Electrochemical Impedance Spectroscopy Plots Research Articles

A new multifunctional electrocatalyst based on PbS nanostructures decorated with graphene/polyaniline-modified glassy carbon electrode for selective detection of non-steroidal anti-inflammatory drug naproxen

Naproxen (NAP), a well-known anti-inflammatory drug, has also been considered for its antiviral prospective and acceptable potential for in vitro activity against serious respiratory syndrome-related coronavirus (SARS-CoV) and anti-influenza activity. However, designing a selective, sensitive and efficient electrocatalyst for the determination of NAP is still a great challenge. In this research, a new electrocatalytic sensor was constructed for the electrochemical recognition of NAP by a glassy carbon electrode modified with PbS nanostructures incorporated graphene/polyaniline nanocomposite. The synthesized samples were characterized by physicochemical analyses like EDS, XRD, FTIR, FESEM, and PL. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) were carried out to examine the electrocatalytic behavior of the modified electrodes. The EIS plot obviously demonstrated rapid electron transport at low frequencies for the PbS/graphene/PANI/GC electrode. It was observed that the PbS/graphene/PANI/GC electrode exhibited better-defined oxidation peaks, and greater peak currents for NAP detection compared to other electrodes. Under the optimum conditions, the proposed PbS/graphene/PANI nanoplatform provided a reliable linear range of 1 to 100 µM with a detection limit as low as 0.08 μM. Meanwhile, the PbS/graphene/PANI electrode possessed acceptable selectivity, good repeatability with an RSD of about 2.6 %, and a reduction of about 3 % after two weeks, and long-term stability of about 97 % of its original response for the recognition of NAP. Furthermore, the constructed electrode demonstrated NAP detection in real samples, such as human plasma and urine with good recoveries ranging from 98.8 % to 99.9 %, suggesting its promising prospects in clinical diagnostics.

Influence of applied potential on tin content in electrodeposition of Zn–Sn alloy coatings and its effect on corrosion protection

In the present work, the electrochemical deposition of Zn–Sn alloy at different applied potentials is studied. The deposits were prepared from a chloride bath on a stainless steel substrate (SS) using cyclic voltammetry, chronoamperometry and anodic linear stripping voltammetry methods. X-ray diffraction, scanning electron microscopy and energy dispersive were used to study the structural, morphological and chemical composition of the deposits. The corrosion behavior of the elaborated samples was studied by open circuit potential (OCP), Tafel plot and electrochemical impedance spectroscopy (EIS) in 3.5 wt-% NaCl solution. Results indicated that the Zn–Sn alloy coatings exhibit a synergistic property combining the barrier behavior afforded by Sn and strong passive behavior of Zn. Electrochemical measurements obtained by Tafel and EIS plots revealed that Zn–Sn alloy coatings obtained at more positive potential of −1.1 V present best corrosion resistance.

Nitrogenated derivatives of furfural as green corrosion inhibitors for mild steel in HCl solution

The ability of nitrogenated derivatives of furfural to act as corrosion inhibitors for mild steel in 1molL−1 HCl solution was evaluated using weight-loss measurements, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). The imine 2-((furan-2-ylmethylene)amino)ethan-1-ol (1) and the mixture of 2-(furan-2-yl)-1,3-oxazinane and 3-((furan-2-ylmethylene)amino)propan-1-ol (2a+b) presented, respectively, 81.9% and 84.4% of inhibition efficiency towards the mild steel acidic corrosion at 5×10−3molL−1, room temperature and 2-h immersion time. Polarization curves showed more effective inhibition in the cathodic process. EIS plots indicated an increase in the polarization resistance with enhancement of inhibitor concentration. The adsorption of the evaluated inhibitors obeyed the Langmuir adsorption isotherm. The ΔG°ads and ΔH°ads values obtained suggest a physical nature adsorption of inhibitors (1) and (2a+b). The physisorption could be explained by the coulombic interaction between the protonated forms of the inhibitor molecules due to the acid medium with the negatively charged surface. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface morphologically and chemically, respectively. Quantum chemical calculations were applied to correlate electronic structure parameters of inhibitors with their corrosion inhibition efficiency.

