Nanorod Electrode Research Articles

The properties of ZnO nanorods modified by Au nanoparticles for galactose biosensor application

Galactose biosensor based on ZnO nanorods were fabricated and modified through the addition of Au nanoparticles. The sol-gel method was utilized to grow ZnO nanorods on indium tin oxide-coated glass substrates (FTO) and the the Au nanoparticles were modified on ZnO nanorods by hydrothermal method. Well aligned hexagonal structured ZnO nanorods with a diameter from 40 to 60 nm were obtained. The Au nanoparticles (Au NPs) were spheres and they had diameter from 6 to 8 nm. After these Au NPs were attached to ZnO nanorods electrode, galactose oxidase enzyme (GOx) was immobilized on this electrode in 3.5 hours to form the working electrode in galactose biosensor (GOx|Au-ZnO|FTO). The cyclic voltammetry method (CV) was used to test the activity of the working electrode in galactose solution 200 mM concentration. The CV result showed that the current intensity of the GOx|ZnO|FTO electrode in galactose solution is about 0.085 µA/mm2. On the other hand, with the GOx|Au-ZnO|FTO electrode, this value increases to 0.2 µA/mm2.

Development of templated RuO2 nanorod and nanosheet electrodes to improve the electrocatalytic activities for chlorine evolution

Development of templated RuO2 nanorod and nanosheet electrodes to improve the electrocatalytic activities for chlorine evolution

Two-dimensional optical fiber-based dye-sensitized solar cell simulation: the effect of different electrodes and dyes

A fiber-based dye-sensitized solar cell (DSSC) is a flexible wearable power resource. In order to find the real properties of the device, this system needs to be simulated. The 2-D optical fiber-based dye-sensitized solar cell is simulated by the finite element method (FEM) in order to explore the effects of $$\hbox {TiO}_{2}$$ nanorod and nanoparticle electrodes thickness and also the effects of different dyes on short-current density and efficiency of the cell. DSSCs with $$\hbox {TiO}_{2}$$ nanorod electrodes had higher short-circuit current and efficiency due to higher electron mobility than those with $$\hbox {TiO}_{2}$$ nanoparticle electrodes. The efficiency of DSSCs made by N719 was higher than that of DSSCs with different other dyes, due to better light absorption and lower rate of recombination.

Fabrication of NiO quantum dot-modified ZnO nanorod arrays for efficient photoelectrochemical water splitting

NiO quantum dot (QD)-modified ZnO nanorod arrays with enhanced photoelectrochemical activity under simulated sunlight were prepared via hydrothermal and drop-drying methods. The results show an obviously decreases in the PL emission intensity and UV-to-Visible emission ratio in NiO QD-modified ZnO, indicating that the recombination of the photogenerated charge carrier is greatly inhibited in the heterojunction. Photocurrent density of the QD-modified nanorod photoanode reaches four times higher than its dark current density; the difference between the photo and dark current densities of QD-modified nanorod electrode is nearly two times higher than that of nanorod electrode. NiO QD-modified ZnO nanorods exhibit excellent photoelectrocatalytic activity owing to their large specific surface area and high separation efficiency of photogenerated electron–hole pairs. This study provides a promising strategy for fabricating highly efficient photoanodes for water splitting by configuring a QD-composed p–n junction.

All-solid-state hybrid supercapacitors based on ZnCo2O4 nanowire arrays and carbon nanorod electrode materials

A high-performance, all-solid-state hybrid supercapacitor (HSC) device was assembled successfully. The ZnCo2O4 nanowire array (NA)/carbon nanotube film (CNTF) positive electrode materials and the assembled device possess areal specific capacitances of 1.019 F cm−2 and 158.08 mF cm−2, respectively. A supernal volume energy density of 49.5 mWh cm−3 was obtained when the voltage window increased to 1.5 V. Moreover, the assembled HSC device exhibited good cycling stability with 90.7% initial capacitance retention after 6000 cycles, and the coulombic efficiency remained near 100%.

