The development of more efficient electrical storage is a pressing requirement to meet future societal and environmental needs. This demand for more sustainable, efficient energy storage has provoked a renewed scientific and commercial interest in advanced capacitor designs in which the suite of experimental techniques and ideas that comprise nanotechnology are playing a critical role. Capacitors can be charged and discharged quickly and are one of the primary building blocks of many types of electrical circuit, from microprocessors to large-sale power supplies, but usually have relatively low energy storage capability when compared with batteries. The application of nanostructured materials with bespoke morphologies and properties to electrochemical supercapacitors is being intensively studied in order to provide enhanced energy density without comprising their inherent high power density and excellent cyclability. In particular, electrode materials that exploit physical adsorption or redox reactions of electrolyte ions are foreseen to bridge the performance disparity between batteries with high energy density and capacitors with high power density. In this review, we present some of the novel nanomaterial systems applied for electrochemical supercapacitors and show how material morphology, chemistry and physical properties are being tailored to provide enhanced electrochemical supercapacitor performance.

Extreme deformation of high-entropy alloys increases toughness by converting crystalline structures to amorphous zones.

A scalable spray deposition technique has been adopted to the fabrication of a flexible nanostructured hybrid supercapacitor based on thin film multi-walled carbon nanotube (MWNT) cathodes and hematite (α-Fe₂O₃)/MWNT composite anodes. On the basis of the total weight of the binder-free MWNT and α-Fe₂O₃/MWNT thin film composite electrodes, the hybrid supercapacitor provided a very high specific energy density of 50 Wh kg⁻¹ at a specific power density of 1000 W kg⁻¹ over the potential range 0–2.8 V, which was an energy density 8 times that of identically prepared symmetric supercapacitors with MWNT only electrodes under the same conditions. The superior electrochemical performance of the hybrid supercapacitor arrangement can be attributed to the incorporation of MWNTs into the α-Fe₂O₃ anodes, which leads to a decrease of internal resistance and an improvement in both the ion diffusion behaviour and the integrity of the α-Fe₂O₃ containing films.

International audienceThe potential for MoO use as a supercapacitor electrode in aqueous electrolytes was investigated. α-MoO nanobelts were synthesized using a hydrothermal method and then thin-film electrodes were manufactured by spray deposition. Electrochemical testing in several aqueous electrolytes showed significant charge storage in 1 M HSO with a complex electrochemical activity that was further investigated by X-ray photoelectron spectroscopy and various electrochemical characterization methods. In a 0-1 V (vs Ag/AgCl) electrochemical window, MoO was reduced to a mixture of lower valence oxides with concentrations varying as Mo (5+) > Mo (4+) > Mo (6+), with MoO as the main component at potentials below 0.185 V (vs Ag/AgCl). The degree of redox reversibility was evaluated in order to optimize the electrochemical window for enhanced cyclability. A moderate capacitance of 8.8 F g (64 μF cm) was fully retained for 720 cycles in an optimized electrochemical window of 0.26-0.43 V (vs Ag/AgCl)