Electrocoagulation Process: A Mechanistic Review at the Dawn of its Modeling

During the two last decades, electrocoagulation method (EC) was the focus of many industrial applications and remains a fascinating domain of research. Most published researches concern uses in treating potable water and wastewaters to increase both the removal of dissolved and undissolved contamination. Significant achievements have been realized comprising participations to fundamental comprehension, electrode metals, working parameters, device conception, and economic aspects determinations. Despite the fact that there are several benefits mentioned through the specialized references, the EC large-scale use is not until now viewed as a recognized wastewater technique due to the absence of viable models used in designing device. The present review discusses the mechanisms involved in the EC process and opens a broad perspective on its modeling. The scientific community is near to suggest empirical/theoretical models to present the EC technology as a viable green process. However, more great efforts remain to be accomplished. Technological software developers such as COMSOLTM Multiphysics are invited to insert the EC process in their electrochemistry module to better commercialize this intensified technique and encourage its massive use through the world.


Introduction
Preserving water resources becomes one of the humankind greatest challenges [1,2]. It has to treat many problems such as population growth, deforestation, rapid urbanization, industrialization and warming global climate change [3][4][5]. Now, the availability of potable water is restricted and not assured [6]; water contamination may significantly affect aquatic ecosystems and the accessibility to healthy freshwater [7]. Consequently, there is a necessity to promote performant techniques and methods for depolluting and controlling used waters [8], to preserving widely quality and increase quantity whereas assuring environmental safeguard [9,10]. At the same significance, more performant potable water processes treatment is needed to monitor hazards developed by ecological pollution [11][12][13]; as an illustration, existence of nitrate or fluoride ions at elevated levels [5,14].
The electrocoagulation (EC) technique may be employed for treating potable water and depolluting wastewater [15]. EC includes producing cationic metallic species inside the reactor through accelerated corrosion of consumable metallic anode induced via electric power exercised over the plaques [16]. Following the water acidity, the metallic cations formed electrochemically are instantaneously subjected to aquatic hydrolysis, producing different metallic forms comprising hydroxide flocs (eliminating contaminants through adsorption/settling). Usually, aluminum and iron metals are employed as electrodes due to several benefits: they are abundantly available at low cost, their . 02 . respectively) valence that conducts to a performant elimination of contaminant [17][18][19]. Moreover, concurrent cathodic reaction lets contaminant elimination either upon attachment on cathode pole. In a general manner, the anode and the cathode materials are selected from the identical metal, even if electrochemical dissolution should happen exclusively at the positive pole.
Usually, electrochemical coagulation is performed in two connumber of cases where EC was successfully applied [21,22]. Relatively, EC is an ancient technique, at the same age as electricity [22]. Employing this electrochemistry-based method in treating potable water factories was mentioned during the 19 th century in UK, and treating wastewater factories [23] in the United States in the dawn of the 20 th [24]. In the late 30s, this electrical process has been substituted by conventional coagulation [25,26] and by biological techniques for eliminating colloids and dissolved organic matters in wastewater, respecindeed, the cost of electricity at this time was insupportable.
have been shown once again from the 80s. Several advantages have been mentioned in the written works [28] with the particular disadvantages of EC comparatively with competitive techniques, as listed in (Table 1). However, EC is known for additional problems than those mentioned in Table 1. As an example, the requirement for sludge treatment, even if conventional coagulation [29] and activated sludge method have to stitution of EC sludge is similar to that formed employing conventional coagulation [30,31] when either Al 2 (SO 4 ) 3 .18H 2 O or FeCl 3 identical. On the contrary, a particular problem of EC is that, until recently, there are approximately no detailed surveys of EC modeling for treating water [5].

General technique
Requires repair Treats potable water and used water Electrode passivation over time [5] Integrates oxidation, coagulation, and precipitation (conducting to minimal capital costs [28]) Decreased requirement for chemicals (substituted with metal electrodes and electric power) [32] Lack of systematic reactor design [24] Reduced operating expense Minimal sludge formation Without moving parts [5] Reduced power needs Solar energy may be employed [33] Table 1: this work aims to abridge, debate, and examine  breakthroughs on modeling methods realized for simulating   mental process variables and device conception characteristics features. Subsequently, the principal techniques and design approaches will be assessed and associated with the techno-economic study of the EC method. Ultimately, several views for subsequent investigation and progress will be proposed.

