COMSOL Multiphysics^® 6.0 Release Highlights

Fuel Cell & Electrolyzer Module Updates

For users of the Fuel Cell & Electrolyzer Module, COMSOL Multiphysics^® version 6.0 brings a new material library, predefined formulations for membrane water transport and parasitic currents, and new domain settings for mixed gas/liquid domains. Learn more about the fuel cell and electrolyzer updates below.

New Fuel Cells and Electrolyzers Material Library

A new material library for fuel cells and electrolyzers contains properties for aqueous alkaline electrolytes, molten carbonate electrolytes, polymer electrolytes, and solid oxide electrolytes. The Nafion™ membrane properties include electroosmotic drag, water absorption, gas permeation, and humidity-dependent ionic conductivity.

A polymer electrolyte membrane (PEM) fuel cell modeled with a polymer electrolyte material included in the material library. The results show the gas flow fields, with straight channels on the hydrogen anode side and a flattened mesh structure used on the air cathode side.

• alkaline_electrolyzer
• solid_oxide_electrolyzer
• fuel_cell_cathode_with_liquid_water
• nonisothermal_pem_fuel_cell
• species_transport_in_the_gas_diffusion_layers_of_a_pem_fuel_cell
• transport_phenomena_in_a_polymer_electrolyte_fuel_cell_membrane_-_electrode_assembly
• low_temperature_pem_fuel_cell_with_serpentine_flow_field
• current_density_distribution_in_a_solid_oxide_fuel_cell

Adsorbing-Desorbing Species

The modeling capabilities of the existing Electrode Surface boundary condition have been expanded with a set of predefined equations that keep track of surface site occupancy and surface concentration of adsorbed species. The new Adsorbing-Desorbing Species section allows you to model the adsorption-desorption kinetics and thermodynamics at electrode surfaces in combination with multistep electrochemical reactions.

The concentration variation in a deformed geometry of a through-hole via after copper deposition.

Transport of Species Across Fuel Cell and Electrolyzer Membranes

The membranes in fuel cells and electrolyzers allow some diffusion of dissolved gases between the hydrogen and oxygen compartments. It is especially difficult to hinder the transport of hydrogen. The Hydrogen Fuel Cells and Water Electrolyzers interfaces are now updated to include the crossover of hydrogen, oxygen, and nitrogen in membrane fuel cells and electrolyzers. The reaction between hydrogen and oxygen is then considered as a parasitic reaction that lowers the efficiency of the process. Additionally, you can account for water vapor permeation and define electroosmotic water drag (the transport of water molecules due to interaction with protons).

The Settings window shows the Membrane Transport section where you can include the crossover of oxygen and hydrogen from their respective compartments, as well as electroosmotic water drag.

View this new feature in the following tutorial models:

• nonisothermal_pem_fuel_cell
• species_transport_in_the_gas_diffusion_layers_of_a_pem_fuel_cell
• transport_phenomena_in_a_polymer_electrolyte_fuel_cell_membrane_-_electrode_assembly
• fuel_cell_with_serpentine_flow_field

Mixed Gas/Liquid Domains for Alkaline Electrolyzers

As water is electrolyzed, hydrogen and oxygen evolution occur in the cathode and anode compartments, respectively. The gas bubbles change the flow field in the electrode compartments and may lower the electrolyte conductivity of bubbles that are entrained between the electrodes. The Water Electrolyzer interface now accounts for the hydrogen and oxygen volume fractions in the electrode compartments. The settings for this functionality are available from the Gas-Electrolyte Compartment domain nodes in the model tree. The Alkaline Electrolyzer tutorial model shows this new feature.

The velocity of the liquid electrolyte in the hydrogen compartment (left) and oxygen compartment (right). The electrolyte accelerates with the buoyancy provided by the gas evolution at the planar electrode surface at the left and right of the cell. The Settings window for the volume force in the Euler–Euler two-phase flow interface is also shown in the figure. Two Gas-Electrolyte Compartment features, for the hydrogen and oxygen compartments respectively, are present in the Water Electrolyzer interface.

Condensation-Evaporation in Gas Domains in Fuel Cells and Electrolyzers

The condensation and evaporation of water influences the transport properties and energy balances in fuel cells and electrolyzers. In high-fidelity models, these processes have to be accounted for. For this reason, there is a new predefined Water Condensation-Evaporation feature that allows you to add these processes to the gas domains. This functionality makes it much easier to account for condensation and evaporation in fuel cells and electrolyzers. You can see this new feature in the Fuel Cell Cathode with Liquid Water tutorial model.

The Settings window for the Water Condensation-Evaporation feature that accounts for condensation of liquid water as well as the transport of liquid water in the gas diffusion electrodes in a fuel cell unit cell.

