CuO Nanowires Research Articles

Near-Ideal Copper Oxide Heterostructure Design for Photoelectrochemical Water Splitting.

In recent years, photoelectrochemical (PEC) hydrogen generation through water splitting has gained significant attention as a carbon-free solar-to-energy conversion strategy. Among various materials, copper oxides, specifically cupric oxide (CuO) and cuprous oxide (Cu2O), have been extensively investigated for their suitable band positions and prominent performance, particularly in heterostructures. However, previously reported heterostructures, such as CuO layers on Cu2O, are not ideal configurations in terms of photoelectrical properties. In this study, we introduce the fabrication approach for an ideal heterostructure consisting of Cu2O nanowires on a CuO/Cu2O mixed-phase film, fabricated by a straightforward electrochemical/thermal method. The Cu2O nanowire with Cr layer (CNwC) shows potential for solar energy harvesting due to its suitable band positions and narrow bandgap, enabling enhanced photoabsorption across the entire visible spectrum. A thin chromium (Cr) layer underlying the nanostructure contributes to the formation of the ideal copper oxide heterostructure, acting as an adhesive and protective layer. The Cr layer is oxidized during the fabrication process of the CNwC and supports the hydrogen evolution reaction for water splitting. Moreover, the anodization time critically influences the phase composition, size, and density of the nanowires. Under optimal conditions, collective and slanted Cu2O nanowires can absorb incident light, maximizing both photon absorption and photon-to-energy conversion efficiency.

Investigating the effect of Cu underlayer and FTO etching towards photoelectrochemical performance enhancement of Cu2O photoelectrode

Cuprous oxide (Cu2O) exhibits potential as a photoactive material for photoelectrochemical water splitting, owing to its appropriate bandgap, efficient charge carrier separation, and ability to enhance solar-driven hydrogen production. This study investigates the influence of substrate etching, Cu underlayer and Cu2O electrodeposition time, and annealing time on enhancing the photoelectrochemical (PEC) performance. Electrodeposition and thermal oxidation techniques were used to fabricate the Cu2O/Cu/FTOe-A photocathode. It has been observed that FTO etching improves adhesion, light transmission, and efficiency. A Cu underlayer also impacts the PEC performance, wherein an ideal thickness of Cu leads to enhanced PEC performance. This study also focuses on the annealing time that leads to CuO layers and nanowires forming on the Cu2O surface. The structural and chemical changes before and after annealing are confirmed via XRD, XPS, AFM and FESEM analyses. UV–Vis analysis also reveals that the presence of Cu underlayer, FTO etching, and the annealing process affect the electrical properties and light absorption capacities of the Cu2O photoelectrode. Electrochemical impedance analysis (EIS) and Mott-Schottky analysis have provided insights into the enhanced charge transfer properties and band bending in the Cu2O/Cu/FTOe-A, resulting in enhanced PEC performance. Overall, this study provides significant insights into the understanding and enhancement of Cu2O/Cu/FTOe-A photocathodes for potential use in PEC water splitting applications.

Rectifying Heterointerface Facilitated C-N Coupling Dynamics Enables Efficient Urea Electrosynthesis Under Ultralow Potentials.

Electrocatalytic C-N coupling for urea synthesis from carbon dioxide (CO2) and nitrate (NO3-) offers a sustainable alternative to the traditional Bosch-Meiser method. However, the complexity of intermediates in co-reduction hampers simultaneous improvement in urea yield and Faradaic efficiency (FE). Herein, we developed a Cu/Cu2O Mott-Schottky catalyst with nanoscale rectifying heterointerfaces through precise controllable in-situ electroreduction of Cu2O nanowires, achieving notable FE (32.6-47.0%) and substantial yields (6.08-30.4 μmol h-1 cm-2) across a broad range of ultralow applied potentials (0 to -0.3 V vs. RHE). Operando synchrotron radiation-Fourier transform infrared spectroscopy (SR-FTIR) confirmed the formation of *CO intermediates and C-N bonds, subsequently density functional theory (DFT) calculations deciphered that the Cu/Cu2O rectifying heterointerface modulated *CO adsorption, significantly enhancing subsequent C-N coupling dynamics between *CO and *NOH intermediates. This work not only provides a groundbreaking and advanced pathway for C-N coupling, but also offers deep insights into copper-based heterointerface catalysts for urea synthesis.

