R. Ranjusha

Ultra fine MnO2 nanowire based high performance thin film rechargeable electrodes: Effect of surface morphology, electrolytes and concentrations

The present study demonstrates a novel approach by which titanium foils coated with MnO2 nanowires can be processed into a high surface area electrode for rechargeable energy storage applications. A detailed study has been performed to elucidate how surface morphology and redox reaction behaviors underlying these electrodes impact the cyclic and capacitive behavior of the electrode. These nanowires were synthesized hydrothermally and exhibited an aspect ratio in the order of 102. BET analysis revealed that these MnO2 nanowires show a high surface area of 44 m2 g−1. From the analysis of the relevant electrochemical parameters, an intrinsic correlation between the capacitance, internal resistance and the surface morphology has been deduced and explained on the basis of relative contributions from the faradic properties of the MnO2 in different electrolytes. Depending on the type of surface morphology incorporated, these thin film nanowire electrodes exhibited specific mass capacitance value as high as 1050 F g−1 and 750 F g−1 measured from cyclic voltammetry and charge–discharge curves respectively. It has been shown that electrodes based on such nanowires can allow significant room for improvement in the cyclic stability of a hybrid supercapacitor/battery system. Further, a working model supercapacitor in cylindrical form is also shown exhibiting a capacitance of 10 F.

Fabrication and performance evaluation of button cell supercapacitors based on MnO2 nanowire/carbon nanobead electrodes

The present study provides in detail experimental results on the synthesis and characterization of carbonized MnO2 nanowires for fabricating large surface area, high power and energy density rechargeable electrodes for supercapacitor/battery applications. High aspect ratio MnO2 nanowires carbonized with camphoric carbon composed of nanobeads were utilized for this purpose. The graphitic nature of these nanobeads was confirmed through Raman spectroscopy and X-ray photoelectron spectroscopy, where a predominance of sp2 hybridization was observed. The relative contributions of the carbon nanobeads’ influence on the capacitive and diffusion controlled processes underlying these thin film electrodes have been mathematically modelled. The electrodes were fabricated into thin films (thickness ∼30 μm) by co-electrophoresis onto titanium foils exhibiting a surface area of ∼50 m2 g−1. CHN analyses revealed an electrophoretic co-deposition of carbon nanobeads along with MnO2 nanowires onto the titanium foils. From the electrochemical studies, an intrinsic correlation between overall specific capacitance, electrode internal resistance and its conductivity has been defined and explained in different electrolyte systems. These electrodes exhibited specific mass capacitance values as high as 1200 ± 18 F g−1. High cyclic stability was observed at the end of 10 000 cycles, which was attributed to the low oxide dissolution of ∼0.02 ppm in the electrolyte as measured by inductively coupled plasma atomic emission spectroscopy studies. Further, a working model of a button cell was also studied based on these thin film electrodes, which exhibited a capacitance of ∼1.2 F. These thin film electrodes exhibited an energy density of 96 Wh kg−1 and a peak power density of 32 kW kg−1.

Gold–chitin–manganese dioxide ternary composite nanogels for radio frequency assisted cancer therapy

Gold nanoparticles (Au-NPs) based chitin-MnO2 ternary composite nanogels (ACM-TNGs) were prepared by the regeneration of chitin along with MnO2 nanorods (5–20 nm) and the incorporation of 10 nm sized Au-NPs to make “ACM-TNGs”. They were characterized with FT-IR, TG, and UV spectroscopy. The SEM showed spindle shaped 200 nm sized chitin–MnO2 nanogels (chitin–MnO2 NGs), whereas ACM-TNGs had spindle sizes of 220 nm. The ACM-TNGs were compatible up to 1 mg mL−1 and showed uptake into L929, HDF, MG63, T47D and A375 cell lines without affecting the cellular morphology. ACM-TNGs showed conductivity, and heating under a radio frequency (RF) source at 100 W for 2 min. They also showed the ability to kill breast cancer cells under RF radiation at 100 W for 2 min, when compared with the chitin–MnO2 NGs. The RF assisted ablation of breast cancer cells was confirmed by a live/dead assay. These results suggests that ACM-TNGs could be useful for the RF assisted cancer cells ablation with minimal toxicity compared with MnO2 nanorods.

