Dual-functional Ni₉S₈/Co₉S₈ nanowires for high-energy storage and efficient water splitting

In the face of surging global energy demands and increasing environmental pollution, the development of efficient energy storage and conversion technologies has become critically important. In this study, a series of three-dimensional transition metal-doped Ni₉S₈/Co₉S₈ nanowire electrode materials were synthesized via a hydrothermal method, and their performance as supercapacitor electrodes and bifunctional electrocatalysts for water splitting was systematically investigated. The electronic structure and morphology of the materials were effectively modulated through doping with Cr, Ce, Fe, Mo, and W, leading to significantly enhanced electrochemical performance. Among them, the Cr–Ni₉S₈/Co₉S₈–0.04 electrode, with a Cr doping concentration of 0.04 mM, exhibited an areal specific capacitance of 1128 C cm^-2 at 1 mA cm^-2 and a gravimetric specific capacitance of 485 C g^-1 at 1 A g^-1. As an electrocatalyst, it delivered overpotentials of 227.6 mV for the oxygen evolution reaction (OER) and 117.4 mV for the hydrogen evolution reaction (HER) at 10 mA cm^-2. Further comparative analysis of the effects of different transition metal dopants revealed that Mo-Ni₉S₈/Co₉S₈-0.04 exhibited the best overall performance, with OER and HER overpotentials reaching 161.6 mV and 125.4 mV, respectively. Additionally, its gravimetric and areal specific capacitances reached 674.5 C g^-1 at 1 A g^-1 and 1834 C cm^-2 at 1 mA cm^-2. Moreover, the Cr-Ni₉S₈/Co₉S₈-0.04 electrocatalyst required only 1.42 V to drive a current density of 10 mA cm^-2 in overall water splitting, demonstrating excellent bifunctional catalytic activity. This study provides a novel strategy for synergistically modulating the electrochemical properties of sulfide composite materials through multi-element doping.