Hypothetical Context of EC Technique
EC merges distinct mechanisms that may be electrochemical (metal dissolution and water reduction, pollutant electrooxidation or electro-reduction, etc.), chemical (acid/base equilibria with varying pH, hydroxide precipitation, a redox reaction in the solution, etc.) and physical (physical adsorption, coagulation, cessively or in parallel ( Figure 1). Figure 1 focuses on the intricacy and the interaction among the routes of the electrochemical

EC reactions
During the electrochemical coagulation technique, metal species are formed inside the recipient through dissolving electrochemically the metallic plaque, frequently in Fe or Al [5].

•
At the anode, the metal is oxidized into cations: In Equation (1), Z is the number of electrons carried during the anodic dissolution phenomenon per mole of metal. In the situation of an elevated anode potential, there is a great probability • At the cathode: water is reduced into hydrogen gas and hydroxyl anions: ode may be computed employing Faraday's law (Equation 6). Consequently, the amount of metal m depends on the residence period t and the electric current I [5]: In Equation (6), M is the atomic weight of the electrode metal, and F is Faraday's constant. Nevertheless, Faraday's law (ϕ=1) is correct if all the electrons in the reactor take part exclusively in the metal-liberation phenomenon at the anode. In the case of parallel reactions happening, a corrective term, designated , is employed to take into mental solubilization of the anode [40,41]. Generally, this term is smaller than 1 [42]; however, ϕ may be bigger than one if the chemical and the electrochemical oxidation routes of the metal verse equilibrium reactions that correspond to the acid/base, tion of these elimination routes is a function of pollutant species (   [5]. Nevertheless, concerning the positive ions liberated from the positive pole, the frequent event is the generation of Fe(OH) 3(s) / Al(OH) 3(s) that show low solubility and easily settle. Consequently, dissolved contaminants in water can as well be attached by tion removal routes implicate [5]: . 04 . ■ happens through Fe(OH) 3(s) /Al(OH) 3(s) , adsorption, and complexation. As an example, phosphates are eliminated upon complexing and/or by precipitating with Fe(OH) 3(s) /Al(OH) 3(s) and/ or by attachment on the latter. At the same time, the soluble organic matter reduction may be explained by the co-precipitation and/or to complexation and/or to the electrostatic attraction on the surface of Fe(OH) 3(s) /Al(OH) 3(s) . Concerning the complexahydrous iron moiety or Al(OH) 3(s) (Equations (7) and (8)  ■ Adsorbing directly contaminants on the electrodes surfaces: particularly for F-because of the electro-condensation ure 2). Practically, there is frequently a dominant mechanism for each pollutant depending on the type of this contaminant [5].

Mechanism Description
Compression of the double layer the bulk solution and conducts to decreasing the repulsive forces among particles [49].

Charge neutralization
Charge neutralization is realized through adsorption of ionic metal species/hydronium cations/hydroxyl anions or by the precipitation of charged hydroxide precipitates onto the may be illustrated through a variation of the zeta potential throughout the isoelectric point.
Frequent cases are listed in Table 2, and more information may be noted in survey articles on EC [22,54].
Simultaneously, colloids and emulsions are as well neutralized through injecting coagulant without interruption from elecpenchant of colloids to destabilize or to persist distinctly and scattered is a consequence of the net inter-particles force that is envisaged upon the addition of opposing forces among the attractive van der Waals and the repulsive forces of the electrical approximation [63]. Neutralizing routes are listed in Table 3 [5]. During the EC operation, these neutralization routes (Figure 3) can happen together or one by one following the characteristics of the water/wastewater to remedy, the contaminants to be eliminated, the working situations (particularly electric current), and the type of the metal. Opposite to dissolved contaminants, the controlling pathway is, consequently, more laborious to describe since it is frequently more related to working situations than on bilized colloids and the precipitates [66,67]. Flocculation perforand the collision velocity of colloids [5,49].
Since reducing dissolved matters implicates attachment and entrapment, the routes of dissolved and solid matters are in themmay thus be eliminated physically from water, in the device or employing a downstream process ( Figure 4). In the recepient, cantation [68,69]. Moreover, decantation and EF may as well be

