Nanorod Array Electrode Research Articles

Reduced Graphene Oxide Decorated Titanium Nitride Nanorod Array Electrodes for Electrochemical Applications

This work describes the fabrication and characterization of a new high surface area nanocomposite electrode containing reduced graphene oxide (rGO) and titanium nitride (TiN) for electrochemical applications. This approach involves electrochemically depositing rGO on a high surface area TiN nanorod array electrode to form a new nanocomposite electrode. The TiN nanorod array was first formed by the glancing angle deposition technique in a DC (Direct Current) sputtering system. GO flakes of ~1.5 μm in diameter, as confirmed by Dynamic Light Scattering (DLS), were electrodeposited on the nanostructured TiN electrode via the application of a fixed potential for one hour. The surface morphology of the as-prepared rGO/TiN electrode was evaluated by scanning electron microscopy (SEM) and the presence of rGO on TiN was confirmed by Raman Microscopy. The CV shows an increase in the capacitive current at rGO/TiN as compared to TiN. The rGO decorated TiN electrode was then used for analyzing the electrocatalytic oxidation of ascorbic acid and dopamine, and the reduction of nitrate by CV and linear sweep voltammetry (LSV), respectively. CV or LSV show that the electrochemical kinetics of these three analytes are significantly faster on rGO/TiN than TiN itself. Overall, the rGO/TiN electrode showed better electrochemical behavior for biomolecules like ascorbic acid and dopamine as well as another target analyte, nitrate ions, compared to TiN by itself.

Oxygen vacancy-regulated nanorod array electrodes for boosting the electrocatalytic synthesis of ammonia from nitrate wastewater.

The adsorption of nitrate is the key to enhancing the electrocatalytic nitrate reduction reaction (NitRR). Herein, a typical hydrolysis-coupled redox (HCR) reaction has been designed to prepare unique 3D Cu/Fe2O3 core-shell nanorod array cathodes with controllable oxygen vacancy concentrations for NitRR. The optimal Cu/Fe2O3-13 achieves a high nitrate conversion of 99.10% and ammonia selectivity of 98.30%. The outstanding electrochemical performance is attributed to the enhancement mechanism of OVs and a unique nanorod array structure with a high density of surface-exposed OVs and high-throughput transport pathways for ion-aspects.

Enhancing Energy Storage via Confining Sulfite Anions onto Iron Oxide/Poly(3,4-Ethylenedioxythiophene) Heterointerface.

Multiple oxidation-state metal oxide has presented a promising charge storage capability for aqueous supercapacitors (SCs); however, the ion insert/deinsert behavior in the bulk phase generally gives a sluggish reaction kinetic and considerable volume effect. Herein, iron oxide/poly(3,4-ethylenedioxythiophene) (Fe2O3/PEDOT) heterointerface was constructed and enabled boosted Faradaic pseudocapacitance by dual-ion-involved redox reactions in Na2SO3 electrolytes. The Fe2O3/PEDOT interface served as a "bridge" to couple electrode and anion SO32- and exhibited a strong force and stable bonding with SO32-, thus providing an additional Faradaic charge storage contribution for SCs. Significantly, the PEDOT-capsulated Fe2O3 nanorod array (Fe2O3@PEDOT) electrode presented a specific capacitance of 338 mF cm-2 at 1 mA cm-2 with 1 M Na2SO3 electrolyte, which was twice that of the pristine Fe2O3 nanorod electrode. The boosted interfaced Faradaic reaction of SO32- partially hindered the intercalation of Na+ in the Fe2O3 bulk phase, efficiently favoring the electrochemical stability.

Rational Construction of a Triple-Phase Reaction Zone Using CuO-Based Heterostructure Nanoarrays for Enhanced Water Oxidation Reaction.

The development of high-efficiency oxygen evolution reaction (OER) electrocatalysts for the production and conversion of clean energy is paramount yet also full of challenges. Herein, we proposed a simple and universal method to precisely fabricate the hierarchically structured CuO/TMOs loaded on Cu foil (CuO/TMOs/CF) (TMO represents Mn3O4, NiO, CoO, and CuO) nanorod-array electrodes as a highly active and stable OER electrocatalyst, employing Cu(OH)2/CF as a self-sacrificing template by the subsequent H2O2-induced chemical deposition (HiCD) and pyrolysis process. Taking CuO/Mn3O4/CF as an example, we systematically investigated its structure-performance relationship via experimental and theoretical explorations. The enhanced OER activity can be ascribed to the rational design of the nanoarray with multiple synergistic effects of abundant active sites, excellent electronic conductivity of the metallic Cu foil substrate, strong interface charge transfer, and quasi-superhydrophilic/superaerophobic property. Consequently, the optimal CuO/Mn3O4/CF presents an overpotential of 293 mV to achieve a current density of 20 mA cm-2 in 1.0 M KOH media, comparable to that of commercial RuO2 (282 mV), delivering excellent durability by the electrolysis of water at a potential of around 1.60 V [vs reversible hydrogen electrode (RHE)] without evident degeneration. This work might offer a feasible scheme for developing a hybrid nanoarray OER electrocatalyst via regulating electron transportation and mass transfer.

