CuO Nanowires Research Articles

Refinement of Nanoporous Cu by Polyvinylpyrrolidone and Photodegradation of Methyl Orange by Cu2O Nanowires and Nanoporous Cu Photocatalysts

Refinement of nanoporous Cu (NP Cu) by the addition of Polyvinylpyrrolidone (PVP) in HF solution during dealloying of Ti40.6Zr9.4Cu40.6Ni6.3Sn3.1 amorphous ribbons and effect of the surface coverage of Cu2O nanowires obtained by immersing NP Cu in dehydrated ethanol on the photodegradation of methyl orange (MO) pollutants were investigated. The sizes of pores and ligaments of NP Cu decrease significantly with the increase of PVP concentration in the dealloying solutions, accompanied by a drastic decrease in the surface diffusivity and the dislocation defect densities. The surface coverage of Cu2O nanowires becomes higher with an increase of the PVP reagents. The Cu2O nanowires@nanoporous Cu (Cu2O@NP Cu) catalysts show excellent photocatalytic activity towards the degradation of MO under the sunlight due to the existence of large amounts of heterojunctions between Cu2O nanowires and Cu ligaments in nanoscale.

Construction of Cobalt Porphyrin-Modified Cu2O Nanowire Array as a Tandem Electrocatalyst for Enhanced CO2 Reduction to C2 Products.

Here, the molecule-modified Cu-based array is first constructed as the self-supporting tandem catalyst for electrocatalytic CO2 reduction reaction (CO2RR) to C2 products. The modification of cuprous oxide nanowire array on copper mesh (Cu2O@CM) with cobalt(II) tetraphenylporphyrin (CoTPP) molecules is achieved via a simple liquid phase method. The systematical characterizations confirm that the formation of axial coordinated Co-O-Cu bond between Cu2O and CoTPP can significantly promote the dispersion of CoTPP molecules on Cu2O and the electrical properties of CoTPP-Cu2O@CM heterojunction array. Consequently, as compared to Cu2O@CM array, the optimized CoTPP-Cu2O@CM sample as electrocatalyst can realize the 2.08-fold C2 Faraday efficiency (73.2%vs 35.2%) and the 2.54-fold current density (‒52.9vs ‒20.8mAcm-2) at ‒1.1V versus RHE in an H-cell. The comprehensive performance is superior to most of the reported Cu-based materials in the H-cell. Further study reveals that the CoTPP adsorption on Cu2O can restrain the hydrogen evolution reaction, improve the coverage of *CO intermediate, and maintain the existence of Cu(I) at low potential.

Wide detection range for non-enzymatic glucose monitoring by utilizing LDHs-coated CuO nanowires in biological media

Inorganic nanostructured materials show significant potential in improving diabetes treatments by serving as glucose-sensing elements that eliminate the requirement for expensive enzymatic agents. However, most non-enzymatic sensors suffer from limited selectivity and reliability, which compromise their suitability for practical applications to body fluids. In this study, we developed a novel non-enzymatic glucose sensor that exhibits a remarkable selectivity and high detection range (<8 mM) in real human serum. The sensor operated effectively across a wide range of glucose concentrations, with the ability to detect glucose levels of up to 8 mM in human serum. Critically, the sensor demonstrated a significant resistance to interference from other substances, which is a common challenge in biological sensing. Rigorous testing confirmed the precision of the sensor, as evidenced by its impressively low relative standard deviation (RSD) of less than 1.56 %, thereby highlighting its consistent reliability for potential clinical applications. Overall, the CuO nanowires (NWs)-NiFe layered double hydroxides (LDHs) sensor is significantly promising as a reliable, highly reversible, and cost-effective solution for glucose detection and continuous glucose monitoring systems.

Crystal structure optimization of copper oxides for the benzyl alcohol oxidation reaction.

In this work, experimental and theoretical analyses reveal that different types of Cu wires significantly change the adsorption properties of reactant molecules and the benzyl alcohol oxidation reaction performance. In particular, CuO nanowires in situ grown on Cu foam exhibit the best performance with a low potential of 1.39 V at a current density of 200 mA cm-2, high selectivity to benzoic acid production, and good operational stability.