Case of Al electrodes
For Al electrodes, only just the half-oxidation reaction among Al 3+ /Al pursues Equation (1), because Z = 3. More than the chemical equations presented above, additional monomeric spe-cies are produced from the instantaneous hydrolysis of Al 3+ cations following the acid/base reactions (Equations (9)-(12)) and Al 3+ amount [5,38].
Aluminum speciation and partition may be drawn from E-pH Pourbaix diagrams if the implied reactions are under thermody-stants for acid/base reactions and standard reduction potentials listed in Table 4 [5].
Practically, dissolved Al 3+ cations dominate if pH is less high than than 10, during the time that the insoluble Al(OH) 3(s) form takes control apart from that [5]. Lewis acidity of aluminum equilibrates the generation of OH -fore, monomeric and polymeric species provoke lately the production of the amorphous Al(OH) 3(s) important surface areas useful for fast adsorbing dissolved organic matters and trapping colloids [70][71][72][73]: Auxiliary reactions can happen on the electrodes because of a simple chemical attack of aluminum under acid or alkaline conditions, respectively [8,37]: 2Al EC process overpasses the expected level predicted using Faraday's law [5]. Consequently, the faradic yield φ is more important than 100% and may attain 200% [38].
A problematic issue of EC technique is the passivation of the cathode since it elevates both the cell voltage and the energy ed through optimizing the current reversal frequency [74] or NaCl injection to accelerate pitting corrosion upon a chemical reaction between Cl -corrosion of dissolved Al electrodes is a function of two mechanisms [75]: corrosion in the existence of chloride ions may be described [78]:

Case of Fe electrodes
aqueous medium through Fe-EC are more complicated than with Al, because anode oxidation may conduct either to ferrous or ferric cations [5,79,80]: Fe 2+ and Fe 3+ may be hydrolyzed in the recipient. Moreover, they may generate several monomeric and polymeric species whose proportions are function of the Fe 3+ level and the pH degree: Fe(OH) 2+  and Fe(OH) 3 up the acid/base and equilibrium constants and standard reduction potentials of monomeric species [5].   Table 5: Equilibrium constant and standard reduction potential of iron species [5].
In spite of certain confusion in large part of the literature about the implied stages of Fe-EC, contemporary references largely hypothesis that the anode oxidation liberates Fe 2+ since it has been established that the dissolution proportion of Fe 3+ may be 2+ to Fe 3+ is a function of pH and the dissolved oxygen amount [84]. When pH is acid, ferrous cations oxidize very slowly in the presence of dissolved O 2 (Equation (21)); however, if pH is neutral or alkaline, ferrous cations are instantaneously converted into Fe(OH) 2 (Equation (22)) which is immediately oxidized by dissolved O 2 to Fe(OH) 3 (Eq. (23)) [5]: Fe 2+ + 2OH -→ Fe(OH) 2 As a result, several references mentioned that the Fe dissolution obeys to the Faraday's law with a faradic yield comprised in the -ly solubilized evaluated using Faraday's law and the quantity of detected solubilized Fe founded on Z = 2 [5]. If pH is acid, ϕ is bigger than 100%; at the same time, if pH alkaline, the opposite is correct. At smaller pH degrees, acceptable interpretations are identical to those mentioned for aluminum: chemical corrosion and pitting corrosion at both electrodes in the existence of certain ionic species, like Cl - [5,75]. At bigger pH degrees, the since additional reactions happen next to the anode, comprising oxygen formation (Equation (2)). If pH is alkaline, Fe oxidation conducts to Fe(III) production following Equation (20) in the Fe amount generated since Fe(III) production needs 3 electrons instead of 2 for Fe(II) and consequently, a more important current level for attaining the equal Fe amount is necessitated [5,81].
Moreover, there are two additional dissimilarities with aluminum is ~9-10 with iron electrodes even though pH is acid [84,87]. (2) Fe 2+ is greatly dissolvable and thus not able of a performant colloidal particles destabilization upon Fe(OH) 3 , consequently in-Fe-EC necessitates one or more of the next optimization methods for the Fe 3+ formation [5,84]: • Aerating the water to augment the solubilized O 2 amount and Fe 2+ oxidation; • Augmenting the pH level to 7.5 or bigger to encourage the Fe 2+ oxidation velocity; Adding oxidant like Cl 2 that may be formed upon oxidization of the Cl - . 08 . ferrous oxidation happens in the bulk solution, following: Cl 2 + H 2 O → ClOH + Cl -+ H + (24) 2Fe 2+ + 2HOCl → 2Fe 3+ + 2OH -+ Cl 2 (25) Considering the electric current consumed through Cloxidation, this method is not performant unless the water/wastewater to purify holds more than 600 mg Cl -/L.
• Elevating the operation period to attain total ferrous oxidation.
is the smaller cost of Fe, about 0.5-0.8 US$/kg, while Al cost is comprised between 1.5 and 3 US$/kg [5].
working situations like current or voltage and residence period, to (2) water characteristics like pH, alkalinity and conductivity trode surface area, electrode inter-distance) [5].

