Diffusion Phenomena Research Articles

Electrochemical Hydrogen Compression and Its Optimization through Computational Modeling

Climate change resulting from the heavy use of fossil fuels poses a serious threat to our environment. It is critically important to find alternatives to combustion-based energy technologies and promote renewable energy production. Hydrogen is a leading candidate for the transportation sector as a carbon-free fuel with high energy density. Hydrogen can be produced in a carbon-neutral manner via water electrolysis and other means. However, the establishment of the hydrogen infrastructure still faces serious challenges such as storage. Due to its lightweight nature, hydrogen is very difficult to store either as a compressed gas or as a liquid. Typically, hydrogen is compressed using mechanical compressors which contain moving parts that require frequent maintenance adding to their cost and complexity. Electrochemical compression (ECC) is a promising alternative to mechanical compressors. ECC is an electrochemical device that uses a proton exchange membrane (PEM) to compress the gas. When a voltage is applied across the PEM, low-pressure hydrogen supplied to the anode is oxidized to generate protons and electrons. The electrons are driven through the external circuit by the power source, whereas the protons travel through the PEM towards the cathode. The protons and electrons recombine via the cathodic reduction to obtain hydrogen at elevated pressure. The currently available knowledge base regarding electrochemical compressors has mainly resulted from experimental studies and less attention has been paid to modeling. The current work presents a comprehensive three-dimensional model of a single cell ECC that incorporates the relevant electrochemical phenomena as well as physical processes including water transport. It also takes into account the important phenomenon of back diffusion due to the pressure difference between the cathode and anode that limits the achievable pressure in the cathode compartment. Simulations were conducted for the pressurized cathode case . It was observed that back diffusion limits the compression ratio to a value well below that predicted by Nernst equation. Additionally, the effects of membrane thickness, temperature, and applied voltage on ECC performance are analyzed. The results show that there is a tradeoff between different objectives that must be addressed to optimize the ECC process. For example, thinner membranes permit faster compression rates but at the cost of increased back diffusion. Similarly, higher temperatures improve the pressure efficiency and the compression rate but at a higher operational cost. The results also show that ECC is more efficient at lower voltages because the associated compression ratio is smaller which consequently reduces back diffusion; however, such small voltages do not allow higher pressures. As a result of these tradeoffs, all design parameters need to be optimized simultaneously. This study offers valuable insights on the effect of different parameters on ECC performance. The results suggest that ECC is a viable alternative to conventional technologies for hydrogen compression. Back diffusion significantly reduces ECC efficiency; therefore, ECCs would benefit from membranes with low hydrogen diffusivity. The results provide a foundation for the modeling, analysis, and optimization of a full scale ECC system. Keywords—Hydrogen; Computational Model; Back Diffusion; Electrochemical Compression; Optimization;

Lithium Ion Transport in Al-Doped LiZr2(PO4)3 Solid Electrolyte for Li-Air Batteries: Experimental and Molecular Dynamics Study with a Touch of Machine Learning

In the last few decades, crystalline group of NASICON due to its high ionic conductivity have experienced a sharp development and became a promising candidate for the future lithium batteries. To choose the right candidate for solid electrolyte among NASICON group we employed machine learning assisted logistic regression model. Lithium Zirconium Phosphate (LZP) is selected based on the results from the ML tool. We focused on the Al doping effects on the pure LZP and also the diffusion phenomenon of Li-ion due to temperature variations using molecular dynamics simulations. LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) tool had been used for the purpose mentioned. These simulations were based on the Buckingham potentials. The framework of Li1+xAlxZr2-x(PO4)3 solid electrolyte for Li-air batteries have been analyzed at different temperatures. The computational results clearly fit in with the experimental results and hence validating the computational code. The Al doping significantly effects both the Li-ion conductivity and the diffusivity and confirms as a promising candidate to be used as solid electrolyte in Li-air batteries. Acknowledgement This work was supported by the National Research Foundation (NRF) of Korea funded by the Korean government (2020R1A4A1019227, 2020R1A2C1012439, & 2018R1D1A1B07048307). References (1) Xu, H. H.; Wang, S. F.; Wilson, H.; Zhao, F.; Manthiram, A. Y-Doped NASICON-Type LiZr2(PO4)3 Solid Electrolytes for Lithium Metal Batteries. Chemistry of Materials, 29 (17) (2017) 7206-7212, DOI: 10.1021/acs.chemmater.7b01463(2) Noda, Y.; Nakano, K.; Takeda, H.; Kotobuki, M.; Lu, L.; Nakayama, M. Computational and Experimental Investigation of the Electrochemical Stability and Li-Ion Conduction Mechanism of LiZr2(PO4)3. Chemistry of Materials, 29 (17) (2017) 8983-8991, DOI: 10.1021/acs.chemmater.7b01703(3) I. N. Reddy, B. Akkinepally, C. V. Reddy, A. Sreedhar, T. J. Ko, and J. Shim, "A systematic study of annealing environment and Al dopant effect on NASICON-type LiZr2(PO4)3 solid electrolyte," Ionics, 26(9) (2020) 4287-98, DOI: 10.1007/s11581-020-03622-5