Ytterbium modification of pristine and molybdenum-modified hematite electrodes as a strategy for efficient water splitting photoanodes

In recent years, the surface modification of photoanodes for photoelectrochemical water splitting with passivation overlayers has attracted considerable attention. In this respect, a novel, easy and simple methodology to introduce ytterbium oxide as an overlayer on hematite nanorod electrodes is reported in this work. The hematite electrodes were synthesized by means of a chemical bath method, while the ytterbium precursor was introduced through an impregnation method (drop-casting). FE-SEM, XRD, and XPS were employed to characterize the electrode both structurally and morphologically. The reported results reveal that the impregnation method did not cause apparent changes in the hematite structure and morphology, retaining the nanorod structure. Importantly, adding ytterbium yields a significant improvement in the photo-activity (14x at 1.23V vs RHE) without altering significantly the photo-onset. The obtained results suggest that ytterbium induces the formation of a passivating layer, pointing to the fact that other lanthanide oxides would behave similarly. A study of a bifunctional modification of hematite employing ytterbium and molybdenum was also carried out. It reveals that the photocurrent obtained by employing both strategies increases with respect to that obtained with the application of only one of the procedures. Importantly, the order in which modification is done greatly affects the final electrode performance. Understandably, the best results are obtained when Mo is introduced prior to Yb, leading to a synergetic effect in the sense that the resulting photocurrent is larger than the sum of the photocurrents obtained through the application of one of the modifiers.

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...

Preparation of One-dimensional Bamboo-like Cu2-xS@C Nanorods with Enhanced Lithium Storage Properties

Nanostructure construction and surface modification are effective ways to improve the electrochemical performances of electrode materials, especially for the conversion reaction-based materials. In this study, one-dimensional carbon coating bamboo-like Cu2-xS nanorods have been delicately designed in a template-free method. The structure and morphology are well characterized via different instruments such as X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Tested in lithium batteries as the anode, the Cu2-xS@C electrode shows superior electrochemical performances to pristine Cu2-xS. At 1 and 2 C, the Cu2-xS@C nanorod electrode releases 309 and 277mAhg−1 after 300 cycles. At high rates of 15 and 22 C, the electrode still exhibits 269 and 264mAhg−1. The kinetics of electrodes are also investigated by means of cyclic voltammetry (CV) and galvanostatic intermittence titration (GITT) measurements, proving the enhanced electrochemical properties. Thus, the one-dimensional bamboo-like Cu2-xS voided nanorods can be a promising candidate for high-performance batteries.

Optimization of an electrode made from CdS–ZnO nanorods for hydrogen generation from photoelectrochemical splitting of water

Array structures of CdS-sensitized ZnO nanorods (NRs) were fabricated on conducting substrates of indium tin oxide (ITO) that serve as working electrodes in photoelectrochemical (PEC) cells for the generation of hydrogen by splitting of water. The ZnO NRs were synthesized by the hydrothermal method at low temperature with different growth times; structures of CdS-sensitized ZnO NRs were created by the dipping method with various dipping times to optimize the efficiency of splitting water. It was found that maximum photoconversion efficiency of an electrode made from CdS-sensitized ZnO NRs with a growth time of 3 h and a dipping time of 30 min under simulated solar irradiation of 100 mW cm−2 was about 2.7%. The rate of evolution of H2 gas generated from the water-splitting process was also measured. A maximum rate of 22 ml cm−2 was achieved after 1 h exposure, which is higher than with CdS–ZnO NR electrodes in previous studies.

Facile synthesis of low-dimensional SnO2 nanostructures: An investigation of their performance and mechanism of action as anode materials for lithium-ion batteries

Owing to high-energy density of rechargeable lithium-ion batteries (LIBs), they have been investigated as an efficient electrochemical power sources for various energy applications. High theoretical capacities of tin oxide (SnO2) anodes have led us a path to meet the ever-growing demands in the development of high-performance electrode materials for LIBs. In this paper, a facile approach is described for the synthesis of porous low-dimensional nanoparticles and nanorods of SnO2 for application in LIBs with the help of Tween-80 as a surfactant. The SnO2 samples synthesized at different reaction temperatures produced porous nanoparticles and nanorods with average diameters of ~7–10nm and ~70–110nm, respectively. The SnO2 nanoparticle electrodes exhibit a high reversible charge capacity of 641.1mAh/g at 200mA/g after 50 cycles, and a capacity of 340mAh/g even at a high current density of 1000mA/g during the rate tests, whereas the porous nanorod electrodes delivers only 526.3mAh/g at 200mA/g after 50 cycles and 309.4mAh/g at 1000mA/g. It is believed that finer sized SnO2 nanoparticles are much more favorable to trap more Li+ ion during electrochemical cycling, resulting in a large irreversible capacity. In contrast, rapid capacity fading was observed for the porous nanorods, which is the result of their pulverization resulting from repeated cycling.

