Silver Nanowires Wrapped in Zinc and Nickel Oxides Show Boosted Catalytic and Energy-Storage Power

Researchers have crafted a new class of coaxial nanostructures in which ultrathin silver nanowires are sheathed first in zinc oxide and then, in a further twist, in a mixed zinc/nickel oxide shell. The resulting materials, described as Ag@Zn and Ag@Zn/Ni nanocables, combine the celebrated plasmonic and conductive properties of silver with the catalytic and pseudocapacitive virtues of two abundant, inexpensive metal oxides. According to the team, the hybrid cables outperform their uncoated counterparts across optical, catalytic and electrochemical tests, pointing toward applications in water purification chemistry, supercapacitor electrodes and next-generation electronic devices.

The synthesis relied on the polyol method, a versatile wet-chemical technique in which ethylene glycol serves simultaneously as solvent and reducing agent. The researchers preheated the glycol to 160 degrees Celsius, then introduced silver nitrate together with polyvinylpyrrolidone, a polymer that caps the growing crystals and steers them into long, straight wires. Seed particles formed first, and anisotropic growth followed, yielding silver nanowires with diameters of roughly 60 to 75 nanometres and lengths on the micrometre scale. Zinc acetate solutions of two different concentrations, 0.1 and 0.3 molar, were then added to grow the zinc oxide coating, producing samples labelled Z1 and Z3. For the mixed-oxide variants, zinc acetate and nickel acetate were injected together, giving the ZNM1 and ZNM3 nanocables.

Scanning electron microscopy revealed how dramatically the shell chemistry reshapes the architecture. Pure silver nanowires displayed smooth surfaces and diameters up to about 75 nanometres, while zinc-coated cables thickened to 75–85 nanometres, their surfaces studded with cubic nanoparticles and spherical particles ranging from around 100 nanometres to a micron. Adding nickel pushed the diameters to 85–95 nanometres and produced a striking zoo of morphologies, including irregular hexagonal crystals, quadrangular pyramidal crystals and clustered spheres spanning one to three microns. The team attributes this heterogeneity to nickel’s influence on nucleation dynamics and to synergistic effects between the two oxide-forming metals that alter surface energy minimisation during growth.

Transmission electron microscopy confirmed the coaxial design at higher resolution. The images showed elongated one-dimensional structures with a crystalline metallic silver core and a continuous oxide shell, with uniform contrast along their lengths indicating homogeneous composition. At low precursor concentrations, isotropic shapes such as cubes and triangular bipyramids dominated, whereas higher concentrations favoured elongated rods and wires. Some samples showed partial fragmentation and aggregation attributed to mechanical stress during grid preparation, and the thickest cables reached diameters near 85 nanometres with lengths up to ten micrometres, sometimes bundling together with ultrathin companions attached.

X-ray diffraction established the crystallographic foundations of the composites. Peaks at 38.2 and 44.7 degrees corresponded to the (111) and (200) planes of face-centred cubic silver, with no impurity phases detected. Additional reflections at 31.82 and 34.33 degrees matched the (100) and (002) planes of crystalline zinc oxide. Applying the Debye–Scherrer equation gave average crystallite sizes of about 35 to 36 nanometres, and the analysis showed that crystallite size shrank as the zinc and zinc/nickel salt content increased. Because the silver ion radius of 114 picometres exceeds that of zinc at 74 picometres, substituting silver into the lattice expands the unit cell, and the measured lattice parameters tracked these substitutions. An intense peak at 38.02 degrees signalled anisotropic growth of silver along the (111) direction, with the nickel/zinc shell growing coaxially in the same phase, evidence of atomic-level alloying between the metals.

Optical measurements highlighted the plasmonic fingerprints of the silver core and the electronic tuning imposed by the shells. The bare nanowires showed sharp surface plasmon resonance peaks at 356 and 386 nanometres from the transverse mode, while the zinc-coated cables shifted these features, with a peak at 319 nanometres and a prominent band at 358 nanometres, and a slight redshift appearing as zinc concentration rose. Band gap energies fell steadily with increasing metal doping, from 3.220 electronvolts for Z1 down to 2.8 electronvolts for the most heavily doped mixed-oxide sample, a narrowing that reflects deliberate modification of the electronic structure. Photoluminescence spectroscopy added further nuance: band-edge emission sat at 380 nanometres for Ag@Zn and shifted marginally to 383 nanometres with nickel, while deep-trap emission linked to defect states moved from 522 to 513 nanometres. Crucially, the composite catalysts showed much weaker photoluminescence intensity than the bare wires, indicating that the silver cores suppress electron–hole recombination and lengthen the lifetime of photoexcited charge carriers, a property that directly benefits catalysis.

