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Oxidation–Reduction Reactions
Published in Paul Mac Berthouex, Linfield C. Brown, Chemical Processes for Pollution Prevention and Control, 2017
Paul Mac Berthouex, Linfield C. Brown
The number of electrons exchanged during a redox reaction must balance. The net charge must be the same on both sides of the equation in order to account for the electrons that are transferred. The number of electrons gained by the molecules containing the oxidizing species (which is reduced) must equal the number of electrons lost by the molecules containing the reducing species (which is oxidized).
Three-Dimensional Nanostructured Electrode Architectures for Next Generation Electrochemical Energy Storage Devices
Published in Ranjusha Rajagopalan, Avinash Balakrishnan, Innovations in Engineered Porous Materials for Energy Generation and Storage Applications, 2018
Both primary and secondary batteries make use of Faradaic or oxidation-reduction (redox) reactions to store electronic charges. The term redox reactions refer to a class of chemical reactions in which electron transfer takes place between participating molecules. The atom or molecule that gives up one or more electrons in a redox reaction is the reducing agent and is said to be oxidised after the reaction. For each reducing agent in such a reaction, there has to be a complementary oxidising agent that is reduced by electron transfer. In some redox reactions such as combustion of hydrocarbons, the electron transfer takes place during the atomic rearrangement of the reacting molecules and no electrical current is involved. On the other hand, in an electrochemical cell, the reducing and oxidising agents in the form of the two electrodes are physically separated from one another and electron transfer manifests as an electrical current between the two electrodes. During discharge of a battery, the anode loses electrons and is oxidised. The cathode gains electrons and is chemically reduced. The electrons are transferred from the anode to cathode via an external circuit and deliver energy to a load such as a resistor or light emitting diode. The energy of the electrons is related to the free energy of the redox reaction involved in the battery and can be calculated using the Nernst equation (Conway 1999). In the rechargeable batteries which are of interest here, the redox reactions are all reversible. During charging of the battery by an external power supply, the anode gains electrons (reduction) while the cathode loses electrons (oxidation). As a result, the anode of a secondary battery is always the negative terminal while the cathode is always the positive terminal regardless of the mode of use. It is also important to point out that the battery is an asymmetric EES device with different cathode and anode materials. Electric charge is stored within the bulk volume of the cathode and anode.
Oxidation of iminodiethanol by Ce (IV) in microheterogeneous system: a comprehensive kinetic analysis
Published in Journal of Dispersion Science and Technology, 2023
Ranjan Kumar Padhy, Sarita Sahu
Electron transfer reactions are intrinsic part of myriad number of metabolic processes to produce energy for sustenance of life. Besides biological, a large number of industrial, environmental and pharmaceutical issues can be addressed through processes that involve redox reactions. Kinetic studies of these electron transfer reactions help in understanding the mechanistic pathways. Oxidation of alcohols to aldehydes or acids is a significant industrial and biological process and hence has been studied extensively.[1–8] Hydrophilic iminodiethanol (a secondary amine) is extensively used in industries for the production of fine chemicals, surfactants, pharmaceuticals[9,10] and hence is the choice as substrate in the present work. In continuation of our earlier work with surfactants and redox reactions,[11–15] we present here the Mn(II) catalyzed oxidation of iminodiethanol by Ce(IV) in acidic conditions in surfactant medium. Although literatures are available[16–20] on the oxidation of iminodiethanol with various oxidizing agents, they present varied kinetic models viz; kinetic expressions, rate determining steps, equilibrium conditions and varied product formation. Also, there is no information on the oxidation process in the microheterogeneous medium that we have executed in the present case. The degradation technique adopted by Yaser et al.[20] used UV radiation process and they have not reported the influence of any parameters besides the effect of pH. While working with similar substrates, Singh et al.[16] has predicted an acid as the reaction product, Shukla et al. and Aswathi et al.[19] has concluded an aldehyde as the final product whereas Puttaswamy et al.[18] has confirmed the formation of a mixture of aldehyde and acid. The selection of Ce(IV), a versatile reagent as oxidant is done because Ce(IV) and Ce(III) form an excellent redox couple with a reduction potential of 1.28–1.70 volts of (Ce3+, Ce4+) in different acidic environment.[21–27] The choice of Mn(II) as the catalyst for the purpose is because of its extensive use in homogeneous catalysis.
CMOS electrochemical measurement circuit for biomolecular detection
Published in International Journal of Electronics, 2018
Wei-Chiun Liu, Shao-Te Wu, Bin-Da Liu, Chia-Ling Wei
In this work, urinalysis for melatonin detection is the main purpose of the proposed system with inexpensive biosensors. In contrast to the blood test from human body, urinalysis is non-invasive, simple and inexpensive. The proposed system adopts electrochemical reaction detection, which is different from spectroscopy and biomarker detection techniques. Various compounds lose electrons (oxidation) or gain electrons (reduction) during reduction-oxidation (redox) reactions. This work adopts cyclic voltammetry to record the current change of the redox reaction to the periodic triangle wave signal. The proposed voltammetry potentiostat chip works in a three-electrode configuration, with the working electrode (WE), reference electrode (RE) and counter electrode (CE) soaked in a conductive electrolyte solution for biomolecular measurements. The WE serves as a surface where the electrochemical reaction occurs and the current can be detected. The RE provides a stable and known electrode potential. The high stability of the electrode potential is acquired by employing the redox system containing constant concentrations of each target molecule of the redox reactions; no current flows through the RE. The CE provides the required current for the WE. For example, if there is 100 μA current flowing into the WE, there will be 100 μA flowing out of the CE. The proposed circuit can sense bidirectional currents in the range of ±15–±1500 µA with high linearity and can be integrated with a data acquisition (DAQ) card for cyclic voltammetry measurements. Using the current readout circuit reduces the current used for redox sensing to the range of ±0.1–±10 µA; this fixed current flows into the capacitor. A current-to-time converter achieves high resolution by converting the fixed current into the digital pulses taken to charge or discharge a capacitor. The duty cycle of the digital pulses is proportional to the magnitude of the redox current. The improved comparator can control itself and generate a clock signal without any external clock input signal in the current-to-time converter. The switches of the current readout circuit are controlled by the voltage detection circuit for the positive and negative flow of current in the redox reactions. In this work, the magnitude of the redox current at the WE is directly converted to proportional digitized time measurements without any complex analog-to-digital conversion circuit. Different from the voltage readout-type circuit (Chen, Liu, Li, Xiao, & Chen, 2016; Ghoreishizadeh et al., 2014, 2017; Mross et al., 2015), the proposed circuit converts the sensed current into digitized time. However, the proposed circuit can still achieve high linearity and measure a wide current range. The measurement results would be read easily when the proposed circuit is integrated with the general digital system.