Pseudocapacitive Mechanism Research Articles

Nano-organic polymers with rich redox sites as anode materials for dual-ion batteries

Organic electrode materials (OEMs) are considered one of the potential electroactive materials used in rechargeable batteries due to their high availability, low price, and sustainability. Nevertheless, the high solubility of their organic small molecules and their low electrical conductivity limit their practical applications. In this study, porous nanorods organic conjugated polymer were successfully prepared by a solvothermal method using 1,4,5,8-naphthalenetetracarboxylic anhydride and azodicarbonamide as precursors for dual-ion battery anodes. The successful synthesis of polymer extends the π-conjugated structure, effectively reducing its solubility in organic electrolytes. Moreover, the azo group (NN) in the polymer was easily conjugated with the adjacent aromatic ring, increasing the utilization of the active site, thereby improving the conductivity of the material so that the polymer has a high discharge capacity (90.5 mAh g−1 at 2 C, up to 96 % capacity retention). Even with a high rate of 10 C, the polymer still exhibits excellent electrochemical performance (50.0 mAh g−1 at 270 cycles). Moreover, reaction kinetics tests show that the electrode material was based on a pseudocapacitive storage mechanism influenced by diffusion and double-layer control. Therefore, the design strategy of such a material paves the way for the application of dual-ion batteries.

Assessment of electrochemical removal mechanisms of diverse transition metal dichalcogenides for caesium ion removal in wastewater treatment

Abstract Effective treatment of radioactive wastewater is crucial for broader nuclear energy adoption, with caesium radionuclides (most exist in the form of caesium chloride) presenting challenges due to their long half-life and biological hazards. Conventional adsorbents like zeolites and carbon-based materials, including graphene, face limitations in adsorption capacity due to the formation of electric double layers (EDL). This has led to the investigation of alternatives such as transition metal dichalcogenides (TMDs) e.g., MoS2, MoSe2, and WSe2, which offer promising galleries for caesium ion removal. Aside from extensively studied MoS2, there is limited research on the adsorption mechanisms and capacities of other TMDs like MoSe2 and WSe2. Here, we conduct a comparative study examining the removal mechanisms and capacities of exfoliated MoS2, MoSe2, and WSe2 nanosheets, alongside an evaluation of these properties in relation to graphene. Our investigation reveals distinct removal mechanisms and capacities among these three materials for capturing caesium ions in a variety of mechanisms. MoS2 nanosheets primarily utilise a pseudocapacitive charge storage mechanism via intercalation, as evidenced by a total charge storage of 0.78 C g1, with only 2.6% stored via EDL formation. In contrast, MoSe2 predominantly relies on EDL formation, with almost 60% of the total 0.54 C g1 charge storage attributed to this mechanism. Lastly, WSe2 exhibits a combination of both charge storage behaviours, with a total charge storage of 0.77 C g1, of which 14% is due to EDL formation. This research highlights the potential efficacy of TMDs as viable materials for caesium removal, offering an appealing alternative to conventional adsorbents and likely fostering advancements in water treatment technologies.

Unveiling magnetite metal-organic frameworks for asymmetric pseudo-supercapacitor with high energy density and magnetocapacitance

Utilizing innovative techniques for electrode fabrication and incorporating novel energy storage concepts through external stimuli forces is crucial for enhancing the specific capacity and commercial feasibility of energy storage devices. The performance of supercapacitors hinges on both capacitive behavior, which enhances charge-discharge characteristics and power density, and ion-diffusion behavior, which boosts energy density. This study delves into the impact of external magnetic fields on supercapacitor performance by enhancing pseudo-capacitive behavior through a facile redox pathway and promoting the diffusion coefficient of the electrolyte. We presented magneto-electrophoretic deposition (M-EPD) to apply a high-surface-area zeolitic imidazolate framework (ZIF), which serves as a robust binder-free strategy. Specifically, the Fe3O4-ZIF-67 nanocomposite is uniformly supported on ferromagnetic nickel foam (NF) and demonstrates an impressive specific capacitance of 656.7 F g−1 (328.4 C g−1) at 1 A g−1. In addition, coin cell supercapacitors assembled with Fe3O4-ZIF-67/NF as positive and Fe3O4-ZIF-67-MWCNT/CF as negative electrodes achieve outstanding energy density (103.3 W h kg−1) at a power density of 750 W kg−1, coupled with excellent cycling stability (83.61 % capacity retention) after 10,000 cycles at 20 A g−1. Notably, the cell exhibits superior magnetocapacitance and the highest diffusion coefficient under an external magnetic field of 100 mT. The energy density reaches 163.2 W h kg−1 at a power density of 750 W kg−1, with a coulombic efficiency of 77.7 %. This represents a 1.58-fold enhancement compared to the absence of the magnetic field. The results demonstrated that ferromagnetic coupling between metal−oxygen−metal centers is enhanced via oxygen 2p orbitals, thereby creating a facile pseudocapacitance mechanism. The ZIF-67 shell further regulates the charge-discharge behavior of the electrode through the interplay between diffusive and capacitive mechanisms. This work introduces a promising new approach for preparing high-surface-area MOF-based electrodes and stimuli-responsive, high-performance electrochemical energy storage devices.

