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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.

Tin-plated copper tubes have been widely used in cold and hot water service systems. However, leakage accidents caused by pitting corrosion can occur in such tubes; therefore, it is necessary to evaluate the effects of major environmental factors on the occurrence of local corrosion to ultimately suppress this corrosion. In the present study, the anodic polarization curves of a tin-coated copper electrode were measured in simulated freshwater containing Cl−, SO42−, and HCO3−. The anodic current increased suddenly and sharply due to the breakdown of the passive layer and the initiation and growth of pitting generation at the pitting potential. The pitting potential shifted to a more negative direction with increasing Cl− and SO42− concentrations. In contrast, the pitting potential shifted to more noble potentials upon increasing the HCO3− concentration, indicating that HCO3− has an inhibitory effect on pitting attack by Cl− and SO42−. The quantitative relationship between each anion concentration and the pitting potential was determined by multiple regression analysis. A plot of the pitting potential predicted from the created regression equation and the measured values of the pitting potential showed a positive linear relationship.

Paper-based electrochemical biosensors are a promising alternative to conventional biosensors. Herein, a screen-printed paper-based electrochemical flow biosensor was developed. The sensor comprise...

We developed a novel sticker device that can convert any metal or alloy into the working electrode of a three-electrode system, enabling simple and accurate measurement. The sticker, containing a counter electrode and a stable and accurate liquid junction-type reference electrode, is attached to the metal or alloy; meanwhile the surface exposed from a hole in the device functions as the working electrode. This sticker device was fabricated by screen-printing. The polarization curve of the copper and tin-plated copper measured using the sticker device exhibited approximately the same behavior as that obtained for the conventional three-electrode system. The characteristics of various materials can be easily evaluated using this system by only dropping a small amount of solution.

A major issue during battery operation is hydrogen evolution (HE) at the negative electrode surfaces of Mg. However, during the current methods used for analyzing HE, the pH increases because of the HE reaction, which critically affects battery performance. Therefore, herein, a channel flow electrode system was applied in the in situ detection of hydrogen gas (HG) generated on Mg dissolution by gas chromatograph. This method enabled HG detection without an increase in pH upon Mg dissolution because electrochemical measurements could be performed under laminar flow. The HE efficiencies of Mg dissolution were thus estimated at various applied current densities.

Highly functional polymer-gel materials that include highly conductive gels, moving gels, and stimulation-responsive gels are important in a number of applications, including actuators, microrobots, and artificial muscle; hence, the development of new gels with superior properties is an important objective. Herein, we report the fabrication of a flexible electrochemical actuator by the direct transfer of a carbon electrode, formed by screen-printing on a silicone sheet, onto the surface of a poly(acrylic acid) gel containing cupric ions, which was prepared by immersing the poly(acrylic acid) gel in a 0.1 mM copper sulfate solution. Due to the oxidation of copper and the reduction of cupric ions, when potentials of 0.6 V and −0.7 V are alternately applied to the poly(acrylic acid)-cupric-ion gel actuator, it repeatedly expands and contracts along with concomitant copper-ion redox transformations when immersed in 0.1 M aqueous sodium perchlorate. This actuator demonstrated a 0.29% change in expansion ratio, which is 2.3-times larger than that of a previously reported electrochemical actuator (0.13%) formed with a sputtered gold electrode on a conventional polymer substrate.

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.

Poly(glycidyl methacrylate) (poly(GMA)) bearing pendant glycidyl groups, grafted on the surface of MgO-templated carbon (MgOC), is useful for forming strong multipoint covalent bonds with amino fun...