Single bubble dynamics on a TiO2 photoelectrode surface during photoelectrochemical water splitting

The bubble evolution on the photoelectrode surface in photoelectrochemical water splitting can change the mass transfer of gaseous products and induce additional resistance. In this paper, the growth and nucleation of a single oxygen bubble over a titanium dioxide (TiO2) nanorod-array electrode was investigated. The results indicate that the resistance decreases significantly due to the decrease of dissolved gas concentration at the beginning of bubble growth period. Because the effect of electrolyte constriction offsets the concentration-lowering effect, the resistance is almost constant in the later stage of bubble growth. The increase of light intensity leads to longer bubble waiting time and growth time, larger bubble diameter and smaller contact angle. Moreover, the bubble nucleation frequency increases due to the improved reaction rates at higher potential. A force balance model is constructed to predict the bubble departure diameter. It is found that the forces preventing the bubble departure from the photoelectrode surface are mainly surface tension and Marangoni force, which account for 82% and 18%, respectively.

Synthesis of NiSe nanorod array structure as a binder-free cathode for an aqueous rechargeable Ni–Zn battery

Co0.33Ni0.67Se nanorod array electrode synthesized by a simple two-step solvothermal method on Ni foam and demonstrated good electrochemical performances for supercapacitor and aqueous rechargeable Ni–Zn battery.

Construction of hierarchical Cu2+1O@NiCoAl-layered double hydroxide nanorod arrays electrode for high-performance supercapacitor

Abstract Here we report the construction of a kind of electrode material with excellent capacitive performance composed of Ni, Co and Al layered double hydroxide (NiCoAl-LDH) nanosheets branched on Cu2+1O nanorod arrays (Cu2+1O@NiCoAl-LDH) on copper foam current collector, which is obtained via an easy in situ chemical oxidation reaction in combination with hydrothermal method. The as-prepared Cu2+1O@NiCoAl-LDH electrode presents observably enhanced electrochemical performance with an outstanding specific capacitance (2932 F g−1 at 0.75 A g−1), and extraordinary cycling stability (94.27% of the initial capacitance maintained after GCD test for 6000 cycles), which are much superior to those of Cu(OH)2 and Cu2+1O@NiCo-LDH electrodes. Additionally, the Cu2+1O@NiCoAl-LDH nanorod arrays, as a positive electrode material, can also be utilized to assemble a hybrid supercapacitor (HSC) device with an activated carbon (AC) electrode (negative electrode). The energy density of the assembled HSC device can up to 61.83 Wh kg−1 with a working voltage of 1.5 V, meanwhile the power density is 749.93 W kg−1. Furthermore, a few Light Emitting Diode (LED) indicators with different shape combination can be lit up by the assembled HSC devices, demonstrating the practicability of the HSC device.

Constructing a TiO2/PDA core/shell nanorod array electrode as a highly sensitive and stable photoelectrochemical glucose biosensor.

Developing stable PEC glucose biosensors with high sensitivity and low detection limit is highly desirable in the biosensor field. Herein, a highly stable and sensitive enzymatic glucose photoelectrochemical biosensor is rationally designed and fabricated by constructing TiO2/PDA core/shell nanorod arrays. The TiO2 nanorod as the core has the advantages of increasing charge transportation towards interfaces and enhancing the absorption of incident sunlight due to its single-crystal nature and one dimensional array structure. The PDA shell not only induces a rapid charge transfer across the interfaces but also stabilizes the biosensor performance by avoiding the decomposition of enzymes induced by the strong oxidizing holes from the TiO2 core. A remarkable performance with an ultrahigh sensitivity of 57.72 μA mM−1 cm−2, a linear range of 0.2–1.0 mM, a glucose detection limit of 0.0285 mM (S/N = 3) and a high sensitivity of 8.75 μA mM−1 cm−2 in a dynamic range of 1.0–6.0 mM were obtained for the glucose detection. This study might provide a strategy for constructing inorganic/organic core/shell structures with a satisfactory PEC performance.

