In this study, amorphous manganese oxide (MnO₂) nanostructured thin films were synthesized by a simple hydrothermal method. It is well known that the nanostructure plays a crucial role in energy storage applications. Herein, MnO₂ nanostructures ranging from plates to flakes were synthesized without the use of any hard or soft templates. The 4+ oxidation state of Mn was confirmed by X-ray photoelectron spectroscopy. The MnO₂ nanoflake structure has a specific surface area of 46 m²g⁻¹, which provides it with an excellent rate capability and an exactly rectangular cyclic voltammogram (CV) curve. The MnO₂ nanoflake electrode has a high specific capacitance of about 433 Fg⁻¹, an energy density of 60 Whkg⁻¹ at 0.5 mAcm⁻², and an excellent cyclic stability of 95% over 1000 CV cycles in 1 M aq. Na₂SO₄. Kinetics analysis of the charge storage in the nanoflake MnO₂ sample shows a 55.6% diffusion-controlled contribution and 44.4% capacitive-controlled contribution to the total current calculated at a scan rate of 100 mVs⁻¹ from the CV curve.

One-dimensional crystal growth enables the epitaxial integration of III-V compound semiconductors onto a silicon (Si) substrate despite significant lattice mismatch. Here, we report a short-wavelength infrared (SWIR, 1.4–3 μm) photodetector that employs InAs nanowires (NWs) grown on Si. The wafer-scale epitaxial InAs NWs form on the Si substrate without a metal catalyst or pattern assistance; thus, the growth is free of metal-atom-induced contaminations and is also cost-effective. InAs NW arrays with an average height of 50 μm provide excellent anti-reflective and light trapping properties over a wide wavelength range. The photodetector exhibits a peak detectivity of 1.9 × 10⁸ cm·Hz^1/2/W for the SWIR band at 77 K and operates at temperatures as high as 220 K. The SWIR photodetector on the Si platform demonstrated in this study is promising for future low-cost optical sensors and Si photonics.

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.