Energy balance electrochemical process

Electrical, and the mechanical forms of energy, are included in the work term in an energy balance. Electrical energy will only be significant in energy balances on electrochemical processes. 

The optimization of an electrochemical reactor calls for a full description of the process to accomplish the specific objective of the mass and the energy balances together with heat transfer considerations and thermodynamic and enthalpy changes that are related to the unit cell and the whole stack [1,2]. A full description of the kinetics of both processes, the electric properties of the cell components, and the hydrodynamic aspects of the entire cell is also required. 

Whether an electrochemical process releases or absorbs free energy, it always involves the movement of electrons from one chemical species to another in an oxidation-reduction (redox) reaction. In this section, we review the redox process and describe the half-reaction method of balancing redox reactions. Then we see how such reactions are used in electrochemical cells. 

Extension of the dyad schemes of Fig. 1 to triads and multicomponent systems with carefully balanced electrochemical and spectroscopic properties has led to remarkable achievements along the mimicking of the fundamental processes of light energy collection and storage (via charge separation. CS) taking place in natural systems. Dealt with in Fig. 2 is a representative example that conveniently illustrates the approach fol-... 

Since the energy balance is based on thermodynamics, we will summarize some important concepts in Section 10.2.1 before applying them to an electrochemical process in Section 10.2.2. 

As we said at the beginning of this section, an energy balance of the process is essential. A major user of energy is the electrochemical reactor, which will be considered next. 

An analysis of the energy balance and economics of CO2 recycling to hydrocarbon fuels estimated that the full system can feasibly operate at 70% electridty-to-liquid fuel efficiency, and the price of electricity, needed to produce synthetic gasoline, is only 1.0-1.5% of the present sales price of gasoline. In regions where inexpensive renewable electricity is currently available, such as Iceland, fuel production may already be economical. The dominant costs of the process are the electricity cost and the capital cost of the electrochemical cell, where this capital cost is significantly increased, when operating intermittently (on renewable power sources such as solar and wind) [42]. 

An electrical potential difference between the electrodes of an electrochemical cell (called the cell potential) causes a flow of electrons in the circuit that connects those electrodes and therefore produces electrical work. If the cell operates under reversible conditions and at constant composition, the work produced reaches a maximum value and, at constant temperature and pressure, can be identified with the Gibbs energy change of the net chemical process that occurs at the electrodes [180,316]. This is only achieved when the cell potential is balanced by the potential of an external source, so that the net current is zero. The value of this potential is known as the zero-current cell potential or the electromotive force (emf) of the cell, and it is represented by E. The relationship between E and the reaction Gibbs energy is given by... 

The usual procedures for the conception of electrochemical reactors arise from the mass conservation laws and the hydrodynamic structure of the device. In fact, four types of balances can be considered energy, charge, mass, and linear movement quantity. Since the reactor must include the anodic and the cathodic reactions, it is possible to make a complete balance for the mass. The temperature also governs the stability of a chemical reactor, but in the case of an electrochemical device, the charge involved in the entire process has to be considered first [3-5]. 

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