Rectifying Heterointerface Facilitated C‐N Coupling Dynamics Enables Efficient Urea Electrosynthesis Under Ultralow Potentials

Electrocatalytic C‐N coupling for urea synthesis from carbon dioxide (CO2) and nitrate (NO3‐) offers a sustainable alternative to the traditional Bosch‐Meiser method. However, the complexity of intermediates in co‐reduction hampers simultaneous improvement in urea yield and Faradaic efficiency (FE). Herein, we developed a Cu/Cu2O Mott‐Schottky catalyst with nanoscale rectifying heterointerfaces through precise controllable in‐situ electroreduction of Cu2O nanowires, achieving notable FE (32.6‐47.0%) and substantial yields (6.08‐30.4 μmol h‐1 cm‐2) across a broad range of ultralow applied potentials (0 to ‐0.3 V vs. RHE). Operando synchrotron radiation‐Fourier transform infrared spectroscopy (SR‐FTIR) confirmed the formation of *CO intermediates and C‐N bonds, subsequently density functional theory (DFT) calculations deciphered that the Cu/Cu2O rectifying heterointerface modulated *CO adsorption, significantly enhancing subsequent C‐N coupling dynamics between *CO and *NOH intermediates. This work not only provides a groundbreaking and advanced pathway for C‐N coupling, but also offers deep insights into copper‐based heterointerface catalysts for urea synthesis.

Novel dual-photoelectrode Z-scheme PEC system for efficient TBBPA removal and debromination: Performance and promoting mechanism

Herein, a novel dual-photoelectrode Z-scheme photoelectrocatalytic system is created to achieve efficient synergistic anodic oxidation and cathodic reduction for TBBPA degradation and debromination. Based on the polydopamine-modified N-doped TiO2 nanotubes (PN-TNTs) photoanode and polydopamine-modified Cu2O nanowires (PC-CNWs) photocathode, the degradation, debromination and mineralization were 99.4%, 77.7% and 52.1% at 0.7 V under visible light for 2 h. The introduction of PDA enhances the visible light absorption by the TiO2 photoanode and protects the Cu2O photocathode from photocorrosion. The main active species identified by electron paramagnetic resonance (EPR) and scavenger experiments as •OH and e− were found to promote the degradation and debromination of TBBPA by oxidation and reduction, respectively. The degradation pathway of TBBPA was determined by Density Functional Theory (DFT) calculations and HPLC-MS analyses. Comparing the intermediates of single and dual chambers, it demonstrated that the photocathode was able to achieve the continuous debromination of TBBPA and intermediates, which reduced the toxicity. Finally, the stability, reusability and energy consumption were evaluated, confirming the feasibility of the system.

Reasonable Design and Deep Insight of Efficient Integrated Photorechargeable Li-Ion Batteries by Using a Cu/CuO/Cu2S Electrode.

Herein, Cu-foam-supported CuO nanowire arrays covered with Cu2S nanosheet substrates (Cu/CuO/Cu2S) are adopted as efficient photoelectrodes for photorechargeable lithium-ion batteries (PR-LIBs). The assembled PR-LIB exhibits remarkable solar energy conversion efficiency alongside superior lithium storage capabilities. Without an electrical power supply, the photocharged PR-LIB sustained a discharge process for 63.0 h under a constant current density of 0.05 mA cm-2. The corresponding solar-to-electrical energy conversion efficiency is 4.50%, which is an impressive achievement among recently reported contemporary technologies. Mechanism investigation shows that the Cu/CuO/Cu2S photogenerated carriers augment the extraction and insertion of Li+ according to different oxidation and reduction reactions in the charging and discharging reactions. This research delineates a refined model system and proposes innovative directions for developing efficient heterojunction photoelectrodes, significantly propelling the development of PR-LIB technology.

