A New Fabrication Method of Chloride Sensor for Wat...

Jo Nov 24, 2024

Chloride sensors have found wide application in the fields of environment monitoring, tideland agriculture, soil science and water supply systems since chloride is widely distributed in the form of compound in nature. Although high chloride concentrations in environmental samples do not cause harm to the human body, they can cause severe corrosion in metallic pipes, leading to the destruction of water systems and to the increase in the concentration level of metal ions in drinking water. Therefore, the maximum allowable Cl⁻ level of 250mg·L⁻¹ has been established by the World Health Organization (WHO) for drinking water and natural water.

Usually, chloride ions in solution can be measured by gravimetry, titrimetry, spectrophotometry, potentiometry, coulometry and ion chromatography. Among them, the major applications in the industrial field are spectrophotometry, potentiometry (ISE), and coulometry.

For this purpose, optical, fluorescent, and electrochemical sensors have been developed. Optical sensors enable measurement regardless of the pH or temperature of the solution, and fluorescent sensors have the advantages of good selectivity and high sensitivity to Cl^- and short response time. However, these sensors are relatively expensive and have shortcomings of short lifetime due to photolysis or bleaching of the sensing materials.

In many cases, electrochemical sensors use potentiometry based on the half-cell potential of a silver/silver chloride (Ag/AgCl) electrode measured compared to a reference electrode at equilibrium. The potentiometric determination of chloride by Ag/AgCl electrode has been widely used in harsh applications due to its low cost, simple fabrication and long-term stability.

Kim Kyong Il, a researcher at the Faculty of Electronics, has proposed a new and simple fabrication method of a highly sensitive Ag/AgCl chloride sensor for real-time measurement of water quality. He fabricated the working electrode by electrodeposition and melt deposition of AgCl + Ag₂S on the surface of Ag wire and coating the PVC film on it.

The study showed a good linear relationship between the logarithm of chloride ion concentration and the electrode potential when the chloride ion concentration in tap water, seawater and agricultural irrigation water ranged from 5×10^-4 to 1mol·L^-1. The potential response was affected by pH, but the ions commonly present in environmental samples such as K⁺, Ca²⁺, Na⁺, NO₃^-, SO₄^- were not affected.

For more details, please refer to his paper “A Simple Fabrication Method of Chloride Sensor Based on Hot-Dipped Ag/AgCl@PVC for Water Quality Monitoring” in “Water Air Soil Pollut” (SCI).

A Method for Grounding Resistance Calculation of Ve...

Jo Nov 24, 2024

Grounding plays a very important role in ensuring safe and reliable operation of power systems and protecting people and electrical equipment. The continuous increase in the voltage level and scale of power systems has resulted in the increasing strictness of the technical requirement for grounding devices. Grounding resistance is an important index to evaluate the effectiveness and safety of the grounding system.

The grounding resistance is usually rated at 10Ω for thunderbolt protection, and 1Ω or less than that at large scale substations.

The factors influencing the grounding resistance of the vertical electrode are the radius and length of the electrode, the soil resistivity and the embedding depth. It is essential for the design of the vertical grounding electrode to get a mathematical model of the grounding resistance that comprehensively reflects the influences of the factors on the grounding resistance of the vertical grounding electrode.

Many authors have published their research results for the mathematical modeling on the grounding resistance of vertical grounding electrodes, but they considered only the length and diameter of the vertical grounding electrode and the soil resistivity.

The length and diameter of the vertical electrode as well as the embedding depth affect the grounding resistance.

Kwon Hye Yong, a section head at the Faculty of Electrical Engineering, has obtained a mathematical model for the grounding resistance of a vertical electrode that accurately reflects the influence of embedding depth in a homogeneous soil, and verified its accuracy through computer simulation analysis and field measurements at different soil resistivity conditions.

The computational results by the proposed model agree with the results of computer simulation analysis and field measurements.

For more information, please refer to her paper “A Method for Grounding Resistance Calculation of the Vertical grounding electrode” in “Electric Power Systems Research” (SCI).

Real-time Analysis of Vanadium Species (V(IV)/V(III...

Jo Nov 23, 2024

Currently, redox flow batteries are the most promising candidates for renewable energy storage in the field of MW-scaled electrical energy storage technologies, among which vanadium redox flow batteries (VRFBs) have advantages of wide application range, low maintenance cost, strong load balancing capability, long cycle life, etc.

In VRFBs, electrolyte is one of the important components, which has a significant impact on device performance and cost.

During the continuous electrolyte preparation, the vanadyl sulfate (V(IV)) solution from the mixing reactor is continuously in contact with the cathode of several cascaded cells, and the V(IV) solution is partially reduced to the V(III) solution in the first cell, and then completely converted to V(III) in the final cell. During electrochemical reduction, a solution of V(IV)/V(III) ratio 1:1, i.e., a neutral solution and a solution V(III) from the final cell, is used for VRFBs. Therefore, the real-time analysis of each vanadium species in the electrolyte preparation process is essential and of great significance.

Potentiometric titration is commonly used to directly determine vanadium electrolyte concentration. This method is not suitable for online monitoring because it is time-consuming and requires experiments. Recently, digital image-based methods have been selected for quantitative analysis in analytical chemistry. Moreover, the use of digital image analysis has attracted considerable attention in studying electrochemical processes with color changes. Digital image acquisition is a non-contact, non-invasive, cost-effective technique and it can overcome certain problems in classical spectroscopic analysis such as reduced and scattered spectral signals. These analytical methods have advantages such as low cost, high analytical accuracy and short analysis time.

Jon Sang Mo, a researcher at the Faculty of Chemical Engineering, has proposed a digital image-based analytical method to determine the concentration of vanadium species (V(IV)/V(III)) in the process of vanadium electrolyte preparation. Since this method is simple in procedure and less time-consuming compared to other analytical methods, it could be applied to real-time analysis in the process of electrolyte preparation.

You can find the details in his paper “Analysis of vanadium species(V(IV)/V(III) in the electrolyte manufacturing process for vanadium redox flow battery using digital image” in “Journal of Electroanalytical Chemistry” (SCI).