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Fundamentals of Semiconductor Photoelectrochemistry
Published in Anirban Das, Gyandshwar Kumar Rao, Kasinath Ojha, Photoelectrochemical Generation of Fuels, 2023
Mamta Devi Sharma, Mrinmoyee Basu
part of the electrode, i.e., half-cell can be considered like equation 2.8. Here the electrode is dipped in an electrolyte solution and an equilibrium is established between the oxidant and the reductant due to the exchange of electrons for the process. The measured potential of the half-cell is the electrode potential, and in standard conditions, it is named as standard electrode potential.
Reactions and Electrolytes
Published in Marc J. Assael, Geoffrey C. Maitland, Thomas Maskow, Urs von Stockar, William A. Wakeham, Stefan Will, Commonly Asked Questions in Thermodynamics, 2022
Marc J. Assael, Geoffrey C. Maitland, Thomas Maskow, Urs von Stockar, William A. Wakeham, Stefan Will
Hence, by measuring the emf of a galvanic cell, under conditions as close as possible to reversible (i.e. as the current drawn tends to zero), it is possible to obtain the Gibbs energy change for the cell reaction. This could also be obtained from the electrode potential of the two half-cell reactions but they cannot be measured in isolation, only as part of an electrochemical cell. Instead, by convention, the standard electrode potential E⦵ for any individual electrode reaction is measured in a cell relative to a standard hydrogen electrode (SHE) where the activities of all the reactants are unity. This SHE is formed by bubbling hydrogen at 0.1 MPa (i.e. fugacity p˜ = 1) and 298.15 K over an inert platinum electrode in an acidic solution (e.g. HCl) with hydrogen ion activity aH+ = 1; it is depicted as Pt|H2|HCl, with a half-cell reaction H++e−→12H2.
Biological fouling and corrosion resistance of Ni-based coating on AH32
Published in Surface Engineering, 2023
Su Zhiwei, Zhou Yanwen, Yan Caibo, Zhang Kaice
Marine steel must be exposed to seawater for a long time, and the corrosion resistance of steel and coated steel is required. Samples of the AH32 steel and NiCrAlY and NiCrAlY(Ag) coatings were soaked in simulated seawater for 30 min to obtain stable corroded surfaces before the tests. The polarisation curves are shown in Figure 6, and the corrosion potentials and current densities are listed in Table 2. The corrosion potentials of the AH32, NiCrAlY, and NiCrAlY(Ag) coatings vary slightly. The corrosion current densities of the AH32 and NiCrAlY(Ag) coatings were of the order of 10−5 A, which was one order higher than that of the NiCrAlY coating, 4.85× 10−6 A cm−2. The corrosion resistance of a Ni-based spray coating with a rough surface and porous structure might deteriorate compared to that of Ni-based body materials [35], and that of aluminium is also poor in marine environments [36]. Therefore, the corrosion current of Ni-coated AH32 decreased by only one order of magnitude. The standard electrode potential of Ag is 0.8 V and that of Al is −1.6 V [37]. The addition of Ag increased the potential difference between the coatings, which increased the corrosion current density. The rough surfaces and holes of the porous coatings may provide pathways for corrosion particles [38].
Influence of zinc-dipping on electroless nickel coating on magnesium alloy
Published in Surface Engineering, 2019
Xiurong Guan, Hongda Zhu, Jingwei Shi, Shouqiang Wei, Zhongcai Shao, Xiaoyi Shen
Electroless plating can form cathodic protective coatings with uniform thickness, corrosion resistance and wear resistance on the surface of magnesium alloys, which is one of the important methods for surface treatment of magnesium alloys [9–13]. The standard electrode potential of magnesium and nickel was −2.36 and −0.25 V, respectively. The difference between them is so great that it is difficult for a nickel to deposit directly on the surface of magnesium [14]. Therefore, a pre-impregnated layer as medium coating is necessary, and the potential of the pre-impregnated layer such as the conversion coating is between that of magnesium and nickel [15]. The standard electrode potential of zinc was −0.76 V; adding a good adhesion layer of zinc between magnesium and nickel is beneficial to the deposition of metallic nickel [16–18]. The zinc coating can be well combined with magnesium and subsequent nickel coating, and can cover the defects of the surface of the magnesium alloy substrate, which is beneficial to obtain ideal coating. Therefore, it is of great significance to study the pretreatment of zinc dipping.
Monitoring of chloride-induced corrosion in steel rebars
Published in Corrosion Engineering, Science and Technology, 2018
Chengming Lan, Muhuiti Tuerhan, Caiping Liu, Hui Li, B. F. Spencer
The nominal resistance value of each strain gauge in the chain is 120 Ω; a quarter bridge with temperature compensation is used in data acquisition. During the experimental process, the measured strain from each gauge is sampled at 5 Hz. The experimental setup of potentiostatic accelerated corrosion tests is shown in Figure 4. First, the corrosion monitoring sensor is fixed on a loading frame, and the prestrain is imposed by nuts on both sides of the sensor. Then, the potentiostatic accelerated corrosion test is performed by using an electrochemical workstation (PARSTAT 4000). The cell used is a typical three-electrode system fitted with a platinum sheet as a counter electrode and a saturated calomel electrode (SCE, standard electrode potential is 0.244 V at 25°C vs. Standard hydrogen electrode [36]) as a reference electrode. The exposed regions on the corrosion monitoring surface of the sensor play the role of the working electrode, which is submerged in 3.5%wt NaCl solution.