Designing CuO@MnCo2O4 nanowire arrays electrode on copper foam and foil substrates via chemical synthesis methods for asymmetric supercapacitor

In this study, CuO nanowires were grown on copper foam (Cufoam) and copper foil (Cufoil) substrate with a cost-effective anodization method as core, and then MnCo2O4 nanowires were grown by hydrothermal synthesis method and three-dimensional (3D) core-shell nanowire arrays (NWAs) were obtained. The synthesized CuO NWAs, which provide a high surface area, contribute to the capacitance with the faradaic redox reaction and act as a current collector for the MnCo2O4 NWAs. Therefore, the 3D electrode design can increase the redox reaction, shorten the ions diffusion pathway, and exhibit low intrinsic resistance. The areal capacitance values of Cufoil/CuO, Cufoam/CuO, and Cufoam/CuO@MnCo2O4 electrodes were obtained at a current density of 0.5 mA cm−2 as 0.21, 1.02, and 2.82 F cm−2, respectively. The Cufoam/CuO@MnCo2O4 NWAs electrode exhibits excellent cycling stability of 97.3 % retention after 5000 cycles. In addition, an asymmetric supercapacitor (ASC) device was assembled by using the Cufoam/CuO@MnCo2O4 electrode and active carbon (AC) as the positive and negative electrodes, respectively. The ASC device operates in a potential range of 0–1.5 V and an energy density of up to 7.1 × 10−2 mWh cm−2 at a power density of 1.56 mW cm−2. This work may contribute to developing low-cost materials for energy storage devices.

Superhydrophobic, mechanically durable, highly transparent surface covered with CuO/PDMS composite nano-tips using one-step wet oxidation process of Cu/PDMS multilayer

In this study, a mechanically durable, transparent, and superhydrophobic CuO/polydimethylsiloxane (PDMS) composite nano-tips surface was fabricated by a wet oxidation process of a Cu/PDMS multilayer structure. A growth mechanism for the CuO/PDMS composite nano-tips was proposed accounting for the superhydrophobic characteristics of the CuO/PDMS nanostructured surface: During wet oxidation, as CuO nanowires form and grow, the PDMS surface in contact with Cu is dragged up along the CuO nano-tips surface, eventually becoming a CuO/PDMS nanocomposite superhydrophobic surface. The fabricated CuO/PDMS nano-tips surface showed superhydrophobicity with a water contact angle of 158°, and optical transmittance of up to 93.8 % in the 400–700 nm wavelength range. Additionally, the mechanical durability of the fabricated surfaces was also investigated. Repeated touching force (∼1.0 kgf), stretching (∼100 %), and bending (∼100°) 1000-cycle test results confirm the mechanical durability of the CuO/PDMS nanostructured surface. As a mechanically durable, transparent, and superhydrophobic film, the CuO/PDMS nanostructured surface was used as protective film for a touch screen. This study offers novel insights into the durability of artificial superhydrophobic surfaces and the synthesis methods of metal oxide-polymer nanocomposites.

Morphology and valence state evolution of Cu: Unraveling the impact on nitric oxide electroreduction

Ammonia (NH3) serves as a critical component in the fertilizer industry and fume gas denitrification. However, the conventional NH3 production process, namely the Haber-Bosch process, leads to considerable energy consumption and waste gas emissions. To address this, electrocatalytic nitric oxide reduction reaction (NORR) has emerged as a promising strategy to bridge NH3 consumption to NH3 production, harnessing renewable electricity for a sustainable future. Copper (Cu) stands out as a prominent electrocatalyst for NO reduction, given its exceptional NH3 yield and selectivity. However, a crucial aspect that remains insufficiently explored is the effects of morphology and valence states of Cu on the NORR performance. In this investigation, we synthesized CuO nanowires (CuO-NF) and Cu nanocubes (Cu-NF) as cathodes through an in situ growth method. Remarkably, CuO-NF exhibited an impressive NH3 yield of 0.50 ± 0.02 mg cm−2 h−1 at −0.6 V vs. reversible hydrogen electrode (RHE) with faradaic efficiency of 29.68% ± 1.35%, surpassing that of Cu-NF (0.17 ± 0.01 mg cm−2 h−1, 16.18% ± 1.40%). Throughout the electroreduction process, secondary cubes were generated on the CuO-NF surface, preserving their nanosheet cluster morphology, sustained by an abundant supply of subsurface oxygen (s-O) even after an extended duration of 10 h, until s-O depletion ensued. Conversely, Cu-NF exhibited inadequate s-O content, leading to rapid crystal collapse within the same timeframe. The distinctive current–potential relationship, akin to a volcano-type curve, was attributed to distinct NO hydrogenation mechanisms. Further Tafel analysis revealed the exchange current density (i0) and standard heterogeneous rate constant (k0) for CuO-NF, yielding 3.44 × 10−6 A cm−2 and 3.77 × 10−6 cm−2 s−1 when NORR was driven by overpotentials. These findings revealed the potential of CuO-NF for NO reduction and provided insights into the intricate interplay between crystal morphology, valence states, and electrochemical performance.

