For the sustainable growth of future generations, energy storage technologies like supercapacitors and batteries are becoming more and more common. However, reliable and high‐performance materials’ design and development is the key for the widespread adoption of batteries and supercapacitors. Quantum dots with fascinating and unusual properties are expected to revolutionize future technologies. However, while the recent discovery of quantum dots honored with a Nobel prize in Chemistry, their benefits for the tenacious problem of energy are not realized yet. In this context, herein, chemical‐composition tuning enabled exceptional performance of NiCo₂O₄(NCO)/graphene quantum dots (GQDs) is reported, which outperform the existing similar materials, in supercapacitors. A comprehensive study is performed on the synthesis, characterization, and electrochemical performance evaluation of highly functional NCO/GQDs in supercapacitors delivering enhanced energy efficiency. The high‐performance, functional NCO/GQDs electrode materials are synthesized by the incorporation of GQDs into NCO. The effect of variable amount of GQDs on the energy performance characteristics of NCO/GQDs in supercapacitors is studied systematically. In‐depth structural and chemical bonding analyses using X‐ray diffraction (XRD) and Raman spectroscopic studies indicate that all the NCO/GQDs composites crystallize in the spinel cubic phase of NiCo₂O₄ while graphene integration evident in all the NCO/GQDs. The scanning electron microscopy imaging analysis reveals homogeneously distributed spherical particles with a size distribution of 5–9 nm validating the formation of QDs. The high‐resolution transmission electron microscopy analyses reveal that the NCOQDs are anchored on graphene sheets, which provide a high surface area of 42.27 m²g⁻¹ and high mesoporosity for the composition of NCO/GQDs‐10%. In addition to establishing reliable electrical connection to graphene sheets, the NCOQDs provide reliable 3D‐conductive channels for rapid transport throughout the electrode as well as synergistic effects. Chemical‐composition tuning, and optimization yields NCO/GQDs‐10% to deliver the best specific capacitance of 3940 Fg⁻¹ at 0.5 Ag⁻¹, where the electrodes retain ≈98% capacitance after 5000 cycles. The NCO/GQD‐10%//AC asymmetric supercapacitor device demonstrates outstanding energy density and power density values of 118.04 Wh kg⁻¹ and 798.76 W kg⁻¹, respectively. The NCO/GQDs‐10%//NCO/GQDs‐10% symmetric supercapacitor device delivers excellent energy and power density of 24.30 Wh kg⁻¹ and 500 W kg⁻¹, respectively. These results demonstrate and conclude that NCO/GQDs are exceptional and prospective candidates for developing next‐generation high‐performance and sustainable energy storage devices.

This work for the first time unfurls the fundamental mechanisms and sets the stage for an approach to derive electrocatalytic activity, which is otherwise not possible, in a traditionally known wide band-gap oxide material. Specifically, we report on the tunable optical properties, in terms of wide spectral selectivity and red-shifted band gap, and electrocatalytic behavior of iron (Fe)-doped gallium oxide (β-Ga₂O₃) model system. X-ray diffraction (XRD) studies of sintered Ga_2–xFe_xO₃ (GFO) (0.0 ≤ x ≤ 0.3) compounds provide evidence for the Fe³⁺ substitution at Ga³⁺ site without any secondary phase formation. Rietveld refinement of XRD patterns reveals that the GFO compounds crystallize in monoclinic crystal symmetry with a C2/m space group. The electronic structure of the GFO compounds probed using X-ray photoelectron spectroscopy data reveals that at lower concentrations, Fe exhibits mixed chemical valence states (Fe³⁺, Fe²⁺), whereas single chemical valence state (Fe³⁺) is evident for higher Fe content (x = 0.20–0.30). The optical absorption spectra reveal a significant red shift in the optical band gap with Fe doping. The origin of the significant red shift even at low