The rational design of transition metal oxides with tailored electronic structures and defect chemistries is critical for advancing high-performance supercapacitors. Herein, we report the engineering of cobalt oxide (Co₃O₄) gels through controlled sol–gel synthesis and rare earth (RE) incorporation using neodymium (Nd), gadolinium (Gd), and dual neodymium/gadolinium (Nd/Gd) doping. X-ray diffraction (XRD) confirmed the preservation of the cubic spinel structure with systematic peak shifts and broadening, evidencing lattice strain, oxygen vacancy generation, and defect enrichment. Field-emission scanning electron microscopy (FE-SEM) analyses revealed distinct morphological evolution from compact nanoparticle assemblies in pristine Co₃O₄ to highly porous, interconnected frameworks in Nd/Gd–Co₃O₄ (Nd/Gd-Co). X-ray photoelectron spectroscopy (XPS) verified the stable incorporation of RE ions, accompanied by electronic interaction with the Co–O matrix and enhanced oxygen defect states. Electrochemical measurements demonstrated that the Nd/Gd–Co electrode achieved a remarkable areal capacitance of 25 F/cm² at 8 mA/cm², superior ionic diffusion coefficients, and the lowest equivalent series resistance (0.26 Ω) among all samples. Long-term cycling confirmed 84.35% capacitance retention with 94.46% coulombic efficiency after 12,000 cycles. Furthermore, the asymmetric pouch-type supercapacitor (APSD) constructed with Nd/Gd–Co as the positive electrode and activated carbon as the negative electrode delivered a wide operational window of 1.5 V, an areal capacitance of 140 mF/cm², an energy density of 0.044 mWh/cm², and 89.44% retention after 7000 cycles. These findings establish Nd/Gd-Co gels as robust and scalable electrode materials and demonstrate that RE co-doping is an effective strategy for bridging high energy density with long-term electrochemical stability in asymmetric supercapacitors.

Rare-earth oxides possess distinctive electronic configurations, tunable oxidation states, and inherent structural robustness, making them highly attractive for advanced energy storage applications. Among these, neodymium oxide (Nd₂O₃) stands out due to its high surface redox activity, structural stability, and favorable band alignment, enabling efficient charge storage in electrochemical devices. In this study, Nd₂O₃ electrodes were synthesized via a sol–gel method with systematically varied precursor concentrations (1 mM, 3 mM, and 5 mM) to elucidate the impact of synthesis on crystallinity, morphology, and electrochemical performance. X-ray diffraction (XRD) confirmed the formation of the hexagonal Nd₂O₃ phase, with the 3 mM sample (Nd-2) exhibiting the sharpest reflections, indicative of enhanced crystallinity and reduced lattice defects. X-ray photoelectron spectroscopy (XPS) revealed trivalent Nd species and both lattice and surface oxygen, providing abundant redox-active sites. Field Emission Scanning Electron Microscope (FE-SEM) showed Nd-2 possessed a hierarchically interconnected fibrous network decorated with fine granules, maximizing active surface area and facilitating rapid ion diffusion. Electrochemical testing demonstrated that Nd-2 achieved an areal capacitance of 20 F cm⁻², a diffusion-controlled pseudocapacitive contribution of ~84.9%, and retained 86.3% capacitance over 12,000 cycles. An asymmetric supercapacitor with Nd-2 and activated carbon delivered an energy density of 0.132 mWh cm⁻², power density of 1.8 mW/cm², and 81.1% capacitance retention over 7000 cycles. These results highlight the critical role of precursor concentration in tailoring structure and electrochemical performance, establishing Nd₂O₃ as a promising electrode for high-performance energy storage devices.

