Magnetic field effects on the rest potential of ferromagnetic electrodes

Various magnetic field effects have been reported in the electrochemical literature. While it is well established that an applied field can significantly influence mass transport processes in solution and surface morphology, the effects of a magnetic field on both the rate of electron transfer and electrochemical equilibria are more controversial. It has been recently reported that the rest potential of ferromagnetic electrodes such as iron in solutions of their salts may be altered by the application of fields in the 1 T range and it has been proposed that the effect might have some application in sensors. Such effects are entirely unexpected given that the magnetic energy, μ_BB, is nearly three orders of magnitude smaller than the thermal energy at room temperature. We have investigated the shift in the rest potential of the ferromagnetic electrodes, Fe, Co and Ni in an applied magnetic field, in the presence of different electrolytes. In the case of iron, the effects were sufficiently large to be measured by a dc method, but for cobalt and nickel it was necessary to use an alternating field with a frequency of 0.2 Hz and a Perkin Elmer 7265 lock-in detector. The anodic shift for iron is shown. The shift for cobalt and nickel electrodes in solutions of their salts was ∼1 mV, but was also in the anodic direction, contrary to the report of Waskaas and Kharkats (1999). No effect was observed for a copper electrode in any solution, or for an iron electrode in a diamagnetic solution. We attribute the shift in rest potential to increases in the surface concentration of cations such as Fe²⁺ due to the magnetization of the electrode. From the slope of the ΔV(B) curve, we infer that the magnetic field gradient due to the stray field near the rough electrode surface provides the force driving convection on a micrometer scale close to the electrode.