You can design a small electromagnet and put your Electrochemical cell in between the poles, Magnetic field dependent electrochemistry helps to deposit magnetic thin films and also helps to sense the magnetic ions concentration.
We found that a simple way to do it was to put some magnets underneath a screen printed electrode; https://www.researchgate.net/publication/264350783_The_Oxygen_Reduction_Reaction_in_Ferrofluids_Towards_Membrane-less_and_Spill-less_Gas_Sensors
Article The Oxygen Reduction Reaction in Ferrofluids: Towards Membra...