# Effect of Gaskets Geometry on the Performance of a Reverse Electrodialysis Cell

^{1}

^{2}

^{*}

## Abstract

**:**

^{2}. Results show that the geometry of the cell components directly influences the physicochemical principles governing the RED process and is closely related to the cell output parameters. In turn, it is possible to increase the performance of a RED cell by optimizing the gasket geometry by reducing dead zones.

## 1. Introduction

- Cell design and components (materials, equipment and cell geometry);
- Hydrodynamics (flow distribution, pressure drop);
- Mass transport (mass distribution);
- Energy transport (potential and current distribution).

- Thickness of the gaskets. Flow velocities are higher within thinner compartments, and this can reduce the formation of dead zones and generate a more uniform flow distribution [18];
- Spacers characteristics. Filament spacing, diameter, arrangement, and angle affect the flow pattern, velocity distribution, flow regime, pressure drops, and mass transport [6];
- Gaskets geometry. The geometry of the gasket can influence the distribution of the solutions in the compartments; this promotes fluid mixing, reducing polarization phenomena and electrical resistance [18].

## 2. Materials and Methods

#### 2.1. Reverse Electrodialysis Cell

^{2}. The nylamid endplates were manufactured ‘in house’ using a CNC. The material was selected due to its hardness and mechanic strength [2,3]. Two dimensionally stable titanium mesh electrodes (10 × 10 cm

^{2}) coated with ruthenium and iridium (Magneto Special Anodes BV) were placed on the plates, and a silicon gasket was used to prevent leakage of the electrode rinse solution. Polymeric ion exchange membranes (AEM and Fujifilm CEM Type 1) (FUJIFILM Manufacturing Europe BV, Tilburg, The Netherlands) were used. The membranes were conditioned in 0.3 M NaCl solution for 24 h. Table 1 shows the main characteristics of the membranes used.

#### 2.2. Feed Solutions

_{4}Fe(CN)

_{6}/K

_{3}Fe(CN)

_{6}redox couple was selected because it does not present voltage losses due to parasitic reactions. To improve conductivity, NaCl was used as the support electrolyte. The concentration of the support electrolyte was selected based on an average salinity between the concentrated solution and the diluted solution. This system has the advantage of being bidirectional if DSA electrodes are used, so it is possible to change the flow direction [2]; besides that, they have a longer useful life because they do not participate in the reaction [22].

_{4}[Fe(CN)

_{6}]·3H

_{2}O), 0.1 M potassium ferricyanide (K

_{3}[Fe(CN)

_{6}]), and 0.3 M NaCl of analytical grade (Sigma-Aldrich, Mexico City, Mexico). All solutions were prepared with deionized water at room temperature (20 °C).

#### 2.3. Gasket Geometry

#### 2.4. Gaskets Optimization

^{2}).

^{2}and 137 cm

^{2}, respectively. The total area difference between the two spacers is 5 cm

^{2}, representing an area difference of 3.5%. Reducing the area is expected to increase the velocity and reduce the areas of low velocity or stagnation that can influence concentration polarization phenomena and resistance in the compartment.

#### 2.5. Calculations and Measurement of Parameters

_{ext}) in the range of 0.5–100 ohm to obtain the V-I curve and the P-I curve. The power (P) obtained by the cell for each value of external resistor was calculated with Equation (1):

_{IEM}) can be calculated using an approximation of the Nernst equation [2], presented in Equation (2):

_{IEM}is the membrane selectivity (%), R is the ideal gas constant (8.314 J/mol K), T is the temperature expressed in Kelvin, z is the valence of the ion in solution, F is the Faraday constant, γ

_{c}and γ

_{d}are the activity coefficient of the concentrated and dilute solutions, respectively; and C

_{c}and C

_{d}are the concentration of the concentrated and dilute water (mol/L).

_{AEM}and E

_{CEM}). The electrical potential of a RED cell depends on the number of unit cells within the device (N); to calculate the cell potential (E

_{cell}), Equation (3) is used:

_{cell}) is calculated with Equation (4), while the electric current (I) can be calculated with Equation (5) [2]:

_{AEM}and R

_{CEM}are the resistance of the membranes (Table 1), and R

_{H}and R

_{L}are the resistance of the high and low concentration solutions, obtained from the conductivity of the solutions (Table 2).

