Sustainable high-energy-density asymmetric supercapacitor and efficient electrocatalytic water splitting: synergistically engineered borophene with an MnO2/rGO nanocomposite.

Supercapattery and overall water-splitting devices are emerging technologies for storing energy and producing carbon-free fuel sources. Highly multifunctional electrodes are key components for achieving efficient performance in supercapattery and overall water-splitting devices. In this work, a significant synthesis strategy is adopted to prepare reduced borophene oxide (namely borophene) using an MnO2/rGO nanocomposite, and the composite electrode exhibits high diffusivity as an electrocatalyst for supercapattery and water splitting applications. In addition, the large surface and peculiar porous properties of the MnO2/borophene/rGO nanocomposite enabled it to achieve a high specific capacitance of 756.4 F g-1 (907.7 C g-1) at a current density of 1 A g-1. Likewise, the composite electrode sustained 95% capacitance retention after 10 000 cycles at a current density of 10 A g-1. The supercapattery device attained a high specific energy density of 90.01 Wh kg-1 at a power density of 1099.5 W kg-1 and an operating potential of 2.2 V, and it maintained 95% durability after 10 000 cycles. Also, the performance of the supercapattery device was assessed for real-time applications using a light-emitting diode (LED) as the load, and the device was tested for a sustained period of 30 days. In terms of electrocatalytic performance, the MnO2/borophene/rGO nanocomposite exhibited a low overpotential of 220 mV with a Tafel slope value of 136 mV dec-1 for the OER and 107 mV with a Tafel value of 88 mV dec-1 for the HER at a current density of 10 mA cm-2. The enhanced morphology, storage, and electrocatalytic activities of the bifunctional MnO2/borophene/rGO nanocomposite strengthen its electrochemical performance. The MnO2/borophene/rGO nanocomposite has the potential to advance sustainable supercapattery and electrolyzer applications across the energy, manufacturing, and transportation sectors due to its significant storage and conversion performance.