Fuel Cell & Electrolyzer Module Updates
For users of the Fuel Cell & Electrolyzer Module, COMSOL Multiphysics® version 6.4 introduces new power loss variables, the ability to define gas inflow proportionally to species consumption in the electrode reaction, and more flexible species modeling. Learn more about these updates and more below.
Inlet Stoichiometric Feeds
To model the common situation in an operating fuel cell or electrolyzer where the inlet flow rate of the gas mixture is set proportionally to the cell current to ensure excess species in the cell is consumed, a Stoichiometric feed checkbox has been added to the H2 Inlet and O2 Inlet nodes of the Hydrogen Fuel Cell and Water Electrolyzer interfaces. This addition can be viewed in the following tutorial models:
O2-in-H2 and H2-in-O2 Mixtures
To enable more advanced models related to aging, parasitic reactions, and start–stop scenarios, the Hydrogen Fuel Cell and Water Electrolyzer interfaces now allow H2 to be enabled as an active gas species in the O2 Gas Mixture settings and O2 to be enabled as an active gas species in the H2 Gas Mixture settings. This update can be viewed in the Carbon Corrosion in a Polymer Electrolyte Membrane Fuel Cell tutorial model.
Power Loss Evaluation Variables
It is now possible to evaluate the magnitude of total power losses in a fuel cell or electrolyzer and compare losses among individual components, such as the electrolyte, electrode, and current conductor, using newly introduced power loss variables in the Electrochemistry interfaces.
The power losses are defined by considering the losses in the Gibbs free energy of all reacting and transported species, enabling differentiation between ohmic, concentration, and activation losses. These variables are available locally on domains and boundaries, as integrated values over the entire cell, or per individual model tree feature node.
This functionality can be viewed in the tutorial models Mass Transport and Electrochemical Reaction in a Fuel Cell Cathode and Current Density Distribution in a Solid Oxide Fuel Cell.
Load Cycle
To enable simpler setup of complex cycling schemes, a new Load Cycle feature has been added to most of the Electrochemistry interfaces. This feature can be used to define arbitrary charge–discharge load cycles, where Voltage, Power, Current, C-rate, and Rest steps may be added in any sequence. For each step in the load cycle, one or multiple dynamic continuation or break (switching) criteria can be defined, which may be based on time, voltage, or current limits as well as user-defined conditions using arbitrary variable expressions. In addition to the versatile load cycle definition options, the new feature also allows for automatic definitions of current and voltage probes as well as solver stop conditions.
With the Subloop subfeature, it is possible, for instance, to intermix long-term charge–discharge cycling tests with reference performance tests. Note that the Power and Subloop subfeatures are only available in the Battery Design Module and the Fuel Cell & Electrolyzer Module.
Aqueous Electrolyte Transport
For modeling aqueous electrolytes featuring weak acids, weak bases, ampholytes, and generic complex species — and for applications such as mechanistic corrosion modeling, electrochemical models of biological systems, and electrochemical sensor modeling — a new Aqueous Electrolyte Transport interface computes the potential and species concentration fields in a dilute aqueous electrolyte. The transport is defined by the Nernst–Planck equations, incorporating diffusion, migration, and convection, together with electroneutrality and the self-ionization equilibrium reaction of water (autoprotolysis). Due to its more efficient handling of equation reactions and easier model setup, the new interface may be more preferable to use in some cases than the more generic Tertiary Current Distribution, Nernst–Planck interface.
Automatic Initialization of Ion-Exchange Membrane Models
To ensure electroneutrality and compliance with Donnan equilibria, the Ion-Exchange Membrane feature in the Tertiary Current Distribution, Nernst–Planck interface now includes an Add Donnan shift to initial values option. This option automatically shifts the initial concentration and potential values specified in the Initial Values feature for the active Ion-Exchange Membrane domain node, assuming that the user-defined values represent the values for a bulk liquid electrolyte in equilibrium with the membrane. The shifted initial values are then used as initial values for the solver. Enabling this option typically simplifies model setup by eliminating the need to sweep the membrane’s fixed space charge to a desired nonzero value through an additional study step.
Periodic Condition
A new Periodic Condition feature has been added to the Darcy's Law and Richards' Equation interfaces to easily enforce periodicity for the flow between two or more boundaries. In addition, it is possible to create a pressure difference between source and destination boundaries, either by specifying the pressure jump directly or by prescribing a mass flow. The periodic condition is typically used to model representative volume elements and compute effective properties for use in homogenized porous media.
Pressure Jump Option for the Free and Porous Media Flow Coupling
The Free and Porous Media Flow Coupling has a new option to include a pressure jump across the free–porous boundary. This makes it possible to model, as examples, the osmotic pressure at a semipermeable membrane supported by a porous spacer material or a pressure jump due to capillary pressure in the case of multiphase flow.
New and Updated Tutorial Models
COMSOL Multiphysics® version 6.4 brings new and updated tutorial models to the Fuel Cell & Electrolyzer Module.
Ohmic and Activation Losses in a Polymer Electrolyte Membrane Water Electrolyzer Cell
Carbon Corrosion in a Polymer Electrolyte Membrane Fuel Cell
Liquid Alkaline Electrolyzer with Concentrated Electrolyte Transport
