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(Invited) Building Supercapacitors with Earth-Abundant Materials

Sunday, 28 May 2017: 09:00
Grand Salon C - Section 15 (Hilton New Orleans Riverside)
D. Sarkar, D. D. Sarma, and A. K. Shukla (Indian Institute of Science)
Hematite (α-Fe2O3) is an environment-friendly and earth-abundant negative electrode material for electrochemical supercapacitors. It has high theoretical specific-capacitance with a suitable operating-potential-window. However, its use as positive electrode material has been limited. In the light of the foregoing, we have investigated the feasibility of using α-Fe2O3 both as positive and negative electrodes to examine its versatility in supercapacitors. On the other hand, MnO2 has been investigated extensively as positive electrode in supercapacitors because of its striking electrochemical activity. But MnO2 exhibits poor electronic conductivity and has low-rate capability. To address this issue, a core-shell nanorod-based positive electrode is designed combining the aforesaid traits of α-Fe2O3 and MnO2. In the core-shell design, MnO2 shell serves as active site for surface or near-surface based fast and reversible faradaic reactions while α-Fe2O3 nanorod core facilitates electron transfer towards current collector. As a consequence of this synergy, α-Fe2O3/MnO2 core-shell nanorod electrode shows improved electrochemical performance in terms of capacitance and rate capability within a potential window of 0-1 V in comparison to individual component materials. Moreover, the assembled asymmetric supercapacitor (ASC) using α-Fe2O3/MnO2 core-shell nanorods and pristine α-Fe2O3 nanorods as respective positive and negative electrodes exhibit a volumetric capacitance of ~ 1.3 F/cm3 at a scan rate of 10 mV/s within a potential window of 0-2 V with nearly 78% capacitance retention at a scan rate of 400 mV/s. Interestingly, the ASC delivers a maximum energy density of ~ 0.46 mWh/cm3 at a current density of 0.5 mA/cm2; the power density of the ASC being 550 mW/cm3 at a current density of 5 mA/cm2 while energy density reaches ~ 0.35 mWh/cm3.