Owing to the remarkable adjustability of layers, layered double hydroxides (LDHs) can adopt superior conductivity and a charge-storage capacity. However, controlled tuning of layers spacing in LDHs is a major challenge, and they can suffer from stacking issues, structural degradation, and issues with interstitial ion insertion. Herein an effective strategy of exchanging interlayer ions within laminates was efficiently realized. Despite the layered spatial structure and morphological perturbation, the exchange of carbonate ions (CO₃ ²⁻) by sulfate anions (SO₄ ²⁻) into the interlayers of the NiFe-LDHs nanostructure revealed an expansion of the layer spacing and rapid ion intercalation. A three-fold enhancement of the specific capacitance in NiFe-LDHs with sulfate anions (NFS), i.e. 527 F g⁻¹, was achieved over NiFe-LDHs with carbonate anions (NFC), i.e., 171 F g⁻¹, at 0.5 A g⁻¹ in 6 M KOH aqueous electrolyte. Further, the aqueous hybrid supercapacitor (AQHS) of NFS-LDHs nanoplates displayed a high specific capacitance of 30 F g⁻¹ at 0.5 A g⁻¹, with a high energy density of 11 W h kg⁻¹ and a power density of 5500 W kg⁻¹. It eventually exhibited a tremendous capacitance retention of 83% at 3 A g⁻¹ with a coulombic efficiency of 82% at up to 10 000 cycles. Thus the expansion of the layer spacing resulted in enhanced ionic intercalation, and improved conductivity and redox activity, underscoring the potential of NFS-based LDHs for advancing the performance of aqueous hybrid supercapacitors.

The pursuit of efficient and economical catalysts for water splitting, a critical step in hydrogen production, has gained momentum with the increasing demand for sustainable energy. Among the various electrocatalysts developed to date, cobalt oxide (Co₃O₄) has emerged as a promising candidate owing to its availability, stability, and catalytic activity. However, intrinsic limitations, including low catalytic activity and poor electrical conductivity, often hinder its effectiveness in electrocatalytic water splitting. To overcome these challenges, substantial efforts have focused on enhancing the electrocatalytic performance of Co₃O₄ by synthesizing composites with conductive materials, transition metals, carbon-based nanomaterials, and metal–organic frameworks. This review explores the recent advancements in Co₃O₄-based composites for the oxygen evolution reaction and the hydrogen evolution reaction, emphasizing strategies such as nanostructuring, doping, hybridization, and surface modification to improve catalytic performance. Additionally, it examines the mechanisms driving the enhanced activity and stability of these composites while also discussing the future potential of Co₃O₄-based electrocatalysts for large-scale water-splitting applications.

Gas sensors based on graphene have gained considerable attention because of graphene’s remarkable properties, such as its extensive surface area, impressive electrical conductivity, and exceptional mechanical strength. This review critically analyzes recent developments in functionalization strategies designed to enhance the sensitivity, selectivity, and stability of graphene-based sensors. It discusses various chemical, physical, and hybrid functionalization methods, illustrating how surface alterations affect graphene’s interaction with target gas molecules. The paper also investigates the fundamental sensing mechanisms, including charge transfer, carrier mobility modulation, and Schottky barrier modification, to provide a thorough understanding of sensor response characteristics. Additionally, it highlights emerging applications in environmental monitoring, healthcare diagnostics, and industrial safety, demonstrating the transformative potential of these sensors in real-world settings. Finally, the review addresses challenges concerning reproducibility, long-term stability, and large-scale production, while also offering future insights on utilizing innovative nanomaterials and artificial intelligence to advance the next generation of graphene-based gas sensing technologies.