Engineering Mn Vacancies to Enhance Ion Kinetics in Layered Manganese Silicate for High-Energy and Durable Intercalation Pseudocapacitance.

Transition metal silicates (TMSs) are potential electrodes for aqueous metal-ion intercalation pseudocapacitors owing to their superior theoretical capacity and high structural stability. However, the narrow interlayer spacing and intrinsic inert basal plane of TMSs lead to sluggish ions and charge transfer, causing an undesirable energy storage performance. Herein, rich Mn vacancies are introduced in layered manganous silicates (M2-xS@FA) to expedite K+ diffusion, while enhancing charge storage capacity and prolonging lifespan. In situ characterizations validate the K+ intercalation pseudocapacitance mechanism with evident crystal structure and valence state variations in M2-xS@FA. Both theoretical calculations and electrochemical experimental evaluations elucidate the imperative role of Mn vacancies in enhancing K+ diffusion kinetics and electron transfer through increased interlayer spacing and activated basal plane. Mn vacancies further boost the charge storage capacity by providing additional K+ storage sites, while simultaneously reinforcing local atomic bonding within M2-xS@FA, thereby augmenting structural stability. The assembled aqueous asymmetric solid-state cell, featuring a M2-xS@FA cathode, demonstrates exceptional power and energy densities (144.08 W h kg-1 at 375.80 W kg-1) and ultralong lifespan (100% capacity retention after 10,000 cycles). This work heralds a paradigm whereby modulating cation vacancies in layered TMSs significantly enhances K+ storage and stability for high-energy intercalation pseudocapacitance.

Controlling Structure and Morphology of MoS2 via Sulfur Precursor for Optimized Pseudocapacitive Lithium Intercalation Hosts

AbstractMolybdenum disulfide (MoS2)‐based electrode materials can exhibit a pseudocapacitive charge storage mechanism induced by nanosized dimension of the crystalline domains, which is why control over material structure via synthesis conditions is of significance. In this study, we investigate how the use of different sulfide precursors, specifically thiourea (TU), thioacetamide (TAA), and L‐cysteine (LC), during the hydrothermal synthesis of MoS2, affects its physicochemical, and consequently, electrochemical properties. The three materials obtained exhibit distinct morphologies, ranging from micron‐sized architectures (MoS2 TU), to nanosized flakes (MoS2 TAA and LC). While all three synthesized samples exhibit pseudocapacitive Li+ intercalation properties, the capacity retention of the latter two consisting of nanosized flakes is further improved at high cycling rates. The individual charge storage properties are analyzed by operando X‐ray diffraction, dilatometry, and 3D Bode analysis, revealing a correlation between the morphology, porosity, and the electrochemical intercalation behavior of the obtained electrode materials. The results demonstrate a facile strategy to control MoS2 structure and related functionality by choice of hydrothermal synthesis precursors.

Magnetic transition magnetocaloric and supercapacitor behavior in synthesized Sn0.6Mn0.1Ge0.3Te alloys

