A simple question, which remains ignored in the field of supercapacitors is: will the device performance be affected near a magnetic field, if it is fabricated using electrode materials that are also magnetic? It is shown in this paper that the answer is: yes, it will be appreciably affected! The modulation in the specific capacitance is a convoluted picture of variation: diffusion mechanics of solvated cations, Nernst layer at the interface, magnetoresistance, and associated I–V response. The magnetic field also has direct control on the value at which saturation in specific capacitance is observed in such devices. Nearly a 170% increase in energy density at 1 A g−1 is observed by varying the magnetic field from 0 to 5 mT and a ten fold increase in power density is observed at 5 mT when current density is increased from 1 to 5 A g−1. These results clearly show that electronic circuitry designed using supercapacitors needs to be reworked/designed if it is to be used in or around magnetic environment. To prove the concept and have a complete picture in one article, the paper presents results on nanosized magnetic metal oxides based on the four ferromagnetic elements, Fe, Co, Mn, and Ni.

A scalable and facile synthesis of MnCo2O4 hierarchical microstructures for applications in supercapacitors and reduction catalysis.

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Comparative study of TMO based hollow and solid nanostructures for supercapacitor applications.

Contrary to what has been recently reported for electrode material MnO 2 , Mn 3 O 4 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 Mn 3 O 4 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 Na 2 SO 4 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.