Remediation of H2S gas using reusable UV-activated Fe2O3-containing ZSM-5 and Silica

We report H2S gas removal using UV-irradiated Fe2O3-containing ZSM-5 (UV-Fe@ZSM-5) and Silica (UV-Fe@Silica) via adsorption-oxidation process at room temperature. The UV-irradiated adsorbents showed an increased H2S removal performance (∼12.6–17.8%) compared to the un-irradiated adsorbents. Maximum adsorption efficiency of 83.4% was recorded for UV-Fe@ZSM-5 in the optimized conditions (10 ppm of H2S, 0.5 g L‒1 of adsorbent, 90 min). The kinetic data fitted to the intra-particle diffusion indicating H2S adsorption as a pore diffusion phenomenon. Among the two adsorbents, UV-Fe@ZSM-5 was found highly reusable where the adsorption performance of 76% reached 46% in the tenth cycle. The adsorbents showed good structural stability, which was also translated in their X-ray diffraction patterns. The X-ray photoelectron spectroscopic analysis showed absence of S in the adsorbents suggesting complete oxidation of adsorbed H2S gas. In the low concentration study (1 ppm H2S), UV-Fe@ZSM-5 outperformed UV-Fe@silica, and within 30 min the concentration dropped below 0.7 ppb.

Finite difference simulations for magnetically effected swirling flow of Newtonian liquid induced by porous disk with inclusion of thermophoretic particles diffusion

Heat and mass transfer analysis of viscous liquid flow generated by rotation of disk has generated prodigious interest due to promising utilizations in numerous processes such as thermal energy generation systems, turbine rotators, geothermal energy preservations, chemical processing, medicinal instrumentations, computing devices and so forth. In view of such extraordinary utilizations in numerous engineering procedures existent exertion is excogitated to disclose flowing phenomenon over rotating disk. To raise the importance of current analysis influential physical aspects like magnetic field, permeability, Dufour and Soret diffusion phenomenon are also incorporated. Subsequently, flow field distributions are analyzed for suction and injection cases. Modelling is structured via PDE’s by obliging constitutive conservation laws. Boundary layer approach is executed to reduce complexity of attained partial differential system. Transformations developed by Karman are implemented to convert developed differential framework into ODE’s. Implicitly finite differenced technique known as Keller Box is engaged to find solution of coupled intricate high order ordinary differential equations. Influence of flow controlling parameters on associated distributions are revealed through graphical and tabular representations. The related quantities of engineering interest like coefficients of wall drag force, along radial and tangential directions are also computed. Credibility of presently computed results is established by constructing comparison with previously published literature. It is inferred that magnetic strength parameter enhances tangential and radial components of velocity whereas contrary trend is depicted in axially directed velocity. In addition, temperature and momentum distributions show up surging attribute versus magnetic field parameter. All associated profiles have exhibited decrementing aspects against suction parameter. It is also revealed that increment in Soret tends to produce depreciation in temperature profile whereas concentration distribution is enhanced.