Gold-Nanoparticle-Decorated Titanium Nitride Electrodes Prepared by Glancing-Angle Deposition for Sensing Applications

Titanium nitride (TiN) and gold (Au)-decorated TiN nanorod array electrodes were fabricated on Au substrates using glancing-angle deposition (GLAD), and the electrochemical properties of these materials were investigated in potassium chloride and buffered solutions containing potassium ferricyanide, ascorbic acid, uric acid, and dopamine. Cross-sectional scanning electron microscopy images depict an array of vertical nanocolumns that are ∼30 nm in width and ∼300 nm in height with sharp pointed apexes. The atomic percent ratio of N to Ti is 40:60, as revealed by X-ray photoelectron spectroscopy. Decoration of the GLAD-produced TiN nanorods with Au nanoparticles reduces the width between nanocolumns from ∼23 to ∼15 nm and improves the electroactivity of the electrodes. The capacitive current in potassium chloride increases by a factor of 2, and the electron-transfer rate of potassium ferricyanide increased by 4. The addition of Au nanoparticles to the TiN nanorod support also significantly improves the elec...

Synthesis of AuPd nanoparticle-decorated graphene-coated ZnO nanorod arrays with enhanced photoelectrochemical performance and stability.

AuPd nanoparticle-decorated graphene-coated ZnO nanorod (ZNR) array electrodes (ZNR@Gr/AuPd) were synthesized via electrostatic self-assembly followed by solution reduction methods. The morphologies of ZNR@Gr/AuPd were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM), which indicated that ZNR was well-coated by graphene with 3–5 layers and uniformly decorated with AuPd nanoparticles (about 5 nm). UV-Vis diffuse reflectance and photoluminescence spectra were obtained to analyze the optical properties. The photoelectrochemical (PEC) properties were also evaluated; the results indicated that the photocurrent density was 2.27 mA cm−2 at 0.8 V versus Ag/AgCl, which was 7.1 times that of bare ZNR. The sample also displayed enhanced PEC stability (91.3%), which prevented photocorrosion. Finally, a proposed PEC mechanism of ZNR@Gr/AuPd was illustrated to explain the charge transfer and the role of graphene and AuPd nanoparticles in the improvement of PEC performance and stability. The ZNR@Gr/AuPd electrode shows excellent PEC performance and stability, exhibiting promising potential in the generation of H2.

Efficient bifunctional vanadium-doped Ni3S2 nanorod array for overall water splitting

A nickel foam-supported vanadium-doped Ni3S2 nanorod array electrode has been demonstrated as a robust bifunctional electrocatalyst for overall water splitting.

Ti-MOF derived TixFe1−xOy shells boost Fe2O3 nanorod cores for enhanced photoelectrochemical water oxidation

TixFe1−xOy shells, in-situ formed from thermal treatment of a Ti-containing metal organic framework, NH2-MIL-125(Ti), significantly boost the photoelectrochemical water oxidation efficiency of Fe2O3 nanorod cores. The NH2-MIL-125(Ti) was coated on the surface of the Fe2O3 nanorods with a solvothermal process, followed by a two step calcination to afford the TixFe1−xOy shell/Fe2O3 core nanorod arrays. The TixFe1−xOy shell/Fe2O3 core nanorod array electrode exhibited much improved photoelectrochemical activities over the pristine Fe2O3 nanorod array electrode, boosting photo-current densities to 26.7 folds of that achieved by the pristine Fe2O3 nanorod array electrode at 1.23 V (vs. RHE) under illumination of simulated sun light of AM 1.5 G. The success may be attributed to the much enhanced charge separation enabled by the hole trapping heterojunction of TixFe1−xOy shell/Fe2O3 core. The photoelectrochemical stability of the TixFe1−xOy shell/Fe2O3 core nanorod array electrode was excellent, retaining 98.9% of the initial photo-current density after a 5 h continuous operation. This work is the first demonstration of MOF derived core-shell heterojunction for large improvements of PEC water splitting efficiencies, and can be readily extended to a wide range of catalyst design.