concentrations of Fe (x = 0.05) is attributed to the strong sp–d exchange interaction originated from the 3d⁵ electrons of Fe³⁺. The optical absorption edge observed at ≈450 nm with lower intensity is the characteristic of Fe-doped compounds associated with Fe³⁺–Fe³⁺ double-excitation process. Coupled with an optical band-gap red shift, electrocatalytic studies of GFO compounds reveal that, interestingly, Fe-doped Ga₂O₃ compound exhibits electrocatalytic activity in contrast to intrinsic Ga₂O₃. Fe-doped samples (GFO) demonstrated appreciable electrocatalytic activity toward the generation of H₂ through electrocatalytic water splitting. An onset potential and Tafel slope of GFO compounds include ∼900 mV, ∼210 mV dec^–1 (x = 0.15) and ∼1036 mV, ∼290 mV dec^–1 (x = 0.30), respectively. The electrocatalytic activity of Fe-doped Ga-oxide compounds is attributed to the cumulative effect of different mechanisms such as doping resulting in new catalytic centers, enhanced conductivity, and electron mobility. Hence, in this report, for the first time, we explored a new pathway; the electrocatalytic behavior of Fe-doped Ga₂O₃ resulted due to Fe chemical states and red shift in the optical band gap. The implications derived from this work may be applicable to a large class of compounds, and further options may be available to design functional materials for electrocatalytic energy production.

We report on the impedance spectroscopic characterization of Sm and Ho doped Ni ferrite materials, namely <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">Ni</mml:mi><mml:mi mathvariant="normal">O</mml:mi><mml:mi>.</mml:mi><mml:msub><mml:mi mathvariant="normal">Fe</mml:mi><mml:mrow><mml:mn>1.925</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">Sm</mml:mi><mml:mrow><mml:mn>0.075</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>NiO.Fe1.925Sm0.075O3 and <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">Ni</mml:mi><mml:mi mathvariant="normal">O</mml:mi><mml:mi>.</mml:mi><mml:msub><mml:mi mathvariant="normal">Fe</mml:mi><mml:mrow><mml:mn>1.925</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">Ho</mml:mi><mml:mrow><mml:mn>0.075</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>NiO.Fe1.925Ho0.075O3 , to demonstrate their improved electrical properties compared to pure NiO. <mml:math display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="normal">Fe</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>Fe2O3 . Sm and Ho doped Ni ferrites crystallize in the cubic inverse spinel phase with a very small amount of <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">Sm</mml:mi><mml:mi mathvariant="normal">Fe</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>SmFeO3 and <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">Ho</mml:mi><mml:mi mathvariant="normal">Fe</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>HoFeO3 as the additional phase, respectively. Atomic force microscopy measurements indicate that the bulk grains are approximately <mml:math display="inline"><mml:mrow><mml:mn>2</mml:mn><mml:mo>–</mml:mo><mml:mn>5</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi>μ</mml:mi><mml:mi mathvariant="normal">m</mml:mi></mml:mrow></mml:math>2–5μm in size while the grain boundaries are thin compared to bulk grains. Frequency variation of the dielectric constant shows the dispersion that can be modeled with a modified Debye’s function, which considers the possibility of more than one ion, contributing to the relaxation. The resistivity values (at <mml:math display="inline"><mml:mrow><mml:mn>3.5</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi>KHz</mml:mi></mml:mrow></mml:math>3.5KHz ) of <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">Ni</mml:mi><mml:mi mathvariant="normal">O</mml:mi><mml:mo>.</mml:mo><mml:msub><mml:mi mathvariant="normal">Fe</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>NiO.Fe2O3 , <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">Ni</mml:mi><mml:mi mathvariant="normal">O</mml:mi><mml:mo>.