Photocatalytic Degradation of Malachite Green Dye Using Zinc Sulfide Nanostructures

AbstractZinc Sulfide (ZnS) get important attention as a semiconductor photocatalyst among other transition metal sulfides due to its fascinating and extraordinary properties. Here ZnS nanoparticles are synthesized by hydrothermal method using zinc acetate and sodium sulfide as precursors. The structural properties of ZnS was studied by using X‐Ray Diffraction technique (XRD).Exact fitting and crystal information of the sample was obtained from Rietveld refinement with Crystallographic Open Database (COD). It shows that ZnS follows cubic structure without any impurity peaks. Crystallite size and lattice strain values are calculated by using Williamson‐Hall (W−H) Plot method. As temperature increases, the particle size also going to increases due to atomic diffusion phenomena. Tauc plot indicates that the bandgap values decreases with increasing temperature. Accurate determination of bandgap values was analyzed by Boltzmann fitting using sigmoid function. Chemical states of elements were obtained with X‐ray Photoelectron Spectroscopy (XPS).Surface morphology and elemental analysis of ZnS nanoparticles was determined from Field Emission Scanning Electron Spectroscopy (FESEM) and Energy Dispersive spectroscopy (EDS). Then the photocatalytic dye degradation efficiency of synthesized particles for Malachite Green (MG) dye was evaluated. From the studies it was found that ZnS is an efficient photocatalyst and it can be used as a perfect future material to avoid the water pollution.

Influence of molecular transport on burning rate and conditioned species concentrations in highly turbulent premixed flames

Apparent inconsistency between (i) experimental and direct numerical simulation (DNS) data that show the significant influence of differential diffusion on the turbulent burning rate and (ii) recent complex-chemistry DNS data that indicate mitigation of the influence of differential diffusion on conditioned profiles of various local flame characteristics at high Karlovitz numbers, is explored by analysing new DNS data obtained from lean hydrogen–air turbulent flames. Both aforementioned effects are observed by analysing the same DNS data provided that the conditioned profiles are sampled from the entire computational domain. On the contrary, the conditioned profiles sampled at the leading edge of the mean flame brush do not indicate the mitigation, but are significantly affected by differential diffusion phenomena, e.g. because reaction zones are highly curved at the leading edge. This observation is consistent with a significant increase in the computed turbulent burning velocity with decreasing Lewis number, with all the results considered jointly being consonant with the leading point concept of premixed turbulent combustion. The concept is further supported by comparing DNS data obtained by allowing for preferential diffusion solely for a single species, either atomic or molecular hydrogen.

An explicit iterative scheme for 3D multicomponent heat conducting flow simulation

This paper presents the development and testing of time integration scheme for the system of hydrodynamic equations of gas mixture. These equations take into account the phenomena of multicomponent diffusion and heat transfer. The governing equation system is discretized by the finite volume approach on three-dimensional unstructured grids. According to the algorithm, computation of any single time step is split into the sequence of hyperbolic and parabolic stages. The hyperbolic subtask is solved using the Godunov-type scheme. The parabolic subtask is solved by the explicit iterative Chebyshev scheme, which is algorithmically simple and does not involve tuning parameters. This stage addresses dissipative fluxes (viscosity, multicomponent diffusion and thermal conductivity). The number of the explicit iterations is determined by the convective time step and by the upper bound for the discrete diffusion operator. The resulting scheme ensures the fulfillment of the conservation laws at the discrete level. The computer code can be used in highly parallel computing for large-scale simulation. The proposed approach is recommended for applied problems in which convective and dissipative processes are in close interaction, particularly for problems of plasma physics and astrophysics.

Effect of viscosity on stability and accuracy of the two-component lattice Boltzmann method with a multiple-relaxation-time collision operator investigated by the acoustic attenuation model

A two-component lattice Boltzmann method (LBM) with a multiple-relaxation-time (MRT) collision operator is presented to improve the numerical stability of the single relaxation time (SRT) model. The macroscopic and the momentum conservation equations can be retrieved through the Chapman-Enskog (C-E) expansion analysis. The equilibrium moment with the diffusion term is calculated, a diffusion phenomenon is simulated by utilizing the developed model, and the numerical stability is verified. Furthermore, the binary mixture channel model is designed to simulate the sound attenuation phenomenon, and the obtained simulation results are found to be consistent with the analytical solutions. The sound attenuation model is used to study the numerical stability and calculation accuracy of the LBM model. The simulation results show the stability and accuracy of the MRT model and the SRT model under different viscosity conditions. Finally, we study the influence of the error between the macroscopic equation of the MRT model and the standard incompressible Navier–Stokes equation on the calculation accuracy of the model to demonstrate the general applicability of the conclusions drawn by the sound attenuation model in the present study.