The dezincification corrosion is a major limiting factor for use of brass in the plumbing system as it may cause the water leakage accident. It is well known that the porous copper rich layer is formed on the brass surface due to the dezincification corrosion, namely, the selective dissolution of zincoccurs on the brass surface1,2. We have developed the real-time surface observation system with channel flow double electrode to examine the dissolution behavior of copper and magnesium3-5. In the present study, a real-time cross-sectional surface observation system was developed to investigate the dezincification corrosion behavior of brass during electrochemical measurement. An electrochemical cell was made using transparent acrylic plates. An electrochemical measurement was performed by a three-electrode system. The brass plate and the platinum wire were used as the working electrode and the counter electrode, respectively. A KCl-saturated silver/silver chloride electrode was used as the reference electrode. The electrolyte solution was 0.5 M NaCl containing 5 mM NaHCO3. The temperature of electrolyte solution was kept at 60 oC. The brass plate was fixed at wall surface of the electrochemical cell to record the video of the brass cross-section. The video of the brass cross-section was taken by an optical microscope combined with a charge-coupled device camera under the galvanostatic polarization for 24 h. The brass cross-section under the galvanostatic polarization was successfully observed from the video recording, indicating that the dissolution of brass progressed inhomogeneously in the depth direction. We estimated the erosion depth from the cross-sectional surface images at each measurement time. The results demonstrated that the erosion depth was increased with time under galvanostatic polarization. The dissolution process involving preferential dissolution of zinc or the simultaneous dissolution of zinc and copper was discussed based on the video images and the potential changes of brass during the measurement. References: 1) H.W. Pickering, C. Wagner, J. Electrochem. Soc., 7, 114 (1967). 2) Y. Hoshi et al., J Solid State Electrochem, 19, 3551 (2015). 3) Y. Hoshi et al., J. Electrochem. Soc., 164, C450 (2017). 4) Y. Hoshi et al., Surf. Finish. Soc. Jpn., 69, 34 (2018). 5) Y. Hoshi et al., J. Electrochem. Soc., 165, C243 (2018).

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. Keywords: Reference electrode, Silver/silver sulfate, Screen-printing, Long-term stable, Instantaneously usable

An instantaneously usable fully printed paper-based three-electrode system was developed for use as cost-effective and disposable biosensors and ion sensors. The three-electrode system was composed...

Knowledge of the electrochemical parameters of the components of lithium ion batteries (LIBs) during charge–discharge cycling is critical for improving battery performance. An in-situ electrochemical impedance spectroscopy (in-situ EIS) method, where galvanostatic-controlled EIS is used to analyze a battery, enables the simultaneous acquisition of impedance spectra and charge–discharge curves. In the present paper, the in-situ EIS was used to investigate LiCoO2 electrodes with different particle sizes. The semicircles in the instantaneous impedance spectra acquired during charge–discharge were smaller than those in the impedance spectrum corresponding to an equilibrium state. In addition, the charge transfer resistance Rct during the discharging process was larger than that during the charging process; thus, hysteresis, defined as a difference between the Rct during discharging and that during charging, was observed. The particle size in the active material and the charge/discharge rate affected the magnitude of the Rct hysteresis, indicating that the in-situ EIS is useful for investigating electrode materials capable of high-rate charge–discharge processes.

The printable paper-based enzymatic biofuel cell (PBFC) to directly power small devices is an important objective for realizing cost-effective and disposable energy harvesting devices. In the present study, a screen-printed circular-type PBFC, composed of a series of 5 individual cells, was constructed. The PBFC exhibited the open circuit potential of 2.65 V and maximum power of 350 μW at 1.55 V, which were sufficient to illuminate an LED without requiring a booster circuit. The output voltage of this PBFC can also be easily adjusted as required.

A novel paper‐based biofuel cell with a series/parallel array structure has been fabricated, in which the cell voltage and output power can easily be adjusted as required by printing. The output of the fabricated 4‐series/4‐parallel biofuel cell reached 0.97±0.02 mW at 1.4 V, which is the highest output power reported to date for a paper‐based biofuel cell. This work contributes to the development of flexible, wearable energy storage device.

A new analytical method was developed to determine the electrochemical impedance of lithium-ion rechargeable batteries (LIRB) at an arbitrary state of charge (SOC). Wavelet transformation (WT) is one of the waveform analysis methods, which allows the determination of frequency domain data as a function of time. The frequency domain data are obtained by convolution integral of a mother wavelet and original time domain data via the WT. A complex Morlet mother wavelet is used to obtain the complex number data in the frequency domain. The time series data of input current and output voltage signals are recorded by superimposing the double pulse current as an input signal to constant charge current for the charge of LIRB without stopping galvanostatic polarization. The double pulse current is composed of symmetrical positive and negative square waves. In this case, the SOC of LIRB is not affected by the input signal because the total amount of charge calculated from double pulse current is 0C. The impedance spectrum of LIRB at SOC 25% is determined in the frequency range from 0.1 to 100 Hz during charge/discharge cycles without stopping galvanostatic polarization for the charge/discharge.

Boron-doped diamond powder (BDDP) was prepared using various sizes of diamond powder (DP) core (300–2600 nm), and the electrochemical properties of a screen-printed electrode obtained using the BDD...

