Pseudocapacitors store energy on/near the surface of electrode materials through redox reactions, whose capacitive activity thus depends on the electronic states of the surface and interface, and electronic conductivity of the electrode materials. Here, we report a simple strategy to prepare the hybrid nanostructure of NiCo₂O₄@rGO with the controllable composition by depositing graphene oxide (GO) on the NiCo₂O₄ scaffold combined with chemical reduction. By combining NiCo₂O₄ mesoporous nanosheets with reduced graphene oxide (rGO), the hybrid electrode shows significant improvement in electrical conductivity, as well as more electrochemically active sites and short transport path lengths for both electrons and ions. Moreover, resulting from the Schottky electric field at the interface of NiCo₂O₄ and rGO, NiCo₂O₄ exhibits superior electron collection efficiency, thus contributing to the redox reactions on/near the surface of NiCo₂O₄. Benefiting from the rational structural features and excellent electrical conductivity, the designed NiCo₂O₄@rGO hybrid electrode demonstrates high specific capacitance (3.6 F cm⁻² at a current density of 5 mA cm⁻²), good rate capability and superior cycling stability (90% of the initial capacitance can be retained after 2000 charge/discharge cycles). This work provides a new strategy for high-performance supercapacitor electrodes by combining capacitive (especially carbons) and faradaic (redox electroactive) materials.

Practical applications of next-generation stretchable electronics hinge on the development of sustained power supplies to drive highly sensitive on-skin sensors and wireless transmission modules. Although the manufacture of stretchable self-charging power units has been demonstrated by integrating stretchable energy harvesters and power management circuits with energy storage units, they often suffer from low and unstable output power especially under mechanical deformation and human movements, as well as complex and expensive fabrication processes. This work presents a low-cost, scalable, and facile manufacturing approach based on laser-induced graphene foams to yield a self-powered wireless sensing platform. 3D porous foams with high specific surface area and excellent charge transport provide an efficient flow of triboelectric electrons in triboelectric nanogenerators. The surface coating or doping with second laser irradiation on these foams can also form a 3D composite to provide high energy density in micro-supercapacitor arrays. The integration of a triboelectric nanogenerator and power management circuits with micro-supercapacitor arrays can efficiently harvest intermittent mechanical energy from body movements into stable power output. 3D foams and their composites patterned into various geometries conveniently create various deformable sensors on large scale at low cost. The generated stable, yet high, power with adjustable voltage and current outputs drives various stretchable sensors and wireless transmission modules to wirelessly measure pulse, strain, temperature, electrocardiogram, blood pressure, and blood oxygen. The self-powered, wireless, wearable sensing platform paves the way to wirelessly detect clinically relevant biophysical and biochemical signals for early disease diagnostics and healthy aging.

An asymmetric supercapacitor offers opportunities to effectively utilize the full potential of the different potential windows of the two electrodes for a higher operating voltage, resulting in an enhanced specific capacitance and significantly improved energy without sacrificing the power delivery and cycle life. To achieve high energy and power densities, we have synthesized an all-solid-state asymmetric supercapacitor with a wider voltage range using Fe-doped Co₃O₄ and three-dimensional reduced graphene oxide (3DrGO) as the positive and negative electrodes, respectively. In contrast to undoped Co₃O₄, the increased density of states and modified charge spatial separation endow the Fe-doped Co₃O₄ electrode with greatly improved electrochemical capacitive performance, including high specific capacitance (1997 F g⁻¹ and 1757 F g⁻¹ at current densities of 1 and 20 A g⁻¹, respectively), excellent rate capability, and superior cycling stability. Remarkably, the optimized all-solid-state asymmetric supercapacitor can be cycled reversibly in a wide range of 0–1.8 V, thus delivering a high energy density (270.3 W h kg⁻¹), high power density (9.0 kW kg⁻¹ at 224.2 W h kg⁻¹), and excellent cycling stability (91.8% capacitance retention after 10 000 charge–discharge cycles at a constant current density of 10 A g⁻¹). The superior capacitive performance suggests that such an all-solid-state asymmetric supercapacitor shows great potential for developing energy storage systems with high levels of energy and power delivery.