Green Approach to Corrosion Inhibition of Mild Steel in Hydrochloric Acid by 1-[Morpholin-4-yl(thiophen-2-yl)methyl]thiourea

The inhibition effect of novel Mannich base 1-[morpholin-4-yl(thiophen-2-yl)methyl]thiourea on the corrosion of mild steel in 0.5 M hydrochloric acid solution was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements and surface examination through scanning electron microscope (SEM) technique. The results showed that Mannich base is an effective corrosion inhibitor and the inhibition efficiency increases with increase in concentration of the inhibitor. The corrosion behavior of mild steel in 0.5 M HCl without and with the inhibitor at various concentrations was studied at the temperature range of 303–333 K. Potentiodynamic polarization measurements showed that the Mannich base is a mixed-type inhibitor. EIS plots indicated that the presence of the inhibitor increases the charge transfer resistance of the corrosion process, increasing the inhibition efficiency. Temperature studies revealed that inhibition efficiency increased up to 323 K and beyond which inhibitor efficiency decreased because of desorption of inhibitor. The adsorption of inhibitor on mild steel surface is an endothermic reaction and is best described by the Langmuir adsorption isotherm. The surface adsorbed film was analyzed using SEM.

Investigation of the structural and electrical behavior of LiFePO4 as cathode material for energy storage application

The present work reports the structural and electrochemical impedance spectroscopy (EIS) of LiFePO4 cathode material synthesized via hydrothermal technique by using CTAB (Cetrimonium bromide) as a surfactant. XRD analysis reveals that LiFePO4 crystallizes in the orthorhombic phase with Pnma space group. The average crystallite size calculated through Scherrer formula is found to be 21 nm. FESEM analysis divulges that as synthesized sample have disc type morphology and the size distribution was found to be in the range of 150–650 nm. The electrochemical analysis is done using a three-electrode technique with Ag/AgCl as the reference electrode. Cyclic Voltammetry (CV) results confirm the anodic and cathodic current peaks corresponding to the oxidation and reduction reactions respectively. The standard cell potential estimated through the CV plots is found to be, Eʘ = 0.34. The electrolytic resistance and charge transfer resistance estimated through EIS plots in the frequency range of 10–105 Hz with 2 M NaOH solution as the electrolyte is found to be, Rsol = 4.1 Ω, and Rct = 35 Ω, respectively. Simulation for an equivalent circuit model is done using CHI760E software which confirms the partially polarizable nature of the as-prepared LiFePO4 cathode material. The impedance behavior of LiFePO4 cathode material can be analyzed to verify its physicochemical properties, hence, the study concludes that as synthesized LiFePO4 can be utilized as an efficient cathode material for energy storage applications.

A high-sensitive electrochemical DNA biosensor based on a novel ZnAl/layered double hydroxide modified cobalt ferrite-graphene oxide nanocomposite electrophoretically deposited onto FTO substrate for electroanalytical studies of etoposide

The combination of layered double hydroxides (LDHs), cobalt ferrite (CoFe2O4) and graphene oxide (GO) creates a ternary nanocomposite that can incredibly improve advantages of each compound; this is an impressive way to attain multifunctional materials with attractive properties. In this study, a new high-sensitive electrochemical DNA biosensor was fabricated for the electroanalytical studies of etoposide using a novel ZnAl/layered double hydroxide modified cobalt ferrite-graphene oxide nanocomposite (GO/CoFe2O4/ZnAl-LDH) that was electrophoretically deposited (EPD) on the fluorine tin oxide (FTO) substrate. This DNA biosensor was prepared via electrostatic adsorption of DNA onto the GO/CoFe2O4/ZnAl-LDH/FTO electrode. The electrochemical behavior of electrodes was characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). EIS plot obviously demonstrated a rapid electron transport at low frequencies for GO/CoFe2O4/ZnAl-LDH. Differential pulse voltammetry (DPV) and square wave anodic stripping voltammetry (SWASV) were employed for the electrochemical detection of ETO. The results revealed that DNA/GO/CoFe2O4/ZnAl-LDH/FTO bioelectrode had ultrahigh sensitivity to ETO with the detection limit of 0.0010 μM in the linear range of 0.2–10 μM. In addition, the developed biosensor revealed precise reproducibility and excellent stability of about 95% of the initial activity after 6–7 weeks. On the other hand, the present bioelectrode was also capable of discriminating different interferences and was also used to detect etoposide in real samples such as human blood plasma, serum and urine with good recoveries, ranging from 97.0% to 104.0%. The obtained results of the excellent performance of this biosensor could be assigned to the active reaction sites and good electrochemical activity of nanocomposites, hence helping increase the DNA immobilization and accelerate the electron transfer more effectively on the surface electrode.