In this study, a systematic investigation was undertaken to elucidate the influence of polymeric surfactants such as polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and their hybrid combination (PVP/PEG) on the structural, morphological, and electrochemical evolution of Fe₂O₃ electrodes designed for high-performance supercapacitor applications. Fe₂O₃ nanostructures were synthesized via a controlled hydrothermal route, wherein the surfactant composition was precisely tuned to modulate crystal growth, particle dispersion, and surface active-site density. Detailed physicochemical characterization revealed that hybrid PVP/PEG incorporation induced a hierarchically nanograined morphology with optimized porosity. The optimized PVP/PEG-Fe electrode exhibited the largest CV area, lowest equivalent series resistance (0.33 Ω), and superior areal capacitance of 9.17 F cm⁻² at 8 mA cm⁻², attributed to accelerated redox kinetics and efficient ion diffusion. Long-term cycling demonstrated remarkable structural resilience, with ~85.1% capacitance retention after 12,000 cycles. Furthermore, an asymmetric pouch-type supercapacitor (PVP/PEG-Fe//AC) was assembled to validate practical performance, achieving a wide potential window of 1.5 V, an areal capacitance of 0.260 F cm⁻², energy density of 0.081 mWh cm⁻², and coulombic efficiency of 95.73% after 7000 cycles. This work highlights the critical role of cooperative polymer–metal oxide interactions in achieving structural uniformity, optimized electrochemical kinetics, and long-term durability, offering a versatile strategy for engineering cost-effective, high-performance transition metal oxide electrodes for next-generation flexible energy storage devices.

This study presents a dual surfactant-assisted hydrothermal approach for the synthesis of Co₃V₂O₈ (CoVO) nanostructures and their surfactant-modified derivatives, PVP-assisted Co₃V₂O₈ (P-CoVO) and PVP–SDS co-assisted Co₃V₂O₈ (P/S-CoVO), which were directly grown on nickel foam. The use of PVP and SDS enabled controlled nucleation and growth, yielding a hierarchical nanoflower-like morphology in P/S-CoVO with increased porosity, a higher surface area, and uniform structural features. Comprehensive physicochemical characterization confirmed that surfactant incorporation effectively modulated particle size, dispersion, and active-site availability. Electrochemical measurements demonstrated that P/S-CoVO exhibited superior performance, with the largest CV area, low equivalent series resistance (0.52 Ω), and a maximum areal capacitance of 13.71 F cm⁻² at 8 mA cm⁻², attributable to rapid redox kinetics and efficient ion transport. The electrode also showed excellent cycling stability, retaining approximately 83.7% of its initial capacitance after 12,000 charge–discharge cycles, indicating robust structural integrity and interfacial stability. Additionally, an asymmetric supercapacitor device (P/S-CoVO//AC) delivered a high energy density of 0.082 mWh cm⁻², a power density of 1.25 mW cm⁻², and stable operation within a 1.5 V potential window. These results demonstrate that cooperative surfactant engineering provides an effective and scalable strategy to enhance the morphology, electrochemical kinetics, and durability of Co₃V₂O₈-based electrodes for next-generation high-performance supercapacitors.

The rational design of cost-effective and highly active electrocatalysts for overall water splitting remains a critical challenge for sustainable hydrogen production. Herein, we report a two-dimensional reduced graphene oxide (rGO)-supported Mo₂S₃ nanohybrid catalyst with a tunable electronic structure engineered through interfacial coupling. The intimate integration of Mo₂S₃ nanoflakes with conductive rGO nanosheet facilitates rapid electron transport, enhanced active site exposure, and optimized adsorption energetics for reaction intermediates. Structural and spectroscopic analyses confirm strong electronic interaction between Mo₂S₃ and rGO, leading to modulated charge density distribution and improved intrinsic catalytic activity. Electrochemical evaluations reveal significantly reduced overpotentials for oxygen evolution reaction (OER) with 166 mV overpotential at 10 mA cm⁻² current density, along with favorable Tafel kinetics with 38.1 mV dec⁻¹ and long-term operational stability in alkaline electrolyte. The rGO-Mo₂S₃-2||Pt-C cell delivers 10 mA cm⁻² at 1.64 V, indicating efficient alkaline water splitting. The enhanced performance is attributed to synergistic effects arising from electronic modulation, enhanced active sites, and accelerated interfacial charge transfer.