Abstract
<title>Abstract</title> <p> The direction toward a hydrogen economy, along with rapid advancements in battery technology, urges the scientific community to develop new materials that are low-cost, sustainable, and efficient. Effective green hydrogen production offers a viable substitute for traditional fuels and effectively supports the achievement of SDGs 7 and 13. The rapid charge-discharge capability of supercapacitors makes them suitable for integration with batteries to enhance both power output and overall cycle life. This work describes the development of a low-cost, efficient oxide-sulphate structural type with exemplary supercapacitance and electrocatalytic water-splitting capabilities. The single crystal of the electroactive material was synthesised via a high-temperature phase transformation strategy and characterised by various physical and chemical techniques. The system exhibited an overpotential of 145 mV at 10 mA cm <sup>− 2</sup> for the hydrogen evolution reaction (HER), which is close to the HER potential of the well-known Pt/C system. A low charge transfer resistance (R <sub>ct</sub> ) of 5.82 Ω, obtained from the Nyquist plot, supported the conducting nature of the material. The system exhibited a high specific capacitance of 692 F g <sup>− 1</sup> at 1 A g <sup>− 1</sup> , and the energy and power densities were calculated to be 15.37 Wh kg <sup>− 1</sup> and 200 W kg <sup>− 1</sup> , respectively. The electrochemical analyses unambiguously confirmed the versatility of the material for charge storage and hydrogen generation applications. </p>