Self-made Electrode Research Articles

An All-Solid-State Ag/AgCl Reference Electrode Based on the Polydopamine Coating

A solid thin film Ag/AgCl reference electrode modified by polydopamine (PDA) was developed in order to present a stable and fixed reference potential in solution. The reference electrode consists of a silver film, an AgCl layer and a PDA-modified film. The bare Ag/AgCl reference electrode, Nafion-modified Ag/AgCl reference electrode, PDA-modified Ag/AgCl reference electrode and Nafion-PDA-modified Ag/AgCl reference electrode were fabricated respectively. The sensitivity of these reference electrodes in KCl solution was measured, and the PDA-modified reference electrode had a sensitivity of 2.1 mV/pCl. Then the stability and reversibility were tested in different solutions in buffer and cyclic voltammetric characteristics was also investigated. The results showed that the reference electrode modified by PDA was stabled in PBS solution within a month, with a standard deviation of 1.4 mV. The response potential of electrode modified by PDA always recovers to a relatively stable potential and the deviation is less than 5 mV in different pH buffer solutions. The PDA-modified reference electrode also showed minimal drift over 50 cyclic voltammetry tests compared to other reference electrodes. The reference electrode modified by PDA has good reproducibility, and the sensitivity of the sensor composed of the self-made electrode is close to that of the commercial reference electrode.

Imaging XAFS Study on Reaction Distribution of Composite Electrode Used As Commercial Lithium-Ion Battery

Demands for large-scale lithium-ion batteries for electric vehicles and grids have increased in order to reduce CO2 emissions in consideration of the global environment. To improve the reliability for practical large-scale batteries, further improvements in safety, rate capability, and cycle life are required. One of the unique behaviors taking place in lithium-ion battery composite electrodes is an inhomogeneous reaction of active materials.1 Since the heterogeneous reaction behavior induces overcharge and degradation of local active materials, the homogeneous charge-discharge reaction should be required. Ouvrard et al. reported that an inhomogeneous electrode reaction was caused during the charge-discharge process in LiFePO4 lithium-ion battery cathode, which was detected by using X-ray absorption spectroscopy.2 The study concluded that the ionic and electronic connectivity influenced by applied pressure is a crucial parameter for reaction distribution in composite electrodes.In this study, we examine the commercially utilized composite electrodes where enough electronic conduction path is formed. We compare the electrochemical characteristics using the commercial electrodes with self-made composite electrodes prepared in the laboratory and then measured the reaction distribution by imaging XAS.Two types of composite electrodes using LiFePO4 as the active material were used, and their thickness and mass loading were almost similar. Two electrode cells were assembled using 1 M LiFP6 in a solvent mixture of ethylene carbonate (EC) and ethyl metal carbonate (EMC) at a volume ratio of 3:7, and lithium counter electrode. Charge-discharge measurements were performed with an upper limit voltage of 3.6 V and a lower limit voltage of 2.0 V at rates of 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 10, 20, 30, 40 and 50 C. Imaging XAS measurements were performed at beamline BL-4 in Ritsumeikan University SR Center. Fe K-edge XAS was measured in a transmission mode using a two-dimensional detector.As a result of the discharge rate capability test, the capacity retention of 5 C was 92% for the commercial electrode and 5.4% for the self-made electrode, compared with the discharge capacity at 0.1 C, and the self-made electrode showed a remarkable decrease in capacity at high rates. The imaging XAS of the commercial electrodes implies a lack of inhomogeneous reaction after discharging at 5C. The previous reports have shown that the reaction in the planar direction of LiFePO4 proceeds from island-shaped points.3 We assume that the commercial composite electrodes are developed to be improved ionic and electronic connectivity.Reference: J. Liu, M. Kunz, K. Chen, N. Tamura, J. Richardson, J. Phys. Chem. Lett., 1, 2120-2123 (2010).G. Ouvrard, M. Zerrouki, P. Soudan, B. Lestrez, C. Masquelier, M. Morcrette, S. Hamelet, S. Belin, A. M. Flank, F. Baudelet, J. Power Sources, 229, 16-21 (2013).M. Katayama, K. Sumiwaka, R. Miyahara, H. Yamashige, H. Arai, Y. Uchimoto, T. Ohta, Y. Inada, Z. Ogumi, J. Power Sources, 269, 994-999 (2014).

Thermodynamic Study of (KCl + N,N-Dimethylformamide + Water) System Based on Potentiometric Measurements

In this research, the thermodynamic properties of (KCl + N,N-dimethylformamide + water) system were determined based on potentiometric technique. The electromotive force measurements were carried out by using self-made electrodes on the galvanic cell of type Ag|AgCl|KCl (m), N,N-dimethylformamide (w), and H2O (1 – w)|K-ISE in various mass fractions of N,N-dimethylformamide in water (0, 0.10, 0.20, and 0.30) in the molality ranging from 0.0094 to 2.5200 mol·kg–1 at T = (298.2 and 308.2) K and P = 0.1 MPa. Thermodynamic properties modeling was implemented using the Debye–Huckel extended equation, Pitzer ion interaction, and Pitzer–Simonson–Clegg models. Subsequently, unknown parameters for each model were determined and utilized to calculate the thermodynamic properties such as the mean activity coefficients, the osmotic coefficients, the excess Gibbs free energy, and the solvent activity for the system under investigation.

