Biomass materials with representative morphologies and compositions were employed to study the activation effect of KHCO₃. As the activation time increased from 1 to 3 h, the products derived from puffed rice and pleurotus eryngii achieved a hierarchical porous structure, while the products derived from cotton still presented a microporous structure. In the electrochemical test of a three-electrode system, the specific capacitance of these products was 352, 319, and 216 F g⁻¹, respectively. In the two-electrode system, the PR-2-based symmetric supercapacitor presented with a specific capacitance of 280.7 F g⁻¹ at 0.5 A g⁻¹, and the energy density of 14.03 Wh kg⁻¹ at 150.04 W kg⁻¹ and an energy density retention of 73.7% was at an even higher power density of 8380.4 W kg⁻¹. After 10,000 cycles of charging and discharging at 5 A g⁻¹, the specific capacitance retention of the supercapacitor reached 108.8%. Based on the experimental analysis, a likely mechanism for the formation of pores was proposed. The results indicate that biomass materials with soft layered or a network structure are the best candidates to obtain a hierarchical porous structure by KHCO₃ activation.

Low electrical conductivity and sluggish charge storage kinetics are the key issues of orthorhombic niobium pentoxide (T-Nb₂O₅) for sodium-ion batteries. Here, we report on an approach for improving the electrochemical properties of T-Nb₂O₅ using fluorine substitution and carbon modification strategies. The obtained orthorhombic niobium oxyfluoride/carbon nanobelt composite (T-Nb₂O_5−xF_y⊂C-NBs) displayed significantly improved electrochemical properties with sodium ion storage capacity as high as 292 mA h g⁻¹ at 0.05 A g⁻¹, along with an excellent cycling stability over 10 000 cycles at 1 A g⁻¹ (0.002% capacity decay per cycle) as measured using a half cell. An intercalation-pseudocapacitance mechanism (1.0–3.0 V vs. Na/Na⁺) for storing sodium ions was observed in T-Nb₂O_5−xF_y⊂C-NBs, along with a conversion reaction mechanism (<0.2 V vs. Na/Na⁺), leading to an improved energy storage performance and faster kinetics. Density functional theory calculations revealed that the fluorine-substituted niobium oxyfluoride possesses energetically more favourable sodiation sites and lower diffusion barriers compared to the pristine T-Nb₂O₅. Characterisation results confirmed that the self-assembled T-Nb₂O_5−xF_y⊂C-NBs exhibit a hierarchical nanoarchitecture with T-Nb₂O_5−xF_y nanoslabs uniformly embedded in a carbon nanobelt matrix to form arrays, enabling excellent electron conductivity and electron/ion transport, as well as structural stability against cycling. Benefitting from both the compositional and structural advantages of the T-Nb₂O_5−xF_y⊂C-NBs composite, a sodium-ion capacitor fabricated with T-Nb₂O_5−xF_y⊂C-NBs as the anode and a commercial activated carbon as the cathode delivered energy densities of 86.8 and 32.1 W h kg⁻¹ at power densities of ∼250 and 18 000 W kg⁻¹, respectively.

The nitrogen-doped MXene carbon nanosheet-nickel (N-M@CNi) powder was successfully prepared by a combined process of electrostatic attraction and annealing strategy, and then applied as the separator coating in lithium–sulfur batteries. The morphology and structure of the N-M@CNi were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectrum, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption method. The strong LiPS adsorption ability and high conductivity are associated with the N-doped carbon nanosheet-Ni modified surface. The modified separator offers the cathode of Li–S cell with greater sulfur utilization, better high-rate adaptability, and more stable cycling performance compared with the pristine separator. At 0.2 C the cell with N-M@CNi separator delivers an initial capacity of 1309 mAh g⁻¹. More importantly, the N-M@CNi separator is able to handle a cathode with 3.18 mg cm⁻² sulfur loading, delivering a capacity decay rate of 0.043% with a high capacity retention of 95.8%. Therefore, this work may provide a feasible approach to separator modification materials towards improved Li-S cells with improved stability.

There has been considerable interest in building switching functions into self-assembled monolayers with switching actuated by external stimuli such as light, electrical current, heat, pressure or chemical changes. In this study, dual switching functionality has been built into azobenzene based molecular monolayers. Switching behaviour has been compared for unsubstituted azobenzene monolayer adsorbates and two other monolayers whose ortho position on the terminal phenyl group is substituted by ethyl and isopropyl chains, respectively. The dual molecular switching functionality with light or protonation actuation is compared. EGaIn contacts to the monolayers have been used to record the J–V curves and characterize the on/off switching. This is complemented with further characterization by transition voltage spectroscopy (TVS), ultraviolet photoelectron spectroscopy (UPS), water contact angle determination, atomic force microscopy (AFM) and theoretical computations. It is concluded that side chains (the ethyl and isopropyl groups) are able to decouple neighbouring azobenzene adsorbates which promotes the photo-efficiency of isomerisation and switching. In addition, acid treatment is also applied to these three molecular layers to try to achieve dual stimuli actuation. The absorption wavelength of the azobenzene moiety red shifts by ∼100 nm for all the three protonated molecules. In the case of the unsubstituted azobenzene, its triggering wavelength is totally reversed once it is protonated. A logic truth table has been constructed for the SAM device, which shows that the simple azobenzene molecular layers exhibit the behaviour of an ‘AND’ logic gate which uses blue light and acid as two inputs.