•Interpretation of EIS with a double semicircle and a straight line.•Simultaneous, but different diffusion types depending on position on electrode.•Semi-infinite or finite length diffusion can be ...present in enzyme electrodes.•Explains the relationship between reaction plane location and EIS characteristics.
Herein, a different interpretation of electrochemical impedance spectra with a double semicircle and a straight line obtained for systems involving diffusion processes is proposed. Simulations of electrochemical impedance spectra of mediator-type enzyme electrodes by using the finite element method revealed that under certain conditions, diffusion can be a combination of apparent semi-infinite and finite length, with the diffusion type differing depending on the position on the electrode or the diffusion direction. The Nyquist plot of a system with one charge transfer and the mixed-type diffusion shows a semicircle for the charge transfer, a second semicircle for finite length diffusion (short Warburg impedance), and a straight line for semi-infinite diffusion (Warburg impedance). In mediator-type enzyme electrodes with a free-diffusing enzyme and a mediator, such mixed-type diffusion can be observed at medium substrate concentrations when the reaction plane is close to the electrode at the edges and farther away in the middle of the electrode. These simulation results may help (bio-)electrochemists to more accurately interpret impedance spectra and gain better understanding of the phenomena occurring at mediator-type enzyme electrodes and other cases involving diffusion.
The optimal conditions for fabricating a screen-printed diamond electrode for the sensitive detection of l-cysteine (Cys), a non-essential amino acid, were investigated. As-grown (AG-), ...hydrogen-terminated (H-) and oxygen-terminated boron-doped diamond powders (O-BDDP) were prepared, and BDDP-printed electrodes were fabricated using BDDP-containing inks. Comparing the linear sweep voltammograms of Cys at AG-BDDP-, H-BDDP-, and O-BDDP-printed electrodes, among the three samples, the H-BDDP-printed electrode was found to be the most suitable for the sensitive detection of Cys at low concentrations, showing a steep slope in its calibration curve and a low background current density. In addition, the H-BDDP-printed electrode exhibited a lower limit of detection (0.620 μM) and a more negative oxidation peak potential (+0.663 V vs. Ag/AgCl) and wider linear concentration range (1–194 μM) than a H-boron-doped diamond (BDD) thin-film electrode. It is thought that a slight amount of sp2 carbon on the BDDP contributed to these optimal properties. Using the H-BDDP-printed electrode, Cys was detected in a solution containing electroactive interferents (glutathione and methionine) with a recovery of 86–104%. Therefore, it was concluded that the H-BDDP-printed electrode can be used as a highly sensitive and disposable electrochemical sensor for Cys detection.
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•Screen-printed diamond electrodes have been developed for l-cysteine detection.•H-BDDP-printed electrode was found to be suitable for sensitive l-cysteine detection.•The optimal size of H-BDDP for l-cysteine detection was discussed.•Selective l-cysteine detection was demonstrated in the presence of interferents.•The BDDP-printed electrodes should be useful for disposable and sensitive sensors.
•In-situ EIS was applied to the evaluation of LIRB.•The successive impedance spectra were measured during charge–discharge sequence.•The Rct for the deintercalation of lithium was larger than that ...for the intercalation.
In-situ electrochemical impedance spectroscopy (in-situ EIS) was applied to the investigation of electrochemical properties of lithium-ion rechargeable batteries (LIRB). The in-situ EIS enables us the simultaneous measurements of the impedance spectra with charge/discharge curves by galvanostatic control. In the present paper, successive impedance spectra of positive and negative electrodes were determined by using three-electrode cell. For example, the impedance spectra of positive electrode during the charge and discharge allow the information regarding the deintercalation and intercalation of lithium, respectively, in LIRB. The charge transfer resistances of both positive and negative electrodes showed the hysteresis versus the state of charge (SOC) during charge–discharge sequence. These results indicate that the charge transfer resistance for the deintercalation is larger than that for the intercalation in the cases of both positive and negative electrodes in LIRB.
Lithium-ion batteries (LIBs) are being used as power sources for use in electric vehicles and aircraft, and so on. Early detection technique of battery deterioration is required with the spread ...adoption of electric vehicles and aircraft. Electrochemical impedance spectroscopy is a powerful method to evaluate the internal state of LIB. We recently have proposed a method to determine the impedance spectra of LIB by wavelet transformation (WT) of the external input and the output signals. In the present paper, the impedance spectra were determined by performing WT on the charge curves of the LIB without an external input signal. A capacitive semicircle and Warburg impedance appeared in the impedance spectrum determined by the WT, which is roughly consistent with the impedance spectrum measured by a frequency response analyzer (FRA). In addition, the new impedance determination method was applied to the evaluation of deteriorated batteries. The diameter of the semicircle increased with fading the battery capacity. Curve fitting was applied to the spectra determined by the WT. The sum of the resistance related to electrode structure, Rc, and the charge transfer resistance, Rct, increased as the capacity loss increased. Moreover, the parameter values were in good agreement with those calculated from the impedance measured using FRA, indicating that this new impedance determination method is useful for evaluation of deteriorated batteries. Furthermore, we emphasize that this method can diagnose the battery deterioration simply by charging the battery.
