A comprehensive modeling method for proton exchange membrane electrolyzer development

https://doi.org/10.1016/j.ijhydene.2021.02.170Get rights and content

Highlights

  • Modeling scopes and methods are presented to facilitate PEMEC development.

  • Electrochemical, thermal-fluid, and transport processes are integrated.

  • A PEMEC modeling tool implements the add-on modules in ANSYS/Fluent.

  • Modeling outcomes provide design and performance insights.

Abstract

Hydrogen attracts significant interests as an effective energy carrier that can be derived from renewable sources. Hydrogen production using a proton-exchange membrane (PEM) electrolyzer can efficiently convert renewable power via water splitting in wide scales—from large, centralized generation to on-site production. Mathematical models with multiple scales and fidelities facilitate the continuing improvements of PEM electrolyzer development to improve performance, cost, and reliability. The model scopes and methods are presented in this paper, which also introduces a comprehensive PEM electrolysis modeling tool based on computational fluid dynamics (CFD) software, ANSYS/Fluent. The modeling tool incorporates electrochemical model of a PEM electrolysis cell to simulate the performance of coupled thermal-fluid, species transport, and electrochemical processes in a product-scale cell or stack by leveraging the powerful meshing generation and CFD solver of ANSYS/Fluent. The thermal-fluid modeling includes liquid water/gas two-phase flow and simulates a PEM electrolysis cell by using Fluent user-defined functions as add-on modules accounting for PEM-specific species transport and electrochemical processes. The modeling outcomes expediate PEM electrolyzer scaling up from basic material development and laboratory testing.

Introduction

Fuel cell systems have been deployed for various applications, primarily in the distributed power generation and transportation sectors [1,2]. The deployment of fuel cell electric vehicles and transition to a hydrogen economy have attracted great attention in obtaining carbon-free hydrogen supplies [[3], [5], [6]]. Hydrogen is an attractive energy carrier for carbon-free power generation and transportation [3], and it enables long driving distances for long-haul trucks or heavy-duty vehicles [1]. Various technologies are available or under development for hydrogen production from different energy sources including conventional hydrocarbon fuels such as coal or natural gas, or carbon-free sources such as electrolysis water splitting by using renewable electricity. Of various water splitting methods, a proton-exchange membrane (PEM) electrolyzer is a promising device that enables a wide range of hydrogen production scales—from centralized generation to distributed supply. However, the cost and performance of PEM electrolyzer limit their broad economic applications, and continuing improvements are needed for cost reduction and performance improvements [7,8].

The PEM electrolyzer technology is on the path for commercialization, and its performance is under sustaining improvements. Carmo et al. [8] have provided a comprehensive review of the PEM electrolysis technologies and the scope of the research status. The review ranges from electrolyzer material, components, and modeling, and it discusses the method and role of the modeling in improving PEM electrolyzer performance. Fig. 1 shows a cross-section of a single channel and details the different species of transport inside an electrolysis cell. In an operating electrolyzer cell, two-phase flow occurs when liquid water enters the cell, and gaseous hydrogen and oxygen are generated and mixed within the liquid- or gas-phase water from vaporization and water crossover. The gas/liquid two-phase flow benefits the thermal management in PEM electrolyzer but causes complexity in modeling species transport and electrochemical processes.

Fig. 1 shows the mass transport and electrochemical processes within a typical PEM electrolysis cell (PEMEC). The overall water-splitting process is H2O(l) → H2(g) + 1/2O2(g), which results in the coexistence of liquid water and gas phases on both sides. PEMEC components include flow distribution channels inside separate plates, porous transport layers, and a membrane-electrode assembly (MEA) comprised of a proton exchange membrane, anode catalyst layer, and cathode catalyst layer. The PEMEC MEA often uses the perfluorosulfonic acid polymer Nafion® membrane as the solid proton-conducting electrolyte. Protons are transported across the membrane from anode to cathode. Water also crosses the membrane via electroosmotic drag or diffusion, which are both modeled in this work.

Oxygen is generated at the anode side and mixes with the liquid water and water vapor. Electrons are derived from the electrochemical oxygen evolution reaction (OER) at the anode, and travel through an external circuit back to the cathode. Electrons and protons recombine at the cathode to produce hydrogen gas. Hydrogen produced at the cathode side will be separated from water crossover through the membrane. Experimentally probing the multi-physics processes within an operating PEMEC, such as species distributions, spatially varying current densities, and thermal fluid flow, is nearly impossible. Therefore, modeling tools in various scales are useful to complement experiments. Modeling results can provide insight and understanding of the component design and material properties on PEMEC performance. Computational modeling can simulate the transport and electrochemical processes to aid the development of PEMECs efficiently and cost effectively. Modeling outcomes in various scopes provide details inside an electrolyzer and help optimize designs and operating conditions through so-called computational experiments.

Section snippets

Overview of PEMEC modeling

PEMEC modeling includes multi-physics and multiscale approaches, spanning from membrane/electrode electrochemical and catalytic processes to cell or stack performance. To analyze the PEMEC designs from a single cell to a large stack, PEMEC models involving thermal-flow distributions can be built upon multi-dimensionality, ranging from a lumped parameter or 0-dimensional (0-D) models, 1-dimensional (1-D), 2-dimensional (2-D), to 3-dimensional (3-D) models. While 1-D and 2-D models can

PEMEC model description

To simulate the PEMEC, the mixture model in Fluent was used to solve the multiphase flow in the electrode components and was coupled to customized UDFs that model the electrochemical processes. UDFs are add-on modules that can integrate with the Fluent solver and are used to define source terms and material properties. Using UDFs leverages the capacity and robustness of the Fluent software, while extending its PEMEC modeling capability.

