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.

Hierachical nanosheets of Co3O4 can deliver specific capacitance of ∼402 F g–1, which is 50% higher than that obtained using simpler disc shaped (∼230 F g–1) or conventional solid structures (∼150 F g–1). A simple question is then asked: should the particles showing other morphologies be discarded? As the electrode material is to be used in green or renewable energy technologies, the carbon footprint of each particle morphology was determined using the life cycle assessment (LCA) studies. The results led to inferences, which were strikingly different from those generally expected. It was seen that simpler morphologies, prepared using easier synthesis protocols, had five-times lower CO2 footprints than hierarchical morphology (nanosheets). The results become extremely critical for proposing their large scale industrial use. They clearly indicate that the choice of nanostructured metal oxides in energy storage devices will have to be relooked from the aspect of their own environmental impacts. Particles with lowest environmental impact but comparable specific capacitances will win over other counterparts.

No abstract

No abstract

No abstract