ZnO Nanorod Electrodes Research Articles

Alkali metal cations at work: Enhancing CO2 electroreduction to CO on ZnO nanorods

Oxide-derived zinc, an abundant and cost-effective electrode material alternative to gold and silver, has exhibited high activity for the electroreduction of CO2 to CO (CO2RR). However, the impact of cations on the CO2RR activity remains unexplored. In this study, we investigated the effect of three alkali metal cations (Cs+, K+, and Li+) on the CO2RR over a ZnO nanorod electrode, using a rotating ring disk electrode (RRDE) technique. Cyclic voltammetry of the Pt ring in the RRDE tip reveals a consistent trend in the buffering capacity of these cations (Cs+ > K+ > Li+), as evidenced by the availability of OH⁻ ions for CO electrooxidation and hydrogen oxidation reactions (HOR). Cs+ showed a pronounced effect on the activity of the CO2RR to CO since it can regulate OH⁻ concentration and maintain the local pH. This study addresses the ongoing debate concerning the effects of cations; interfacial electric field and buffering capacity; and elucidates the relationship among electrolyte/cation, local pH dynamics, and the CO2RR activity towards CO over the active oxide-derived Zn electrodes, all derived from the fast and facile RRDE technique.

Enhancement of electrochemical detection performance towards 2,4,6-trinitrotoluene by a bottom layer of ZnO nanorod arrays

The ZnO nanostructure layers have been widely investigated as electrodes for sensors due to their intrinsic advantages such as high active area and low cost. In this work, to enhance the detection properties of ZnO nanostructural electrodes, self-organized ZnO nanorod arrays were synthesized using the chemical bath deposition (CBD) method on FTO glasses and ZnO nanoparticles. The fabricated ZnO electrodes on the two different substrates were characterized by SEM, TEM, XRD, and XPS. Subsequently, the detection performance of ZnO nanorod electrodes was electrochemically measured in a 2,4,6-trinitrotoluene (2,4,6-TNT) solution by CV and EIS. The differences in current densities between the ZnO electrodes were determined by the width of the ZnO nanorods, resulting in a ∼45% higher detection efficiency with F-CBD (the ZnO nanorods on FTO) electrodes compared to S-CBD (the ZnO nanorods on ZnO nanoparticles) electrodes.

Comprehensive evaluation of photoelectrochemical performance dependence on geometric features of ZnO nanorod electrodes.

The impact of geometric features, light absorption spectra, and electrochemical active surface area on photoelectrochemical properties was investigated in this work. Nanoforests of ZnO nanorods with rationally controlled morphologies were grown on ITO substrates by the hydrothermal method and utilized as a model for this purpose. The size of the nanorods was systematically adjusted by varying the concentration of polyethyleneimine as a cation surfactant in the growth solution. It was found that the emergent geometric characteristics (i.e. the aspect ratio) increased almost at the same pace as the electrochemically active surface area, but the light scattering effect slightly increased as a result of the random spatial orientation of the nanorods. The large surface area and the void space between nanorods increased the photon-to-current conversion efficiency by promoting the hole transfer process at the electrode/electrolyte interface. A maximum photocurrent density of 0.06 mA cm-2 (0.5 V vs. NHE) for smaller diameter and length ZnO nanorods (ZnO-P1) was obtained under 365 nm UV light illumination. Additionally, we provide visual evidence that a shorter photogenerated hole diffusion distance results in improved charge separation efficiency using Mn2+ as the photogenerated hole imaging agent. Therefore, the present work demonstrates a facile strategy for nanoforest morphology improvement for generating strong contact at the ZnO NR electrode/electrolyte interface, which is favourable in energy conversion and storage technologies.

Performance of Dye Sensitized Solar Cells (DSSCs) with ZnO Nanorod Electrode in Different Seed Solution

Studies of comparing the performance of photoelectrode for dye-sensitized solar cells (DSSCs) continue to be carried out and developed. The ZnO nanorods as an electrode for DSSCs have been shown to have high electron collection due to the capability of electron photoexcitation and increased electron transport. Various methods of making ZnO nanorods have been studied and developed. However, the method requires controlled conditions under high temperature and pressure, thus limiting the commercialization of ZnO nanorods. Therefore, the seed solution-based hydrothermal method was chosen in the ZnO nanorod deposition process because it is an effective method, low-cost and easier fabrication process. The method of growing ZnO nanorod was carried out with three times of growing for 6 hours. ZnO nanorod was synthesized using different seed solutions, namely sample 1 and sample 2 by using methoxy and isopropanol, respectively. In this work, the SEM image shows the growth of ZnO nanorods vertically aligned on the FTO substrate and resulted in a smaller diameter for the isopropanol seed solution. The smaller diameter of the ZnO nanorod provides a larger surface area then increasing the total amount of dye attached to the ZnO nanorod and improve the photovoltaic performance.