Impact of the electric current
I is the most important parameter of EC. Practically, EC depends on the current density i that is described continuity equation implies current conservation amongst the anode and the cathode; in fact, the current density may vary amongst the electrodes [5]: Current density dictates the coagulant injection from the anode and the hydrogen gas (H2) production from the cathode among contaminants, coagulant and gas micro-bubbles, and ulvariation through EC operation in the form of a function of water alkalinity. As a result, the current seems to form a dynamic lation stages [89] and encourages the electromigration of ions and charged colloidal particles [18].
Cell voltage is linked in the form of equilibrium potential, anode electric energy consumption may be formulated in the form of contact period t employing [5]: Since the electric energy needed for the EC method is related to the electric current and potential as described in Equation (27), EC may be performed either upon the (1) galvanostatic or (2) through monitoring and/or modifying the current imposed over electrodes; at the same time, for the second one, it is the imposed cell voltage that is monitored and/or changed in the form of quantity of coagulant needed to be liberated in the EC device [5].
the EC performance. As an example, additional reactions can happen mainly, and overdosing may reverse the charge of the colloidal particles and disperse them another time conducting consequently to a diminution of the coagulant performance and a decrease of the anode lifetime [5].
characteristics and the concentration of contaminants to be eliminated from water; as an example, from 0.01 A/m 2 to 880 A/m 2 . Optimum current density must be evaluated following additional working indicators. To employ the EC reactor during a large time without stopping for maintenance, the current density is proposed to be among 20 and 25 A/m 2 [77]. Moreover, high current augments voltage and ohmic drop among anode and cathode. Ohmic drop or IR drop is a consequence of the ohmic resistance of the electrolyte R, which may be described as follows [5]: here d designates the inter-electrode gap, and k the water electric conductivity. If i augments, and U has tendency to the IR drop electric power changes as RI 2 diminished upon reducing the gap among the plaques and augmenting the electrode surface area and the water conductivity [66]. Employing current reversal (switching anode and cathode electrically) is helpful to decrease maintenance price; however, its impact on contamination elimination is not ascertained until this moment.

Impact of the water pH
Besides the electric current, pH is an additional fundamental pa-es because it dictates the hydrolyzed metal species produced in in Section 2, investigating the Al and Fe speciation as a result from hydrolysis of their corresponding cations dictated upon thermodynamic equilibrium is crucial to explain the manner by which pH participates in imposing the stages of the electrochem-the charged soluble monomeric species on their respective hy-agulant species and their near contaminants may be determined from electrostatic interactions. Researchers such as Jiménez et al. [81] mentioned a detailed description taking into account these stages, i.e., double-layer compression, neutralization and sweep of several contaminants depending on the predominating hymay be at the same degree understood throughout the thermodynamics linked to the electrochemistry as described upon the diagram of a useful electrode material that, once superimposed on E-pH diagram of water, conducts to a diagram well described of thermodynamically stable metal species in the aqueous medium, i.e., immunity, passivation, and corrosion, which lets to predict the corresponding electrode stability and its dissolution behavior in water throughout describing the stable aqueous spe-Researchers [51] examined the Al and Fe speciation intending to determine the predominance diagrams of corresponding hydroxides and to evaluate a fraction of undissolved hydroxides as a function of pH taking into account only monomeric species. For Al electrode, it has been established that the quantity of undissolved Al(OH) 3 augments importantly with elevating pH from 4.5 to 7 to the detriment of aluminum hydroxide ions and the reverse is correct for a pH from 7 to 10; at the same time, amorphous metal hydroxide is not detected above the latter pH value. For the Fe electrode, the amount of undissolved iron hydroxide 7, iron hydroxide ions are not present in the predominance ditheoretical computation founded on equilibrium constants and pH for a concentration of 10 -2 M for both electrode metals [5].
would augment for acidic pH; however, it may diminish for alkaproduction at the cathode; while the diminution of pH is linked + protons near the anode and the additional reactions like water ly elevated with Al electrodes due to the generation of aluminate anions at elevated pH [39].
It was mentioned that the bicarbonate alkalinity ameliorates at a small degree the contaminants elimination performance [96]; moreover, it aids to reduce the hardness throughout precipitation of CaCO 3 due to the hydroxyl anions formed upon water reduction near the cathode [5,46].