Prediction of Europium Retention in Perovskite: Potential Candidates for an Engineering Barrier in the Disposal of Radioactive Waste

Perovskites, such as tausonite, are crystalline metal oxides with excellent optical and photocatalytic properties and have also been used successfully in the retention of metals, simulating the isotopes of uranium and plutonium. In this work, different pseudo-order and thermodynamic models were studied to achieve the prediction of the sorption of Eu3+ (chemical analogous for actinides) in tausonite. The effects of gamma irradiation and temperature on the structural characteristics of the material were determined, as an additional step in the evaluation of material as an engineering barrier in the disposal of radioactive waste. The results obtained show that the tausonite is resistant to the gamma irradiation and thermal energy. Likewise, it was possible to determine that europium sorption occurs through an exothermic and spontaneous reaction, as well as through the formation of surface complexes, where Eu3+ ions bind to sites on the tausonite by dipole-dipole interaction. Furthermore, it was shown that the sorption mechanism is influenced by diffusive phenomena, which participate in the formation of surface complexes. Additionally, a new sorption model with respect to pH was proposed, which allowed determining the physical parameter π. The evidence obtained suggests that π is a physical parameter that relates pH to an optimal value and could explain the equilibrium between the surface complexes that tausonite forms with europium. Likewise, the evidence suggests that 50 kg of tausonite would have the capacity to retain at least 26.59 g of alpha-emitting radionuclides, equivalent to a waste package (900 kg) with a maximum activity of 4000 Bq/g.

Understanding the Operating Mechanism of Aqueous Pentyl Viologen/Bromide Redox-Enhanced Electrochemical Capacitors with Ordered Mesoporous Carbon Electrodes.

Compared to traditional electric double-layer capacitors, redox-enhanced electrochemical capacitors (redox-ECs) show increased energy density and steadier power output thanks to the use of redox-active electrolytes. The aim of this study is to understand the electrochemical mechanisms of the aqueous pentyl viologen/bromide dual redox system at the interface of an ordered mesoporous carbon (CMK-8) and improve the device performance. Cells with CMK-8 carbon electrodes were investigated in several configurations using different charging rates and potential windows. The pentyl viologen electrochemistry shows a mixed behavior between solution-based diffusion and adsorption phenomena, with the reversible formation of an adsorbed layer. The extension of the voltage window allows for full reduction of the viologen molecules during charge and a consequent increase in the specific discharge energy delivered by the cell. Investigation of the mechanism indicates that a 1.5 V charging voltage with a 0.5 A g-1 charging rate and fast discharge rate produces the best overall performance.

A modelling and simulation study of anaerobic digestion in plug-flow reactors

A mathematical model for anaerobic digestion in plug-flow reactors is proposed on the basis of mass balance considerations. The model consists of a system of parabolic partial differential equations for the variables representing the concentrations of the bio-components constituting the waste matrix and takes into account convective and diffusive phenomena. The plug-flow reactor is modelled as a one-dimensional domain; the waste matrix moves in the direction of the reactor axis and undergoes diffusive phenomena which reproduce the movement of the bio-components along the reactor axis due to a gradient in concentration. The velocity characterizing the convection of the waste matrix is not fixed a priori but it is considered as an additional unknown of the mathematical problem. The variation in the convective velocity allows to account the mass variation occurring along a plug-flow reactor due to the conversion of solids. The equation governing the convective velocity is derived by considering the density of the waste matrix within the reactor constant over time and the sum of the volume fractions of the bio-components constituting the waste matrix constrained to unity. The waste matrix undergoes biochemical transformations catalyzed​ by anaerobic microbial species which lead to the production of gaseous methane, the final product of the anaerobic digestion process. Biochemical processes are modelled using a simplified scheme and a differential equation is used to describe the dynamics of the produced gaseous methane. A finite difference scheme is used for the numerical integration. Model consistency is showed through numerical simulations which investigate the effect of the variation of some operating parameters on process performance. The model is then applied to a real case scenario of engineering interest. Simulations produce results in good agreement with experimental observations.

