# Numerical Analysis of the Effect of Liquid Water during Switching Mode for Unitised Regenerative Proton Exchange Membrane Fuel Cell

^{*}

## Abstract

**:**

^{−1}water velocity was the best-performing parameter in achieving optimal distribution. Among different flow field configurations, the serpentine design achieved the best flow distribution due to its single-channel model. Modification and refinement in the form of flow field geometric structure can be performed to further improve the water transportation behaviour in URPEMFC.

## 1. Introduction

## 2. Methods

^{2}, whereas the active area of the symmetry flow field is 15 × 15 mm

^{2}. The dimension of the flow channel has a cross-sectional area of 1.0 × 1.0 mm

^{2}. The parallel model configuration has straight channels bifurcating perpendicularly from the inlet flow path and merging together leading to the outlet. Next, the serpentine model features a simple single-channel design with multiple sharp U-shaped turning points. Finally, the symmetry model, which is a flow field design created for this study, has a flow channel angling towards the inlet at 45°, directing the flow towards the outlet.

## 3. Results and Discussion

#### 3.1. Water Velocity

^{−1}showed the best flow uniformity across all flow field designs. Figure 2 presents the distribution performance in terms of the volume fraction of liquid water after reaching a steady state throughout different flow fields. The main finding is that the parallel flow field struggled to achieve a uniform flow distribution in all channels due to its geometric structure. Even though the water velocity of 0.5 m·s

^{−1}in the parallel flow field displayed unsatisfactory flow distribution, it worsens at a lower velocity, as shown in Figure 3a. Another behaviour observed in the parallel flow field as the inlet velocity increased is the increasing amount of back-flow in the channels. This could be due to the increasing pressure that has built up on the last channel, which forces water back into the previous channels. A potential solution to this is capturing the fluid velocity across the domain through further CFD simulation and optimising the pressure drop in the flow field.

^{−1}(Figure 3), all flow field designs experienced difficulty in forming substantial liquid film across all channels, thus leading to poor flow distribution. This result is in line with other studies, where a higher inlet velocity is preferable to increase the efficiency of the mass transfer of liquid reactant and also to achieve a better gas removal rate [9,17]. At an increased velocity of 0.75 m·s

^{−1}, no noticeable improvement was observed at a steady state for both symmetry and serpentine configurations. As shown in Figure 4f, symmetry flow field showing similar flow pattern as Figure 2c. Furthermore, the parallel flow field achieved a steady state at 0.15 s, as shown in Figure 5c. Then moving towards the serpentine flow field shown in Figure 6f, again similar flow pattern was observed. A higher water velocity resulted in the build-up of liquid film across the flow field at a higher rate leading to a steady state, but the flow distribution was significantly affected by the flow field geometric structure. As the temperature of the fluid is excluded from this simulation study, it is to be noted that the effect of water velocity on the interaction of the two-phase flow has been reported to have a correlation with operating temperature [18]. Therefore, there is a further improvement on the current flow field design with optimisation in both the flow rate of liquid water and temperature simultaneously.

#### 3.2. Flow Field Configuration

## 4. Conclusions

^{−1}achieved notably better liquid water distribution. As for the flow field design, the parallel flow field showed the worst distribution performance. The serpentine flow field achieved good flow distribution for the most part due to its single-channel design. The symmetry flow field struggled to achieve a uniform flow distribution, but with optimised water velocity, an optimal flow distribution can be obtained. This study successfully demonstrated the flow pattern of two-phase flow in the flow field using the VOF method. Future studies can utilise this simulation method to evaluate new flow field designs or improve the geometric design of existing flow fields. As the mass transport study has been a focus for more than 10 years in PEMFC, this simulation is expected to provide a more realistic approach to simulate the transport through GDL [25]. A more comprehensive model can also be produced by introducing the hydrophobicity or hydrophilicity of the material, the temperature of the fluid, and the pressure differential between the system and the reactant supply storage in order to conduct a more comprehensive optimisation of the mode switching process.

