular, it demonstrated a much better stability and methanol tolerance than Pt/C under the same conditions. Because of its outstanding electrochemical performance and ease of synthesis, CuAg@Ag/N-GNS material was expected to be a promising low-cost catalyst for ORR in alkaline fuel cell applications.

Preparation and catalytic activity of magnetic bimetallic nickel/copper nanowires

Nowadays, 4-nitrophenol (4-NP), one of the most toxic pollutants of waste water, is capturing more attention in the field of sewage disposal.

Solvothermal fabrication of thin Ag nanowires assisted with AAO

Silver nanowires were synthesized using solvothermal method assisted with AAO. AAO here is playing a role as a heterogeneous medium that can promote PVP molecules to form into one dimensional template and thus guiding the growth of Ag nanowires.

Pt-free silver nanoalloy electrocatalysts for oxygen reduction reaction in alkaline media

Silver nanoalloy electrocatalysts with comparable activity and better stability than commercial Pt/C for oxygen reduction reaction (ORR) in advanced metal–air batteries and fuel cells.

Ag-Cu nanoalloyed film as a high-performance cathode electrocatalytic material for zinc-air battery

A novel Ag50Cu50 film electrocatalyst for oxygen reduction reaction (ORR) was prepared by pulsed laser deposition (PLD) method. The electrocatalyst actually is Ag-Cu alloyed nanoparticles embedded in amorphous Cu film, based on transmission electron microscopy (TEM) characterization. The rotating disk electrode (RDE) measurements provide evidence that the ORR proceed via a four-electron pathway on the electrocatalysts in alkaline solution. And it is much more efficient than pure Ag catalyst. The catalytic layer has maximum power density of 67 mW cm(-2) and an acceptable cell voltage at 0.863 V when current densities increased up to 100 mA cm(-2) in the Ag50Cu50-based primary zinc-air battery. The resulting rechargeable zinc-air battery exhibits low charge-discharge voltage polarization of 1.1 V at 20 mAcm(-2) and high durability over 100 cycles in natural air.

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.

A highly flexible platform for nanowire sensor assembly using a combination of optically induced and conventional dielectrophoresis

The number and position of assembled nanowires cannot be controlled using most nanowire sensor assembling methods. In this paper, we demonstrate a high-yield, highly flexible platform for nanowire sensor assembly using a combination of optically induced dielectrophoresis (ODEP) and conventional dielectrophoresis (DEP). With the ODEP platform, optical images can be used as virtual electrodes to locally turn on a non-contact DEP force and manipulate a micron- or nano-scale substance suspended in fluid. Nanowires were first moved next to the previously deposited metal electrodes using optical images and, then, were attracted to and arranged in the gap between two electrodes through DEP forces generated by switching on alternating current signals to the metal electrodes. A single nanowire can be assembled within 24 seconds using this approach. In addition, the number of nanowires in a single nanowire sensor can be controlled, and the assembly of a single nanowire on each of the adjacent electrodes can also be achieved. The electrical properties of the assembled nanowires were characterized by IV curve measurement. Additionally, the contact resistance between the nanowires and electrodes and the stickiness between the nanowires and substrates were further investigated in this study.

Well-coupled graphene and Pd-based bimetallic nanocrystals nanocomposites for electrocatalytic oxygen reduction reaction

In this paper, a series of well-coupled graphene (G) and MPd3 (M = Fe, Cu, Ag, Au, Cr, Mo, W) nanocrystals nanocomposites (G-MPd3 NCPs) have been synthesized via a versatile electrostatic assembly and hydrogen reduction strategy, i.e., sequential assembly of coordination anions and cations on excess cationic polymer modified graphene oxide to form composite precursors and then thermal treating under H2/Ar gases atmosphere. In those NCPs, the MPd3 components are uniform and smaller than 10 nm, which are well anchored on G with "naked" or "clean" surfaces. By adjusting reaction temperature, the interplay of MPd3 nanocrystals and G can be well-controlled. Below 700 °C, no sintering phenomena are observed, indicating the unprecedented dispersion and stability effect of G for MPd3 nanocrystals. All the obtained NCPs can be directly used to catalyze oxygen reduction reaction in alkaline media. Compared with single component, monometallic, and some reported non-Pt catalysts, greatly enhanced electrocatalytic performances are observed in those NCPs due to strong synergistic or coupling of their constituents. Among them, G-FePd3 NCPs exhibit the highest catalytic activity, but their current density needs to be improved compared with G-CrPd3, G-MoPd3, and G-WPd3 ones. This work not only provides a general strategy for fabricating well-coupled G-MPd3 NCPs but also paves the way for future designing multicomponent NCPs with multiple interfaces to apply in alkaline fuel cells.