Understanding the Origin of Magnetic Field Dependent Specific Capacitance in Mn₃O₄Nanoparticle Based Supercapacitors

Abstract

Contrary to what has been recently reported for electrode material MnO2, Mn3O4 actually shows reduction in the specific capacitance values under magnetic field. This observation cannot be explained by the earlier suggested reasons such as varying magnitude of Lorentz force, Nernst layer, ion-concentration at solid electrolyte interphase and the probability of intercalation/de-intercalation probability. An additional factor viz., magneto-dielectric constant, has to be invoked to understand the suppression of specific capacitance. The paper also presents a new template-free room temperature synthesis protocol for obtaining Mn3O4 nanoparticles. These particles, when used in three electrode configuration, return a specific capacitance of ∼290 F g−1 at a scan rate of 10 mV s−1 and ∼221 F g−1 at current density of 0.5 A g−1 in combination with 1 M Na2SO4 as electrolyte. Nearly 50% change in specific capacitance is observed as a function of magnetic field strength. The underlying reasons are presented. The paper shows that the use of magnetic transition metal oxides based electrochemical capacitors near magnetic field will have to be revisited.