Best practices for electrochemical characterization of supercapacitors

Graphene Doped Carbon‐Gels and MnO2 for Next Generation of Solid‐State Asymmetric Supercapacitors

“…The low resistivity of all investigated cells was also revealed by the electrochemical impedance spectroscopy measurements performed (Figure 5). The Nyquist plots presented in Figure 5a clearly show the very low resistivity for all cells (i. e., intercept with abscissa), besides the absence of evident loops, which are generally attributed to charge transfer resistance and interface resistances [30,31] . In this regard, the NAG − /NAG + capacitor shows a higher distributed resistance, characteristic of usual porous carbon electrodes, which appears as a typical Warburg impedance with a 45° slope in the transition region, owing to the semi‐infinite diffusion of ionic species through the pores.…”

“…Figure 5b also shows at very low frequencies (i. e., from 0.03 to 0.001 Hz) an increased resistance for all cases that occurs after long timescales, due to the slow diffusion of ions (i. e., Na + ) into the deep pores of electrodes, especially in this case when they are made with a high loading (e. g., >3–4 mg cm −2 ) of active materials (e. g., carbon gels and MnO 2 ). In literature, these deviations from the vertical response at very low frequencies (i. e., millihertz range) are attributed to the presence of capacitance dispersions, which appear with a phase angle less than 90 degrees [31] and deviation from pure EDLC behaviour without diffusion limitation [32] or undesirable side‐reactions, which produce leakage currents and self‐discharge of supercapacitors [33] . Furthermore, this type of phenomena is further evaluated by Bode diagrams, where the phase angle with frequency is shown (Figure S5) and where three main zones can be defined and compared: (i) interfacial charge transfer, (ii) ion diffusion in the electrode pores, and (iii) capacitive behaviour of the device.…”

“…The Nyquist plots presented in Figure 5a clearly show the very low resistivity for all cells (i. e., intercept with abscissa), besides the absence of evident loops, which are generally attributed to charge transfer resistance and interface resistances. [30,31] In this regard, the NAG À /NAG + capacitor shows a higher distributed resistance, characteristic of usual porous carbon electrodes, which appears as a typical Warburg impedance with a 45°slope in the transition region, owing to the semi-infinite diffusion of ionic species through the pores. The other two cells, GAG À /GAG + and GAG À /MnO 2 + , clearly show lower Warburg impedance and a steeper vertical point distribution.…”

Neural Network Models for Estimating the Impact of Physicochemical and Operational Parameters on the Specific Capacity of Activated-Carbon-Based Supercapacitors

“…Supercapacitors have several advantages as energy storage applications, including high energy density and long cycle life. − The electrode plays a crucial role in supercapacitors, and carbon has been highlighted as the most popular electrode material as a result of its excellent chemical and physical properties. − Researchers are eager to enhance the specific capacitance of activated-carbon-based electrodes to improve the performance of supercapacitors. For instance, they modified the pore structure, surface functional groups, and specific surface area to increase the specific capacitance. ,− The modification work on the capacitor electrode, however, solely relies on a few empirical formulas or vague theoretical models, and there is currently no widely accepted theory to improve capacitance systematically. − As a result, the quoted statistics for capacitance can be pretty unstable (ranging from 10 to 800 F/g) depending upon the materials and testing conditions. ,− A comprehensive evaluation technique is required to predict the capacitive characteristics of activated-carbon-based supercapacitors accurately.…”

Novel Two-Dimensional MoC/MnSe Composites for Supercapacitors and Hydrogen Evolution Reaction

“…Increase in energy demand has paved the way to develop technologies to convert energy from renewable energy sources, and there is an urgent need for a clean environment and transition to a sustainable energy future. Energy storage and conversion such as hydrogen evolution reaction (HER) and supercapacitors (SCs) are fulfilling the criteria of green energy sources. − Recently, two-dimensional (2D)-based inorganic materials have emerged as a new research hotspot due to their cost-effectiveness, eco-friendly nature, and beneficial mechanical, structural, and electronic properties. − Researchers are actively exploring different types of 2D-based inorganic materials, such as metal oxides, sulfides, nitrides, carbides, selenides, and composite materials, to harness their unique properties for various applications such as energy storage, catalysis, electronics, and sensors. − In particular, transition metal selenides, such as CoSe, NiSe, CuCo-Se, MoSe 2 @CN, NiVSe, Cu-ZnSe@NC, WSe 2 @SnSe 2 , and MnSe, have received considerable attention compared to metal oxides and alloys due to their unique physiochemical properties and stability − and are interestingly used in sensors as well as renewable energy technologies. − Furthermore, transition metal selenides show promising performance in HER due to their intrinsic metallic properties . In particular, MnSe exhibits notably enhanced electronic conductivity compared with oxide and sulfide counterparts.…”