Exploring Anion Exchange Phase Transformations in 1D Solid Systems

Phase transformations through ion exchange reactions represent a relatively new strategy, offering a promising route for synthesizing complex and metastable morphologies and phases in nanoscaled solid ionic materials, which are challenging or even impossible to achieve through standard bottom-up approaches. Moreover, they provide a unique opportunity to investigate the mechanisms and new, yet unexplored phenomena accompanying the chemical modifications in the solid state. These mechanisms remain largely unknown and unexplored, thereby limiting the full potential of ion exchange reactions as one of the primary synthesis or modification strategies for complex ionic nanomaterials. In this study, copper oxide (CuO) nanowires were prepared via thermal oxidation method and used as a template material to explore oxide-sulfide anion exchange transformation mechanism. Following the synthesis, CuO nanowires underwent treatment with sulfur-containing gases in both thermal and non-thermal environments under various conditions to achieve a controllable exchange of oxygen anions with sulfur. The mechanisms underlying these transformations were unraveled with the use of electron microscopy. The copper oxide–sulfide system is particularly intriguing due to the promising properties of copper oxide and sulfide in gas sensing, solar cells, energy storage systems, and photocatalysis. The full or partial transformation between the two phases can therefore represent a route to manipulate and enhance the properties desired for each application.

Thermal oxidation CuO nanowire gas sensor for ozone detection applications

In this study, cupric oxide nanowires (CuO NWs) on patterned interdigitated electrodes (PIEs) used as ozone (O3) gas sensors, were successfully fabricated using thermal oxidation and the microelectromechanical systems (MEMS) technique. After the thermal oxidation process, CuO NWs with different heights and densities were fabricated using a pure copper seed layer with a thickness ranging from 0.5 μm to 2 μm. In this experiment, a low temperature, low concentration, and repeatable CuO NWs gas sensor was fabricated, which can detect O3 gas at a low concentration of 50 ppb and low temperature of 100°C with a high sensor response (40%). The concentration response of this gas sensor shows an increasing linear trend, with an increase of O3 concentration in the range of 50 ppb - 300 ppb. Additionally, the results indicated that this CuO NWs gas sensor is more selective for O3 than CO, CO2, C2H5OH, C3H6O, NO2, or NH3. While CuO has been less studied in O3 detection compared with other semiconducting metal oxide materials, CuO NWs show potential applications in gas sensing devices for low-temperature and low-concentration O3 environmental monitoring.

Enhancing SERS sensitivity of semiconductors through constructing CuO@TiO2 heterojunctions via atomic layer deposition

Semiconductors hold great promise for surface-enhanced Raman scattering (SERS) applications. Various strategies have been proposed to address the challenge of low SERS sensitivity in semiconductors, with the construction of heterojunctions being among the most effective approaches. In this study, CuO@TiO2 heterojunctions were fabricated by depositing a precisely controlled layer of TiO2 film onto the surface of CuO nanowires (CuO NWs) using the atomic layer deposition (ALD) technique. This approach significantly enhances the SERS sensitivity of CuO NWs, and the SERS performance of the semiconductor heterojunction can be further optimized by accurately adjusting the thickness of TiO2. The SERS activity exhibits systematic variations with the TiO2 thickness across the CuO@TiO2-Rhodamine 6G (R6G) system, with the optimal SERS performance of the heterojunction substrate achieved at a TiO2 thickness of 250 cycles. This finding highlights the substantial influence of TiO2 coating thickness on the photo-induced charge transfer (PICT) processes within the CuO@TiO2-R6G system. Furthermore, CuO@TiO2 heterojunctions demonstrate exceptional stability and uniformity. As a result, this study holds significant importance in enhancing the SERS performance of oxide semiconductors, designing optimal semiconductor heterojunction SERS substrates, and investigating thickness-dependent charge transfer mechanisms in semiconductors.

Size-Dependent Thresholds in CuO Nanowires: Investigation of Growth from Microstructured Thin Films for Gas Sensing.