The Cell Performances of DSSCs with ZnO Nanorod Electrodes

To date, dye-sensitized solar cells (DSSCs) based on TiO2 nanoparticles have been widely investigated due to their high conversion efficiency. However, constructing TiO2 into a structure of nanorods with a high aspect ratio is difficult to be achieved. On the other hand, nanorod/nanowire arrays may provide some advantages, such as an efficient pathway for electron transport and a larger surface area for dye absorption. ZnO is one kind of metal oxides that can be formed into nanorods easily with various methods. Here, we reported our works on the preparation of ZnO nanorods and investigate its DSSC performance. We found that the cell performance was very affected by the diameter of the nanorods, which may then indicate that charge transfer and charge extraction processes are more effective in the cell with a smaller nanorod diameter.

Enhanced photoelectrocatalytic degradation of tetrabromobisphenol a from tip-decorated ZnO nanorod electrode with Bi2S3 nanoparticles

Tip-decorated ZnO/Bi2S3 photoelectrode was synthesized on a FTO substrate from chemical bath deposition and electrochemical deposition to investigate the photoelectrocatalytic (PEC) degradation of tetrabromobisphenol A (TBBPA). XRD, SEM, UV–vis and PL techniques were employed to evaluated the crystal structure, surface morphology, light absorbance properties and efficiency of carriers’ separation of the obtained electrode, respectively. The ZnO/Bi2S3 photoelectrode yielded a photocurrent density of 15.3 mA/cm2 upon ultraviolet and visible light irradiation, which was 6.6 and 10.9 times that of the original ZnO and Bi2S3, respectively. The enhanced photoelectrochemical properties is due to the improved light absorption of Bi2S3 nanoparticles and accelerated electron‐transfer pathway of ZnO nanorods. The stability of the photoelectrode was evaluated by recycling degradation experiments for 3 times. The intermediates of TBBPA degradation were also identified and a possible pathway was proposed.

The effect of indium doping on photovoltaic properties of chemically synthesized zinc oxide thin-film electrodes

Photovoltaic (PV) performance of chemically synthesized indium-doped zinc oxide (IZO) nanorod electrodes has been investigated by photocurrent density-voltage (J-V). The indium (In) concentration was varied from 2 to 6 at.% for IZO. The J-V measurements as performed under a dark condition and a simulated white light of 80 mW/cm2 confirmed increase in PV performance with the IZO electrodes, making a peak with the 4 at.% In concentration. The investigated properties of the synthesized In-doped ZnO nanorod electrodes (structural and optical) strongly agreed with the PV results and well support the enhanced PV performance of the IZO electrodes. This clearly indicates that IZO electrodes would be preferred against undoped ones in PV solar cell application.

Facile synthesis and electrochemical properties of carbon-coated ZnO nanotubes for high-rate lithium storage

ZnO is an important functional material, and a nanotube structure is beneficial for various applications. Here, we report the facile synthesis and electrochemical properties of carbon-coated ZnO nanotube materials as Li rechargeable battery anodes. ZnO nanorod was first synthesized via a simple hydrothermal method. Subsequently, the material was annealed with a carbon precursor, forming free-standing, carbon-coated ZnO nanotubes. The carbon-coated nanotube structure is beneficial to alleviate volume changes of the ZnO active material during Li insertion and extraction processes as well as to improve the electrochemical reaction kinetics. Electrochemical test results demonstrate that the carbon-coated ZnO nanotube electrodes deliver improved the cycling performance compared with ZnO nanorod electrodes. Better rate performance than carbon-coated ZnO nanoparticle electrodes was also achieved.