Investigation into the Corrosion Behavior of Copper/Aluminum Associated with Electric/Electronic Devices in Marine Environment

Corrosion behavior of copper/aluminum was investigated using cyclic wet/dry corrosion test in natural seawater by electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM). The higher charge transfer resistance (Rct) and film resistance (Rf) at 15 d of w/d cyclic corrosion test were shown by EIS plots. The anodic surface releases Al3+ and Cu+ ions into the electrolyte, and the cathodic surface consumes dissolved oxygen. These ions and dissolved oxygen are detected by applying appropriate tip potential in SECM technique. The results showed that the corrosion activity of aluminum was accelerated due to the potential difference of the sample. The scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX) analysis showed the enrichment of Cu and Al in corrosion products at the surface of Cu/Al sample after electrochemical analysis. The focused ion beam/transmission electron microscopy (FIB-TEM) analysis confirmed the presence of the nanoscale oxide layers containing Cu and Al in the corrosion product of the Cu/Al sample. The formation of corrosion products has a beneficial effect on corrosion resistance of Cu/Al sample.

Synthesis of Reduced Graphene Oxide/Titanium Dioxide Nanotubes (rGO/TNT) Composites as an Electrical Double Layer Capacitor.

Composites of synthesized reduced graphene oxide (rGO) and titanium dioxide nanotubes (TNTs) were examined and combined at different mass proportions (3:1, 1:1, and 1:3) to develop an electrochemical double layer capacitor (EDLC) nanocomposite. Three different combination methods of synthesis—(1) TNT introduction during GO reduction, (2) rGO introduction during TNT formation, and (3) TNT introduction in rGO sheets using a microwave reactor—were used to produce nanocomposites. Among the three methods, method 3 yielded an EDLC nanomaterial with a highly rectangular cyclic voltammogram and steep electrochemical impedance spectroscopy plot. The specific capacitance for method 3 nanocomposites ranged from 47.26–165.22 F/g while that for methods 1 and 2 nanocomposites only ranged from 14.03–73.62 F/g and 41.93–84.36 F/g, respectively. Furthermore, in all combinations used, the 3:1 graphene/titanium dioxide-based samples consistently yielded the highest specific capacitance. The highest among these nanocomposites is 3:1 rGO/TNT. Characterization of this highly capacitive 3:1 rGO/TNT EDLC composite revealed the dominant presence of partially amorphous rGO as seen in its XRD and SEM with branching crystalline anatase TNTs as seen in its XRD and TEM. Such property showed great potential that is desirable for applications to capacitive deionization and energy storage.

Effect of Cu content on exfoliation corrosion and electrochemical corrosion of A7N01 aluminum alloy in EXCO solution

The exfoliation corrosion (EXCO) sensitivities and electrochemical corrosions of A7N01 aluminum (Al) alloys with 0.074% and 0.136% Cu contents were investigated in EXCO solution. The exfoliation corrosion developed more rapidly for the alloy with 0.136% Cu by expressing higher exfoliation rate and deeper corrosion pits as observed by SEM and laser confocal scanning microscopy (LCSM). In EXCO solution, the alloy with 0.136% Cu content showed lower open-circuit potential (OCP) than the alloy with 0.074% Cu content. The alloy with 0.136% Cu content had bigger “hysteresis loop” in cyclic polarization curve which meant lower self-passivation ability. In electrochemical impedance spectroscopy plot, its curvature radius and capacitance index were lower. The electrochemical test results revealed that the alloy with 0.136% Cu content showed more severe electrochemical corrosion than the alloy with 0.074% Cu content, consistent with the exfoliation corrosion results. The microstructures of two alloys were observed through optical microscopy (OM) and transmission electron microscopy (TEM). The continuous distribution of the equilibrium precipitate [Formula: see text]-MgZn2 on grain boundaries, the decreasing of the width of precipitate-free zone (PFZ) and the coarse Cu–Fe–Si–rich phase were responsible for the higher corrosion sensitivity of the Al alloy with 0.136% Cu than that of Al alloy with 0.074% Cu content in EXCO solution.