Water Gas Shift Reaction in the Hydrogen Compartment in Fuel Cells and Electrolyzers

Carbon monoxide in the hydrogen compartment in fuel cells and electrolyzers may poison the catalyst. A possible solution to the poisoning issue is to develop designs incorporating catalysts for the water gas shift reaction (WGSR). In this reaction, carbon monoxide is oxidized with water to produce carbon dioxide and hydrogen and in fuel cells, hydrogen can further boost the anode performance. With COMSOL Multiphysics^® version 6.0, there is a new predefined Water Gas Shift Reaction feature that allows you to add the WGSR to the hydrogen compartment.

The settings for the Water Gas Shift Reaction feature.

Porous Slip for the Brinkman Equations Interface

The boundary layer in flow in porous media may be very thin and impractical to resolve in a Brinkman equations model. The new Porous slip wall treatment feature allows you to account for walls without resolving the full flow profile in the boundary layer. Instead, a stress condition is applied at the surfaces, yielding decent accuracy in bulk flow by utilizing an asymptotic solution of the boundary layer velocity profile. The functionality is activated in the Brinkman Equations interface Settings window and is then used for the default wall condition. You can use this new feature in most problems involving subsurface flow described by the Brinkman equations and where the model domain is large.

The flow and concentration field of a porous reactor model.

Heat Transfer in Porous Media

The heat transfer in porous media functionality has been revamped to make it more user friendly. A new Porous Media physics area is now available under the Heat Transfer branch and includes the Heat Transfer in Porous Media, Local Thermal Nonequilibrium, and Heat Transfer in Packed Bed interfaces. All of these interfaces are similar in function, the difference being that the default Porous Medium node within all these interfaces has one of three options selected: Local thermal equilibrium, Local thermal nonequilibrium, or Packed bed. The latter option has been described above and the Local Thermal Nonequilibrium interface has replaced the multiphysics coupling and corresponds to a two-temperature model, one for the fluid phase and one for the solid phase. Typical applications can involve rapid heating or cooling of a porous medium due to strong convection in the liquid phase and high conduction in the solid phase like in metal foams. When the Local Thermal Equilibrium interface is selected, new averaging options are available to define the effective thermal conductivity depending on the porous medium configuration.

In addition, postprocessing variables are available in a unified way for homogenized quantities for the three types of porous media. View the new porous media additions in these existing tutorial models:

• freeze_drying
• frozen_inclusion
• porous_microchannel_heat_sink_optimization
• geothermal_doublet

Nonisothermal Flow in Porous Media

The new Nonisothermal Flow, Brinkman Equations multiphysics interface automatically adds the coupling between heat transfer and fluid flow in porous media. It combines the Heat Transfer in Porous Media and Brinkman Equations interfaces.

The Free Convection in a Porous Medium tutorial model makes use of the new nonisothermal flow functionality. Temperature (K) in a porous structure subjected to temperature gradients and subsequent free convection.

Greatly Improved Handling of Porous Materials

Porous materials are now defined in the Phase-Specific Properties tabulated in the Porous Material node. In addition, subnodes may be added for the solid and fluid features where several subnodes may be defined for each phase. This allows for the use of one and the same porous material for fluid flow, chemical species transport, and heat transfer without having to duplicate material properties and settings.

The new Materials node for Porous Material exemplified on a multiscale model of a packed bed.

Nonisothermal Reacting Flow

There are now Nonisothermal Reacting Flow multiphysics interfaces that automatically set up nonisothermal reacting flow models. The Reacting Flow multiphysics coupling now includes the option to couple the Chemistry and Heat transfer interfaces. Using this coupling, the cross-contributions between heat and species equations like enthalpy of phase change or the enthalpy diffusion term are included in the model. The temperature, pressure, and concentration dependence of different quantities and material properties are also automatically accounted for, making it possible to perform heat and energy balance using the corresponding predefined variables.

Temperature distribution in a tubular reactor.

New and Updated Tutorial Models

COMSOL Multiphysics^® version 6.0 brings new and updated tutorial models to the Fuel Cell & Electrolyzer Module.

Alkaline Electrolyzer

Alkaline water electrolysis is a well-established industrial process for producing hydrogen gas. In the cell, hydrogen gas is formed at the cathode whereas oxygen gas is formed at the anode. This example investigates the impact of the gas formation on the performance of an alkaline electrolysis cell.

Application Library Title:
alkaline_electrolyzer
Download from the Application Gallery

Low-Temperature PEM Fuel Cell with Serpentine Flow Field

Current distribution in a low-temperature PEMFC when using serpentine-based flow field patterns. The cell is operated in counterflow mode so that the oxygen and hydrogen inlet flow streams are located at opposite sides. Relatively dry inlet gas compositions are used so that the cell relies on self-humidification for achieving good performance.

Application Library Title:
pemfc_serpentine_flow_field
Download from the Application Gallery

Nonisothermal PEM Fuel Cell

This tutorial models the coupled electrochemical reactions, charge and species transport, and heat transfer in a polymer electrolyte membrane (PEM) fuel cell. For the gas flow fields, straight channels are used on the hydrogen anode side, whereas a flattened mesh structure is used on the air cathode side.

Application Library Title:
nonisothermal_pemfc
Download from the Application Gallery