Bending Durable and Recyclable Mesostructured Perovskite Solar Cells Based on Superaligned ZnO Nanorod Electrode

Though high‐quality perovskite films can be achieved under low‐temperature, the efficient charge selective materials, such as the most widely used TiO2, require high‐temperature sintering process, hindering mass production with roll‐to‐roll process by using flexible substrate. Here, a low‐temperature (90 °C) process is developed for preparing superaligned ZnO nanorods (SAZNRs), serving as mesostructured scaffold in direct contact with the perovskite layer. By rational design of the length of the SAZNRs, the perovskite solar cell (PSC), reaches a highest power conversion efficiency of ≈13.8% with largely suppressed hysteresis behavior. More importantly, this nano‐array design demonstrates outstanding mechanical robustness after being incorporated onto the flexible substrate, resulting in a performance preservation of 90% after 1000 bending cycles with a curvature radius of 4 mm. Finite element analysis indicate that the reduction of device performance after bending is ascribed to the cracks occurred in AZO stress concentration layer, which is attested by experiment as well. Besides, the SAZNRs ETM can be reused for fabricating new perovskite solar cells with comparable photovoltaic performance in a time‐saving and scalable manner, paving the way for industrial production of PSCs.

Nano-engineering of p–n CuFeO2-ZnO heterojunction photoanode with improved light absorption and charge collection for photoelectrochemical water oxidation

The effective utilization of abundant visible solar light for photoelectrochemical water splitting is a green approach for energy harvesting, to reduce the enormous rise of carbon content in the atmosphere. Here, a novel efficient design strategy for p–n type nano-heterojunction photoanodes is demonstrated, with the goal of improving water splitting efficiency by growing low band gap p-CuFeO2 nanolayers on n-ZnO nanorods by an easy and scalable electrochemical route. The photoconversion efficiency of p–n CuFeO2/ZnO photoanodes is found to be ∼450% higher than that of pristine ZnO nanorod electrodes under visible solar light illumination (λ > 420 nm, intensity 10 mW cm−2). The p–n CuFeO2/ZnO nano-engineering not only boosts the visible light absorption but also resolves limitations regarding effective charge carrier separation and transportation due to interfacial band alignment. This photoanode also shows remarkably enhanced stability, where the formation of p–n nano-heterojunction enhances the easy migration of holes to the electrode/electrolyte interface, and of electrons to the counter electrode (Pt) for hydrogen generation. Therefore, this work demonstrates that p–n nano-engineering is a potential strategy to design light-harvesting electrodes for water splitting and clean energy generation.

Role of AuxPt1–x Clusters in the Enhancement of the Electrochemical Activity of ZnO Nanorod Electrodes

This study quantitatively elucidates the role of metal clusters in the electrochemical activation of metal-oxide nanostructured electrodes. Through the deposition of nearly monodisperse AuxPt1–x (x = 0, 0.5, 1) clusters, smaller than 3 nm, on the ZnO nanorod (NR) electrode surface, a controlled enhancement of charge transfer and activation of electrocatalytic processes was achieved. The interfacial electrical states of the hybrid electrodes were probed by electrochemical impedance spectroscopy (EIS). Analysis of the charge-transfer resistance and interface capacitance, estimated by modeling EIS curves in different bias regimes, indicated the presence of a large amount of active donor states (∼1020 cm–3) at the surface of the ZnO NRs. Decoration of the ZnO NRs with AuxPt1–x clusters strongly increased the charge-transfer process at the cluster–ZnO/electrolyte interface. This induced a more effective depletion of the electron charge available in the donor states of the ZnO NRs, leading to the formation of a...

Detection of 2-Butanone for the Diagnosis of <I>Helicobacter Pylori</I> Using Graphene and ZnO Nanorod Electrodes

Detection of 2-Butanone for the Diagnosis of <I>Helicobacter Pylori</I> Using Graphene and ZnO Nanorod Electrodes

Synthesis and characterization of TiO2 on ZnO-nanorod layer for high-efficiency electrochemiluminescence cell application

In this research paper, we present the fabrication of an electrochemiluminescence (ECL) cell with TiO2 on ZnO-nanorod electrodes via the dip-coating technique. The TiO2 nanoparticles coated on ZnO nanorods (TiO2-ZNRs) were grown on transparent conductive oxide (TCO) glass by the dip-coating technique. The electrode of TiO2-ZNRs for ECL cells has the structure F-doped SnO2 (FTO) glass/Ru(II) complex [Ru(bpy)32+]/TiO2-ZNRs/FTO glass. The TiO2-ZNRs were coated on FTO glass by spin-coating and dip-coating methods. The X-ray diffraction system, scanning electron microscope, and spectral brightness analyzer were used to confirm the successful formation of the structure and the morphological properties. The threshold voltage at the start of light emission was 2.25 V for TiO2-ZNRs and was lower than 3.25 V for bare FTO. The threshold voltage was l2.5 V for ZNRs. The electrical and optical properties of the TiO2-ZNRs ECL cell were 30.76 cd/m2 light intensity, 0.067 mA output current, 0.268 cd/A (at 9.67 mA/cm2) current efficiency, and 0.068 lm/W ECL efficiency at 5 V and 60 Hz. The peak intensity of the TiO2-ZNRs-based ECL cell at a wavelength of 621 nm exhibited a dark orange color and was independent of the type of electrode used. The use of TiO2-ZNRs could improve the ECL efficiency and long-lifetime stability.

