Fuel Cell & Electrolyzer Module
New Functionality in Version 6.4
Aqueous Electrolyte Transport interface
A new Aqueous Electrolyte Transport interface is now available. This interface computes the potential and species concentration fields in a dilute aqueous electrolyte. The new interface is specialized for modeling aqueous electrolytes featuring weak acids, weak bases, ampholytes, and generic complex species and can, for instance, be used for mechanistic corrosion modeling, electrochemical models of biological systems, and electrochemical sensor modeling.
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. The transport is defined by the Nernst–Planck equations, including diffusion, migration, and convection, in combination with electroneutrality and the self-ionization equilibrium reaction of water (autoprotolysis).
Power loss variables
New power loss variables have been introduced in the Electrochemistry interfaces. By using the new variables, it is possible to evaluate the magnitude of the total power losses in a battery cell and compare the losses of the individual components (such as the separator, electrode, and current conductor).
The power losses are defined by considering the losses in the Gibbs free energy of all reacting and transported species, which allows for differentiation between ohmic, concentration, and activation losses.
The variables are available both locally on domains and boundaries, as integrated variables for the whole cell, or integrated per individual model-tree feature node.
The power loss variables can be accessed during results visualization under Power losses (in the relevant Electrochemistry interface submenu) when clicking either Insert expression or Replace expression.
Load Cycle node
A new Load Cycle node has been added to the Primary Current Distribution, Secondary Current Distribution, and Tertiary Current Distribution interfaces as well as the Hydrogen Fuel Cell and Water Electrolyzer interfaces. The node may be used to define arbitrary charge–discharge load cycles by adding Voltage, Power, Current, and Rest child nodes, which are executed in sequence.
For each node in the load cycle sequence, the user may define one or multiple dynamic continuation or break (switching) criteria, which may be based on time, voltage, or current limits, as well as user-defined conditions using arbitrary variable expressions. By using the Subloop child node, dynamic switching between different cycling schemes is also possible.
The Load Cycle node also allows for automatic definitions of current and voltage probes, as well as solver stop conditions.
The Load Cycle node is available both as a boundary node for porous electrode and current conductor domains and as a child node of the Electrode Surface, Highly Conductive Porous Electrode, Thin Porous Electrode, Perforated Electrode Surface, Sacrificial Anode Surface, and Thin Electrode Surface nodes.
Initial Values for the Ion-Exchange Membrane Node in the Tertiary Current Distribution, Nernst–Planck Interface
The Ion-Exchange Membrane node in the Tertiary Current Distribution, Nernst–Planck interface has a new Add Donnan shift to initial values option, which is enabled by default when creating a new model. The new option automatically shifts the initial concentration and potential values specified by the user in the Initial Values node 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.
The new option facilitates easier model setup since it typically excludes the need to sweep the fixed space charge of the membrane to a desired nonzero value using an additional study step.
The new option is enabled by default in new models, which means that Java API backward compatibility may be affected by the change.
Default Solver and Study step updates
Reaction forces are no longer stored by default by the time-dependent solver. This improves performance for 1D models storing all solutions.
The recovery damping factor in the default solver for stationary study steps in most Electrochemistry interfaces has been reduced to 0.1 (from 0.75). This may improve convergence in certain cases.
The Free and Porous Media Flow interface and Reacting Flow, H2 Gas Phase and Reacting Flow, O2 Gas Phase multiphysics nodes now support the Frequency-Domain Perturbation study step.
Hydrogen Fuel Cell and Water Electrolyzer Interfaces
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O2 may now be enabled as an active species in the H2 Gas Mixture settings.
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H2 may now be enabled as an active species in the O2 Gas Mixture settings.
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In the H2 Inlet and O2 Inlet nodes, when using the Mass flow rate as an Inlet flow type, a new Stoichiometric feed checkbox has been added (enabled by default). The option is used 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 in order to ensure excess species in the cell is consumed. The new default may impact Java API backward compatibility.
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The partial pressure variables are no longer regularized; that is, the nonnegative lower limit has been removed. This generally improves convergence due to nonvanishing gradients and may affect the convergence behavior of models created in previous versions.
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A Solve for electrolyte phase potential checkbox has been added in the (renamed) Electrolyte and Membrane Transport section of the settings for the main (top) interface node. When this checkbox is cleared, user-defined models for the electrolyte ion transport can be incorporated.
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The settings for the Out-of-plane thickness (2D and 1D with axial symmetry) and the Cross-sectional area (1D) properties have been moved from being defined on individual boundary nodes to a common edit field in the settings of the main (top) interface node.
Fuel Cell and Electrolyzer Material Library
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The Potassium Hydroxide, KOH material has been modified to use an analytic function, which allows for easy plotting of the electrolyte conductivity as a function of T and C.
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A new polymer electrolyte material, PiperION®, Liquid Equilibrated, Hydroxide Form, has been added, with data for the electrolyte conductivity as a function of T.