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Summary: Replacing oxygen in an oxide‐based material with sulfur can produce improved flexibility and more efficient electron transport in its structure leading to enhanced electrical performance. Herein, facile template‐free growth of free‐standing cobalt (II, III) oxide (Co3O4) on Ni foam via a mild hydrothermal technique followed by its transformation to cobalt (II, III) sulfide (Co3S4) via an ion‐exchange is reported. The microstructural morphology, phase, and porosity of the prepared Co3O4 and Co3S4 are characterized by FESEM, XRD, Raman, XPS, TEM, and BET analyses. The electrochemical performance of the Co3S4 film with a microporous morphology is considerably superior to that of Co3O4, exhibiting a high specific capacitance of 1604 F g−1 (905 F g−1 for Co3O4), the excellent restorative ability of ~99% at 1 A g−1 (~96% for Co3O4), and good retention of 98% at 10 A g−1 (~70% for Co3O4). The Co3S4 electrode shows excellent capacitance endurance even after 10 000 charge/discharge cycles and a high energy density of 128.32 Wh kg−1 at 0.72 kW kg−1. A fabricated symmetric Co3S4 supercapacitor device also reveals superior charge/discharge, restorative, and retention performances compared to a Co3O4 one. The excellent supercapacitive performance of phase‐transformed Co3S4 electrode is due its large electrochemically active surface area along with synergetic effect of small charge transfer resistance and high relative diffusion coefficient. [ABSTRACT FROM AUTHOR]

Due to their atomic thicknesses and semiconducting properties, two-dimensional transition metal dichalcogenides (TMDCs) are gaining increasing research interest. Among them, Hf- and Zr-based TMDCs demonstrate the unique advantage that their oxides (HfO2 and ZrO2) are excellent dielectric materials. One possible method to precisely tune the material properties of two-dimensional atomically thin nanomaterials is to adsorb molecules on their surfaces as non-bonded dopants. In the present work, the molecular adsorption of NO2 and NH3 on the two-dimensional trigonal prismatic (1H) and octahedral (1T) phases of Hf and Zr dichalcogenides (S, Se, Te) is studied using dispersion-corrected periodic density functional theory (DFT) calculations. The adsorption configuration, energy, and charge-transfer properties during molecular adsorption are investigated. In addition, the effects of the molecular dopants (NH3 and NO2) on the electronic structure of the materials are studied. It was observed that the adsorbed NH3 donates electrons to the conduction band of the Hf (Zr) dichalcogenides, while NO2 receives electrons from the valance band. Furthermore, the NO2 dopant affects than NH3 significantly. The resulting band structure of the molecularly doped Zr and Hf dichalcogenides are modulated by the molecular adsorbates. This study explores, not only the properties of the two-dimensional 1H and 1T phases of Hf and Zr dichalcogenides (S, Se, Te), but also tunes their electronic properties by adsorbing non-bonded dopants. [ABSTRACT FROM AUTHOR]