Rapid impedance measurement using chirp signals for electrochemical system analysis

Energy storage (batteries) and conversion devices (fuel cells) operate based on electrochemical principles. Electrochemical impedance spectroscopy (EIS) is an important experimental technique that can be used to optimize the performance of these devices at the design stage. Further, EIS can also be used for non-invasive, in-situ diagnostics of device performance, while operational. While EIS is a powerful technique, the instrumentation required for implementation can be bulky and the time for analysis could also become unacceptable, particularly for online applications. The proposed work is an investigation and development of a rapid impedance measurement technology using large bandwidth and short duration diagnostic signals. The key concept behind the approach is the use of a particular definition of instantaneous frequency in tandem with chirp signals for testing. The instantaneous frequency definition allows one-to-one time frequency mapping and the chirp signal incorporates a wide bandwidth of frequencies. As a result, a novel impedance plot qualitatively, and largely quantitatively, matching the corresponding EIS plot is generated. Consequently, any diagnostic approach based on EIS can potentially be realized using the proposed approach. The impedance plots are generated in a very short time making the approach amenable for online applications. In-silico validation of the proposed method on few equivalent circuits of electrochemical systems is presented in this work; future work will include experimental validation of the technique on real electrochemical systems.

The formation and electrochemical property of lithium-excess cathode material Li1.2Ni0.13Co0.13Mn0.54O2 with petal-like nanoplate microstructure

Lithium-excess oxide shows great potential for its high specific capacity of exceeding 280 mAh g−1. However, the poor rate capability caused by the poor electrochemical kinetics condition as well as the structure instability block the way of its application. Here, we aimed to improve the kinetics circumstance for lithium ion transference through the material bulk by synthesizing lithium-excess oxide with high specific surface area. Petal-like nanoplates and nanoparticles with excellent electrochemical performance were obtained at different sintering temperatures and times by the electrospinning-sintering method, which facilitates the sufficient contact of electrode and electrolyte and helps to reduce the polarization during the electrochemical reaction process. Cyclic voltammetry tests verify that a portion of oxidized oxygen is reduced reversibly at 3.0 V and the reduction of oxygen contributes to the discharge capacity. Electrochemical impedance spectroscopy plots illustrate the ameliorative electrochemical kinetics is conductive to the oxidation of oxygen at 4.5 V.

Effect of immersion time on the passive and electrochemical response of annealed and nano-grained commercial pure titanium in Ringer's physiological solution at 37 °C

In the present study, various electrochemical tests were used to investigate the passive and electrochemical response of annealed and nano-grained commercial pure Titanium in Ringer's physiological solution at 37°C. Nano-grained pure Titanium, which typically has an average grain size of 90±5nm, was obtained by six-cycle accumulative roll bonding process. Polarization and electrochemical impedance spectroscopy plots illustrated that as a result of grain refinement process, the passive response of the nano-grained sample was improved compared to that of its coarse-grained counterpart in Ringer's physiological solution. Mott–Schottky analysis indicated that the passive films behaved as n-type semiconductors in Ringer's physiological solution and grain refinement did not change the conductivity type of the passive films. Additionally, Mott–Schottky analysis showed that the donor density decreased by grain size reduction. Finally, nano-grained sample appeared to be more suitable for implant applications, mainly due to the formation of thicker and less defective oxide film.

