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This report presents a single-step deposition of crystalline and catalyst-free cobalt nitride (CoN) and zinc nitride (Zn3N2) electrodes on a flexible current collector for highly efficient flexible supercapacitors. These proposed electrodes take full advantage of mechanical strength, electrochemical stability, and tremendous electrical conductivity with excellent adhesion to a flexible current collector and show high capacitive performance with outstanding cyclic life. The asymmetric supercapacitor (ASC) was constructed using CoN as a negative electrode and Zn3N2 as a positive electrode, assembled with 1 M Na2SO4 aqueous electrolyte soaked Whatman filter paper as the separator. This ASC exhibits a wider voltage window (up to 2 V), good capacitance (75.4 Fg−1), and high specific energy (42 Wh kg−1) with good capacitance retention (93.6% for the flat cell and 80.1% for the 80° bend cell) over 5000 charging discharging cycles. Therefore, this design of ASC potentially expands the performance of high frequency and flexible electronics.

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Single crystalline α- and γ-MnS thin films have been deposited on Si and ITO substrates by reactive DC sputtering (Ar:H2S 2:1) of a manganese target for electrochemical energy storage application. We found that working pressure was one of the major parameters while optimizing the crystallinity of thin films, whereas the phase tuning (γ to α) was primarily controlled by temperature variations. The temperature was varied from RT to 450 °C, keeping the gas pressure constant at 10 mTorr optimized value, resulting in a transition between two different polymorphs of MnS as confirmed by XRD results. AFM and contact angle measurements were also performed to study the surface roughness, wetting properties, and surface energy calculations of prepared thin films. α-MnS films prepared at 400 °C were found to have a maximum contact angle of 118° and a minimum free surface energy (γSV) of 8.38 mN/m. Moreover, we have also studied the phase dependent electrochemical properties and found that γ-MnS thin films prepared at ambient substrate temperature displayed the highest specific capacitance of 178.3 F/g at a scan rate of 5 mV/s with superior charge-discharge rates in neutral electrolytes. As the substrate temperature was increased to 300 °C, we observed a continuous decrease in the respective specific capacitance values, and α-MnS electrodes were found to have a minimum specific capacitance of 120 F/g. The enhanced electrochemical performance of γ-MnS thin films can be attributed to the superior water interacting properties (θw = 90.4°) and its wurtzite structure, which enables easy penetration of electrolytes into the active materials.

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