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

- Peng, X.; Taie, Z.; Liu, J.; Zhang, Y.; Peng, X.; Regmi, Y.N.; Fornaciari, J.C.; Capuano, C.; Binny, D.; Kariuki, N.N.; et al. Hierarchical Electrode Design of Highly Efficient and Stable Unitized Regenerative Fuel Cells (URFCs) for Long-Term Energy Storage. Energy Environ. Sci.
**2020**, 13, 4872–4881. [Google Scholar] [CrossRef] - Paul, B.; Andrews, J. PEM Unitised Reversible/Regenerative Hydrogen Fuel Cell Systems: State of the Art and Technical Challenges. Renew. Sustain. Energy Rev.
**2017**, 79, 585–599. [Google Scholar] [CrossRef] - Wang, Y.; Xu, H.; He, W.; Zhao, Y.; Wang, X. Lattice Boltzmann Simulation of the Structural Degradation of a Gas Diffusion Layer for a Proton Exchange Membrane Fuel Cell. J. Power Sources
**2023**, 556, 232452. [Google Scholar] [CrossRef] - Vincent, I.; Lee, E.-C.; Kim, H.-M. Solutions to the Water Flooding Problem for Unitized Regenerative Fuel Cells: Status and Perspectives. RSC Adv.
**2020**, 10, 16844–16860. [Google Scholar] [CrossRef] - Guo, H.; Guo, Q.; Ye, F.; Ma, C.F.; Zhu, X.; Liao, Q. Three-Dimensional Two-Phase Simulation of a Unitized Regenerative Fuel Cell during Mode Switching from Electrolytic Cell to Fuel Cell. Energy Convers. Manag.
**2019**, 195, 989–1003. [Google Scholar] [CrossRef] - Guo, Q.; Guo, H.; Ye, F.; Xing, L.; Ma, C.F. A Numerical Study of Dynamic Behaviors of a Unitized Regenerative Fuel Cell during Gas Purging. Int. J. Hydrogen Energy
**2022**, 47, 22203–22214. [Google Scholar] [CrossRef] - Yuan, X.M.; Guo, H.; Ye, F.; Ma, C.F. Experimental Study of Gas Purge Effect on Cell Voltage during Mode Switching from Electrolyser to Fuel Cell Mode in a Unitized Regenerative Fuel Cell. Energy Convers. Manag.
**2019**, 186, 258–266. [Google Scholar] [CrossRef] - Guo, Q.; Guo, H.; Ye, F.; Ma, C.F.; Liao, Q.; Zhu, X. Heat and Mass Transfer in a Unitized Regenerative Fuel Cell during Mode Switching. Int. J. Energy Res.
**2019**, 43, 2678–2693. [Google Scholar] [CrossRef] - Bazarah, A.; Majlan, E.H.; Husaini, T.; Zainoodin, A.M.; Alshami, I.; Goh, J.; Masdar, M.S. Factors Influencing the Performance and Durability of Polymer Electrolyte Membrane Water Electrolyzer: A Review. Int. J. Hydrogen Energy
**2022**, 47, 35976–35989. [Google Scholar] [CrossRef] - Yuan, X.M.; Ye, F.; Liu, J.X.; Guo, H.; Ma, C.F. Voltage Response and Two-Phase Flow during Mode Switching from Fuel Cell to Water Electrolyser in a Unitized Regenerative Fuel Cell. Int. J. Hydrogen Energy
**2019**, 44, 15917–15925. [Google Scholar] [CrossRef] - Guo, H.; Zhao, Q.; Ye, F. An Experimental Study on Gas and Liquid Two-Phase Flow in Orientated-Type Flow Channels of Proton Exchange Membrane Fuel Cells by Using a Side-View Method. Renew. Energy
**2022**, 188, 603–618. [Google Scholar] [CrossRef] - Guo, Q.; Guo, H.; Ye, F.; Ma, C.F. Effect of Liquid Water Accumulation in Electrolytic Cell Mode on Start-up Performance of Fuel Cell Mode of Unitized Regenerative Fuel Cells. Energy Convers. Manag.
**2022**, 254, 115288. [Google Scholar] [CrossRef] - Li, H.Y.; Guo, H.; Ye, F.; Ma, C.F. Experimental Investigation on Voltage Response to Operation Parameters of a Unitized Regenerative Fuel Cell during Mode Switching from Fuel Cell to Electrolysis Cell. Int. J. Energy Res.
**2018**, 42, 3378–3389. [Google Scholar] [CrossRef] - Ashrafi, M.; Kanani, H.; Shams, M. Numerical and Experimental Study of Two-Phase Flow Uniformity in Channels of Parallel PEM Fuel Cells with Modified Z-Type Flow-Fields. Energy
**2018**, 147, 317–328. [Google Scholar] [CrossRef] - Cao, Y.; El-Shorbagy, M.A.; Dahari, M.; Cao, D.N.; Din, E.M.T.E.; Huynh, P.H.; Wae-hayee, M. Examining the Relationship between Gas Channel Dimensions of a Polymer Electrolyte Membrane Fuel Cell with Two-Phase Flow Dynamics in a Flooding Situation Using the Volume of Fluid Method. Energy Rep.
**2022**, 8, 9420–9430. [Google Scholar] [CrossRef] - Bao, Z.; Niu, Z.; Jiao, K. Analysis of Single- and Two-Phase Flow Characteristics of 3-D Fine Mesh Flow Field of Proton Exchange Membrane Fuel Cells. J. Power Sources
**2019**, 438, 226995. [Google Scholar] [CrossRef] - Guo, H.; Guo, Q.; Ye, F.; Ma, C.; Liao, Q.; Zhu, X. Improving the Electric Performance of a Unitized Regenerative Fuel Cell during Mode Switching through Mass Transfer Enhancement. Energy Convers. Manag.
**2019**, 188, 27–39. [Google Scholar] [CrossRef] - Majasan, J.O.; Cho, J.I.S.; Dedigama, I.; Tsaoulidis, D.; Shearing, P.; Brett, D.J.L. Two-Phase Flow Behaviour and Performance of Polymer Electrolyte Membrane Electrolysers: Electrochemical and Optical Characterisation. Int. J. Hydrogen Energy
**2018**, 43, 15659–15672. [Google Scholar] [CrossRef] - Wilberforce, T.; El Hassan, Z.; Ogungbemi, E.; Ijaodola, O.; Khatib, F.N.; Durrant, A.; Thompson, J.; Baroutaji, A.; Olabi, A.G. A Comprehensive Study of the Effect of Bipolar Plate (BP) Geometry Design on the Performance of Proton Exchange Membrane (PEM) Fuel Cells. Renew. Sustain. Energy Rev.
**2019**, 111, 236–260. [Google Scholar] [CrossRef] - Lim, B.H.; Majlan, E.H.; Daud, W.R.W.; Rosli, M.I.; Husaini, T. Numerical Investigation of the Effect of Three-Dimensional Modified Parallel Flow Field Designs on Proton Exchange Membrane Fuel Cell Performance. Chem. Eng. Sci.
**2020**, 217, 115499. [Google Scholar] [CrossRef] - Lim, B.H.; Majlan, E.H.; Daud, W.R.W.; Rosli, M.I.; Husaini, T. Numerical Analysis of Modified Parallel Flow Field Designs for Fuel Cells. Int. J. Hydrogen Energy
**2017**, 42, 9210–9218. [Google Scholar] [CrossRef] - Lim, B.H.; Majlan, E.H.; Daud, W.R.W.; Rosli, M.I.; Husaini, T. Numerical Analysis of Flow Distribution Behavior in a Proton Exchange Membrane Fuel Cell. Heliyon
**2018**, 4, e00845. [Google Scholar] [CrossRef] [PubMed] [Green Version] - Rosli, M.I.; Lim, B.H.; Majlan, E.H.; Husaini, T.; Daud, W.R.W.; Lim, S.F. Performance Analysis of PEMFC with Single-Channel and Multi-Channels on the Impact of the Geometrical Model. Energies
**2022**, 15, 7960. [Google Scholar] [CrossRef] - Lim, B.H.; Majlan, E.H.; Daud, W.R.W.; Husaini, T.; Rosli, M.I. Effects of Flow Field Design on Water Management and Reactant Distribution in PEMFC: A Review. Ionics
**2016**, 22, 301–316. [Google Scholar] [CrossRef] - Pamplona Solis, B.; Cruz Argüello, J.C.; Gómez Barba, L.; Gurrola, M.P.; Zarhri, Z.; TrejoArroyo, D.L. Bibliometric Analysis of the Mass Transport in a Gas Diffusion Layer in PEM Fuel Cells. Sustainability
**2019**, 11, 6682. [Google Scholar] [CrossRef] [Green Version]

