Transition metal oxides used as electrode materials for flexible supercapacitors have attracted huge attention due to their high specific capacitance and surface-to-volume ratio, specifically for cobalt oxide (Co₃O₄) nanoparticles.

Paper—a flexible, foldable, and cost-effective substrate made of one-dimensional cellulose nanofibers (1D-CNF)—is being extensively investigated as a promising aspirant for wearable as well as foldable energy storage appliances. However, the high density of flexible electrodes and structural degradation during charge and discharge remain major challenges, which limit their practical applications. Hence, efforts have been made toward the fabrication of solid-state symmetric and flexible paper-like devices for higher capacitive performance. Nanosized uniform ZnO particles were attached on the 1D-CNF surface via a facile methodology, which significantly improved supercapacitive properties. When assembled into solid-state symmetrical supercapacitors, they exhibited remarkable electrochemical performance (220 F g⁻¹, 30.2 W h kg⁻¹ at 1 A g⁻¹) and excellent cycling stability (88% after 8000 cycles). In contrast, binder/additive-free paper-like flexible solid-state symmetrical supercapacitor devices, which were carbonized at 250 °C for 30 min, exhibited superior performance. In particular, the following were observed: higher specific capacitance (140 F g⁻¹ of 1 A g⁻¹), prominent cycling performance (92% capacity retention) after 8000 cycles, and exceptional flexibility (i.e., no significant decay in the cyclic voltammetry current response/integral area after bending for 100 cycles at 90°). This work will pave the way for the application of green, lightweight, and flexible energy storage paper in wearable and foldable electronic devices.

Tungsten sulfide (WS₂) and tungsten carbide (W₂C) are materialized as the auspicious candidates for various electrochemical applications, owing to their plentiful active edge sites and better conductivity. In this work, the integration of W₂C and WS₂ was performed by using a simple chemical reaction to form W₂C/WS₂ hybrid as a proficient electrode for hydrogen evolution and supercapacitors. For the first time, a W₂C/WS₂ hybrid was engaged as a supercapacitor electrode and explored an incredible specific capacitance of ~1018 F g⁻¹ at 1 A g⁻¹ with the outstanding robustness. Furthermore, the constructed symmetric supercapacitor using W₂C/WS₂ possessed an energy density of 45.5 Wh kg⁻¹ at 0.5 kW kg⁻¹ power density. For hydrogen evolution, the W₂C/WS₂ hybrid produced the low overpotentials of 133 and 105 mV at 10 mA cm⁻² with the small Tafel slopes of 70 and 84 mV dec⁻¹ in acidic and alkaline media, respectively, proving their outstanding interfaced electrocatalytic characteristics. The engineered W₂C/WS₂-based electrode offered the high-performance for electrochemical energy applications.

Nanosized ZnO particles have been synthesized on cellulose nanofiber and boron nitride nanotube surfaces via a hydrothermal route to give a ternary nanostructure and explored flexible papers for the electrochemical and piezoelectric performance.