Impact of cell geometry and electrodes conception
recipient in which the treatment of water happens [5].

Electrodes arrangement:
-ter-electrode gap. Electrodes arrangement may either be easily constituted of an anode and a cathode or be formed of several complicated electrodes settlement may be categorized in monopolar and bipolar electrodes ( Figure 5) [5]. Table 6 summariz-In a general manner, monopolar electrodes necessitate a low electrodes that work under high tension and a smaller current mance considering that it has been established that at the same level BP-S may show an elevated EC performance [97,98]. Mosituations this electrodes arrangement provides an elevated contaminant reduction with a lower energy consumption [99,100], taking into account that bipolar electrode frequently consumes cult to manipulate and requires less maintenance cost throughoperation cost should at the same level be taken into account to . 010 .

Monopolar electrodes in parallel connection (MP-P)
posed of cathodes and anodes arranged alternatively at the same anodic or cathodic potential, respectively. Each pair of cathode/anode corresponds to a small electrolytic cell in which the voltage is the same. the current of each electrolytic cell is additive.

Monopolar electrodes in series connections (MP-S)
trodes is internally linked with each other and has no interconnections all the electrodes is the same, whereas the global voltage is the sum of tension in each electrolytic cell.

Bipolar electrodes in series connections (BP-S)
BP-S comprise two outer electrodes attached to the electric power trodes ( Figure. 6c). Outer electrodes are monopolar, and the inner ones implies that the opposite sides of each bipolar electrode are oppositely charged, the anodic dissolution happens on the positive side; at the same time, the negative side is prone to cathodic reactions [28]. More than the typical rectangular electrodes, there are additional geometrical forms like circular and cylindrical. Electrodes may be placed either vertically or horizontally in EC cell [5]. Even if being scarcely employed, horizontal electrodes in EC batch re- [105].
Inter-electrode gap: It is well-known that if the IR-drop augmeans that energy consumption diminishes with reducing the distance among the electrodes (Equations (27) and (28)) [5]. As the separation among the electrodes becomes lower, more electrochemically produced gas bubbles bring about turbulent well as to a high reaction rate amongst the coagulant species and contaminants [106]. Moreover, inter-electrode distance describes the contact period between the anode and the cathode for a continuous system and the period of operation for a batch reactor for attaining a wanted EC performance. For a complicated electrode placement, inter-electrode separation dictates as well the number of electrodes to arrange in EC cell, if its volume settling features [5,74].
An in-depth discussion of the EC reactor conception may be found in the excellent review of Hakizimana et al. [5].
ments if the electrolytic conductivity is elevated thanks to the reduction of the ohmic resistance of water. Moreover, the electric conductivity contributes to reducing the residence period needed to attain the desired reduction percentage [108]. As a result, energy consumption (UI) is decreased. Usually, NaCl is employed to augment the electrolytic conductivity. In addition, Clanions to reduce the precipitation of calcium carbonate in hard surface [94]. If the current density is elevated, Cl-may as well be oxidized to active chlorine forms, like hypochlorite anions, that may oxidize organic matters [37] and ferrous ions [5] or participate in killing microorganisms in water [109][110][111][112]. To providing 20% of the anion's existent must be Cl- [77].
Nevertheless, there are the limits dictated on conductivity augmentation in drinking water treatment [113]. Indeed, conductivity augmentation throughout the treatment of potable water usat 250 mg/L [5].
Usually, EC process is realized at ambient temperature. During EC operation, the water temperature may increase due to the conductivity is elevated especially in the case of brackish water or seawater treatment [49,109]. In this case, some precautions should be taken such as reducing the applied voltage and decreasing the residence time to avoid overheating of the electric components and circuit [80].

