Before You Start Building Your Model
Introducing Complexity One step at a time
The true art of modeling is knowing what phenomena to include and what phenomena to neglect. Building complexity in a model by adding one additional piece of physics or geometric feature at a time is usually the fastest way to reach the modeling goal. Here are some general tips:
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Start thinking about your cell in the lowest possible dimension. Starting with a 1D model helps to understand the influence of different reactions in an electrochemical system, and gives a good first estimate of current-voltage behavior. Go from 1D to 2D, then from 2D to 3D.
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Every electrode reaction adds numerical nonlinearities to your model. If you have multiple electrode reactions, add them one at a time.
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Start with a simple description of the electrolyte current, such as Secondary Current Distribution. Analyze the results to ensure that the electrochemical model is consistent. Switch only to more complex electrolyte models, or add extra physics such as mass transfer, heat transfer or flow, only if deemed necessary and when satisfied with the results from a simpler case.
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If you are including flow in your model, solve for the flow field first before coupling flow and electrochemistry together.
Modeling Checklist
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Identify which domains are electrode and electrolyte. How will their conductivity be assessed?
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What is happening on the electrode-electrolyte interfaces? Do both the anode and the cathode need to be modeled? Do either need to be modeled as domains, or can they be treated as boundaries?
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What electrochemical reactions take place at the electrode surfaces to cause charge transfer? Can you parameterize their thermodynamics? Do you know the equilibrium potentials? Can you parameterize their kinetics — and are the kinetics ever going to be important? If not, ignore them.
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What is the system reference potential used to quote equilibrium potentials? Where is the system ground?
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Are charge carriers in the electrolyte plentiful with respect to the drawn current density, or is charge depletion important? Be aware of nonlinear effects that may make convergence more difficult.
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If you are performing a time-dependent study, do your initial conditions have a consistent current-voltage relationship?
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What other physics interfaces need to be coupled? How does charge transfer influence these physics interfaces?