This is the first report demonstrating proof of concept for the passive, non-invasive extraction and in situ potentiometric detection of human sweat chloride ions (Cl
−
ions) using a stable printed ...planar liquid-junction reference electrode-integrated hydrogel-based touch-sensor pad without activities such as exercise to induce perspiration, environmental temperature control, or requiring cholinergic drug administration. The sensor pad was composed entirely of a screen-printed bare Ag/AgCl-based chloride ion-selective electrode and a planar liquid-junction Ag/AgCl reference electrode, which were fully covered by an agarose hydrogel in phosphate-buffered saline (PBS). When human skin contacted the hydrogel pad, sweat Cl
−
ions were continuously extracted into the gel, followed by in situ potentiometric detection. The planar liquid-junction Ag/AgCl reference electrode had a polymer-based KCl-saturated inner electrolyte layer to stabilize the potential of the Ag/AgCl electrode even with a substantial change in the chloride ion concentration in the hydrogel pad. We expect this fully screen-printed sensor to achieve the low-cost passive and non-invasive daily monitoring of human Cl
−
ions in sweat in the future.
We developed an instantaneously usable screen-printed silver/silver sulfate (Ag/Ag2SO4) reference electrode with long-term stability. The reference electrode was composed of a Ag layer, a Ag/Ag2SO4 ...layer, an inner electrolyte layer, and a liquid junction layer printed successively on a polyimide substrate. The liquid junction and inner electrolyte layers were prepared using a silica gel–poly(vinylidene difluoride) ink. The open-circuit potentials in different electrolyte solutions were compared to that measured using a commercial reference electrode. The fabricated reference electrode stabilized the potential shift within 30 min and gave 437 mV vs. saturated KCl/Ag/AgCl measured in a 1 M KNO3 solution; the result was in good agreement with the theoretical value. Furthermore, the fabricated reference electrode remained stable for 20 days. This Ag/Ag2SO4 reference electrode showed potential for application in measurement systems where contamination by chloride ions is not desirable.
•Ag/Ag2SO4 reference electrode was fabricated using screen printing technology.•It showed long-term stability and could be used instantaneously.•It indicated stable potential in solutions with a low chloride ion concentration.•It could be used for potential measurements in batteries and capacitors.
This study investigates the effect of chemical surface termination on the electrochemical characteristics of boron-doped diamond powder (BDDP). The aim is to realize highly sensitive electrochemical ...detection of ciprofloxacin (CIP) on BDDP-printed electrodes. To this end, we prepared oxygen-terminated BDDP (O-BDDP) and hydrogen-terminated BDDP (H-BDDP), and mixed them with an insulating polyester (PES) resin binder to obtain BDDP ink for the printed electrode. Scanning electron microscopy of the BDDP-printed electrodes revealed that the O-BDDPs were partially covered with PES resin, while the H-BDDPs were entirely covered with resin. This structural difference might explain the lower charge-transfer resistance of the Ru(NH3)62+/3+ redox reaction at the O-BDDP-printed electrode than at the H-BDDP-printed electrode. The slope of the calibration curve of the linear sweep voltammogram of CIP was steeper at the O-BDDP-printed electrode than at the H-BDDP-printed electrode and the O-BDD thin-film electrode, and was similar to that at the H-BDD thin-film electrode. Using the O-BDDP-printed electrode, we determined the CIP in artificial buffer-diluted urine in the concentration range 1–30 μM with a recovery of 107%. We conclude that the O-BDDP-printed electrodes provide a highly sensitive and disposable electrochemical sensor for CIP detection.
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Practical use of lithium–sulfur batteries can be realized by using “sparingly solvating electrolytes” such as Li(G4)TFSA (G4, tetraglyme; TFSA, bis(trifluoromethanesulfonyl)amide) solvate ionic ...liquid, superconcentrated electrolyte solutions, and their hydrofluoroether-diluted electrolytes. On the other hand, the battery performance such as C-rate characteristics of lithium–sulfur batteries is different depending on the electrolyte used. In order to investigate the relationship between the discharge reaction and the battery performance for lithium–sulfur batteries with 1,1,2,2-tertafluoroethyl 2,2,3,3-tetrafluoropropyl ether-diluted Li(G4)TFSA, in situ electrochemical impedance spectroscopy has been conducted. During discharge at a high C-rate, a voltage drop was observed in the discharge curve at DOD = 20–35%. The charge transfer resistance of the lithium negative electrode remarkably increased when the voltage drop occurred. Moreover, this increase was only observed for in situ measurements. The charge transfer resistance of the negative electrode is related to the resistance of the Li+ ion dissolution/deposition reaction. During discharging at a high C-rate, the Li+ ion is abundant at the negative electrode interface owing to the changes in the Li+ ion solvation structure, suppressing the Li+ ion dissolution reaction.
We determine the proper placement of the reference electrode for impedance measurements in lithium-ion rechargeable batteries with a three-electrode cell. Calculations of the impedance spectra of the ...positive and negative electrodes and simulations of the current and potential distributions between them are performed using the finite element method. In the simulation, the positive and negative electrodes are symmetrical face to face. Distortions of the loops and artifact inductive loops are observed in the impedance spectra of the positive and negative electrodes when the reference electrode is between or at the edges of the electrodes. These distortions and the diameter of the artifact inductive loops become small when the reference electrode is positioned outside the area between the positive and negative electrodes. Simulations also demonstrate that current from the positive electrode can flow to the reference electrode and then the negative electrode, i.e., part of the reference electrode facing the positive electrode becomes cathode and part of the reference electrode facing the negative electrode becomes anode. Therefore, the dissolution of reference electrode occurs during impedance measurements in a three-electrode cell and the reference electrode should be placed outside of the area between electrodes, where there is no potential modulation and gradient.
•Placement of RE in lithium-ion rechargeable batteries (LIRBs) was studied.•Proper placement of RE in impedance measurements of LIRBs was determined.•Current and potential distributions in LIRBs cell were investigated by FEM.•Dissolution of RE occurs during measurement when RE is inserted between PE and NE.•RE should be placed on the outside position of PE and NE with no potential modulation and gradient.
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