_{d}) and current density (J) are parameters obtained from the active area of the membrane (A

_{mem}) and are calculated with Equations (6) and (7) respectively:

## 3. Results

#### 3.1. Effect of Gasket Geometry on the Potential of the RED Cell

^{2}. Between values of 1 to 3 A/m

^{2}, the responses differ. The theoretical curve shows the ideal ohmic behavior. The deviation from the ideal behavior of experimental responses is due to contributions of non-ohmic resistances in the stack, where G1 tends to move further away. Cipollina et al. [2] point out that non-ohmic resistances are phenomena that decrease the driving force due to changes in concentration at the membrane–solution interface. Non-ohmic resistances can be increased by the presence of dead zones due to a non-uniform distribution of the flow throughout the compartment. Therefore, the reduction of probable dead zones in geometry G2 improved the performance of the RED cell, by increasing the potential and decreasing the cell resistance.

#### 3.2. Effect of Gasket Geometry on the Power Output of the RED Cell

^{2}of possible dead zones in spacer G2.

## 4. Conclusions

^{2}, while the maximum power density achieved with the G2 spacer was 0.1433 W/m

^{2}. It can be concluded that, for our experiments, reducing the total area of the spacer by 3.5% led to an increase in the output power density of 8%. Although statistically the confidence intervals seem to overlap, the G2 gasket reached maximum values that G1 never could. Thus, an improvement was produced.

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

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Parmeters | CEM | AEM |
---|---|---|

Thickness (µm) | 135 | 125 |

Electical resistance (Ω cm^{2}) | 2.7 | 1.3 |

Selectivity (%) | 92 | 92 |

Ion exchange capacity (mol/g) | 1.4 | 1.4 |

^{1}Parameters obtained from the supplier’s technical sheet.

Parameters | Concentrated Solution | Dilute Solution |
---|---|---|

Concentration (M) | 0.6 | 0.05 |

Conductivity (mS/cm) | 49.6 | 5.2 |

Flow rate (mL/min) | 10 | 10 |

Velocity (m/s) | 0.01 | 0.01 |

Temperature (°C) | 20 | 20 |

**Table 3.**Measurements of OCV, short circuit current, and cell resistance with each gasket geometry and theoretical calculations.

Measurement | Open Circuit Voltage (V) | Short Circuit Current (A/m^{2}) | Cell Resistance (Ω) |
---|---|---|---|

Theoretical calculation | 0.1154 | 5.34 | 2.16 |

G1 | 0.0967 | 3.63 | 2.66 |

G2 | 0.0983 | 3.97 | 2.48 |

**Table 4.**Optimum current and power density measurements with each gasket geometry and theoretical calculations.

Measurement | Power Density (W/m^{2}) | Optimum Current Density (A/m^{2}) |
---|---|---|

Theoretical calculation | 0.1541 | 2.71 |

G1 | 0.1326 (±0.02) | 2.18 |

G2 | 0.1433 (±0.06) | 2.38 |

**Table 5.**Comparison between He et al. [19] and proposed spacers.

Spacer | Net Thickness (mm) | Frame Thickness (mm) | Porosity (%) | Manufacturer |
---|---|---|---|---|

He et al. [19] | 0.45 | 0.72 | 86.5 | Tianwei Membrane Technology Co., Ltd., Shandong, China |

Proposed | 0.2 | 0.1 | 51.0 | UNAM, Mexico City, Mexico |

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**MDPI and ACS Style**

Sandoval-Sánchez, E.; De la Cruz-Barragán, Z.; Miranda-Hernández, M.; Mendoza, E. Effect of Gaskets Geometry on the Performance of a Reverse Electrodialysis Cell. *Energies* **2022**, *15*, 3361.
https://doi.org/10.3390/en15093361

**AMA Style**

Sandoval-Sánchez E, De la Cruz-Barragán Z, Miranda-Hernández M, Mendoza E. Effect of Gaskets Geometry on the Performance of a Reverse Electrodialysis Cell. *Energies*. 2022; 15(9):3361.
https://doi.org/10.3390/en15093361

**Chicago/Turabian Style**

Sandoval-Sánchez, Elier, Ziomara De la Cruz-Barragán, Margarita Miranda-Hernández, and Edgar Mendoza. 2022. "Effect of Gaskets Geometry on the Performance of a Reverse Electrodialysis Cell" *Energies* 15, no. 9: 3361.
https://doi.org/10.3390/en15093361