An in situ hydrogen gas detection system was developed to determine the hydrogen evolution rate (HER) from Mg during anodic potentiodynamic polarization (APP) curve measurement. The system, which is composed of an electrochemical cell and a gas-chromatograph, allows for successive determination of HER during the APP curve measurement because evolved gas was delivered directly to the gas-chromatograph using Ar carrier gas. As the HER could be determined every 104 s after starting APP measurement from corrosion potential, the HER could be plotted against polarization potential. It was confirmed that the HER was correlated with anodic current values in the APP curve.

Printable wearable lactate biosensors have attracted significant attention, and printable lactate biofuel cells have gained popularity as suitable power supplies for these sensors. However, realizing an appropriate power supply for the practical application of these sensors as wearable devices, it is necessary to improve the output of lactate biofuel cells. In this study, we fabricated a lactate biofuel cell that employed paper substrate using screen printing. The proposed paper-based biofuel cell (PBFC) features a novel electrode design that affords an open circuit voltage of approximately 3.4 V when using an array with six cells in series. Furthermore, a 6 × 6 array of the lactate biofuel cell, i.e., an array comprising six cells in series and six cells in parallel, yielded a power output of 4.3 mW. To the best of our knowledge, this output of the proposed design is higher than those of previously reported lactate biofuel cells. Arrays of the proposed cell were capable of driving a Bluetooth low-energy device for wireless transmission, without requiring a booster circuit. A commercially available activity meter could be driven for 1.5 h using artificial sweat to fuel a 6 × 6 array of the PBFCs.

Simulations enable fundamental electrochemistry to be more deeply understood and are useful tools for the further development of electrochemical processes. However, important parameter restrictions have thus far limited the applicability of electrochemical simulations. In this study, we developed a realistic model of mediator-type enzyme electrodes to accurately simulate cyclic voltammetry and electrochemical impedance spectroscopy by considering the current arising from electrochemical double-layer charging. Implementation of the finite element method in these calculations resulted in a model with very few boundary conditions. The model was successfully tested for various enzyme and electrode reaction kinetics and subsequently adapted to describe immobilized enzymes and mediators. The insight gained through this study has implications for the further development of biosensor and biofuel cell technologies.

A biofuel cell that can generate electricity using only water is expected to be used as a new energy harvester for an emergency power supply. A new 4-series/4-parallel structured paper-substrate biofuel cell was prepared using a fuel supply paper preloaded with glucose and phosphate buffer salts. When a power generation test was conducted by supplying water to the fuel-preloaded paper, the paper-based biofuel cell produced an output approximately 90% (0.84 mW) of that obtained by supplying a phosphate buffer containing glucose as the electrolyte. The open-circuit voltage was 2.1 V, and an LED could be powered by simply supplying water to the cell without using a booster circuit.

A three electrode system is widely used to evaluate the corrosiveness of metal. However, three electrode system normally requires various instruments such as a salt bridge, reference electrode, counter electrode and flask. Thus, the three-electrode-type corrosion test is often applied to lab tests rather than field work. To solve the problem, in this study, we developed a new concept of a three electrode system using a sticker device that enables the simple and accurate measurement just only stick the device on a test metal. The three-electrode-type sticker device was fabricated by screen printing. Figure 1 (a) shows the model of the sticker device. A reference electrode with a liquid junction developed previously in our group1) used for the reference electrode part. A silver layer, a silver-silver chloride layer, a liquid junction layer, and a saturated KCl layer were also forms on the PET substrate by screen printing. A working electrode part of the sticker device has a 2 mm diameter hole. Electrochemical measurements can be performed by attaching this device to the measurement target. In this study, tin-plated copper and copper was used as a substrate. At the reference electrode of the sticker device, a solution is penetrated from the liquid junction layer, and the saturated KCl layer absorbs the solution to form a saturated KCl aqueous solution, and functions as a reference electrode. Figure 1 (b) shows the results of the open circuit potential measurement at the reference electrode of the sticker device. The open-circuit potential was stable at a solution concentration in the range of 10 ppm to 300 ppm after 60 seconds. Also, it was found that open-circuit potential was within ± 15 mV vs. SSE. It was confirmed that the potential after 300 seconds of immersion were almost constant in that each solution concentration, and that the device reference electrode had a stable with potential independent of the solution concentration. Figure 1 (c) shows polarization curve of the tin-plated copper measured using the sticker device. When the working electrode potential was scanned to the noble side, the current drastically increase due to the occurrence of pitting corrosion between -0.2 V and 0.1 V, depending on the solution concentration. The pitting potential was confirmed to have a positive correlation with the chloride ion concentration. Reference 1) M. Komoda, I. Shitanda, Y. Hoshi, and M. Itagaki, Electrochemistry, 87, 65 (2018). Figure 1