This study comprehensively investigates the structural, microstructural, vibrational, magnetic, and magnetocaloric properties of novelty Sn0.6Mn0.1Ge0.3Te alloys synthesized using the sealed tube solid-state reaction method. The observed magnetic behavior showcases a transition from paramagnetic (PM) to ferromagnetic (FM) phases at the Curie temperature TC = 29 K. Notably, magnetic entropy change (−ΔSM), relative cooling power (RCP), and refrigerant capacity (RC) are calculated as 1.5 J/kg-K, 42.05 J/kg, and 37.39 J/kg, respectively, under a magnetic field of 60 kOe. Arrott curve analysis further validates the magnetic phase transition, affirming a second-order transition between FM and PM phases. Critical exponents (β, γ, and δ) are derived from field-dependent magnetic entropy changes around the second-order transition and strongly agree with the mean field model. These critical exponents establish a clear correlation between critical behavior and magnetocaloric effects, reinforcing the potential of Sn0.6Mn0.1Ge0.3Te alloys for magnetocaloric applications. Investigations into the electrochemical properties of the alloy have indicated that it exhibits a specific capacitance of 152.9 F/g at a scan rate of 20 mV/s, demonstrating a predominantly pseudocapacitive charge storage mechanism. Additionally, the alloy has proven to be highly stable, retaining 94.2 % of its specific capacitance after 10,000 cycles.

Inducing and Understanding Pseudocapacitive Behavior in an Electrophoretically Deposited Lithium Iron Phosphate Li-Metal Battery as an Electrochemical Test Platform.

Our study has effectively employed electrophoretic deposition (EPD) using AC voltage to develop a lithium iron phosphate (LFP) Li-ion battery featuring pseudocapacitive properties and improved high C-rate performance. This method has significantly improved the battery's specific capacity, achieving an impressive 100 mAhg-1 at a 5 C discharge rate, which showcases its superior high-rate capability. Additionally, the battery displayed excellent reversibility during its performance cycles. These results confirm the EPD method's efficacy in improving LFP electrode performance, yielding notable improvements in cycling stability and high-rate capability. The enhanced capacity and high-rate performance of the electrophoretic-deposited LFP electrodes are largely due to the fast kinetics facilitated by pseudocapacitive behavior-induced charge storage and a high Li-ion diffusion constant measured in our EPD-deposited LFP electrodes. This underscores the practicality of our approach and the development of a fundamental test platform to investigate the pseudocapacitive charge storage mechanism in electrodes with typical battery-like behavior.

Electrodeposition fabrication of graphene oxide/α-MnO2/polyaniline hierarchical porous electrodes with large hybrid specific capacitance for efficient U(VI) electrosorption

The radioactive pollution caused by the excessive discharge of uranium-containing wastewater generated from nuclear industry posed harmful effect to the ecological environment and human health. Herein, the electrodeposition of polyaniline on graphene oxide/α-MnO2 surface was conducted to fabricate novel hierarchical porous graphene oxide/α-MnO2/polyaniline (GMP) electrodes with large specific capacitance for U(VI) electrosorption through hybrid capacitance deionization (HCDI). As expected, the prepared GMP have high specific capacitance, small electrochemical impedance, and excellent electrosorption performance. Among the different GMP composites, GMP-2 presents the highest specific capacitance (303.85 F/g) and largest electrosorption capacity of U(VI) (330.41 mg/g at 0.9 V and pH4.0), indicating that its electrosorption capacity is closely related to the specific capacitance. Moreover, GMP-2 showed good selectivity for U(VI) electrosorption through pseudocapacitive mechanism. The XPS and FTIR characterization indicated that apart from hybrid capacitance (EDL and pseudocapacitance) mechanism, complexation and electrostatic interactions were also involved for U(VI) capture. The GMP-2 electrode is facile to fabricate and has excellent electrosorption performance, which could be used in HCDI for radioactive wastewater treatment.

Synthesis, characterization, and synergistic effects of CuS/MnO2 nanocomposite electrodes for high-performance supercapacitors

Metal oxides, metal sulfides, and their derivatives exhibit impressive electrochemical capabilities, offering potential for the creation of novel electrodes with superior performance in supercapacitors. In this study, we introduce a novel binary composite consisting of copper sulfide and manganese oxide (CuS/MnO2). This composite is designed with specific CuS and MnO2 ratios (80 % and 20 %, respectively) to explore their electrochemical behavior and optimize the performance of these nanostructures. According to morphological and structural analysis, it was observed that the synthesis process yielded high-purity nanoparticles and nanorods of CuS and MnO2. Notably, no byproducts were detected, indicating a successful synthesis process. Through a rapid pseudocapacitive charge storage mechanism, the electrochemical investigations reveal that all electrodes in a three-electrode setup tested in 3 M KOH electrolyte solution and the novel CuS/MnO2 electrode exhibit typical capacitive behavior in the potential of 0.0–0.5 V, with good reversibility and charge storage properties (specific capacitance: 451 F g−1, low resistance: 1.21 Ω, cyclic stability: 98.33 % at 4 A g−1 continuously 2000 cycles). Surprisingly, the CuS/MnO2 nanocomposite (NC) exposed high power density is about 1997 W kg−1 and a maximum energy density of 28.19 W h kg−1exceptionally is achieved. The significance of additional transition metal oxide-based electrodes in achieving noticeably better performance is demonstrated by these results.