The formation of Z-scheme CdS/CdO nanorods on FTO substrates: The shell thickness effects on the flat band potentials

CdS/CdO core/shell nanorod photoelectrochemical electrodes were prepared and the working mechanism of n-/n-type Z-scheme band structures is proposed based upon the shell thickness variation. A mild solution chemistry enabled the vertical growth of CdS nanorods on the low-cost conductive glass substrates. The thermal decomposition of Cd(NO3)2·4H2O coated on the CdS nanorod surface successfully introduced CdS/CdO core/shell nanorod electrodes. The formation of CdO shell on CdS nanorods led to the improved photoelectrochemical performance through constructing the n-/n-type Z-scheme band structure. From the Mott-Schottky and the open-circuit potential analyses, the variation in the flat band potentials were monitored to understand the change in the photovoltage of the n-/n-type Z-scheme nanorod electrodes regarding the CdO shell thickness. The core/shell nanorod electrodes having the shell thickness equal to or smaller than the space charge region width exhibited higher photovoltages than those of others. This could be the outcome of the effective charge separation coming from the absence of the bulk region in which the electron transport is disturbed by boundaries. Finally, the optimum CdO shell thickness of CdS/CdO electrodes was determined to be ~2nm and their corresponding photocurrent density was measured to be ~4.35mA/cm2, which is a ~22% increased value compared to that of bare CdS nanorod electrodes.

(Invited) Building Supercapacitors with Earth-Abundant Materials

Hematite (α-Fe2O3) is an environment-friendly and earth-abundant negative electrode material for electrochemical supercapacitors. It has high theoretical specific-capacitance with a suitable operating-potential-window. However, its use as positive electrode material has been limited. In the light of the foregoing, we have investigated the feasibility of using α-Fe2O3 both as positive and negative electrodes to examine its versatility in supercapacitors. On the other hand, MnO2 has been investigated extensively as positive electrode in supercapacitors because of its striking electrochemical activity. But MnO2 exhibits poor electronic conductivity and has low-rate capability. To address this issue, a core-shell nanorod-based positive electrode is designed combining the aforesaid traits of α-Fe2O3 and MnO2. In the core-shell design, MnO2 shell serves as active site for surface or near-surface based fast and reversible faradaic reactions while α-Fe2O3 nanorod core facilitates electron transfer towards current collector. As a consequence of this synergy, α-Fe2O3/MnO2 core-shell nanorod electrode shows improved electrochemical performance in terms of capacitance and rate capability within a potential window of 0-1 V in comparison to individual component materials. Moreover, the assembled asymmetric supercapacitor (ASC) using α-Fe2O3/MnO2 core-shell nanorods and pristine α-Fe2O3 nanorods as respective positive and negative electrodes exhibit a volumetric capacitance of ~ 1.3 F/cm3 at a scan rate of 10 mV/s within a potential window of 0-2 V with nearly 78% capacitance retention at a scan rate of 400 mV/s. Interestingly, the ASC delivers a maximum energy density of ~ 0.46 mWh/cm3 at a current density of 0.5 mA/cm2; the power density of the ASC being 550 mW/cm3 at a current density of 5 mA/cm2 while energy density reaches ~ 0.35 mWh/cm3.