The pitch of wiring on printed circuit boards has become finer for the development of small and lightweight electronic devices. Due to the finer pitch of wire, dew condensation causes a short circuit of wiring easier and there is a risk of breaking the wiring due to slight corrosion. It is crucial to develop a sensor for monitoring dew condensation and corrosion of wiring in order to prevent these corrosion phenomena. Our group 1) has developed a corrosion monitoring sensor with screen printing techniques. This sensor, which has a comb-like structure of silver wiring on the boards, can monitor dew condensation environments using electrochemical impedance spectroscopy (EIS) because of the change of impedance spectra with condensation condition. Aiba 2) et al. have fabricated printed –type corrosion monitoring sensor which can evaluate amount of dew condensation. This sensor, which has wiring of a reference resistance by coating anticorrosion, can quantitatively evaluate dew condensation by standardizing the output impedance from the sensor with reference resistance. In this study, monitoring corrosion sensor that can accurately detect corrosion of wiring and dew condensation was developed using screen printing. Polyimide was used for a substrate of the developed sensor, and silver wiring was printed on the substrate by using screen printing. The silver wiring consists of two parts. The upper and lower parts have comb-like structure and two parallel straight lines, respectively. Corrosion of wiring and dew condensation can be detected by the upper and the lower patterns, respectively. UV irradiation was performed for 10 minutes in an oxygen atmosphere only on the substrate to make hydrophilic partially. Dew condensation on the surface of the corrosion sensor was detected by measuring impedance spectra. The measurements were performed in the chamber that temperature and the relative humidity were set at 25 ℃ and 90 %, respectively. The frequency range of impedance measurements were from 10 mHz to 10 kHz. The amplitude of voltage modulation for the sensor was 10 mV. The voltage during the measurements was set at 0 V. In impedance spectra of the sensor without UV ozone treatment, although dew condensation occurred, the wiring did not short circuit and impedance spectrum remained on the real number axis. On the other hand, in impedance spectra of the sensor with UV ozone treatment, impedance spectrum of capacitive semicircle attributed to short circuit of wiring due to dew condensation was observed, that is, it was possible to detect dew condensation with high sensitivity. References I. Shitanda, A. Okumra, M. Itagaki, K. Watanabe, Y. Asano, Sensor Actuat B-Chem, 139, 292 (2009). A. Aiba, N. Fujii, Y. Hoshi, I, Shitanda, M. Itagaki, J. Electrochem, Soc., 165, C743 (2018).

Lactate has long been known as the indicator for distinguishing aerobic and anaerobic metabolism, and thus is a useful marker for metabolic disorders and the state of exercise [1]. Especially, the continuous monitoring of sweat lactate is a useful non-invasive method for real-time tracking the progress of exercise, e.g. of athletes, or of physical therapy patients. In biosensors for continuous monitoring, the biological recognition element, e.g. lactate oxidase (LOx) has to be immobilized on the electrode. Our group previously reported of a glucose sensor in which glucose dehydrogenase (GDH) was immobilized covalently on screen-printed MgO-templated mesoporous carbon (MgOC) modified by graft polymerization, and showed improved stability [2]. Likewise, in this study, radicals were introduced on the surface of the MgOC by electron beam irradiation. Next, glycidyl methacrylate (GMA) was polymerized on the radicalized MgOC, which resulted in epoxy groups on the surface. Ink was prepared by dispersing this poly(GMA)-MgOC (GMgOC) and a polyvinylidene difluoride (PVdF) derivative in N-methyl-2-pyrrolidone (NMP). The ink then was used for the final layer of the working electrode (WE) of a screen-printed 3-electrode strip. Next, 1,2-naphthoquinone was deposited on the WE as mediator, which is insoluble in water and thus is unlikely to dissolve into sweat during the measurement. Finally, LOx derived from Enterococcus faecium was immobilized on the WE by binding covalently to the epoxy groups. This combination of LOx immobilized on screen-printed GMgOC and naphthoquinone promises the construction of stable lactate biosensors suitable for continuous measurements. Furthermore, in this study, two other points were considered for the design and construction of the sensor device. Firstly, the sensor should be constantly supplied with a minimum amount of sweat, without the supply being interrupted. Secondly, the materials and texture of the parts of the sensor in direct contact with the skin should not be irritating. An integrated flow system can solve both points; it ensures a constant supply of sweat, and limits the material and texture in direct contact with the skin. For the construction of the flow system, first, a mold was formed on a silicon wafer using an epoxy-based negative photoresist. Next a degassed mixture of polydimethylsiloxane (PDMS) monomer and catalyst was poured over the mold and cured at 80°C for 1 hour. In first trials, the sensor and flow system were pressed together tightly onto artificial sweat glands. Leakage was prevented by constructing a connector for the sensor out of conducting adhesive tape. Potassium phosphate buffer (100 mM, pH 7.0) containing various amounts of sodium lactate were pumped through the system at 80 µL/min using a syringe pump. Figure 1a shows the response of this system to varying concentrations of lactate. The spikes at the change of concentration are due to a change in the flow when switching the syringe. The delay between the switch of the syringe and the change in response current is due to the lag time until the lactate reached the sensor. The plot of the response current vs the lactate concentration (Fig. 1b) shows a concentration dependent response up to 20 mM lactate. These results indicate that this system is suitable for measuring sweat lactate continuously. Acknowledgement: This work was partially supported by JST-ASTEP Grant Number JPMJTS1513, JSPS Grant Number 17H02162 and Private University Research Branding Project (2017-2019) from Ministry of Education, Culture, Sports, Science and Technology, and Tokyo University of Science Grant for President's Research Promotion． References [1] M.E. Payne, et al.; Sci. Rep., 9, 13720 (2019). [2] I. Shitanda, et al.; Bull. Chem. Soc. Jpn., 93, 32-36 (2020). Figure 1