</mml:mo><mml:msub><mml:mi mathvariant="normal">Fe</mml:mi><mml:mrow><mml:mn>1.925</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">Sm</mml:mi><mml:mrow><mml:mn>0.075</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>NiO.Fe1.925Sm0.075O3 , and <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">Ni</mml:mi><mml:mi mathvariant="normal">O</mml:mi><mml:mo>.</mml:mo><mml:msub><mml:mi mathvariant="normal">Fe</mml:mi><mml:mrow><mml:mn>1.925</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">Ho</mml:mi><mml:mrow><mml:mn>0.075</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>NiO.Fe1.925Ho0.075O3 compounds are found to be <mml:math display="inline"><mml:mrow><mml:mn>0.1</mml:mn><mml:mo>×</mml:mo><mml:msup><mml:mrow><mml:mn>10</mml:mn></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msup><mml:mspace width="0.3em"></mml:mspace><mml:mi>Ω</mml:mi><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">m</mml:mi></mml:mrow></mml:math>0.1×104Ωm , <mml:math display="inline"><mml:mrow><mml:mn>0.5</mml:mn><mml:mo>×</mml:mo><mml:msup><mml:mrow><mml:mn>10</mml:mn></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msup><mml:mo>,</mml:mo><mml:mi>Ω</mml:mi><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">m</mml:mi></mml:mrow></mml:math>0.5×104,Ωm and <mml:math display="inline"><mml:mrow><mml:mn>0.8</mml:mn><mml:mo>×</mml:mo><mml:msup><mml:mrow><mml:mn>10</mml:mn></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msup><mml:mspace width="0.3em"></mml:mspace><mml:mi>Ω</mml:mi><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">m</mml:mi></mml:mrow></mml:math>0.8×104Ωm , respectively. Impedance spectroscopic analysis indicates the different relaxation mechanisms and their variation with temperature, bulk grain and grain-boundary contributions to the electrical conductivity <mml:math display="inline"><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mi mathvariant="normal">R</mml:mi><mml:mi mathvariant="normal">g</mml:mi></mml:msub><mml:mo>)</mml:mo></mml:mrow></mml:math>(Rg) , and capacitance <mml:math display="inline"><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mi mathvariant="normal">C</mml:mi><mml:mi mathvariant="normal">g</mml:mi></mml:msub><mml:mo>)</mml:mo></mml:mrow></mml:math>(Cg) of these materials. While the conductivity in pure <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">Ni</mml:mi><mml:mi mathvariant="normal">Fe</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>NiFeO4 is predominantly due to intrinsic bulk contribution ( <mml:math display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="normal">R</mml:mi><mml:mi mathvariant="normal">g</mml:mi></mml:msub><mml:mo>=</mml:mo><mml:mn>213</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">k</mml:mi><mml:mi>Ω</mml:mi></mml:mrow></mml:math>Rg=213kΩ and <mml:math display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="normal">C</mml:mi><mml:mi mathvariant="normal">g</mml:mi></mml:msub><mml:mo>=</mml:mo><mml:mn>4.5</mml:mn><mml:mo>×</mml:mo><mml:msup><mml:mrow><mml:mn>10</mml:mn></mml:mrow><mml:mrow><mml:mo>−</mml:mo><mml:mn>8</mml:mn></mml:mrow></mml:msup><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">F</mml:mi></mml:mrow></mml:math>Cg=4.5×10−8F ), <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">Ni</mml:mi><mml:mi mathvariant="normal">O</mml:mi><mml:mi>.</mml:mi><mml:msub><mml:mi mathvariant="normal">Fe</mml:mi><mml:mrow><mml:mn>1.925</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">R</mml:mi><mml:mrow><mml:mn>0.075</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>NiO.Fe1.925R0.075O3 <mml:math display="inline"><mml:mrow><mml:mo>(</mml:mo><mml:mi mathvariant="normal">R</mml:mi><mml:mo>=</mml:mo><mml:mi mathvariant="normal">Sm</mml:mi><mml:mo>,</mml:mo><mml:mi mathvariant="normal">Ho</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:math>(R=Sm,Ho) exhibits distinct grain and grain-boundary contributions to the conductivity.