Vertically Aligned ZnO/InxSy Core–Shell Nanorods for High Efficient Dye-Sensitized Solar Cells

Innovative vertically aligned ZnO / In x S y nanorod (NR) electrodes were prepared by successive ion layer adsorption and reaction (SILAR) technique. The In x S y shell layer was deposited on top of ZnO NR electrodes of two different lengths, ~1.6 μm and ~3.2 μm. Two sulfur contents on the In x S y shell layer with different layer thicknesses were analyzed. These electrodes were fully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), Energy-dispersive x-ray spectroscopy (EDS), Infrared spectroscopy (FT-IR), x-ray photoelectron spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS) and then applied in dye-sensitized solar cells (DSC). Power conversion efficiency of 2.32% was observed when a low-sulfur content In x S y shell layer was applied in comparison to the stoichiometric In 2 S 3 shell layer (0.21%) or the bare ZnO NRs (0.87%). In the case of low sulfur content, a shell layer of In ( OH )x S y or/and In ( OH )3 is formed as observed by the presence of – OH observed by FTIR analyses. The presence of higher amounts of hydroxide groups modifies the bandgap and work function of the In x S y shell and facilitates dye adsorption, increasing the final solar cell performance.

Enhanced photovoltaic performance of quantum dot-sensitized solar cell fabricated using Al-doped ZnO nanorod electrode

ZnO and Al doped ZnO nanorods have been successfully synthesized on ITO substrate via solgel dip coating method without using any catalyst. The X-ray diffraction studies showed that the Al doped ZnO samples are of hexagonal wurtzite structure. The Al ions were successfully incorporated into the ZnO lattice. Scanning electron microscopy images reveal that the average diameter of ZnO nanorods and Al doped ZnO nanorods are ∼300nm and ∼200nm respectively. The energy dispersive X-ray (EDS) analysis confirmed the presence Al in the ZnO thin films. The CdS quantum dot sensitized Al doped ZnO solar cell exhibited a power conversion efficiency of 1.5%.

Optimization of the photoactivity of conducting polymer covered ZnO nanorod composite electrodes

A simple, reproducible, one-step electrochemical synthesis of vertically aligned ZnO nanorod electrode has been worked out. The gradual decrease in the photoelectrochemical performance of the hexagonal ZnO nanorod electrode indicated rapid photodegradation. In order to prevent the n-type semiconductor from photocorrosion, different conducting polymers were deposited on it. Compo- sition and morphology of the hybrids were controlled by carefully changing the electropolymerization parameter (e.g., deposition charge) for the various N or S containing hetero- cycles. Electrochemical measurements proved that the redox activity of these covering polymer layers was preserved in the hybrid configuration. Photoelectrochemical activity of the polymer-covered ZnO nanorods was masked by thicker layers. Thin films however, successfully inhibited the photocorrosion of ZnO while preserving their photoactivity. Effective protection was evidenced using poly(3,4- ethylenedioxypyrrole) (PEDOP) in comparison with polypyr- role (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT).

Effect of ZnO seed layer thickness on hierarchical ZnO nanorod growth on flexible substrates for application in dye-sensitised solar cells