Fig. 3a shows a schematic of the 25 cm2 flow field and

Results and discussion

The electrochemical parameters used in the CFD model were obtained by fitting experimental polarization curves obtained at 60 °C and 80 °C. Experimental conditions used for the validation studies in this work are summarized in Table 4.

The parameters in the electrochemical model were derived from a least-squares fitting method to fit Eq. (33) to the experimental data with the following parameters as variables: RACL (anode catalyst layer roughness factor), RCCL (cathode catalyst layer roughness

Conclusion

Mathematical modeling provides effective insights in PEMEC and product development on various scales and approaches. After comparing various modeling scales and scopes, this paper introduces a computationally efficient modeling framework that encompasses adequate physical understanding of a PEMEC required to study the effects of operating conditions and component design on PEM cell or stack performance. The multi-scale, Multiphysics model incorporates the ANSYS/Fluent CFD solvers and adds

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was authored by the National Renewable Energy Laboratory (NREL), operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. The work was partially supported by the NREL H2@scale Laboratory Directed Research and Development (LDRD) led by Dr. Jennifer Kurtz and Dr. Bryan Pivovar. The authors gratefully acknowledge research support from the HydroGEN Consortium, established under the U.S. DOE, Office of Energy Efficiency

References (67)

  • N.V. Dale et al.

    Semiempirical model based on thermodynamic principles for determining 6 kW proton exchange membrane electrolyzer stack characteristics

    J Power Sources

    (2008)
  • F. Marangio et al.

    Theoretical model and experimental analysis of a high pressure PEM water electrolyser for hydrogen production

    Int J Hydrogen Energy

    (2009)
  • I.V. Zenyuk et al.

    Gas-diffusion-layer structural properties under compression via X-ray tomography

    J Power Sources

    (2016)
  • A.C. Olesen et al.

    Towards uniformly distributed heat, mass and charge: a flow field design study for high pressure and high current density operation of PEM electrolysis cells

    Electrochim Acta

    (2019)
  • H. Ito et al.

    Influence of pore structural properties of current collectors on the performance of proton exchange membrane electrolyzer

    Electrochim Acta

    (2013)
  • J. Nie et al.

    Numerical and experimental study of three-dimensional fluid flow in the bipolar plate of a PEM electrolysis cell

    Int J Therm Sci

    (2009)
  • S. Toghyani et al.

    Thermal and electrochemical analysis of different flow field patterns in a PEM electrolyzer

    Electrochim Acta

    (2018)
  • M. Espinosa-López et al.

    Modelling and experimental validation of a 46 kW PEM high pressure water electrolyzer

    Renew Energy

    (2018)
  • F. Barbir

    PEM electrolysis for production of hydrogen from renewable energy sources

    Sol Energy

    (2005)
  • Z. Kang et al.

    Performance modeling and current mapping of proton exchange membrane electrolyzer cells with novel thin/tunable liquid/gas diffusion layers

    Electrochim Acta

    (2017)
  • K. Bromberger et al.

    Hydraulic ex situ through-plane characterization of porous transport layers in PEM water electrolysis cells

    Int J Hydrogen Energy

    (2018)
  • J. Van Der Merwe et al.

    Characterisation tools development for PEM electrolysers

    Int J Hydrogen Energy

    (2014)
  • C. Rakousky et al.

    An analysis of degradation phenomena in polymer electrolyte membrane water electrolysis

    J Power Sources

    (2016)
  • M. Chandesris et al.

    Membrane degradation in PEM water electrolyzer: numerical modeling and experimental evidence of the influence of temperature and current density

    Int J Hydrogen Energy

    (2015)
  • B. Mohamed et al.

    Using the hydrogen for sustainable energy storage: designs, modeling, identification and simulation membrane behavior in PEM system electrolyser

    J Energy Storage

    (2016)
  • M. Sartory et al.

    Theoretical and experimental analysis of an asymmetric high pressure PEM water electrolyser up to 155 bar

    Int J Hydrogen Energy

    (2017)
  • F. Arbabi et al.

    Feasibility study of using microfluidic platforms for visualizing bubble flows in electrolyzer gas diffusion layers

    J Power Sources

    (2014)
  • O.F. Selamet et al.

    Two-phase flow in a proton exchange membrane electrolyzer visualized in situ by simultaneous neutron radiography and optical imaging

    Int J Hydrogen Energy

    (2013)
  • I. Dedigama et al.

    In situ diagnostic techniques for characterisation of polymer electrolyte membrane water electrolysers - flow visualisation and electrochemical impedance spectroscopy

    Int J Hydrogen Energy

    (2014)
  • K. Ito et al.

    Analysis and visualization of water flow impact on hydrogen production efficiency in solid polymer water electrolyzer under high-pressure condition

    Int J Hydrogen Energy

    (2015)
  • S.S. Lafmejani et al.

    Experimental and numerical study of flow in expanded metal plate for water electrolysis applications

    J Power Sources

    (2018)
  • F. Aubras et al.

    Two-dimensional model of low-pressure PEM electrolyser: two-phase flow regime, electrochemical modelling and experimental validation

    Int J Hydrogen Energy

    (2017)
  • L.F.L. Oliveira et al.

    A multiscale physical model of a polymer electrolyte membrane water electrolyzer

    Electrochim Acta

    (2013)
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