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The rapid depletion of fossil fuels and ever-growing energy demand led to the search for renewable clean energy sources. The storage of renewable energy calls for immediate attention to the fabrication of efficient energy storage devices like supercapacitors (SCs). As an electrode material for SCs, MnO2 has gained wide research interest because of its high theoretical capacitance, variable oxidation state, vast abundance, and low cost. But, the low electric conductivity of MnO2 limits its practical application. The conductivity of MnO2 can be enhanced by tuning the electronic states through substitution doping with cobalt. In the present work, First Principles analysis based on Density Functional Theory (DFT) has been used to examine the quantum capacitance (CQ) and surface charge (Q) of Co-doped MnO2. Doping enhanced the structural stability, electric conductivity, potential window, and quantum capacitance of α-MnO2. The shortened band gap and the presence of localized states near the Fermi improve the CQ of α-MnO2. For narrow potential range (-0.4 to 0.4 V), the CQ is observed to increase with doping concentration. The highest CQ value at -0.4 V is observed to be 1501.45 µF cm-2 for Mn7CoO16 (12.5% doping), three times higher than pristine MnO2 (471.72 µF cm-2). Mn7CoO16 also exhibits better CQ and ‘Q’ at higher negative bias. Hence, it can be used as cathode material for asymmetric supercapacitor. All the results suggest the better capacitive performance of Co-doped α-MnO2 for aqueous SCs and as cathode material for asymmetric supercapacitors.
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