Design of p-CuS/n-CdFe2O4 heterojunction passivated with carbon nanofiber (CNF) for impressive performance in supercapacitor and photoelectrochemical water splitting

One of the most crucial strategies toward creating a greener future by minimizing fossil fuel use is the development of novel nanostructures with enhanced energy storage and energy conversion capacities. In this study, p-type copper sulfide (CuS)–n-type cadmium ferrite (CdFe2O4) heterojunction nanostructures were synthesized and passivated with a carbon nanofiber (CNF) to form a surface charge mediator, resulting in a novel material denoted as CuS–CdFe2O4/CNF. The developed hybrid heterojunction composite demonstrated a specific capacitance of 640 F g−1 at a current density of 0.5 A g−1 and photocurrent density of − 602 μA cm−2 (vs. Ag/AgCl) in the supercapacitor and photoelectrochemical (PEC) water splitting applications, respectively. In supercapacitors, these composites exhibited specific capacitances that were 2.0, 3.2, 1.6, 2.7, and 1.2 times higher than those of the pristine (CuS, CdFe2O4) and binary (CuS/CNF, CdFe2O4/CNF, and CuS–CdFe2O4) components, respectively. The CuS-CdFe2O4/CNF composite exhibited significant cycle stability (84%) even after 5000 cycles. It also demonstrated a photocurrent response of over 50% in PEC water splitting under light illumination compared with that under dark conditions. The creation of a heterojunction interface, which results from the semiconductor properties of p- and n-type materials connected to the CNF surface, is responsible for the outstanding performance of the composite. To develop a specialized charge-transport pathway that produces highly reactive sites, allows quick electron accessibility, reduces RCT, and encourages strong ion diffusion, we added material components to our design. Thus, we expanded the possible applications of current materials in energy-related industries, and dependence on the inherent qualities of materials was decreased. •CuS-CdFe2O4/CNF p-n heterojunctions were synthesized by simple methods.•CNF dopants enhance the charge transfer and separation efficiency of the material.•CuS-CdFe2O4/CNF had 2.0, 3.2x higher specific capacitance than pristine materials.•CuS-CdFe2O4/CNF photoelectrode showed a > 50% photocurrent increase in light.•Enhancement due to pn heterojunctions (CuS, CdFe2O4), reactive sites, and low Rct.