Metal-Organic Frameworks Triggered High-Efficiency Li storage in Fe-Based Polyhedral Nanorods for Lithium-ion Batteries

Recently, metal organic framework (MOF) nanostructures have been frequently reported in the field of energy storage, specifically for Li-ion or Na-ion storage. By inter-separating the active sites of metal cluster and organic ligands, MOF nanostructures are exceptionally promising for realizing fast ion exchange and high-efficiency transportation and addressing the intricate issues that the energy-intensive Li-ion batteries have faced over many years. The related ion-storage mechanism remains to be explored. Is the traditional redox reaction mechanism operative for these nanostructure, as it is for transitional metal oxide? Herein, taking [Fe3O(BDC)3(H2O)2(NO3)]n (Fe-MIL-88B) as an example, an Fe-based metal organic polyhedral nanorods of MIL–88B structure was designed as an anode for Li-ion storage. When tested at 60mAg−1, the nanoporous Fe-MIL–88B polyhedral nanorods retained a reversible capacity of 744.5mAhg−1 for more than 400 cycles. Ex situ characterizations of the post-cycled electrodes revealed that both the transition metal ions and the organic ligands contributed to the high reversible specific capacity. The polyhedral nanorods electrodes held the metal-organic skeleton together throughout the battery operation, although in a somewhat different manner than the pristine ones. This further substantiated that some MOF nanostructures are more appropriate than others for stable lithiation/delithiation processes. State-of-the-art CR2032 full cells showed that a high capacity of 86.8mAhg−1 that was retained after 100 cycles (herein, the capacity for the full cell was calculated based on both the weight of the anode and the cathode, and the charge-discharge rate was 0.25C), when commercial LiFePO4 powders were used as the cathode.

MnO2/g-C3N4 nanocomposite with highly enhanced supercapacitor performance

A novel sandwich-like MnO2/g-C3N4 nanocomposite (NC) based on the integration of high-density MnO2 nanorods (NRs) onto the surfaces of two-dimensional (2D) g-C3N4 sheets has been successfully fabricated through a facile soft chemical route at low temperature. The MnO2/g-C3N4 NC electrode enhanced the supercapacitor (SC) performance, benchmarked against both the bare MnO2 NRs electrode and the MnO2/graphene oxide (GO) NC electrode, exhibiting high specific capacitance of 211 F/g at a current density of 1 A/g, with good rate capacity and cycling stability. The sandwich-like hybrid structure, the unique 2D structure of the g-C3N4 sheets and the presence of nitrogen in the g-C3N4 all contributed to the promising SC performance of the MnO2/g-C3N4 NC. This work demonstrated the advantages of the g-C3N4 sheets over the commonly-used GO sheets in the design of novel hybrid composite for enhanced capacitance performance of MnO2-based electrochemical SCs, and the results could be extended to other electrode materials for SCs.

Comparison of α-NiMoO4 nanorods and hierarchical α-NiMoO4@δ-MnO2 core-shell hybrid nanorod/nanosheet aligned on Ni foam for supercapacitors

Abstract Three-dimensional (3D) hierarchical α-NiMoO 4 @δ-MnO 2 core-shell hybrid nanorods/nanosheets are fabricated directly on Ni foam via a two-step approach which involves hydrothermal and one-pot chelation-mediated aqueous processes. The α-NiMoO 4 nanorods are full covered by ultrathin δ-MnO 2 nanosheets and the morphological evolution process of α-NiMoO 4 @δ-MnO 2 electrode has been investigated by scanning electron microscopy (SEM) at different time intervals. When this hybrid, along with porous Ni foam, is employed as binder-free electrode for supercapacitors, exhibiting high capacitance of 1136 F g −1 at a current density of 2 A g −1 and super-long cycling life with 101.9% retention rate after 5000 cyclic voltammetry cycles, which are much better than the single α-NiMoO 4 nanorod electrode. Moreover, according to the electrochemical impedance spectroscopy (EIS) analysis, it is found that the equivalent series resistance (R s ) and charge transfer resistance (R ct ) of the hybrid electrode are 0.22 Ω and 4.03 Ω, respectively. In view of the outstanding electrochemical performance and the cost-effective fabrication process, this unique integrated nanoarchitecture would hold great promise for electrochemical energy storage.