Fourth kind Chebyshev Wavelet Method for the solution of multi-term variable order fractional differential equations

PurposeMulti-term variable-order fractional differential equations (VO-FDEs) are powerful tools in accurate modeling of transient-regime real-life problems such as diffusion phenomena and nonlinear viscoelasticity. In this paper the Chebyshev polynomials of the fourth kind is employed to obtain a numerical solution for those multi-term VO-FDEs.Design/methodology/approachTo this end, operational matrices for the approximation of the VO-FDEs are obtained using the Fourth kind Chebyshev Wavelets (FKCW). Thus, the VO-FDE is condensed into an algebraic equation system. The solution of the system of those equations yields a coefficient vector, the coefficient vector in turn yields the approximate solution.FindingsSeveral examples that we present at the end of the paper emphasize the efficacy and preciseness of the proposed method.Originality/valueThe value of the paper stems from the exploitation of FKCWs for the numerical solution of multi-term VO-FDEs. The method produces accurate results even for relatively small collocation points. What is more, FKCW method provides a compact mapping between multi-term VO-FDEs and a system of algebraic equations given in vector-matrix form.

MECHANICAL PROCESSES IN TRIBOTECHNICAL UNITS

The study examined the diffusion phenomenon caused by compressive forces in tribotechnical nodes adhering to each other under high contact pressure and the mechanism of rupture of surfaces during surface fatigue. As a result, for two metal surfaces, depending on the nature of the touch, the gravitational and repulsive forces generated during the interaction in any environment are determined based on the number of touches and an analytical expression is obtained to calculate them. Keywords: tribotechnical knot, mutual contact, diffusion phenomenon, surface attraction, molecular contact, mechanical contact.

Phenomenological model for the prediction of Moringa oleifera extracted oil using a laboratory Soxhlet apparatus

Moringa oleifera is an oilseed crop with poten­tial for biodiesel production. The second step in this process is the extraction of oil. Extraction in hot water, with a Soxhlet apparatus and the ultrasound technique are the most commonly used methods. The aim of the present work was to obtain a phenomenological model for the Moringa oleifera oil extraction process using Soxhlet. Effective diffusivity for Moringa oil through the kernels is obtained, using the kinetics of the extraction process (experimentally determined) and the Fick’s diffusion second law for non-steady state. The value of 0.685·10-12 m2/s fully matched reports on effective diffusion coefficient for other solids. It was also verified from the statistical analysis and a linear fit for experimental data that the model can be used to describe the oil extraction process of Moringa oleifera in the Soxhlet extractor, responding to the diffusive phenomenon (process controlled by internal resistance).

Thermodynamics of fluctuations based on time-and-space averages.

We develop nonequilibrium theory by using averages in time and space as a generalized way to upscale thermodynamics in nonergodic systems. The approach offers a classical perspective on the energy dynamics in fluctuating systems. The rate of entropy production is shown to be explicitly scale dependent when considered in this context. We show that while any stationary process can be represented as having zero entropy production, second law constraints due to the Clausius theorem are preserved due to the fact that heat and work are related based on conservation of energy. As a demonstration, we consider the energy dynamics for the Carnot cycle and for Maxwell's demon. We then consider nonstationary processes, applying time-and-space averages to characterize nonergodic effects in heterogeneous systems where energy barriers such as compositional gradients are present. We show that the derived theory can be used to understand the origins of anomalous diffusion phenomena in systems where Fick's law applies at small length scales, but not at large length scales. We further characterize fluctuations in capillary-dominated systems, which are nonstationary due to the irreversibility of cooperative events.

On elemental and isotopic fractionation of noble gases in geological fluids by molecular diffusion

Noble gases are ideal natural tracers to characterize the storage, migration and origin of fluids in geological environments. They are chemically and biologically inert and therefore are only partially separated by physical processes including the one related to the molecular diffusion phenomenon, so called kinetic fractionation. However, its precise quantification is difficult to achieve and its modeling is still open for debates. Thus, in this work, we have investigated the capability of simple and predictive models to estimate elemental and isotopic fractionation of noble gases in various geological fluids. To do so, molecular dynamics simulations on noble gases in water, gas and oil under sub-surface conditions were performed. These numerical results were found to be consistent with previous ones including experiments and molecular simulations when available, i.e. in water. Interestingly, it appeared that the widely used square-root law is able to provide a good prediction for elemental fractionation between noble gases in all solvents, except for helium. Such unexpected result from the theoretical point of view is explained by a peculiar relationship between the molecular mass and the molecular size of noble gas elements. Regarding the noble gas isotopic fractionation, the square-root law is shown to be unable to provide reasonable results, confirming recent experimental and numerical works. As expected, it has been noticed that the kinetic theory relation provides a reasonable estimate of the isotopic fractionation in gas whereas it deteriorates in water and in oil. Finally, using the previous findings, we propose a simple and predictive scheme for the isotopic fractionation of noble gases in all studied geo-fluids which is noticeably better than both the square-root and the kinetic theory relations.

