Ambient plasma treated tungsten disulfide for electrochemical energy applications

Tungsten disulfide (WS2) is modified, by using ambient solution plasma, for electrochemical energy applications which are hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and flexible supercapacitor applications. Herein, the effect of time-dependent plasma treatment on WS2 is investigated, resulting that the optimum time (60 min) shows the best performances of low overpotential of-0.19 V at-10 mA cm-2 and 0.21 V at 10 mA cm-2 with the corresponding Tafel slopes of 113 mV dec- 1 and 124 mV dec- 1 for HER and OER, respectively. In addition, a high specific capacitance of 157.5 F g-1 at 1 A g-1 with an energy density of 14 Wh kg- 1 and power density of 400 W kg-1 for the flexible supercapacitor is obtained. Reliable flexibility with high specific capacitance retention (94.0%) and coulombic efficiency (89.5%) after 5000 cycles are also demon-strated. The increased electrochemically active surface area, lower impedance, and the phase transition from 2H to 1T, compared to the precursor WS2, by the ambient plasma are ascribed to the better HER, OER, and supercapacitor performance.