In situ moulded troilite 2H phase FeS ultrathin electrodes via pulsed laser deposition for flexible solid state high capacity supercapacitor besides boosted electrocatalytic oxygen evolution reaction

Abstract

2D thin metal sulfide nanostructures are very promising in ensuring excellent electrochemical reversible reactions with superior theoretical capacities for flexible energy storage devices. Herein, we have tuned in situ troilite 2H phase FeS thin film nanostructures (250 nm) by a pulsed laser deposition (PLD) technique. The FeS thin film at room temperature (FeS RT) and in situ annealed troilite 2H phase FeS (A650) thin film electrodes exhibit excellent energy storage capability towards an exceptional electrocatalytic oxygen evolution reaction (OER). We further demonstrated an FeS thin film symmetric device (cell-A650) as a functioning voltage window fixed at 1.6 V. Also, the FeS cell-A650 device attained a remarkable volumetric capacitance of 841.25 F cm⁻³ (equivalent volumetric capacity of 330 mA h cm⁻³). In addition, the FeS cell-A650 device exhibited a significant volumetric energy density of 14.95 mW h cm⁻³ and a superior volumetric power density of 6.4 W cm⁻³; further, the FeS cell-A650 device shows noteworthy volumetric capacity retention of 91% over 14 000 GCD cycles. Practical viability tests were carried out by lighting LEDs and running a DC fan. In addition, an FeS (A650) thin film electrode exhibits an exceptional oxygen evolution reaction (OER) performance with an impressive overpotential of 263 mV at a current rate of 10 mA cm⁻² in an alkaline 1 M KOH electrolytic medium, for which durability tests were carried out for over 20 h and it was found to be stable.