Magnetic Effects in Electrocatalysis Studied with Electrochemical Impedance Spectroscopy: The Cases of Oxygen Reduction and Evolution Reactions on Cobalt Ferrite Electrodes

Recent years have witnessed an intense effort to unravel magnetic field effects in electrocatalysis, as they can enhance the performance of common electrocatalysts. Both experimental and theoretical studies have shown that magnetic fields may affect, among others, the macroscopic spin-orbital ordering, charge transport, bubble release, and electron transfer kinetics. This paper highlights Electrochemical Impedance Spectroscopy (EIS) as a tool to analyze and separate the effects of magnetic field on both the oxygen reduction and evolution reactions at cobalt iron oxide electrodes. The unequivocal existence of magnetic field effects is demonstrated through EIS, which provides additional information useful to individuate the magnetic field effects. In the almost superparamagnetic nanoparticles studied here, while the magnetic field impact is positive for oxygen reduction, it turns out to be negligible in the case of oxygen evolution. In addition, this study reveals new significant insights, including the exceptionally slow relaxation kinetics of the magnetic effects and the significance of magnetic-induced surface modifications. The fact that the effects virtually disappear in the presence of electrolyte cesium ions points to the key role of electrode surface states. This study showcases the potential of EIS to probe the effects of permanent magnetic fields in electrocatalysis.