ZnO nanorod (NR) arrays are considered to be suitable for application in flexible photovoltaic devices due to the high surface-to-volume ratio provided by the one-dimensional nanostructure. Hier- archical ZnO NRs were grown on flexible ITO/PEN substrates by sputtering a compact ZnO seed layer followed by chemical bath deposition. The effect of ZnO NR growth with the variation of the seed layer thickness (50, 100, 300, 500 and 800 nm) was studied. It has been found that by varying the seed layer thickness, the individual rod diameter, density and alignment can be controlled. The SEM images confirmed that relatively thin seed layers give rise to more dense films, whereas thick seed layers result in less dense films. The applications of flexible ZnO NR electrodes were tested by employing them in dye- sensitised solar cells (DSSC). The performance of flexible DSSCs was evaluated by studying the key cell parameters. The effect of the seed layer thickness on DSSC performance was investigated. It has been found that the overall cell efficiency increased when the seed layer thickness was varied from 50 to 500 nm, whereas sharp decrease in efficiency was observed when the thickness was further increased to 800 nm. It was found that a seed layer thickness of 500 nm gave the highest overall efficiency of 0.38 % and incident photon-to-electron conversion efficiency of 6.5 %. As well as having good electrical properties, ZnO NR films grown on ITO/PEN by this method have excellent reproducibility, and NR growth is readily controllable. This shows that these films have a wide range of potential applications including flexible energy harvesting and electronic devices.

Applications of highly ordered paddle wheel like structured ZnO nanorods in dye sensitized solar cells

Highly ordered paddle wheel like structured ZnO nanorods have been prepared by the simple sol–gel hydrothermal method. TiO2 nanoparticles are embedded on hydrothermally grown paddle wheel like structured ZnO nanorods. The TiO2 nanoparticle embedded nanorods were used as a photo-anode in dye sensitized solar cells and their photovoltaic performance was analyzed. The TiO2 nanoparticle embedded paddle wheel like structured ZnO nanorod electrodes enhance the adsorption of dye molecules, charge transport and power conversion efficiency. The crystallinity, presence of TiO2 nanoparticle on ZnO nanorods and morphology of the photo-anodes were characterized by X-ray diffraction and scanning electron microscopy studies. The dye molecules adsorbed by the photo-anode were observed by UV–vis absorption spectra. The efficiency of the TiO2 nanoparticle embedded paddle wheel like structured ZnO nanorod based dye sensitized solar cell is 3.25%.

Self-Assembly of NiO-Coated ZnO Nanorod Electrodes with Core–Shell Nanostructures as Anode Materials for Rechargeable Lithium-Ion Batteries

A porous nickel hydroxide shell was self-assembled by hydrolysis of aqueous nickel chloride in the presence of hexagonal ZnO nanorod template at room temperature. The nickel hydroxide shell converted to cubic NiO after heat treatment at 500 °C. Galvanostatic charge and discharge results indicated that the NiO-coated ZnO nanorod electrode is capable of delivering a higher capacity than the bare ZnO nanorod and carbon-coated ZnO nanorod electrodes especially in high-rate charge and discharge processes. The presence of porous NiO shell might prevent the disintegration of ZnO nanorods because of the large volume change during charge and discharge. In addition, the porous NiO shell ensured good electrical contact of ZnO with the current collector and facilitated the charge transfer and transport of lithium ions. The amount of NiO coated on ZnO nanorods significantly affected the electrochemical performance of ZnO electrode toward lithium. Insufficient NiO shell would not provide enough electrical conductivity and protection against disintegration. When the NiO content was higher than 32.6 wt %, the electrode performance could be significantly improved.

Photovoltaic Performance of ZnO Nanorod and ZnO : CdO Nanocomposite Layers in Dye-Sensitized Solar Cells (DSSCs)

Triphenylene diamine sensitizer comprising donor, electron conducting, and anchoring group is synthesized for a potential application in dye-sensitized solar cells. Absorption spectrum, electrochemical and photovoltaic properties of triphenylene diamine have been investigated. Two different electrodes are used for dye-sensitized solar cells. The performances of ZnO nanorod electrodes are compared to ZnO : CdO nanocomposite electrode. Also, the theoretical calculations for HOMO and LUMO orbitals are used to estimate the photovoltaic properties of organic sensitizer in the design stage. ZnO : CdO nanocomposite electrode-based dye-sensitized solar cell sensitized with organic sensitizer exhibits higher efficiencies than ZnO nanorod electrode. For a typical device, a solar energy conversion efficiency (η) of 0.80 based on ZnO : CdO nanocomposite is achieved under simulated AM 1.5 solar irradiation (100 mW cm−2) with a short circuit photocurrent density (Jsc) of 3.10 mA/cm2, an open-circuit voltage (Voc) of 480 mV, and a fill factor (FF) of 0.57. These results suggest that the ZnO : CdO nanocomposite system is a good selection and a promising candidate for electrode system in dye-sensitized solar cells.