Dual-electric-field synergy in CdS/NiCo2S4 heterojunctions for flexible integrated photo-supercapacitors

Abstract

As an emerging energy device capable of directly harvesting and utilizing solar energy, photo-supercapacitors have become an indispensable component of future self-powered systems and a pivotal technology for energy transition. Nevertheless, it remains a major challenge to address the sluggish kinetics and inefficient photogenerated carrier utilization of existing bifunctional photocathode reactions. In this study, interfacial engineering of hierarchical CdS/NiCo₂S₄ heterojunctions is demonstrated through phase-controlled sulfidation, creating vectorial charge transfer highways that enable dual photoactive/energy-storage functionality in solid-state integrated photo-supercapacitors. Theoretical calculations and photoelectrochemical tests show that the incorporation of the CdS layer improves the NiCo₂S₄ photoconductivity, and the photo-built electric field as well as the built-in electric field of the metal semiconductor synergetic facilitates the separated transport of photogenerated carriers. Meanwhile, the photo-excited high-energy electron-hole promotes the electrode reaction kinetics and accelerates the formation of the electric double layer interface. The flexible integrated photo-supercapacitor exhibits the high energy density /power density of 95.6 Wh kg⁻¹/2868 W kg⁻¹ under light and excellent long-lasting photosensitivity, maintaining a capacity increase of about 40 % under intermittent illumination.