Ahsan Javed

MOF-derived MoZnS/MXene heterostructures with strong interfacial coupling enable balanced capacitive–diffusive charge storage. A flexible ZIHSC delivers 989.4 F g ⁻¹ at 8 mA current.

Asymmetric supercapacitors (ASCs) possess the potential to deliver high energy and power densities. However, current systems encounter limitations arising from complex charge-storage mechanisms and from interfacial interactions between electrolyte ions and electrode materials. Herein, the electrochemical response of functionalized multiwalled carbon nanotube (FMWCNT)/α-Fe₂O₃ electrodes in an alkaline KOH electrolyte is investigated. In contrast to pristine FMWCNTs and α-Fe₂O₃, the FMWCNTs/α-Fe₂O₃ heterostructure exhibits a higher specific surface area and porosity, enhancing electrolyte diffusion and access to active sites. A high specific capacitance of 1007.3 F/g is achieved at 4 A/g, attributed to an optimized nanostructure for OH⁻ induced Faradaic redox reactions. These experimental enhancements are consistent with first-principles density functional theory (DFT) calculations. In addition, an ASC utilizing the FMWCNTs/α-Fe₂O₃//Ti₃C₂T_x-MXene configuration delivers a high energy density of 78.3 Wh/kg, a power density of 4072 W/kg, and excellent cycling stability, retaining 90% of the initial capacitance after 10,000 cycles. These findings establish the FMWCNTs/α-Fe₂O₃//Ti₃C₂T_x-MXene configuration as a promising platform for advanced ASCs and provide mechanistic insights into the development of scalable and efficient energy storage devices.

The rapid development of two-dimensional (2D) materials has reshaped modern nanoscience, offering properties that differ fundamentally from their bulk counterparts. As experimental discovery accelerates, the need for reliable computational techniques has become increasingly important. Within the framework of density functional theory, this review explores the critical role of exchange-correlation (XC) functionals in predicting key material properties such as structural, optoelectronic, magnetic, and thermal properties. We examine the challenges posed by quantum confinement, anisotropic screening, and van der Waals interactions, which conventional functionals often fail to describe. Advanced approaches, including meta-generalized gradient approximation, hybrid functionals, and many-body perturbation theory (e.g. GW and Bethe–Salpeter equation), are assessed for their improved accuracy in capturing electronic structure and excitonic effects. We further discuss the non-universality of functionals across different 2D material families and the emerging role of machine learning to enhance computational efficiency. Finally, the review outlines current limitations and emerging strategies, providing a roadmap for advancing XC functionals and beyond, to enable the practical design and application of 2D materials.

The rapid development of two-dimensional (2D) materials has reshaped modern nanoscience, offering properties that differ fundamentally from their bulk counterparts. As experimental discovery accelerates, the need for reliable computational techniques has become increasingly important. Within the framework of density functional theory, this review explores the critical role of exchange-correlation functionals in predicting key material properties such as structural, optoelectronic, magnetic, and thermal. We examine the challenges posed by quantum confinement, anisotropic screening, and van der Waals interactions, which conventional functionals often fail to describe. Advanced approaches, including meta-GGA, hybrid functionals, and many-body perturbation theory (e.g., GW and Bethe-Salpeter equation), are assessed for their improved accuracy in capturing electronic structure and excitonic effects. We further discuss the non-universality of functionals across different 2D material families and the emerging role of machine learning to enhance computational efficiency. Finally, the review outlines current limitations and emerging strategies, providing a roadmap for advancing exchange-correlation functionals and beyond, to enable the practical design and application of 2D materials.

Transition metal dichalcogenides (TMDCs) are one of the material systems of choice toward achieving room temperature quantum coherence. Externally applied strain is used as a more common control mechanism to tune electro-optical properties in TMDCs like molybdenum disulfide (MoS2). However, room temperature electron–phonon interactions in the presence of strain in transition metal dichalcogenides are still not fully explored. In this work, we employ uniaxial strain dependent Raman and photoluminescence (PL) studies on monolayer and bilayer MoS2 to explore electron–phonon physics. Helicity-resolved Raman in MoS2 obeys robust selection rules. Our studies reveal clear modification in these helicity-based selection rules in the presence of moderate uniaxial strain (ϵ = 0.4%–1.2%). The selection rules are restored upon clear symmetry breaking of the in-plane vibrational mode (ϵ > 1.2%). We assign these changes to the onset of Fröhlich interaction in this moderate strain regime. The changes in Raman scattering are accompanied by changes in valley selective relaxation observed through non-resonant photoluminescence (PL). The moderate strain regime also exhibits the onset of PL polarization for indirect excitonic emission under non-resonant excitation. Our experimental observations point toward electron–phonon coupling mechanisms affecting both valley-selective electron relaxation during PL emission as well as polarization-selective Raman scattering of two-dimensional semiconductors at room temperature.