Dual Redox Reaction Sites for Pseudocapacitance Based on Ti and -P Functional Groups of Ti3C2PBrx MXene.

MXenes have extensive applications due to their different properties determined by intrinsic structures and various functional groups. Exploring different functional groups of MXenes leads to improved performance or potential applications. In this work, we prepared new Ti3C2PBrx (x=0.4-0.6) MXene with phosphorus functional groups (-P) through a two-step gas-phase reaction. The acquisition of -P is achieved by replacing bromine functional groups (-Br) of Ti3C2Br2 in the phosphorus vapor. After -Br is replaced with -P, Ti3C2PBrx MXene shows an improved areal capacitance (360 mF cm-2) at 20 mV s-1 compared with Ti3C2Br2 MXene (102 mF cm-2). At a current density of 5 mA cm-2 after 10000 cycles, the capacitance retention of Ti3C2PBrx MXene has not decreased. The pseudocapacitive enhancement mechanism has been discovered based on the dual redox sites of the functional groups -P and Ti.

Dual Redox Reaction Sites for Pseudocapacitance Based on Ti and −P Functional Groups of Ti3C2PBrx MXene

AbstractMXenes have extensive applications due to their different properties determined by intrinsic structures and various functional groups. Exploring different functional groups of MXenes leads to improved performance or potential applications. In this work, we prepared new Ti3C2PBrx (x=0.4–0.6) MXene with phosphorus functional groups (−P) through a two‐step gas‐phase reaction. The acquisition of −P is achieved by replacing bromine functional groups (−Br) of Ti3C2Br2 in the phosphorus vapor. After −Br is replaced with −P, Ti3C2PBrx MXene shows an improved areal capacitance (360 mF cm−2) at 20 mV s−1 compared with Ti3C2Br2 MXene (102 mF cm−2). At a current density of 5 mA cm−2 after 10000 cycles, the capacitance retention of Ti3C2PBrx MXene has not decreased. The pseudocapacitive enhancement mechanism has been discovered based on the dual redox sites of the functional groups −P and Ti.

Recent Progress Using Graphene Oxide and Its Composites for Supercapacitor Applications: A Review

Supercapacitors are prospective energy storage devices for electronic devices due to their high power density, rapid charging and discharging, and extended cycle life. Materials with limited conductivity could have low charge-transfer ions, low rate capability, and low cycle stability, resulting in poor electrochemical performance. Enhancement of the device’s functionality can be achieved by controlling and designing the electrode materials. Graphene oxide (GO) has emerged as a promising material for the fabrication of supercapacitor devices on account of its remarkable physiochemical characteristics. The mechanical strength, surface area, and conductivity of GO are all quite excellent. These characteristics make it a promising material for use as electrodes, as they allow for the rapid storage and release of charges. To enhance the overall electrochemical performance, including conductivity, specific capacitance (Cs), cyclic stability, and capacitance retention, researchers concentrated their efforts on composite materials containing GO. Therefore, this review discusses the structural, morphological, and surface area characteristics of GO in composites with metal oxides, metal sulfides, metal chalcogenides, layered double hydroxides, metal–organic frameworks, and MXene for supercapacitor application. Furthermore, the organic and bacterial functionalization of GO is discussed. The electrochemical properties of GO and its composite structures are discussed according to the performance of three- and two-electrode systems. Finally, this review compares the performance of several composite types of GO to identify which is ideal. The development of these composite devices holds potential for use in energy storage applications. Because GO-modified materials embrace both electric double-layer capacitive and pseudocapacitive mechanisms, they often perform better than pristine by offering increased surface area, conductivity, and high rate capability. Additionally, the density functional theory (DFT) of GO-based electrode materials with geometrical structures and their characteristics for supercapacitors are addressed.