Polymer electrolyte fuel cells (PEFC) is energy converter with high efficiency and operates at low temperatures of 80oC, thus it gains attention as an automotive power plant. Stainless steels, which could be used as a PEFC bipolar plate material, can be made very thin1), and has the advantage that the power density of a single cell can be improved. However, it has been reported that the proton conductivity of the electrolyte membrane decreases due to the dissolved iron and chromium ions from the polarized stainless steels due to the current fluctuation during PEFC operation2-3). In this study, the surface treatment method of stainless steels for improving the corrosion resistance was proposed and the electrochemical properties were evaluated. The anodic polarization curve of stainless steels was measured by a three-electrode system using an electrochemical measurement system (HZ-7000, Hokuto). The working electrode was SUS316L with various surface treatments. A platinum wire and a silver-silver chloride electrode were used for counter and reference electrodes. The electrolyte was 1.0 M H2SO4 (pH 3) containing 1 ppm NaCl and 3ppm NaF. and this electrolyte is defined as a PEFC simulation environment. The measurement temperature was 80oC, the potential scan range was from the immersion potential to 1.5 V vs. SSE, and the potential scan rate was 100 mV min-1. Three types of stainless steels were used for the working electrode: I. SUS316L, II. SUS316L treated by chemical conversion (CC SUS316L), and III. SUS316L anodized in electrolyte for chemical conversion (anodized SUS316L). The electrolyte for chemical conversion was a 1:1 mixture of 0.1 M Na2WO4 aqueous solution and 0.1 M Na2MoO4 aqueous solution, and the temperature of electrolyte for chemical conversion was 25oC. In the treatment II, SUS316L was immersed in the electrolyte for chemical conversion for 5 min. In the treatment III, SUS316L was polarized in a electrolyte for chemical conversion at an applied potential of 1.0 V vs. SSE for 5 min. Figure 1 displays the anodic polarization curves of SUS316L with various surface treatments in the simulated PEFC environment. The anodic polarization curve of SUS316L showed passive range from the immersion potential -0.3 V vs. SSE to 0.7 V vs. SSE and small current peak due to the formation of the passive film around 0 V vs. SSE. In the transpassive region at the potential nobler than 0.7 V vs. SSE, the current density region increased sharply. At potentials nobler than 1.3 V vs. SSE, the current density increased sharply due to electrolysis of water. The shape of the anodic polarization curve of the CC SUS316L was almost the same as that of the SUS316L, however, the polarization curve showed a small current density in the passive and transpassive regions. No passive region was observed in polarization curve of the anodized SUS316L. And compared to SUS316L and CC coating SUS316L, the immersion potential shifted to noble and the current density in the transpassive region decreased. References 1) F, Barbir. “PEM Fuel Cells Theory and Practice”, Academic Press, 4 (2005), 100, 101. 2) A. Pozio, R. F. Silva, M. De Francesco, L. Giorgi, Electrochim. Acta, 48 (2003), 1543-1549. 3) H. Wang, J. A. Turner, J Power Sources, 183 (2008), 576-580. Figure 1