**Figure 1.**Computational domain of flow field models with arrow indicating the flow direction: (

**a**) parallel; (

**b**) serpentine; and (

**c**) symmetry.

**Figure 2.**Steady state flow distribution at velocity = 0.50 m·s

^{−1}: (

**a**) parallel; (

**b**) serpentine; and (

**c**) symmetry.

**Figure 3.**Steady state flow distribution at velocity = 0.25 m·s

^{−1}: (

**a**) parallel; (

**b**) serpentine; and (

**c**) symmetry.

**Figure 4.**Flow distribution with velocity = 0.75 m·s

^{−1}: (

**a**) 0.05 s; (

**b**) 0.10 s; (

**c**) 0.15 s; (

**d**) 0.20 s; (

**e**) 0.25 s; and (

**f**) 0.30 s.

**Figure 6.**Serpentine flow field with velocity = 0.75 m·s

^{−1}(

**a**) 0.05 s; (

**b**) 0.10 s; (

**c**) 0.15 s; (

**d**) 0.20 s; (

**e**) 0.25 s; and (

**f**) 0.30 s.

Parameters | Value |
---|---|

Operating temperature (K) | 293.15 |

Operating pressure (atm) | 1.0 |

Gravity (m·s^{−2}) | 9.81 |

Water-liquid Velocity (m·s^{−1}) | 0.25/0.5/0.75 |

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. |

© 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Low, H.C.; Lim, B.H.
Numerical Analysis of the Effect of Liquid Water during Switching Mode for Unitised Regenerative Proton Exchange Membrane Fuel Cell. *Membranes* **2023**, *13*, 391.
https://doi.org/10.3390/membranes13040391

**AMA Style**

Low HC, Lim BH.
Numerical Analysis of the Effect of Liquid Water during Switching Mode for Unitised Regenerative Proton Exchange Membrane Fuel Cell. *Membranes*. 2023; 13(4):391.
https://doi.org/10.3390/membranes13040391

**Chicago/Turabian Style**

Low, Hock Chin, and Bee Huah Lim.
2023. "Numerical Analysis of the Effect of Liquid Water during Switching Mode for Unitised Regenerative Proton Exchange Membrane Fuel Cell" *Membranes* 13, no. 4: 391.
https://doi.org/10.3390/membranes13040391