Dual-functional Bi₂(Se₀0.8 S₀.₂)₃@C composite for high-performance supercapacitors and visible-light photocatalytic MB degradation

The development of stable, high-density electrode materials for use in advanced electrochemical energy storage systems
is of utmost importance. This study presents a simple one-step chemical precipitation approach for the fabrication of
Bi₂(Se₀.8S₀.₂)₃@C, a sulfur-modified bismuth selenide solid solution coupled with amorphous carbon. The presence of
crystalline bismuth selenosulfide was verified through structural investigation. Morphological analysis revealed a network
of nanosheets embedded within a carbon matrix, facilitating enhanced charge transfer and providing abundant electro�active sites. Electrochemical testing in a 3 M KOH electrolyte showed that the Bi₂(Se₀.₈S₀.₂)₃@C electrode achieved a
specific capacitance of 950 F g⁻¹ at 1 A g⁻¹ and exhibited excellent cycling stability, retaining 98% of its capacitance after
5000 cycles with nearly 100% efficiency. An asymmetric supercapacitor device, using activated carbon as the negative
electrode and Bi₂(Se₀.8S₀.₂)₃@C as the positive electrode, delivered a maximum energy density of 65 Wh kg⁻¹ at 877 W
kg⁻¹ and 35 Wh kg⁻¹ at 3117 W kg⁻¹. Furthermore, after just 20 s of charging, two ASC coin cells connected in series were
able to power multiple LEDs for approximately 10 min, demonstrating excellent power delivery and rapid energy stor�age capability. These results indicate that asymmetric supercapacitors based on sulfur-modified bismuth selenide–carbon
composite electrodes can be highly effective. In addition, Bi₂(Se₀0.8 S₀.₂)₃@C shows enhanced photocatalytic performance
with ~92% MB degradation, higher rate constant (0.0761 min⁻¹), and excellent stability over five cycles due to improved
charge separation.
Keywords Bismuth selenosulfide composite · Amorphous carbon hybrid · Asymmetric supercapacitor · Energy storage
materials