An experimental characterization of cupric oxide nanowire (CuO NW) growth from thermally oxidized, microstructured Cu thin films is performed. We have systematically studied the influence of the thickness and dimension of Cu layers on the synthesis of CuO NW. The objective was to determine the optimum Cu geometries for increased CuO NWs growth to bridge the gap between adjacent Cu structures directly on the chip for gas sensing applications. Thresholds for CuO-NW growth regarding film thickness and lateral dimensions are identified based on SEM images. For a film thickness of 560 nm, NWs with lengths > 500 nm start to grow from the edges of Cu structures with an area ≥ 4 µm2. NWs growing from the upper surface were observed for an area ≥ 16 µm2. NW growth between adjacent thermally oxidized thin films was analyzed. The study provides information on the most relevant parameters of CuO NWs growth, which is mandatory for integrating CuO NWs as gas sensor components directly on microchips. Based on this result, the gap size of the structure was varied to find the optimum value of 3 µm.

Pt single-atom electrocatalysts at Cu2O nanowires for boosting electrochemical sensing toward glucose

In electrochemical biosensors, rational design and synthesis of high-performance electrochemical glucose sensors based on emerging single-atom catalysts (SACs) are paramount. Herein, a facile approach is proposed for dispersing single-atom doping of cuprous oxide (Cu2O) nanowires with Pt on a copper foam substrate (Pt1/Cu2O@CF) via the electrochemical deposition process. The specific nanostructure of the single-atom catalyst has been elaborately revealed with the aid of atomic resolution scanning transmission electron microscopy (STEM) and X-ray absorption fine structure spectroscopy (XAS). The as-fabricated Pt1/Cu2O@CF biosensor with satisfactory scalability exhibits a low limit of detection (1 μM), ultrahigh sensitivity (31.55 mA mM−1 cm−2), excellent selectivity, and robust reliability toward glucose. The first principles simulations reveal that Pt SAC is beneficial to the adsorption of glucose on the surface and further facilitates the electron transfer for the deprotonation process, resulting in high glucose sensing performance. This work sheds light on the applications of SACs for designing ultrasensitive electrochemical biosensors.

Rapidly photocatalytic degradation of toluene boosted by plasmonic effect and Schottky junction on Pt nanoparticles engineered self-supporting Cu2O nanowires

Photocatalytic degradation indoor toluene is one of the most environment-compatible strategies for manufacturing advanced air purifiers. A novel self-supporting photocatalysts, Pt/Cu2O nanowires growing from Cu mesh were constructed using energy-saving methods. The 5 nm Pt nanoparticles are well dispersed on Cu2O, establishing intimate Pt/Cu2O Schottky junction that curtails electron-hole recombination. Additionally, Pt nanoparticles contribute a plasmonic heating effect and an oscillating electric field for accelerating the photocatalytic rates and enhancing overall catalytic activity. By virtue of the Pt/Cu2O Schottky junction and plasmonic effect of the Pt nanoparticles, toluene is efficiently mineralized into CO2 and H2O. The optimal Pt/Cu2O catalyst achieve a toluene elimination rate of 93.65%, with the mineralization degree high up to 92.23%. This study confirms the practicability of the self-supporting Pt/Cu2O catalyst, which figures out new ideas for designing high-performance photocatalyst for removing typical and toxic volatile organic compounds.

The interfacial synergy of hierarchical FeCoNiP@FeNi-LDH heterojunction for efficient alkaline water splitting

In response to the growing demand for clean, green, and sustainable energy sources, the development of cost-effective and durable high-activity overall water splitting electrocatalysts is urgently needed. In this study, the heterogeneous structure formed by the combination of FeCoNiP and FeNi-LDH was homogeneously dispersed onto CuO nanowires generated by in-situ oxidation of copper foam as a substrate using an electrodeposition method. This multilevel structure exhibits excellent bifunctional properties as an electrode material in alkaline solutions, for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) only 206 mV and 147 mV overpotentials are needed to achieve a current density of 100 mA cm−2 respectively. Full water electrolysis is thus enabled to take place at such a low cell voltage as 1.64 V to reach the current density of 100 mA cm−2, which exhibits a long-term stability of 30 h. These improved electrocatalytic performances stem from the construction of multilevel structures. The X-ray photoelectron spectroscopy suggests that strong electron transfer occurs between heterogeneous structures, thus facilitating the OER and HER process. The dispersion of CuO nanowires not only increases the electrochemically active surface areas but also improves the overall hydrophilic and aerophobic properties. This work highlights the positive effect of multilevel structure in the design of more efficient electrocatalysts and provides a reference for the preparation of other low-cost, high-activity bifunctional electrocatalysts.

