Setting up a Study Sequence for Multiphysics Problems
For multiphysics problems, try to adjust the study sequence.
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Solve certain physics interfaces in a sequence. This can in many cases reduce computational time and improve convergence. Analyzing the results when solving a physics interface separately can also help when troubleshooting a nonconverging model.
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A good strategy is often to solve for the potentials only (that is, disable mass transport and flow interfaces), using a stationary study step, before solving the full model in the study sequence. In this way the stationary solution is used as initial values for the following steps. This can be manually by modifying the settings of the study node, or in an automated way by using the using Stationary with Initialization or a Time-dependent with Initialization study as described above.
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In many models the flow profile is only slightly (or not at all) affected by changes in current density. Therefore it can be a good strategy to separately solve for the flow early in the study sequence, and then solve for the other physics interfaces in the subsequent steps. (If the flow is not affected at all by the current distribution, solving for the flow can be disabled entirely in consecutive steps).
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Electrochemistry Interfaces
In the COMSOL Multiphysics Reference Manual:
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Studies and Solvers
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Analyzing Model Convergence and Accuracy
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Achieving Convergence When Solving Nonlinear Equations