Silica-Based Ionogel Electrolyte for Electrical Double Layer Capacitors

Electrochemical Capacitors (ECs), also known as supercapacitors, have now reached the technical maturity for complementing- and sometimes replacing- batteries in a broad range of applications. Conventional electrolytes based on acetonitrile or propylene carbonate solvents have been mainly used in combination with ammonium cations and fluoride anions. Designing solid electrolytes for ECs would be of great interest in the aim of solving packaging issues, corrosion, self-discharge or leaks. Moreover these solid electrolytes could be used for flexible supercapacitors applications. Ionogels are quasi-solid electrolyte obtained from the trapping of an IL into a silica scaffold using a sol-gel process. The first part of our work has been devoted to a better understanding of the non-hydrolytic sol-gel mechanisms occurring during the formation of ionogels, using electrochemical impedance spectroscopy. Change of the conductivity of the sol-gel mixture (a Formic acid and Tetraethyl orthosilicate mixture) shows two different time domains. The mixture conductivity is first decreasing drastically during the first 25 minutes of the sol-gel process, assuming to originate from the in-situ generation of water through esterification reaction. In the second time range (t>25 min), the conductivity tends to level off, associated with a series of chemical reactions. More details about this study will be added during the presentation. In a second part of the talk, we will show the electrochemical performance of an supercapacitors cell assembled with activated carbon as active materials and an ionogel electrolyte containing an ionic liquid mixture (1:1 by weight or molar ratio) of N-methyl-N-propylpiperidinium bis(fluorosulfonyl)imide (PIP13FSI) and N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (PYR14FSI). Cyclic voltammetries and electrochemical impedance spectroscopy plots in a large temperature range (-40°C to +60°C) will be presented and discussed. The ionogel exhibits a high ionic conductivity over a wide temperature range (from 0.2 mS.cm−1 at −40 °C up to 10 mS.cm−1 at 60 °C). The ionogel-based supercapacitor using two activated carbon electrodes can be operated over 3 V cell voltage window. Moreover this all solid-supercapacitor shows a capacitance up to 90 F.g−1 at room temperature. These encouraging results show the interest of developing such devices, including non-toxic and safer electrolytes, packaging issues and flexible devices development.

Papaya peel extract as potential corrosion inhibitor for Aluminium alloy in 1 M HCl: Electrochemical and quantum chemical study

Abstract This paper deals with the corrosion inhibition effect of Papaya peel extract (PPE) on Aluminium alloy (AA) in 1 M HCl. The corrosion tests were performed by using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques (PDP). Maximum inhibition efficiency observed is 95.5% and 98.1% from EIS plot and PDP studies at higher concentration (2.0 g L −1 ) of PPE. Potentiodynamic polarization result shows mainly the cathodic type inhibition for PPE. Surface morphology of AA is carried by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Quantum chemical study is complemented well with the experimental findings of the corrosion inhibition.

Galvanic Corrosion of AA6061 with Other Ship Building Materials in Seawater

The activation of AA6061 Al alloy while coupled with low alloy steel or carbon-carbon composite results in severe corrosion of the former and protection of the latter. Potential drop and E-I kinetics of these couples are nonlinear; hence, the decrease in galvanic current density increases the distance from the “anode (AA6061)/cathode (HSLA steel)” junction, also nonlinear, and seems to be an exponential function of the distance. Electrochemical impedance spectroscopy plots of galvanically coupled AA6061 showed capacitive and inductive loops, with the latter resulting from the activation of AA6061. Scanning electron microscope micrographs of AA6061 coupled with low alloy steel and exposed to seawater showed the presence of pits over Al alloy matrix and near intermetallic precipitates.

Highly improving the electrochemical performance of LiFePO4 modified by metal phthalocyanines as cathode materials

Abstract

Corrosion Performance of AISI-309 Exposed to Molten Salts V2O5-Na2SO4at 700°C Applying EIS andRpElectrochemical Techniques