Rationally designed core-shell of 2D-g-C3N4/Cu2O nanowires heterojunction photocathode for efficient photoelectrochemical water splitting

Copper oxide (Cu2O) is a promising candidate as a high-performance photocathode due to its remarkable cost-to-efficiency ratio for photoelectrochemical (PEC) water splitting. However, fully exploiting the potential of planar Cu2O photocathodes for an efficient PEC performance remains a fundamental challenge owing to the poor light absorption and limited carrier diffusion length. To address these challenges, a graphitic carbon nitride (g-C3N4)/2D-Cu2O nanowires (NWs) with core-shell heterojunction photocathode has developed. The PEC water-splitting analysis reveals that the g-C3N4/Cu2O core-shell NWs photocathode boosted the photocurrent density from 0.83 mA/cm2 to 2.33 mA/cm2 at 0 VRHE (3-fold enhancement) compared with bare Cu2O. The formation of a g-C3N4 shell over the Cu2O core resulted in improved light harvesting as well as facile charge transport from the electrode to the electrolyte. Computational studies also revealed an impressive Gibbs free energy of 0.20 eV for the g-C3N4/Cu2O interface, highlighting its potential as an efficient PEC water-splitting device. These findings demonstrate that incorporating nanostructuring and overlayer strategies can remarkably enhance the PEC performance of Cu2O photocathodes, paving the way for more efficient and cost-effective water-splitting technologies.

Growth and electrochemical properties of CuO nanowires-ZnO microrods composite

We have presented simple two step process to synthesize CuO nanowires - ZnO microrods composite using thermal oxidation and hydrothermal method respectively. The synthesized composite showed monoclinic CuO and hexagonal ZnO. Field emission scanning electron microscopy of the samples showed the randomly oriented CuO nanowires have average diameter ∼200 nm and length ∼10 μm. The ZnO microrods have diameter ∼1 μm and length ∼4 μm. The Raman spectrum of sample of CuO nanowires showed the peaks for Raman active (Ag + 2Bg) modes, while that of composite showed E1 and E2 modes of ZnO indicating lattice disorder and oxygen vacancy, along with Bg mode of CuO. Cyclic voltammetry in 0.1 M NaoH electrolyte of the samples showed pseudocapacitance nature of the material. At scan rate of 10 mV/s the CuO–ZnO composite showed specific capacitance of 57 F/g, while CuO nanowires showed ∼5 mF/g at 5 mV/s scan rate.

CuO@NiCo-LDH core-shell structure for flexible fiber-shaped supercapacitor electrode material

Metal fiber electrodes are of great interest for their excellent electrical conductivity and flexibility, however the limited surface area is unfavorable for the electrochemical performance. Herein, CuO nanowires in-situ growth on one dimensional (1D) Cu wire were obtained by wet chemistry and annealing method, and NiCo-LDH nanoplates were further growth on CuO nanowires by hydrothermal method to fabricate CuO@NiCo-LDH. The combination of CuO nanowires and NiCo-LDH nanoplates creates a three-dimensional (3D) core-shell structure, which improves the specific surface area and the electrochemical properties. In addition, there is a synergistic effect between the highly reactive of NiCo-LDH and the well-conducting of CuO/Cu. The composite presents a high specific capacitance of 1220.4 mF cm−2 at 1 mA cm−2. Moreover, the CuO@NiCo-LDH//activated carbon paper (ACP) asymmetric supercapacitor exhibits an excellent energy density of 20.1 μWh cm−2 at the power density of 556.3 μW cm−2, outstanding cycling stability with specific capacitance retention of 87.1 % after 6000 cycles and good bending performance. This paper provides a novel idea for the reasonable construction of electrode material structure.

Electrical and Thermal Conductivities of Single CuxO Nanowires.

