Electrochemical discharge heat power

Electrochemical calorimetry — is the application of calorimetry to thermally characterize electrochemical systems. It includes several methods to investigate, for instances, thermal effects in batteries and to determine the -> molar electrochemical Peltier heat. Instrumentation for electrochemical calorimetric studies includes a calorimeter to establish the relationship between the amount of heat released or absorbed with other electrochemical variables, while an electrochemical reaction is taking place. Electrochemical calorimeters are usually tailor-made for a specific electrochemical system and must be well suited for a wide range of operation temperatures and the evaluation of the heat generation rate of the process. Electrochemical calorimeter components include a power supply, a device to control charge and discharge processes, ammeter and voltmeter to measure the current and voltage, as well as a computerized data acquisition system [i]. In situ calorimetry also has been developed for voltammetry of immobilized particles [ii,iii]. 

A simplified model, where the heat brought to the substrate by the electrochemical discharges is approximated by a cylindrical uniform heat source of radius b and heat power P0 inside a homogenous material of density p, heat capacity c and thermal conductivity A, is considered (Fig. 5.2). Similar models have been applied successfully in electrical discharge machining [39]. 

In order to estimate P0, one has to first estimate the heat power PE of the electrochemical discharges. Therefore, Equation (5.1) can be used. The interelectrode resistance R can be evaluated by inspecting the slope of the mean I - U characteristics in the ohmic region (the linear part from 5-15 V of the mean I- Ucharacteristics). Typical values for PE are around a few watts (for machining voltages in the range of 30-40 V). 

Electrochemical cell with quartz window and saturated calomel electrode as a reference electrode was used (Fig. 3). Photoelectrochemical measurements were conducted with Pl-50-1 potentiostat under illumination power density of 75 mW/cm. At first the efficiency of energy accumulation (in the form of absorbed hydrogen) was estimated from the cathode discharge curves and from the hydrogen volume released under cathode heating. The volume of hydrogen released was measured in the tailor-made setup. The discharge capacity measurements were performed in electrochemical cell with nickel counter electrode. 

FIGURE 13.7 Schematic of a steady-flow, isothermal, electrochemical reactor. The heat flow arrow is two-headed because heat may flow in or out as needed to hold the temperature constant. The electric power arrow is shown two-headed because if this is an electrochemical cell like those that produce metallic aluminum, then the flow is in, while if it is a fuel cell the electric energy flow is out, and if it is a storage battery the electric energy flow is in while it is charging and out while it is discharging. Only one arrow is shown for reactants or products, but there may be multiple flows in or out, or the flows in and out may be zero, such as for a dry cell battery. 

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