Suppressing volume change and in situ electrochemical atom force microscopy observation during the lithiation/delithiation process for CuO nanorod array electrodes

A big challenge in the high-performance transition metal oxide anode for lithium-ion batteries (LIBs) is relieving the volume changes during the lithiation/delithiation. In this work, CuO nanorod array was produced via glancing angle deposition and directly used as anode materials for thin film electrodes of LIBs. The obtained CuO nanorod array anodes show good LIB performance with a capacity of 220 μAh/cm2/μm tested at 100 μA/cm2 after 80 cycles and excellent rate performance. The obtained properties for CuO nanorod array anodes were much better than thin film anodes without nanorod array structure. In addition, the in situ electrochemical atom force microscopy (EC-AFM) characterization has been used to reveal the enhanced mechanism of CuO nanorod array anodes. On the one hand, CuO nanorods within the electrodes may serve as the hosts for Li+, and ease intercalation by shortening Li+ ion diffusion pathways, resulting in the remarkable cycling stability and rate performance. On the other hand, the “breathing” of CuO nanorod array electrode clearly observed by in situ EC-AFM with the appearance and disappearance of cracks, demonstrated that the nanorod array may act as a buffering to alleviate the giant volume variations during the cycling. As a result, the remarkable stability of the CuO nanorod array electrode allowed its use in a full lithium-ion cell with a pervasive LiCoO2 thin film cathode. Additionally, we also observed the SEI formed on the surface of electrode during cycling, which may benefit the further studies on transition metal oxide as anodes for LIBs.

Hierarchically phosphorus doped bimetallic nitrides arrays with unique interfaces for efficient water splitting

Engineering of nanomaterials with abundant interfaces is vital but remain challenges for the electrocatalysts of renewable energy conversion systems. Benefitting from the efficient synthetic approach, a high degree of controlled design can be attained for the first time in the synthesis of hierarchical catalysts P-NiMo4N5@Ni, in which different morphologies arrays on nickel foam (NF) were achieved via introducing polyoxometalates with the capability of controlling the nucleation and crystal growth. Especially, the optimized twist braid nitrides nanorod arrays electrode P-NiMo4N5@Ni-1 with high surface-to-volume ratio of energetic actives exhibited unprecedented activity as a bifunctional electrocatalyst for water splitting, approaching 50 and 100 mA cm−2 at low cell voltages of 1.59 and 1.66 V, respectively, which is one of the best electrolytic water catalysts. The insights gained through this work may provide novel approach for designing other arrays derived from polyoxometalates with unique surfaces as versatile electrode and provide a design platform to prepare the invertible oxides catalysts from nitrides at high potential with enhanced catalytic performance.

In situ formation of consubstantial NiCo2S4 nanorod arrays toward self-standing electrode for high activity supercapacitors and overall water splitting

Developing high-efficiency, low-cost and environmental friendly electrode materials for both supercapacitors and overall water splitting are significant for renewable energy storage and conversion. Herein, we report a facile consubstantial growth strategy to fabricate subuliform NiCo2S4 nanorod arrays electrode through an in situ growing process, utilizing self-sacrificial Ni foam as substrate and Ni resource. Benefitting from the unique structures, the subuliform NiCo2S4 nanorods can be directly serve as binder-free, trifunctional electrode for overall water splitting with excellent electrocatalytic activity (oxygen evolution reaction with low overpotential of 220 mV at 30 mA cm−2 and hydrogen evolution reaction with low overpotential of 222 mV at 30 mA cm−2) and also as a promising pseudocapacitance electrode with superior electrochemical performance and good stability (high areal capacitance of 8.85 F cm−2 at a current density of 10 mA cm−2 and 94.96% capacitive retention after 10000 cycles). The present work highlights the remarkable advantages of the self-sacrificial strategy for the design of high-performance multifunctional electrode materials.

High sensitivity of TiO2 nanorod array electrode for photoelectrochemical glucose sensor and its photo fuel cell application

Due to the separation of the excitation source and detection signal, the use of photoelectrochemical (PEC) glucose sensors is regarded as a promising electrochemical approach offering high sensitivity for glucose analysis by photoelectrocatalytic oxidation of glucose. In this study, we present a PEC glucose sensor based on TiO2 nanorod array (TiO2NRA) electrode, exhibiting high sensitivity of around 200 μA cm−2 mM−1 in glucose detection for the concentrations in the range of 0.01–0.20 mM. Moreover, the TiO2NRA can be fabricated and used in a photo fuel cell (PFC) to generate electricity. This investigation expands the applications of TiO2 and provides a high sensitive way for glucose sensing.