Cycling Performance of NanocrystallineLiMn2O4Thin Films via Electrophoresis

The present study demonstrates a novel approach by which titanium foils coated with LiMn2O4 nanocrystals can be processed into a high-surface-area electrode for rechargeable batteries. A detailed study has been performed to elucidate how surface morphology and redox reaction behaviors underlying these electrodes impact the cyclic and capacity behavior. These nanocrystals were synthesized by in situ sintering and exhibited a uniform size of ∼55 nm. A direct deposition technique based on electrophoresis is employed to coat LiMn2O4 nanocrystals onto titanium substrates. From the analysis of the relevant electrochemical parameters, an intrinsic correlation between the cyclability and particle size has been deduced and explained in accordance with the Li intercalation/deintercalation process. Depending on the particle size incorporated on these electrodes, it is seen that in terms of capacitance fading, for nanoparticles cyclability is better than their micron-sized counterparts. It has been shown that electrodes based on such nanocrystalline thin film system can allow significant room for improvement in the cyclic performance at the electrode/electrolyte interface.

MnO2 nano/micro hybrids for supercapacitors: “Nano's Envy, Micro's pride”

The present study provides the first reports on a low temperature molten salt route which can generate unique architecture of MnO2 nanospikes arrayed in a peculiar fashion to form micron sized ball morphology. This morphology when employed as supercapacitor electrodes gives an advantage of surface relaxation during the charge–discharge process making it super stable. The study highlights the advantages of nanostructuring of microparticles which can answer the toxicity issues and their potential as a commercial product. This claim in the present study has been validated by cell toxicity study on human dermal fibroblasts, which established that a nano/micro hybrid structure can be relatively less toxic. Cytoskeleton rearrangements were also observed as the size of MnO2 was reduced from micron to nanoscale. A mechanism of the structure formation and the influence of the salt in controlling the process parameters as well as the morphology are also proposed. These electrodes in coin cells exhibited specific mass capacitance value as high as 1100 F g−1 with a power density and energy density of 4.5 W h kg−1 and 14 kW kg−1, respectively.

Cycling Performance of Nanocrystalline LiMn2O4 Thin Films via Electrophoresis

The present study demonstrates a novel approach by which titanium foils coated with LiMn2O4 nanocrystals can be processed into a high-surface-area electrode for rechargeable batteries. A detailed study has been performed to elucidate how surface morphology and redox reaction behaviors underlying these electrodes impact the cyclic and capacity behavior. These nanocrystals were synthesized by in situ sintering and exhibited a uniform size of ∼55 nm. A direct deposition technique based on electrophoresis is employed to coat LiMn2O4 nanocrystals onto titanium substrates. From the analysis of the relevant electrochemical parameters, an intrinsic correlation between the cyclability and particle size has been deduced and explained in accordance with the Li intercalation/deintercalation process. Depending on the particle size incorporated on these electrodes, it is seen that in terms of capacitance fading, for nanoparticles cyclability is better than their micron-sized counterparts. It has been shown that electrodes based on such nanocrystalline thin film system can allow significant room for improvement in the cyclic performance at the electrode/electrolyte interface.

Cycling performance of nanocrystalline LiMn 2 O 4 thin films via electrophoresis

The present study demonstrates a novel approach by which titanium foils coated with LiMn2O4 nanocrystals can be processed into a high-surface-area electrode for rechargeable batteries. A detailed study has been performed to elucidate how surface morphology and redox reaction behaviors underlying these electrodes impact the cyclic and capacity behavior. These nanocrystals were synthesized by in situ sintering and exhibited a uniform size of ∼55 nm. A direct deposition technique based on electrophoresis is employed to coat LiMn2O4 nanocrystals onto titanium substrates. From the analysis of the relevant electrochemical parameters, an intrinsic correlation between the cyclability and particle size has been deduced and explained in accordance with the Li intercalation/deintercalation process. Depending on the particle size incorporated on these electrodes, it is seen that in terms of capacitance fading, for nanoparticles cyclability is better than their micron-sized counterparts. It has been shown that electrodes based on such nanocrystalline thin film system can allow significant room for improvement in the cyclic performance at the electrode/electrolyte interface.