Achieving enhanced pseudocapacitance in MoS2 nanowires rationally sputtered over NiMnIn shape memory alloy for flexible Na-ion supercapacitor

Abstract

The present study reports a flexible supercapacitor device incorporating thin-film electrodes (TFEs) of MoS2 nanowires integrated with NiMnIn shape memory alloy nanoparticles fabricated in situ via magnetron sputtering technique. Electrochemical analyses reveal the MoS2-NiMnIn superior pseudocapacitive charge-storage potential through Na+ and Li+ kinetics, primarily attributed to the synergistically coupled heterojunctions between MoS2 nanowires and NiMnIn nanoparticles resulting in enhanced ionic conductivity, increased specific surface area, improved substrate adherence, and overall better electrical conductivity. Consequently, the flexible MoS2/NiMnIn/SS TFE attains a high specific capacitance of ~487.86 F.g−1 (87.82 mF.cm−2, 355.53 F.cm−3) in 1 M Na2SO4 at 0.7 A.g−1. Moreover, an extensive qualitative and quantitative analysis through voltammetry and AC impedance-derived techniques has been presented, revealing a dominant contribution from surface-controlled capacitive and pseudocapacitive kinetics in both Na+ and Li+ storage. An all-solid-state flexible symmetric supercapacitor (SSC) device fabricated using PVA-Na2SO4 gel electrolyte exhibits a maximum cell capacitance of ~208 F.g−1 (37.57 mF.cm−2, 192.07 F.cm−3) at 0.56 A.g−1. Interestingly, the Na+-charged SSC device presents an attractive balance of high energy (~28.99 Wh.kg−1) and power densities (~12.81 kW.kg−1) while simultaneously delivering an exceptional electrochemical cyclability, retaining ~97.5% over 6000 charge-discharge cycles. In addition, a highly desirable mechanical stability of ~93.68% for the TFE and ~88% for the SSC device at +90° bending over 1000 GCD cycles illustrates the robust structural integrity exhibited by the 3D nanostructured MoS2-NiMnIn material.