The catalytic showcase was the reduction of p-nitrophenol to p-aminophenol by sodium borohydride, a benchmark reaction for water treatment because p-nitrophenol is a persistent organic pollutant. In the untreated mixture, the yellow p-nitrophenolate ion absorbs strongly at 400 nanometres; as the reaction proceeds, this peak fades. The uncoated silver nanowires needed 44 minutes to complete the conversion, the zinc-coated cables cut this to 30 and 24 minutes for Z1 and Z3, and the nickel-containing composites performed best of all, finishing in 16 and 12 minutes for ZNM1 and ZNM3. A clear isosbestic point near 314 nanometres appeared in all spectra, a spectroscopic signature of a clean, direct conversion pathway. The team notes that these catalysts compare favourably with previously reported systems for the same transformation, and they emphasise that zinc offers a cheap, abundant and comparatively non-toxic alternative to more hazardous transition-metal catalysts.

Electrochemical testing painted an equally encouraging picture for energy storage. Cyclic voltammetry in potassium hydroxide electrolyte, using a three-electrode configuration with the nanocables deposited on nickel foam, revealed distinct redox peaks characteristic of pseudocapacitive behaviour. Bare silver nanowires produced current responses of roughly 20 microamperes with symmetrical peaks around the zero-current axis, corresponding to reversible silver oxidation and reduction. The zinc oxide coating raised the current density to about 35 microamperes, improving electron transfer kinetics, while the Ag@Zn/Ni composites delivered the highest response at approximately 60 microamperes, with a broad reduction peak near minus 0.8 volts and multiple oxidation peaks extending up to plus 1.4 volts, reflecting overlapping redox processes from silver, zinc oxide and nickel oxide. Electrochemical impedance spectroscopy, spanning frequencies from 10^-2 to 10^5 hertz, reinforced the story: the silver-coated composites showed the lowest equivalent series resistance, the smallest high-frequency semicircles indicating minimal charge transfer resistance, and shallow low-frequency slopes consistent with low Warburg resistance, all hallmarks of fast, efficient electron transport.

Taken together, the results argue that the whole of these nanocables exceeds the sum of their parts. The silver core supplies conductivity, plasmonic light harvesting and charge-separation assistance; the zinc oxide shell contributes wide-band-gap semiconducting behaviour, chemical stability and catalytic sites; and the nickel oxide component adds high redox activity that multiplies the pseudocapacitive response. Because the shell thickness and composition can be tuned simply by adjusting precursor concentrations, the platform offers a tunable route to bimetallic and mixed-oxide nanostructures without exotic equipment or scarce raw materials, and the polyol approach could plausibly be extended to other metal combinations. The authors suggest the nanocables could serve as electrodes for advanced electronic and energy storage devices, with potential reach into medical, environmental and fuel-cell technologies. For a field searching for ways to stretch precious silver further while squeezing more performance out of earth-abundant oxides, these cable-like hybrids offer a compelling blueprint.

Subject of Research: Synthesis and characterization of silver-core zinc/nickel oxide coaxial nanocables for catalytic and electrochemical applications

Article Title: Hybridized Ag@Zn/Ni nanocables: synergistic enhancements in optical, catalytic, and electrochemical behaviour

Article References: Sharif, S., Ahmad, Z., Choudhary, M. A., Irshad, M. A., Nisar, F., Al-Hussain, S. A., Irfan, A., & Zaki, M. E. A. (2026). Hybridized Ag@Zn/Ni nanocables: synergistic enhancements in optical, catalytic, and electrochemical behaviour. Journal of Saudi Chemical Society, 30(2), Article 21. https://doi.org/10.1007/s44442-026-00069-7

Image Credits: AI Generated

DOI: 10.1007/s44442-026-00069-7

Keywords: nanocables, silver nanowires, zinc oxide, nickel oxide, core-shell nanostructures, polyol method, p-nitrophenol reduction, pseudocapacitance, cyclic voltammetry, electrochemical impedance spectroscopy, surface plasmon resonance, photoluminescence