An efficient electrode based on one-dimensional CoMoO4 nanorods for oxygen evolution reaction

We have developed the CoMoO4 nanorods (NRs) electrode with a specific one-dimensional nanostructure, which exhibited superior electrocatalytic performance for Oxygen Evolution Reaction (OER), such as lower potential (343mV at a current density of 10mAcm−2), Tafel slope (67mV decade−1) and excellent catalytic stability (for 10h). Benefiting from enhancement of electrical conductivity and one-dimensional nanostructure, the CoMoO4 NRs show improved OER activity than Co3O4 cubes, demonstrating that one-dimensional nanostructures could be promising to achieve the OER catalysts with excellent property.

Hematite Nanorod Electrodes Modified with Molybdenum: Photoelectrochemical Studies

AbstractThe preparation of hematite nanorod electrodes modified with molybdenum and their photoelectrochemical behavior for water photooxidation have been addressed in the quest for improved electrodes for water splitting. The hematite nanorods were synthesized through chemical bath deposition, and Mo was added by following two variants of a drop‐casting method based on ammonium heptamolybdate solutions. FE‐SEM, TEM, XRD, and XPS were employed for electrode structural and morphological characterization. The reported results reveal that the impregnation method does not cause significant changes in the hematite structure and nanorod morphology. Importantly, the modification with Mo triggers a significant improvement in the photoactivity of the electrodes, obtaining a photocurrent increase of up to 43×. A specific Mott−Schottky analysis applicable to nanostructured electrodes was performed, revealing that the modification with Mo leads to an increase in electron concentration and to a shift of the flat band potential toward more positive values. A second role of Mo as a passivating agent needs to be invoked to explain the experimental observations. It is worth noting that this modification method allows precise control of the amount of Mo contained in the samples while maintaining the morphology of the electrode.

Controlled synthesis of hierarchical Cu nanosheets @ CuO nanorods as high-performance anode material for lithium-ion batteries

The hierarchical Cu nanosheets @ CuO nanorods nanostructures were fabricated by a facile hydrothermal approach using Cu nanosheets as self-template and nano-substrate in an aqueous solution of NaOH/H2O2. The hierarchical Cu nanosheets @ CuO nanorods electrodes show a high reversible capacity of 620mAh/g after 200 cycles, much higher than that of the pure CuO nanocrystals at a current 0.1C. The excellent electrochemical performance of the hierarchical Cu nanosheets @ CuO nanorods electrode can be attributed to the unique architecture, which not only provides appropriate spaces between nanorod arrays to accommodate the volume change during the discharge/charge process, but also enables fast charge transport owing to the reduced diffusion paths for electrons and induced the Cu nanosheet as the nano-substrates.

α-Fe2O3-Based Core-Shell-Nanorod–Structured Positiveand Negative Electrodes for a High-Performance α-Fe2O3/C//α-Fe2O3/MnOx Asymmetric Supercapacitor

A α-Fe2O3/MnOx core-shell nanorod (NR)-based positive electrode is designed combining the traits of α-Fe2O3 and MnOx with an ultrathin MnOx shell serving as active site for surface or near-surface based fast and reversible faradaic-reactions and α-Fe2O3 NR core facilitating electron transfer toward the current collector. The α-Fe2O3/MnOx core-shell NR electrode shows ameliorated electrochemical performance in terms of capacitance and rate capability within the potential window of 0–1 V in relation to both pristine α-Fe2O3 NR electrode and pristine MnOx thin film electrode. Similarly, α-Fe2O3/C core-shell NR negative electrode is also realized. The assembled α-Fe2O3/C//α-Fe2O3/MnOx core-shell NR asymmetric supercapacitor (ASC) exhibits a volumetric capacitance of ∼ 1.28 F/cm3 at a scan rate of 10 mV/s with nearly 78% capacitance retention at the scan rate of 400 mV/s within a potential window of 0–2 V in aqueous electrolyte medium. Interestingly, the ASC delivers a maximum energy-density of ∼ 0.64 mWh/cm3 and a maximum power-density of 155 mW/cm3, which are higher than the values obtained for α-Fe2O3 //α-Fe2O3/MnOx core-shell NR ASC. Thus the study clearly exhibits the potency of core-shell nano-architechtured electrode design in realizing high-performance, cost-effective and environment-friendly ASCs.