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Ni(OH)2-based materials are widely considered advanced energy storage materials, but their poor cycle performance makes their practical application and commercialization slow. Herein, Ni(OH)2@g-C3N4core-shell (crystal and amorphous) heterojunctions are synthesized. These heterojunctions enhance the specific surface area and ionic diffusion, especially the heterojunction formed by the amorphous shell, which shows robust performance. This heterojunction mainly uses the fast reversible Faraday reaction of battery type as the primary energy storage mechanism. The as-prepared core-shell heterojunction showed nearly double specific capacitance and excellent cycle stability (578.5 F g−1and 109.3 % retentions after 5000 cycles) over pristine Ni(OH)2(285.8 F g−1and 101.6 % retentions after 5000 cycles). Finally, an efficient hybrid supercapacitor is developed via Ni(OH)2@g-C3N4//AC, which combines the advantages of the battery and supercapacitors. The hybrid supercapacitor device shows enhanced capacitance (311.8 F g−1) and outstanding cycle performance (84.3 % retentions after 10,000 cycles). In particular, the energy density of 78.0 Wh kg−1can still be provided while maintaining the power density of 1201.1 W kg−1. This emerging heterostructure offers new insight into Ni(OH)2-based materials in energy applications.

The rapid development of new vehicles and portable electronics has continuously pressured advanced renewable energy-storage technologies to deliver exceptional energy-power outputs and long lifetimes. Hybrid supercapacitors attract attention owing to their outstanding power density, high specific capacitance, and excellent cycling stability. In this study, two-dimensional (2D) g-C3N4nanosheets and 3D CoSe2hierarchical microflower heterojunction electrodes were synthesized using a facile hydrothermal preparation method, and their electrochemical performances were evaluated. Surface morphology analysis demonstrated that the g-C3N4nanosheets were well-dispersed on the CoSe2hierarchical microflower surface. The interstitial contact between CoSe2and g-C3N4effectively narrowed the bandgap energy, enhanced the electrical conductivity, and improved the electrochemical properties. Electrochemical analysis indicated rapid reaction kinetics and significant energy-storage capacity for the CoSe2/g-C3N4heterojunction electrode. Notably, the CoSe2/g-C3N4heterojunction electrode achieved a specific capacitance of 1024.4 F/g at 1 A/g. The assembled CoSe2/g-C3N4heterojunction hybrid supercapacitor device exhibited a high energy (62 Wh/kg), high power density (775 W/kg), and remarkable lifespan after 10,000 cycles. The developed electrode is promising for energy-related device applications.

The interfacial interaction between different materials is favorable to the photoexcited charge separation, and it can also contribute complete performance to their individual benefits and create for the shortcomings to attain a complementary influence. But, it is still challenging to modify the preferred structure and heterojunction interface of catalyst materials using a facile and effective method. In this report, 2D g-C3N4sheets supported 3D star-shaped flower like CuO nanohybrid p-n type heterojunction catalysts were prepared using simple facile synthesis technique and examined their catalytic activity and photoelectrochemical properties. The photocatalytic efficacies of TC using pure g-C3N4, CuO and CuO/g-C3N4were 47.4%, 75.2% and 94.7% within the 30min of visible light irradiation. The enhanced photodegradation performance of nanohybrids catalyst is due to the formation of heterojunction, subsequent in the photoexcited charge carrier’s active separation the improved ability of visible light absorption and development of p-n heterojunction. Moreover, PEC water oxidation properties were examined and CuO/g-C3N4nanohybrid electrodes displays improved PEC properties than the pure CuO and g-C3N4. Furthermore, g-C3N4,CuO and CuO/g-C3N4photoelectrode displays photocurrent density 0.85, 1.60 and 2.30mA/cm-2, respectively. Therefore, 3D/2D nanohybrids with robust ability of visible light absorption could offer a novel method to create effective facilitating the growth of photoelectrodes for the PEC water oxidation and photodegradation for fast and effective antibiotic removal from the environment.