Hybrid MnO/C nanorod arrays derived from a MOF precursor with enhanced oxygen evolution activity

We have successfully synthesized MnO/C nanorod arrays which is the first report of MnO/C nanoarrays derived from Mn-MOFs nanoarrays as precursor, and the contents of C are dependent on the temperature of calcinations of MOFs. The MnO/C-350 nanorod array electrode materials exhibit excellent electrocatalytic performances for oxygen evolution reaction; only a small over-potential of 329 mV versus RHE is needed for a current density of 20 mA cm−2 with a Tafel slope of 70.02 mV dec−1, and the material of MnO/C nanoarrays are superior to all reported MnO catalysts.

Fabrication of the porous MnCo2O4 nanorod arrays on Ni foam as an advanced electrode for asymmetric supercapacitors

In this work, the porous MnCo2O4 nanorod arrays on three-dimensional Ni foam (PMCN@NF) as electrode material have been fabricated through a mild co-precipitating reaction at room temperature followed by a subsequent thermal treatment. The PMCN@NF electrode material have been characterized by XRD, SEM, TEM, EDS-mapping, BET and XPS technologies. The capacitive performances of the PMCN@NF electrode have been investigated by CV, GCD and EIS. This porous structure possesses an average diameter of ∼6.7 nm. BET interface area is measured to be 105.6 m2 g−1 for this PMCN@NF electrode. This PMCN@NF electrode exhibits the good capacitance of 845.6 F g−1 (tested condition: 1 ampere per gram, 1 A g−1). After 2000 cycles test, it shows a 90.2% retention for specific capacitance of the first test. The MnCo2O4//rGO asymmetric supercapacitor with the stable opening voltage of 1.6 V delivers a maximum energy density of 53.7 Wh kg−1 (when the power density is 1600 W kg−1). When this power density up to 8000 W kg−1, it still achieves an energy density of 31.6 Wh kg−1. The cyclic stability of this device after 5000 cycles can achieve an initial capacitance retention of 82.0%. These results indicate that the porous MnCo2O4 nanorod arrays electrode material is a promising functional material for advanced energy conversion and storage equipment.

Dynamics of single bubble departure from TiO2 nanorod-array photoelectrode

Bubble evolution from photo(electro)catalytic water splitting plays a vital role in the interfacial mass transport on photocatalyst surface. However, little success has been achieved to optimize this process, restricted by the poor understanding. Herein, taking photoelectrochemical (PEC) water splitting over a titanium dioxide (TiO2) nanorod-array electrode as a model system, experiments were performed to study single oxygen bubble dynamics by combining electrochemical measurement and high-speed microscopic imaging. The experimental results indicate that the departure of bubble from photoelectrode is retarded by light irradiation, but the traditional bubble departure criterions fail to predict the bubble departure diameters especially in high light intensity. Additional analysis reveals that the light irradiation causes the Marangoni force acting on the evolving bubble, because it induces temperature rise and generates dissolved gas. A modified force balance model for bubble departure from photoelectrode was developed by adding Marangoni force. This modified model that takes account of the light-induced temperature rise and the dissolved gas, agrees well with the experimental data and can be extended to other photo(electro)catalytic reactions.

Binder-free ZnO@ZnSnO3 quantum dots core-shell nanorod array anodes for lithium-ion batteries

In this work, ZnSnO3 quantum dots (QDs), instead of commonly used conductive carbon, are grown on the ZnO nanorod (NR) array to construct the binder-free ZnO@ZnSnO3 QDs core-shell NR array electrode on carbon cloth for lithium-ion battery. The ZnO@ZnSnO3 QDs core-shell NR array electrode exhibits excellent lithium storage performance with an improved cycling performance and superior rate capability compared to the ZnO NR array electrode. At a current density of 200 mAg−1, 15.8% capacity loss is acquired in the ZnO@ZnSnO3 QDs core-shell NR array electrode after 110 cycles with capacity retention of 1073 mAhg−1. Significant increases in reversible capacities from 340 to 545 mAhg−1 and from 95 to 390 mAhg−1 at current densities of 1000 and 2000 mAg−1, respectively, are achieved as the ZnO NR arrays are coated with the ZnSnO3 QD shells. The remarkably improved electrochemical performances result from that the configuration of binder-free ZnO@ZnSnO3 QDs core-shell NR array electrode not only facilitates the charge transfer through the solid electrolyte interface and the electronic/ionic conduction boundary as well as lithium ion diffusion but also effectively accommodates the volume change during repeated charge/discharge processes.