Copper oxide nanowires (NWs) are promising elements for the realization of a wide range of devices for low-power electronics, gas sensors, and energy storage applications, due to their high aspect ratio, low environmental impact, and cost-effective manufacturing. Here, we report on the electrical and thermal properties of copper oxide NWs synthetized through thermal growth directly on copper foil. Structural characterization revealed that the growth process resulted in the formation of vertically aligned NWs on the Cu growth substrate, while the investigation of chemical composition revealed that the NWs were composed of CuO rather than Cu2O. The electrical characterization of single-NW-based devices, in which single NWs were contacted by Cu electrodes, revealed that the NWs were characterized by a conductivity of 7.6 × 10-2 S∙cm-1. The effect of the metal-insulator interface at the NW-electrode contact was analyzed by comparing characterizations in two-terminal and four-terminal configurations. The effective thermal conductivity of single CuO NWs placed on a substrate was measured using Scanning Thermal Microscopy (SThM), providing a value of 2.6 W∙m-1∙K-1, and using a simple Finite Difference model, an estimate for the thermal conductivity of the nanowire itself was obtained as 3.1 W∙m-1∙K-1. By shedding new light on the electrical and thermal properties of single CuO NWs, these results can be exploited for the rational design of a wide range of optoelectronic devices based on NWs.

Ultrasensitive SERS-based detection of prostate cancer exosome using Cu2O–CuO@Ag composite nanowires

Exosome is a recently emerging cancer-associated biomarker for early diagnostic and prognostic owing to their noninvasive, intrinsic stability, and representativeness of primitive cell state. However, the development of convenient and quantitative methods for exosome analysis remains technically challenging. Here, we proposed a cost-effective assay for the direct capture and rapid monitoring of exosomes utilizing the multifunctional surface enhanced Raman scattering (SERS) substrate, which consisted of Cu2O–CuO nanowires prepared by a simple thermo-oxidative growth method and subsequently sputtered with Ag NPs. This reticulate substrate made up of interlaced one-dimensional nanowires that highly favored for exosome recognition and collection. Particularly, the electromagnetic hotspots with high density were uniformly distributed on the nanowires due to uniform physical deposition, facilitating robust SERS property with an enhancement factor (EF) of 3.3 × 108 and signal reproducibility with a relative standard deviation (RSD) of 13%. In addition, the presence of Cu2O–CuO heterojunction enabled further elevation of the SERS performance attributed to the effective charge transfer, triggering a significant chemical enhancement effect. Finally, clinical validation with the serum specimens of prostate cancer patients indicated that the proposed immunosensor possessed great potential for application in rapid cancer screening and diagnosis.

Defect-dependent mechanical and electrical properties of laser-processed CuO nanowires

Narrow bandgap p-type semiconducting metal oxide nanowires (NWs), such as copper oxide (CuO), have gained significant attention for their potential in the development of electrical nano-devices. Tailoring the mechanical and electrical properties of CuO NWs is crucial for optimizing their functionality in specific applications. In this study, we employ nanosecond laser irradiation to precisely modify the properties of individual CuO NWs by inducing point and line defects, including oxygen vacancies and dislocations. Through controlled laser irradiation, we observe a gradual enhancement in the concentration of oxygen vacancies within CuO NWs until reaching a saturation point. The accumulation of vacancies leads to a substantial residual stress, resulting in lattice distortion and misfit. This high residual stress serves as a catalyst for the nucleation of dislocations, subsequently leading to a meaningful enhancement in plasticity. Remarkably, the density of dislocations demonstrates a strong correlation with the duration of laser irradiation. Prolonged irradiation leads to a thermally activated restoration process, where the dislocation configuration transitions from a random distribution to ordered dislocation loops. Mechanical characterization tests indicate that pristine CuO NWs exhibit brittleness, while laser irradiation renders them ductile with improved plasticity. Furthermore, the laser processing of CuO NWs demonstrates an enhancement in their electrical conductivity and optical absorbance.

Reshaping Covalent Nanowires by Exploiting an Unexpected Plasticity Mediated by Deformation Twinning.