The corrosion performance of AISI-309 exposed 5 days to molten salts 50 mol% V2O5-50 mol% Na2SO4at 700°C is reported in this paper. Such evaluation was made using three electrochemical techniques: potentiodynamic polarization curve (PC), electrochemical impedance spectroscopy (EIS), and linear polarization resistance (Rp). FromPC, the Tafel slopes,Icorr, andEcorrwere obtained. From Nyquist and Bode plots, it was possible to determine two different stages; the first one showed just one loop, which indicated the initial formation of Cr2O3layer over the metallic surface; after that, the dissolution of Cr2O3formed a porous layer, which became part of the corrosion products; at the same time a NiO layer combined with sulfur was forming, which was suggested as the second stage, represented by two capacitive loops. EIS plots were in agreement with the physical characterization made from SEM and EDS analyses. Fitting of EIS experimental data allowed us to propose two electrical circuits, being in concordance with the corrosion stages. Parameters obtained from the simulation of EIS data are also reported. From the results, it was stated that AISI-309 suffered intergranular corrosion due to the presence of sulfur, which diffused to the metallic surface through a porous Cr2O3layer.

Effect of SiC Nanoparticles on the Electrochemical Reduction Behaviors of Ionic Bismuth and Tellurium

The effect of SiC nanoparticles on the electrochemical reduction behaviors of ionic bismuth and tellurium was investigated by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The results showed that the addition of SiC nanoparticles in the solution did not change the electrochemical reduction process of ionic bismuth and tellurium on Au electrode, as the shapes and numbers of the peaks in the cyclic voltammograms were not altered, although the peak potentials and peak currents varied a little. However, the electrochemical reduction of ionic bismuth was accelerated by introducing SiC nanoparticles in a Bi unitary solution system for the size reduction of the semicircles in EIS plots. Different from ionic bismuth, the electrochemical reduction of adsorbed HTeO2+ to Te0 was inhibited and enlarged semicircles in EIS plots were observed. In contrast, the reduced semicircles in EIS plots revealed a promoting effect of SiC nanoparticles on the electrochemical reduction of dissociative HTeO2+ to Te0. Bi2Te3/SiC composite has been synthesized by a co-depositing process in solutions containing ionic bismuth, tellurium and SiC nanoparticles combined with anneal treatment.

Characteristics of Photoresist-derived Carbon Nanofibers for Li-ion Full Cell Electrode

Carbon nanofiber electrode has been fabricated for energy storage systems by the electrospinning of SU-8 precursor and subsequent pyrolysis. Various parameters including the applied voltage, the distance between syringe tip and target collector and the flow rate of the polymer affect the diameter of SU-8 electrospun nanofibers. Shrinkage during pyrolysis decreases the fiber diameter. As the pyrolysis temperature increases, the resistivity decreases dramatically. Low resistivity is one of the important characteristics of the electrodes of an energy storage device. Given the advantages of carbon nanofibers having high external surface area, electrical conductivity, and lithium intercalation ability, SU-8 derived carbon nanofibers were applied to the anode of a full lithium ion cell. In this paper, we studied the physical properties of carbon fiber electrode by scanning transmission microscopy, thermal gravimetric analysis, and four-point probe. The electrochemical characteristics of the electrode were investigated by cyclic voltammogram and electrochemical impedance spectroscopy plots.

Diaza-adamantane derivatives as corrosion inhibitor for copper in nitric acid medium

The effect of newly synthesized 6-hydroxy-5,7-diphenyl-1,3-diazaadamantane (HDDA) and 5,7-diphenyl-1,3-diazaadamantan-6-one (DDA) against the corrosion of copper in 1 M HNO3 solution was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and weight loss measurements. These measurements show that the inhibition efficiency (IE %) obtained by these compounds increased by increasing their concentrations, and maximum IE % to 90.84 % for HDDA and 89.87 % for DDA were found at 300 ppm. Data obtained from EIS studies were analyzed by an equivalent circuit model. EIS plots indicated that the inhibitor performance depends on the adsorption of the molecules on the metal surface. Polarization measurements showed that both HDDA and DDA are mixed-type but predominantly cathodic in 1 M HNO3 solution. The adsorption of inhibitors on the copper surface from the nitric acid follows the Langmuir adsorption isotherm with a negative value of free energy, and these values indicated that adsorption of both HDDA and DDA molecules adsorbs physically on the copper surface. The surface morphology was examined by scanning electron microscope and atomic force microscope. Further, theoretical calculations were carried out and relationships between computed parameters and experimental IE % were discussed. All the results confirmed that e HDDA showed better efficiency in 1 M HNO3 compared to DDA.