Global existence results for semi-linear structurally damped wave equations with nonlinear convection

In this paper, we consider the Cauchy problem for semi-linear wave equations with structural damping term [Formula: see text], where [Formula: see text] is a constant. As is now well known, the linear principal part brings both the diffusion phenomenon and the regularity loss of solutions. This implies that, for the nonlinear problems, the choice of solution spaces plays an important role to obtain the global solutions with the sharp decay properties in time. Our main purpose in this paper is to prove the global (in time) existence of solutions for the small data and their decay properties for the supercritical nonlinearities.

Integrating multiple physical properties of microchannel gas flow to extend the Navier–Stokes equations over a wide Knudsen number range

Gas flow in microchannels can be predicted by the Navier–Stokes equations with slip boundary conditions, but only limited to a slightly rarefied flow regime. To improve that, the considerations of the effective mean free path and the volume diffusion phenomena were introduced to the non-kinetic model by previous studies separately. In this study, these two effects, along with the newly proposed wall-to-wall-collision effect, are integrated to extend the Navier–Stokes equations for the planar Poiseuille flows over a wide Knudsen number (Kn) range. The dimensionless mass flow rates calculated by the proposed model can be consistent among different working fluids or flow conditions and mostly agree with the experimental data with Kn≅0.03−57. This analysis facilitates an understanding of the mutual effects on the physical properties of microchannel gas flows and shows a promising prospect for developing a non-kinetic model for highly rarefied flows.

Single file diffusion meets Feynman path integral

The path-integral representation of the Smoluchowski equation is exploited to explore the stochastic dynamics of a tagged Brownian particle within an interacting system where hydrodynamic effects are neglected. In particular, this formalism is applied to a particle system confined to a one-dimensional infinite line aiming to investigate the single-file diffusion phenomenon in this scenario. In particular, the path-integral method is contrasted against the standard many-particle Langevin equation for a system of interacting Brownian particles in a harmonic chain model, exhibiting excellent agreement; in this case of study a formula defined on the whole time-scale for the mean-square displacement, in the thermodynamic limit, is found for the tracer particle in terms of Bessel functions, recovering also the single-file regime. Additionally, a Brownian particle system with paramagnetic interactions is considered near crystallization where the total interaction potential is roughly a harmonic potential. Taking advantage of the path-integral formalism a simple perturbation treatment is carried out to investigate the single file diffusion behaviour when temperature is increased from the crystal phase, where we also validate our findings using Brownian dynamics simulation.

Strategy to Design-Synthesize Bimetallic Nanostructures Using the Alcohol Reduction Method.

Bimetallic nanomaterials have attracted much attention from various fields such as catalysis, optics, magnetism, and so forth. The functionality of such particles is influenced very much by the intermetallic interactions than their individual contribution. However, compared with the synthesis of monometallic nanoparticles, the reaction parameters that need to be controlled for tuning the size, shape, composition, and crystal structure of bimetallic nanoparticles becomes challenging. This study focuses on synthesizing of bimetallic nanostructures using the alcohol reduction method, where the control over the reducing power is conceivable by varying the combination of the alcohol type, complexing agent, and metal salts. Consequently, various Cu-Co nanostructures such as Cu-Co core-shell (size ranged between 40 and 15 nm) and hollow alloy nanoparticles and nanotubes were successfully synthesized by incorporating diffusion and etching phenomena during the reduction reaction. Moreover, time-resolved sampling revealed that the formation of a Cu-Co alloy hollow nanostructure has been realized by the diffusion of the Cu core into the Co shell by controlling the reduction time gap between Cu and Co and the crystal structure besides the reduction sequences. It should be noted that the synthesis of a high-temperature (∼1300 °C) Cu-Co alloy phase was carried out at 170 °C. Among the Cu-Co alloy nanostructures, Cu-Co hollow alloy nanoparticles exhibited enhanced catalytic activity compared to metallic Cu and other Cu-Co nanostructures from the degradation reaction of methylene blue. The enhanced catalytic performance was considered to be mainly due to the alloy structure.