Nanowires (NWs) are among the most studied nanostructures as they have numerous promising applications thanks to their various unique properties. Furthermore, the properties of NWs can be tailored during synthesis by introducing structural defects such as nano-twins, periodic polytypes, and kinks, i.e., abrupt changes in their axial direction. Here, this work reports for the first time the postsynthesis formation of such defects, achieved by exploiting a peculiar plasticity that may occur in nanosized covalent materials. Specifically, in this work the authors found that single-crystal CuO NWs can form double kinks when subjected to external mechanical loading. Both the microscopy and atomistic modeling suggest that deformation-induced twinning along the plane is the mechanism behind this effect. In a single case the authors are able to unkink a NW back to its initial straight profile, indicating the possibility of reversible plasticity in CuO NWs, which is supported by the atomistic simulations. The phenomenon reported here provides novel insights into the mechanisms of plastic deformation in covalent NWs and offers potential avenues for developing techniques to customize the shape of NWs postsynthesis and introduce new functionalities.

Two-way rushing travel: Cathodic-anodic coupling of Bi2O3-SnO@CuO nanowires, a bifunctional catalyst with excellent CO2RR and MOR performance for the efficient production of formate

Electrocatalytic carbon dioxide reduction reaction (CO2RR) generates high value-added products and simultaneously reduces excess atmospheric CO2 concentrations, is regarded as a potential approach to achieve carbon neutrality. However, the kinetic process of the anode oxygen evolution reaction (OER) is slow, resulting in a poor electrochemical efficiency of CO2RR. It is a breakthrough to replace OER with methanol oxidation reaction (MOR), which has more advantageous reaction kinetics. Herein, this work proposed a bifunctional catalyst Bi2O3-SnO modified CuO nanowires (Bi2O3-SnO@CuO NWs) with excellent CO2RR and MOR performance. For CO2RR, Bi2O3-SnO@CuO NWs achieved more than 90% formate selectivity at wide potential windows from −0.88 to −1.08 V (vs. reversible hydrogen electrode (RHE)), peaking at 96.6%. Meanwhile, anodic Bi2O3-SnO@CuO NWs achieved 100 mA cm−2 at a low potential of 1.53 V (vs. RHE), possessing nearly 100% formate selectivity ranging from 1.6 to 1.8 V (vs. RHE). Impressively, by coupling cathodic CO2RR and anodic MOR, the integrated electrolytic cell realized co-production of formate (cathode: 94.7% and anode: 97.5%), minimizing the energy input by approximately 69%, compared with CO2RR. This work provided a meaningful perspective for the design of bifunctional catalysts and coupling reaction systems in CO2RR.

Unravelling the Structure Change and Its Catalytic Consequence of CuO Nanowires Towards CO2 Reduction Reaction

The CO2 reduction reaction (CO2RR) is a complex process with many possible products, and maintaining high selectivity for multi-carbon products remains a challenge. Currently, Cu-based catalysts are the only transition metal catalysts that can produce C2 products, and one of the popular Cu-based catalysts is CuO nanowires (NWs). We studied a series of CuO nanowires ranging from 50 to 200 nm for CO2RR using multiple characterization techniques including transmission electron microscopy(TEM), small angle X-ray scattering (SAXS) and in situ X-ray adsorption spectroscopy. We found that there could be an activation process required for such CuO NWs to serve as efficient CO2RR catalysts. The CuO can go through multiple steps resulting in the severe morphology changes during the activation process, confirmed by TEM and SAXS. In situ XAS results showed that the CuO NWs will be reduced from Cu(II) to Cu(0) during the reaction, consistent with our previous work(1). H-cell testing results also indicated the C2 production can be boosted after specific activation pathway, which highlights the importance of catalyst pre-treatment. These findings not only deepen our understanding of CO2RR mechanism but also provide fundamental insights for CO2RR catalysts synthesis. References (1) Soo Hong Lee, Ian Sullivan, David M. Larson, Guiji Liu, Francesca M. Toma, Chengxiang Xiang, and Walter S. Drisdell. ACS Catalysis, 2020, 10(14), 8000-8011 Acknowledgement The authors acknowledge the funding support from the Laboratory Directed Research and Development Program of the Lawrence Berkeley National Laboratory under the U.S. Department of Energy Contract (No. DE-AC02-05CH11231).