Controlled growth of CuO nanowires on Cu grid via thermal oxidation process with enhanced field electron emission properties

Controlled growth of CuO nanowires on Cu grid via thermal oxidation process with enhanced field electron emission properties

Facile synthesis of TiO2 nanothorn-coated Cu2O nanowires with improved stability and performance for photoelectrochemical water splitting

Copper(I) oxide (Cu2O) based photocathodes are promising in photoelectrochemical (PEC) water splitting due to their bandgap, natural abundance, and low cost. However, the stability issues have impeded their practical application. This study presents a solution through a novel photocathode, TiO2 nanothorns-coated Cu2O nanowires (TCNW), synthesized using simple wet chemical methods. TCNW outperformed pristine Cu2O nanowires (CNW), achieving a stable PEC current density of ∼3.8 mA∙cm−2 at 0 V vs RHE, compared to ∼1.9 mA∙cm−2 of CNW. TCNW also displayed an H2 evolution rate of ∼64.2 μmol∙cm−2∙h−1 with a 93.9% faradaic efficiency, whilst CNW reached only ∼6.8 μmol∙cm−2∙h−1 and 37.3%. These improvements stem from the protective TiO2 nanothorn layer, which enhances light absorption (300–500 nm) and improves charge separation and transfer by forming a p-n junction with Cu2O. This work underscores the importance of well-crafted surface p-n junctions and conformal protective layers in optimizing the efficiency and stability.

Photovoltaic-driven electro-reforming of poly (ethylene terephthalate) (PET) waste plastics and nitrate pollutants

The electrochemical conversion of waste plastics and nitrate pollutants has advantages in the simultaneous achievement of value-added chemical production and environmental pollutants remediation. Here, we report a photovoltaic-driven electro-reforming strategy to convert poly (ethylene terephthalate) (PET) to platform chemical formic acid, and simultaneously reduce nitrate to ammonia. This strategy directly uses commercial silicon photovoltaic panel as the power source that achieves the oxidation of PET hydrolysate to produce formic acid by NiCo2O4/N-doped carbon nanotubes (NCNTs) anode, and the reduction of nitrate-containing wastewater to produce ammonia by CuO nanowires (NWs) cathode. This integrated system exhibits a high Faraday efficiency of 98 % for formic acid production and conversion of 90 % for nitrate under 30 mW cm−2 simulated sunlight. This study suggests that photovoltaic-driven electro-reforming of PET waste plastic coupled with nitrate reduction could be a feasible strategy to realize the sustainable production of chemicals from environmental pollutants.

In Situ Fabrication of Hierarchical CuO@CoNi-LDH Composite Structures for High-Performance Supercapacitors.

Layered double hydroxide (LDH) materials, despite their high theoretical capacity, exhibit significant performance degradation with increasing load due to their low conductivity. Simultaneously achieving both high capacity and high rate performance is challenging. Herein, we fabricated vertically aligned CuO nanowires in situ on the copper foam (CF) substrate by alkali-etching combined with the annealing process. Using this as a skeleton, electrochemical deposition technology was used to grow the amorphous α-phase CoNi-LDH nanosheets on its surface. Thanks to the high specific surface area of the CuO skeleton, ultrahigh loading (̃16.36 mg cm-2) was obtained in the fabricated CF/CuO@CoNi-LDH electrode with the cactus-like hierarchical structure, which enhanced the charge transfer and ion diffusion dynamics. The CF/CuO@CoNi-LDH electrode achieved a good combination of high areal capacitance (33.5 F cm-2) and high rate performance (61% capacitance retention as the current density increases 50 times). The assembled asymmetric supercapacitor device demonstrated a maximum potential window of 0-1.6 V and an energy density of 1.7 mWh cm-2 at a power density of 4 mW cm-2. This work provides a feasible strategy for the design and fabrication of high-mass-loading LDH composites for electrochemical energy storage applications.