EC Modeling
At the best of our knowledge, the consulted references through this review proved the absence of an algorithmic and direct -hension of the respective contributions of several phenomena implied in EC, comprising electrochemical mechanisms, coaguseful to enhance the conception and decrease equipment and operating costs simultaneously. It may easily ensure viable and correct solutions to EC issues, and therefore let us evaluate EC tions [5].
Hakizimana et al. [5] discussed the EC models previously men-sist in reaching more comprehensions in EC devices conception. In a general manner, there are two principal categories of EC modeling: statistical modeling and modeling funded on knowledge. Mathematical modeling usually is destined to searching optimum working parameters in which EC performance will be enhanced. Since EC is a complicated method, modeling founded physical or chemical process happening throughout the technique. Moreover, a particular focus is given to the Computational Fluid Dynamics (CFD) modeling; for which computational

Statistical modeling
Taking into account several physical/chemical processes implicated in EC, the contaminants elimination performance complicatedly is the function of the separated and additional impacts of the key technique parameters (factors). Until now, in the largest part of the investigations performed on water/wastewater treatment using EC, optimization has been reached through modifying a single parameter at the same time maintaining all needs several practice tests and conducts to a weak optimization, like underestimation or overestimation of the parameters [114]. Response surface methodology (RSM) has been employed as a method in many studies to show the impacts of main process factors and their mutual contributions. RSM is used in multiple forms such as the full or partial factorial design (FD) [115,116], central composite design (CCD) [117][118][119][120][121], D-optimal design (DOP) [114], and Box-Behnken design (BBD) [122][123][124][125], etc.

Modeling funded on knowledge a) Phenomenological models
In several studies, EC kinetics has been investigated to model and simulate the EC process. Several research-ride concentration. Moreover, the elimination of contaminants like nitrates [54,126] and heavy metals by EC obeyed to an n-order kinetic model [127].

b)
Modeling detailed mechanisms

Electrochemical phenomena
EC technique is mainly founded on electrochemistry since the electrochemical events are the initiating heart of the whole method. Electrochemistry is viewed as a complicated knowledge since it concerns at the same time charge transport, electrochemical kinetics, comprehension of electrodes interface and thermodynamics.

Adsorption
To better assess the stages implicated in EC and for modeling aim, pure adsorption isotherm and adsorption kinetics models have mainly been employed. Because the quantity of coagulant formed may be evaluated for on the hypothesis of thermodynamic monitoring are mainly the Langmuir and Freundlich isotherms and the ible adsorption that may be followed by multilayer formation [129]. . 012 .

Flocculation modeling
Flocculation is a complicated method during which two or more colliding destabilized colloids adhere tovelocities attributed to gravity. Fixation is a consequence of the interparticle forces [130].

4.
Flotation and settling appears thanks to buoyancy forces and settling thanks to gravity. EF is a function of current density, hydrogen micro-bubbles size (20-50 μm) and particle collection performance by the micro-bubbles [24]. Even if the current density imposes a convenient contaminant reduction mechanism, particularly in batch systems, it is not easy to entirely escape to either settling or EF in favor of the remaining stages, whatever the current density that may be employed.

Complexation
Complexation model is a modern phenomenological model illustrating adsorption equilibrium that is imposed by complexation of suspended matter upon Fe or Al hydroxides for chemical oxygen demand removal.
Modeling utilizing CFD comprehension and enhancement of the EC reactors design for the next future. Many authors have focused reaction rate distribution at the electrodes and the cell voltage. CFD has been employed to examine the distribution of potential and current density because the latter shows the distribution of attack on electrode surface Table 7: EC process statistical modeling and modeling funded on knowledge [5].
rent density inside EC devices and predict complicated inherent processes, particularly if technical restrictions limit an experimental method. Table 7 summarizes the main features of the statistical modeling and modeling funded on knowledge of the EC process [5].

Conclusions
From this review, the main points drawn are listed as below:

1.
Similar experiments, as jar test experiments used in conventional coagulation to determine the optimal coagulant doses, should be conceived using Zeta-meters to control the EC optimal residence time better and metal amount liberated. An empirical method would be suggested to facilitate a direct approach to calculate the EC optimal parameters following the (1) water main characteristics such as electric conductivity, pH, pollutants concentrations and the (2) EC device features like metal type, reactor geometry and batch/continuous mode.

2.
is near to suggest empirical/theoretical models to present the EC remain to be accomplished.

3.
Multiphysics are invited to insert the EC process in their electrochemistry module in their future versions to better commerthrough the world.