Coating the surface of interconnected Cu2O nanowire arrays with HKUST-1 nanocrystals via electrochemical oxidation

Controlling the crystallization of Metal–Organic Frameworks (MOFs) at the nanoscale is currently challenging, and this hinders their utilization for multiple applications including photo(electro)chemistry and sensors. In this work, we show a synthetic protocol that enables the preparation of highly homogeneous Cu2O@MOF nanowires standing on a conductive support with extensive control over the crystallization of the MOF nanoparticles at the surface of the Cu2O nanowires. Cu2O nanowires were first prepared via templated electrodeposition, and then partially converted into the well-known Cu-MOF HKUST-1 by pulsed electrochemical oxidation. We show that the use of PVP as a capping agent during the electrochemical oxidation of Cu2O into HKUST-1 provides control over the growth of the MOF nanocrystals on the surface of the Cu2O nanowires, and that the size of the MOF crystals obtained can be tuned by changing the concentration of PVP dissolved in the electrolyte. In addition, we propose the use of benzoic acid as an alternative to achieve control over the size of the obtained MOF nanocrystals when the use of a capping agent should be avoided.

Photothermal Fabric Based on In Situ Growth of CuO@Cu Fractal Dendrite Fiber for Personal Thermal Management

Advanced personal thermal management fabrics are being developed to realize improved human body thermal comfort and effectively regulate heat exchange between the human body and surroundings. Fiber‐based thermal management fabrics are directly worn on soft and curved multiple curvature human body. Herein, a flexible photothermal fiber based on copper fractal dendrites with abundant CuO nanowires is designed. Well‐aligned Cu fractal dendrite fiber is electrodeposited template freely via a low‐cost and scalable process in an aqueous solution. Then, flexible CuO@Cu fractal dendritic photothermal fiber is fabricated by direct in situ oxidation and calcination of Cu fractal dendrites. Furthermore, the CuO@Cu fractal dendritic photothermal fiber can be woven into photothermal fabric by the traditional jacquard embroidery process. The temperature of photothermal fabric can be adjusted within the range of 35–65 °C by adjusting the number of photothermal fibers, which can be achieved with comfortable wearing of human thermal management and hot compress of hyperthermia to relieve local pain. Therefore, the Cu fractal dendrites have shown considerable potential for promoting the photothermal conversion of flexible personal thermal management.

Synergistic enhancement of external electrical energy in PM filtration with Cu-HHTP@CuO nanowire arrays coated copper mesh

Developing multifunctional purification systems that combine air filtration and antibacterial functionality is a challenging task. However, in designing air filtration materials, achieving a balance between filtration efficiency and pressure drop remains a significant challenge. In this study, we developed a novel filtration material composed of hierarchically 3D Cu-HHTP nanowiskers coated CuO nanowires that were grown in-situ on a copper mesh. Benefitted from the intrinsically electrical conductivity of Cu-HHTP, we combined the composite material with external electrical energy for air filtration. By applying lower electric potential directly (voltage of 5 V), the 3D conductive mesh filter exhibited excellent performances in terms of the PM2.5 removal efficiency (∼99.7%), pressure drop (∼32 Pa at 2 cm s -1), and quality factor (0.187 at 2 cm s -1). Furthermore, after ten cycles of filtration and cleaning, the material maintained a high PM removal rate. In addition to its excellent filtration performance, the composite metal mesh also exhibited outstanding antibacterial activity against both E. coli and S. aureus. The electro-mechanical stability and recyclability of the composite filter make it a cost-effective and environmentally friendly solution for air purification, with promising potential for improving air quality.

Self-supported NiO/CuO electrodes to boost urea oxidation in direct urea fuel cells

Direct urea fuel cells (DUFCs) can be used to treat residual wastewater while generating electricity. Herein, self-supported electrodes consisting of NiO nanosheets vertically grown on CuO nanowires are synthesized to realize the urea oxidation reaction (UOR). Such electrodes show excellent UOR performance requiring 1.39 V vs. RHE to achieve 100 mA/cm2. Besides, DUFCs provide open circuit voltages and power densities up to 0.88 V and 11.35 mW/cm2. Electrochemical characterization and Raman spectroscopy prove the formation of NiOOH to enable the UOR. Mott-Schottky analysis and UV photoelectron spectroscopy show the NiO/CuO p-p heterostructure to facilitate the charge transfer from CuO nanowires to NiO nanosheets. Besides, at a local level, density functional theory calculations show that the presence of CuO modulates the electronic states of Ni at the very NiOOH/CuO interface, which results in stretched Ni-O bonds and a uniquely elongated N-H bond of urea that favors its oxidation.