Charge and Discharge Characteristics of Thermochargeable Galvanic Cells with an  [ Fe (  CN  ) 6 ] 4 −  /  [ Fe (  CN  ) 6 ] 3 −  Redox Couple

Abstract

ConclusionsThe cementation of copper onto aluminum in alkaline solutions is a process which follows a first-order reaction rate law. The rate of cementation is influenced by pH, Cu(II) concentration, surface area, and temperature. An increase in pH leads to an increase in the rate of the Cu cementation process, which is probably related to the simultaneous hydrogen evolution reaction. The rate of the cementation reaction increases with an increase in the Cu(II) concentration or with an increase in temperature.Changes in the surface area during the cementation process are the main reason leading to the inconsistency of the results.Acknowledgments ABSTRACT We present the thermocharge and discharge characteristics and long-term cycling performance of a thermochargeable galvanic cell with carbon fiber electrodes, a ferro/ferricyanide ion redox couple incorporating a cation-exchange membrane, and an extra pair of electrodes on each side of the membrane. This cell is a rechargeable concentration cell. No external charger is needed, and the cell can be used while it is being charged. It also functions as a thermoenergy conversion system, which can store energy. The ratio of discharge capacity to thermocharge capacity was more than 90% when there was a temperature difference between the main electrodes during thermocharging and discharging. When the temperature difference was removed after thermocharging and the cell was discharged, the ratio remained above 80% when the difference during thermocharging was greater than 35°C. Thermocharge and discharge capacities were almost constant for over 40 cycles. The cell retained the advantage of the conventional thermocell with a ferro/ferricyanide ion redox couple; its voltage was constant as long as constant thermal energy was supplied. The cell was discharged from the main electrodes at 0.5 mA/cm2 and constant voltages of the main and extra electrodes for over 1000 h while simultaneously thermocharging from the extra electrodes at the same current density. As a thermoenergy conversion system, our cell showed nearly the same thermal efficiency and power density as the conventional thermocell.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-03-20 to IP

Electrical Power From Nanotube and Graphene Electrochemical Thermal Energy Harvesters

“…P‐SWNT electrodes with an area of 0.25 cm 2 and electrode spacing of 4 cm were used. As shown in Figure 1b, the measured thermoelectric coefficient (∼1.43 mV/K) is in good agreement with previous reports (1.4 to 1.6 mV/K) 15, 28–30. Using the measured thermoelectric coefficient and Equation 1, the entropy change for the ferro/ferricyanide reaction is ‐138 J/mol K.…”

“…Various other redox couples have been proposed for thermocells, such as Cu 2+ /Cu, Fe 2+ /Fe, Pu 4+ /Pu 3+ and Np 4+ /Np 3+ systems 12, 15, 22, 27. Thermocells with the ferro/ferricyanide redox couples have been investigated intensively due to their relatively high thermoelectric power (∼1.4 mV/K) and the large exchange current density associated with this couple,14, 15, 28 which allows high currents to be drawn from the cell. Furthermore, the ferro/ferricyanide couple is not as vulnerable to electrode poisoning by impurities as compared with other redox couples, such as the Fe 3+ /Fe 2+ system 15…”

Hydrovoltaic cells. Part II: Thermogalvanic cells and numerical simulations of thermal diffusion potentials

“…This finding is simply due to the direct relation between these parameters as described by Eqs. (2) and (11). It can be noted how the merging of two flows after the spacer narrows the temperature and potential isovalues between the electrodes.…”

“…It is simply an illustration of the ability to sample energy in places where solutions of elevated temperature are flowing in parallel under laminar conditions (i.e., extraction of a small fraction of the energy instead of a conversion, as the main part of the heat content flows away). When the principle of electrochemical thermocouples is used in stationary systems (employing a cation exchange membrane) higher conversion efficiencies are obtained (i.e., in the order of 0.1%) [11]. The advantages of the present system are that no membrane is required, as in [4][5][6]9,34] and that the system can be installed in places where flowing solutions of different temperatures are already present.…”

“…Such a thermogalvanic cell can be used to extract energy from two solutions of different temperatures flowing in contact, as in previous work dedicated to convective cells [6,8,9]. In contrast, other studies have rather focused on static thermogalvanic cells [9][10][11]. This subject is important as practical methods for extracting the low-grade excess energy from solutions having modulated temperatures are in high demand [12].…”