A comprehensive review highlighting recent advancements in high-performance materials and scalable fabrication techniques for next-generation hybrid supercapacitors.

Copper oxide is considered as an alternative electrode material for supercapacitors due to its low cost, chemical stability and high theoretical specific capacitance. In the present work, nanostructured copper oxide (CuO) films are prepared by radio-frequency (RF) magnetron sputtering, and the influence of the substrate temperature on the microstructure and supercapacitive properties was studied. The copper oxide films prepared at 350 °C exhibit a predominant ($\overline{1}$11) orientation corresponding to the monoclinic Cu(II)O phase with a crystallite size of 24 nm. The surface of the film consists of uniformly distributed oval-like grains providing a high surface roughness of 45 nm. The films exhibit an optical bandgap of 1.68 ± 0.01 eV and an electrical conductivity of 0.4 S cm⁻¹ at room temperature. The as-prepared CuO films deliver a discharge specific capacitance of 387 mF cm⁻² (375 F g⁻¹) at a current density of 1 mA cm⁻² with excellent cyclic capacitance retention of 95% (367 mF cm⁻²) even after 1000 cycles. Hence, these films are potential electrodes for micro-supercapacitors.

Global energy demand continues to grow, and the depletion of fossil fuels, coupled with increasing environmental concerns, underscores the importance of sustainable energy storage solutions. Supercapacitors are promising electrochemical energy storage devices due to their high power density, fast charge–discharge kinetics, and long cycle life. However, the use of conventional fossil-based or hazardous electrode materials limits their sustainability. Biomass-derived carbons (BDCs) offer a renewable, low-cost, and carbon–neutral alternative, with tunable hierarchical porosity, heteroatom doping, and tailored surface chemistry that enhance ion transport, wettability, and electrochemical performance. This review presents a comprehensive overview of recent advances in BDCs for next-generation supercapacitors, covering sources ranging from agricultural residues, fruit and nut peels, and wood to algae and industrial by-products. Synthesis strategies, including pyrolysis, hydrothermal treatment, carbonization, chemical and physical activation, templating, heteroatom doping, and composite formation, are critically discussed in relation to structure–function relationships. Case studies demonstrate the role of BDCs as electric double-layer capacitor hosts, conductive scaffolds, and hybrid electrodes for enhanced energy storage. Key challenges are discussed, including feedstock variability, reproducibility, and the environmental footprints of activation processes. Opportunities are identified in scalable continuous processing, circular economy integration, green activation methods, and hybrid device designs. Finally, standardized metrics, life-cycle and techno-economic assessments, and prototype-scale validations are proposed to accelerate the industrial translation of BDCs into sustainable, high-performance supercapacitor technologies.

Nowadays, there is constant demand for the development of energy storage materials using advanced methodologies. In this scenario, a large-scale environmentally friendly synthesis was chosen to prepare Ni-Co-layered double hydroxide (LDH) composites for asymmetric supercapacitors. The developed materials had a flower-like porous architecture with very low dimensional layers and a large surface area. The developed Ni-Co/LDH composite electrodes showed impressive specific capacitance of 1095.1 F/g at a current density of 1 A/g and maintained 492.5 F/g even at a current density of 20 A/g. In particular, the Ni-Co/LDH composites maintained 86.9% of their initial capacitance even after 5000 cycles at a high current density of 2 A/g. Furthermore, an asymmetric supercapacitor with Ni-Co/LDH composites demonstrated an excellent energy density of 40.7 Wh/kg at a power density of 750 W/kg.

Electrochemical energy storage devices are vital for renewable energy integration and the deployment of electric vehicles. Ongoing research seeks to create new materials with innovative morphologies capable of delivering high specific capacitance for the next generation of customizable energy devices. Carbon nitride is an excellent candidate for electrochemical energy storage devices; however, it has limitations such as layer stacking, poor electric conductivity, a restricted number of electroactive sites, and static electrochemical reaction rates. This research objective is to make porous structures in carbon nitride nanosheets and integrate them with CuO particles to increase surface area and improve electrochemical performance. The use of thermal heating, acidic treatment, and hydrothermal processes accomplishes this. Along with X‐ray diffraction peaks of the CuO phase, a prominent peak (002) at 27.67° indicates the presence of graphitic‐structured carbon nitride. TEM images show that CuO particles are evenly attached to the surface of g‐C₃N₄ nanosheets with lattice intervals of 0.336 and 0.232 nm, which are the (002) and (111) orientations of the g‐C₃N₄ and CuO phases, respectively. Adding CuO nanoparticles to porous g‐C₃N₄ nanosheets avoids layer stacking and provides micro‐ and mesopore channels, increasing the specific surface area (42.60 m² g^-1). The CuO@ porous g‐C₃N₄ electrode delivered 817 F g^-1 of specific capacitance at 1 A g^-1 and admirable capacitance retention (92.3% after 6000 cycles) due to the synergistic impact of its unique composition and structural characteristics. Because of its outstanding electrochemical performance and fascinating discoveries, CuO@ porous g‐C₃N₄ may be employed as a cathode material for high‐performance supercapacitors.