Supercapacitors offer a promising alternative to batteries, especially due to their excellent power density and fast charging rate capability. However, the cycling stability and material synthesis reproducibility need to be significantly improved to enhance the reliability and durability of supercapacitors in practical applications. Graphene acid (GA) is a conductive graphene derivative dispersible in water that can be prepared on a large scale from fluorographene. Here, we report a synthesis protocol with high reproducibility for preparing GA. The charging/discharging rate stability and cycling stability of GA were tested in a two-electrode cell with a sulfuric acid electrolyte. The rate stability test revealed that GA could be repeatedly measured at current densities ranging from 1 to 20 A g⁻¹ without any capacitance loss. The cycling stability experiment showed that even after 60,000 cycles, the material kept 95.3% of its specific capacitance at a high current density of 3 A g⁻¹. The findings suggested that covalent graphene derivatives are lightweight electrode materials suitable for developing supercapacitors with extremely high durability.

There is an urgent need for a simple and up-scalable method for the preparation of supercapacitor electrode materials due to increasing global energy consumption worldwide. We have discovered that fluorographene exhibits great potential for the development of new kinds of supercapacitors aimed at practical applications. We have shown that time control of isothermal reduction of fluorographite at 450 °C under a hydrogen atmosphere led to the fine-tuning of fluorine content and electronic properties of the resulting fluorographene derivatives. Charge transfer resistances (R_ct) of the thermally reduced fluorographenes (TRFGs) were decreased with respect to the pristine fluorographene; however, the R_ctvs. time-of-reduction plot showed a v-shaped profile. The specific capacitance vs. time-of-reduction of TRFG followed the v-shaped trend, which could be the result of the decreasing content of sp³ carbons and increasing content of structural defects. An optimized material exhibited values of specific capacitance up to 539 F g⁻¹ recorded at a current density of 0.25 A g⁻¹ and excellent cycling durability with 100% specific capacitance retention after 1500 cycles in a three-electrode configuration and 96.7% of specific capacitance after 30 000 cycles in a two-electrode setup.

A series of Sc-substituted ε-Fe ₂ O ₃ nanoparticles embedded in a silica matrix were synthesized by a sol–gel process.

Owing to their low cost, good performance, and high lifetime stability, activated carbons (ACs) with a large surface area rank among the most popular materials deployed in commercially available electrochemical double-layer (EDLC) capacitors. Here, we report a simple two-step synthetic procedure for the preparation of activated carbon from natural flax. Such ACs possess a very high specific surface area (1649 m² g^–1) accompanied by a microporous structure with the size of pores below 2 nm. These features are behind the extraordinary electrochemical performance of flax-derived ACs in terms of their high values of specific capacitance (500 F g^–1 at a current density of 0.25 A g^–1 in the three-electrode setup and 189 F g^–1 at a current density of 0.5 A g^–1 in two-electrode setup.), high-rate stability, and outstanding lifetime capability (85% retention after 150,000 charging/discharging cycles recorded at the high current density of 5 A g^–1). These findings demonstrate that flax-based ACs have more than competitive potential compared to standard and commercially available activated carbons.

A simple metal-free electrochemical immunosensor based on nitrogen-doped graphene acid (NGA) for the detection of 25-hydroxy vitamin D ₃ (25-OH D ₃ ) is presented. The use of NGA, with its well-defined chemical composition, high density of carboxyl functional groups, and excellent biocompatibility, provided a stable and efficient platform for biomolecule immobilization without the need for complex surface modifications. The proposed immunosensor demonstrated high sensitivity (1.97 kΩ ng ^‒1 mL cm ^‒2 ) and a working range of 3.96 to 48.83 ng mL ^‒1 , aligning with clinically relevant vitamin D levels. Moreover, the developed immunosensor exhibited excellent specificity, with minimal cross-reactivity and strong resistance to non-specific adsorption. Furthermore, it maintained stable electrochemical performance for up to 30 days, demonstrating its suitability for practical applications. Compared to existing vitamin D sensors, our platform introduces a streamlined fabrication process that avoids heavy metals, improves reproducibility, and enhances accessibility for point-of-care diagnostics. Graphical abstract