In-situ fabrication of CuO/ZnO heterojunctions at room temperature for a self-powered UV sensor

This work presents a novel, low-cost, wet chemical fabrication technique to develop a self-powered photonic sensor. Thin films of zinc and copper were DC-sputtered on an ITO-coated glass slide, followed by an in-situ one-step oxidation of copper and zinc to form CuO (copper oxide) and ZnO (zinc oxide) heterojunctions at room temperature. The surface morphologies and chemical compositions characterized by a scanning electron microscope (SEM), X-ray diffraction (XRD), and an X-ray photoelectron spectroscopy (XPS) analysis confirmed the formation of heterojunctions between p-type CuO nanowires and n-type ZnO nanoparticles. The material's light absorbance was measured using ultraviolet-visible (UV–vis) spectroscopy. The fabricated device works in a photovoltaic mode; as photons strike the substrate, the built-in potential separates excitons, resulting in an electrical current without an external bias. The current-voltage characteristics of the device studied using a 365 nm centered laser radiation revealed an ideal p-n junction behavior. The sensor demonstrated stable and reproducible responsivity and photosensitivity of 0.108 A/W and 114, respectively, under a periodic UV radiation condition.

Fabrication of CuO/Au Nanowires on a Copper Substrate for Ultra-Sensitive SERS Sensors

To optimize the surface-enhanced Raman (SERS) phenomenon on the surface of noble metals, gold nanoparticles were synthesized on the surface of nano-sized copper wires to enhance the dispersion of gold particles on the research surface. A simple experimental procedure was carried out in two stages. First, the thin copper substrate was lightly oxidized with ammonium persulfate in an alkaline environment, then incubated at 200oC for 3 hours to form copper nanowires that exist stably on the substrate surface. Immediately afterward, highly uniform CuO/Au nanowires were formed by the chemical reduction of HAuCl4 on the surface of the oxidized copper plate. The results show that gold nanoparticles of about 5 nm were attached to CuO nanowires with a length of up to 10 µm and a diameter between 100 and 300 nm. The X-ray energy dispersive spectrum demonstrated a uniform distribution of gold particles. The CuO/Au structure was used as a SERS substrate to detect methylene blue at a low concentration of 10 pM corresponding to 2 signals at the peaks 1395 cm−1 and 1625 cm−1 as the C-H and C-C deformation vibrations of the aromatic ring. The logarithms of the methylene blue concentrations were linearly proportional to their SERS signal intensity of methylene blue at the peak of 1625 cm-1 with a value R2 = 0.96. The signals of SERS for methylene blue at twelve different points on the material sample showed no significant differences in both intensity and shape of the spectrum, with an RSD value of 5.9%.

Rapid plasma preparation of CuO nanowires for efficient ammonia synthesis

The conversion of nitrate into high-value ammonia (NH3) by electrochemical means can significantly reduce environmental pollution and alleviate the energy crisis. The development of easily prepared, high-performance electrocatalysts and understanding the origins of their catalytic activity are crucial. In this study, we rapidly prepared an electrocatalyst (P-CuO-10/CF) using plasma technology, subsequently employed under neutral and low nitrate concentration conditions for electrochemical ammonia synthesis. In situ Raman spectroscopy revealed that the as-prepared material underwent an in situ phase transformation to CuO/Cu, its actual active phase, and the transformed CuO exists in an amorphous structure. This heterogeneous structure demonstrated superior nitrate conversion performance, achieving an ammonia yield of 3.57 mg h–1 cm−2 at -0.6 V vs RHE and a Faradaic efficiency of 95.7 %. This strategy expands the application scope of copper-based materials in electrocatalysis and highlights the promising uses of plasma-prepared materials for electrocatalytic nitrate reduction to generate NH3.