Isotype heterojunction graphitic carbon nitride photocathode for photo-accelerated zinc-ion capacitors

Abstract

Photoelectrodes that combine light harvesting and energy storage within a single material represent an effective approach for developing standalone devices for solar energy capture and storage. However, achieving high-performance photoelectrodes requires precise tuning of optical, electrochemical and interface properties. In this study, we introduce an optimization approach designed to improve the charge storage, optical properties, and interface adjustments of graphitic carbon nitride (g-C₃N₄) when used as the photoelectrode material in photo-accelerated zinc-ion capacitors (Photo-ZICs). Through the adjustment of precursor ratios, we successfully introduced a g-C₃N₄ isotype heterojunction electrode via a thermal polycondensation method. This optimized electrode exhibited a performance level four times higher than that of pristine g-C₃N₄ synthesized from urea, even at a high specific current of 10 000 mA g⁻¹. Additionally, it demonstrated an impressive capacity of 37.62 mA h g⁻¹ with a coulombic efficiency of 99.9% after 10 000 cycles. Furthermore, we explored the potential of a dual heterojunction structure by combining the optimized g-C₃N₄ isotype heterojunction with titanium dioxide to create highly efficient Photo-ZICs. These assembled devices exhibited remarkable capacity enhancements and cycling stability even under light exposure. As a proof-of-concept experiment, our findings underscore the significant benefits of isotype heterojunctions in enhancing both energy storage capabilities and solar harvesting efficiency, ultimately leading to the development of highly efficient Photo-ZICs.