Determination and Modeling of Activity Coefficients of Sodium Chloride in (Glycerol + Water) Mixtures Based on Potentiometric Measurements

In this work, the results concerning to the mean activity coefficient measurements for NaCl in the (glycerol + water) system using the potentiometric method are reported. The potentiometric measurements were performed on the galvanic cells without liquid junction of the type: Ag|AgCl|NaCl (m), glycerol (wt%), H2O (1 - wt)%|Na-ISE, in various mixed solvent systems containing 0, 5, 10, 20 and 30 mass fraction percents of glycerol over ionic strength ranging from 0.0020-3 mol kg-1 at T = 298.2 K. The sodium ion selective electrode and Ag-AgCl electrode as self-made electrodes had a reasonably Nernst response. The modified zeolite was used to fabricate the sodium ion selective electrode as electrochemical sensor. The modeling of the investigated system was made based on an extended Debye-Huckel equation, the Pitzer and Pitzer-Simonson-Clegg models. The unknown parameters were determined for each model. The resulting values of the mean activity coefficients, osmotic coefficients and excess Gibbs energy are reported for the studied system.

Electro-catalytic degradation of bisphenol A with modified Co3O4/β-PbO2/Ti electrode

Ti-base Co3O4/β-PbO2 composite electrodes were prepared using electro-deposition and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry and the accelerated life testing, it indicated that the self-made electrode had high activity in electrolysis as well as excellent corrosion resistance and excellent catalytic performance. The results showed that the removal efficiency of CODCr could be reached up to 92.2% after 1.5h electrolysis at NaCl concentration of 0.020 mol·L−1, bisphenol A initial concentration of 20 mg·L−1, applied voltage of 20V, electrode spacing of 7cm and electrolyte pH of 5. The reaction mechanism and kinetics of Co3O4/β-PbO2/Ti composite electrodes electro-catalytic degradation bisphenol A mainly caused by the OH radical attacking parent molecules and the degradation followed pseudo-first-order kinetics.

Tribological properties of cobalt-based alloy coating with different cobalt contents by electro-spark deposition

The cobalt-based alloy coating with different Co contents was deposited on 45 steel by electro-spark deposition with the self-made electrode. The coating has a compact and uniform microstructure with low porosity and no visible microcracks. When Co content increases gradually, oxygen content of coating samples 1–5 decreases first and then increases in the range of 2.52 wt%–3.05 wt%; sample 3 has the lowest oxygen content of 2.52 %. Microhardness of the coating is improved remarkably compared with the substrate (HV 230.18). With Co content increasing, microhardness of the coating samples 1–5 first rises slightly and then declines rapidly in the range of HV 580.61–1052.33. Sample 3 gets the maximum of HV 1052.33, which is about 4.6 times that of the substrate. The coating presents excellent wear resistance, which first increases and then decreases when Co content increases. Sample 3 shows the best wear resistance of about 6.4 times that of the substrate. Main wear mechanism of the coating is abrasive wear and fatigue wear, along with oxidation wear under high speed or heavy load conditions. Cobalt content has an obvious influence on microhardness and tribological properties of cobalt-based alloy coating. When the cobalt content increases, the microhardness and wear resistance of the coating increase firstly and then decrease, the friction coefficient of the coating decreases firstly and then increases.

Self-made non-enzymatic silver electrode from recordable CDs for fast detection of glucose in blood

An electrochemical sensor based on a self-made electrode from recordable CDs was developed for the non-enzymatic detection of glucose by chronoamperometry. We discussed the amperometric current response of glucose with the change of potential, pH and electrode area, and determined the optimum detection conditions. The current response measurements were performed in a phosphate buffered solution (pH 6.5) with a potential of −0.50 V, and presented a linearity over the range of 0.5–13 mmol/L (r = 0.996). The experimental results of the designed sensor demonstrate that this method has merits such as simple operation, low cost and rapid responses. The results of detecting glucose in blood samples were satisfactory.

A simple and versatile PSA system for heavy metal determinations.

An easy to build potentiometric stripping analysis system for heavy metal determinations (Zn, Cd, Pb, Cu) is described which reaches good sensitivity and precision. Main components are an IBM compatible computer, an ADDA-conversion card and two selfmade electrodes, so it can be realized for one tenth of the price of complete commercial systems. A graphite pencil lead covered with a Hg-film is used as working electrode and a Ag/AgCl electrode as a combined reference/counter electrode. Reproducibility and calibration measurements are reported, heavy metal determinations on soil samples are compared with AAS results.