Modulating charge storage mechanism of cobalt-tungsten nitride electrodes using in situ formed metal-p-n heterojunction for ultrahigh energy density supercapattery

Supercapatteries combine both diffusion-controlled and capacitive charge storage mechanisms to simultaneously deliver exceptional power density and energy density. Though developing materials that combine both charge storage mechanisms for use as supercapattery electrodes is difficult, one solution has been to modify a material that inherently has one of these mechanisms so that it also exhibits the other form of charge storage. In the present study, we modulate the electrochemical reconstruction of a W5N4 electrode to modify its charge storage from pure battery-type to pseudocapacitive, thus enhancing its specific capacity and cyclic stability. This modulation was carried out by embedding Co in W5N4 (Co-W5N4), leading to the formation of W and N-doped Co(OH)2 as an active phase and producing a high specific capacity of 2211 C g−1 at 2 A g−1. The incorporation of a thin layer of TiO2 (Co-W5N4/TiO2) through atomic layer deposition minimized tungsten dissolution during reconstruction, thus generating in-situ a dynamic metal–p-n junction heterostructure (Co-W5N4||Co(OH)2||TiO2) that modulated the charge flow, achieving high-rate capability (retaining 53.1 % at 50 A g−1 compared to 2 A g−1) and cyclic stability (82.8 % after 100,000 cycles at a high current density of 40 A g−1). As illustrated by operando electrochemical impedance spectroscopy and physicochemical analysis, the dynamic response of metal–p-n junction sustains the pseudocapacitive charge storage mechanism at high current rate. This study thus demonstrates the formation of metal-p-n heterojunction and describes its dynamic response under actual charge/discharge operating conditions, providing useful information for the design of energy storage electrodes and energy conversion catalysts.

Insights into pseudocapacitive mechanism of aqueous ammonium-ion supercapacitors with exceptional energy density and cyclability

Aqueous ammonium-ion (NH4+) supercapacitors (AASCs) have recently garnered increased concerns but are consistently facing the challenge of lower energy density. Herein, a high-performance electrode (CuCo2S4@CP) with pseudocapacitive property has been synthesized and primordially applied to AASCs. The CuCo2S4@CP electrode has an ultrahigh specific capacity of 1512 C g−1 at 1 A g−1 and a distinguished cyclic stability of 87.74 % after 10,000 cycles. When the CuCo2S4@CP electrode is combined with the activated carbon (AC) negative electrode, the CuCo2S4@CP//AC device exhibits a high specific capacity of 547 C g−1 at 1 A g−1, excellent cycle stability (83.28 % at 10 A g−1), high energy density of 74.17 Wh kg−1, and excellent device consistency. In addition, the charge transfer mechanism of CuCo2S4@CP electrode in NH4+electrolyte has been elucidated. The CuCo2S4 surface density functional theory (DFT) elucidates that NH4+ has a minimal contribution to the surface, implying an insertion behavior of NH4+ within the CuCo2S4 lattice. Subsequent ex-situ characterization further confirms the energy storage process, revealing charge transfer to Co atoms following NH4+ insertion into CuCo2S4. The analysis of charge distribution illustrates an energy storage mechanism wherein the hydrogen bond formed between NH4+ and CuCo2S4 serves as the transport channel for charge transfer, facilitating the process of electrons from NH4+ to Co atoms. Therefore, the pseudocapacitive mechanism of CuCo2S4 with NH4+ provides a blueprint for sustainable energy storage with high energy density in aqueous electrolyte.

From macro to micro: Biomass-derived advanced carbon microtube assembly for sodium-ion batteries

Developing high-rate anode materials for sodium-ion batteries is important to fulfill the requirement of high-power energy storage applications. Amorphous carbon micro-tubes (CMTs) are favorable for fast Na-ion storage, for the open carbon framework provides sufficient electrode/electrolyte contact and the one-dimensional skeleton offers fast electron and ion diffusion pathways. Herein, N, Fe co-doped carbon micron-tubes (NF-CMTs) were synthesized for the high-rate anode by using bulk biomass as the precursor. The transformation from the macro-sized biomass to the micro-sized carbon tubes was endowed by pyrolysis using N and Fe as catalysts. The open carbon frameworks enable capacitive-controlled capacity contribution, while its N-Fe defects offer multiple active sites for fast Na-ion storage. A high-capacity contribution was demonstrated by the pseudo-capacitive mechanism so that the NF-CMTs performed a superior rate capability of 120 mAh g−1 at 2.0 A g−1. The NF-CMTs with stable micro-tube frameworks exhibited high cycling stability over 1200 cycles, which was much superior to the commercial hard carbon anode. This study provides a cost-effective approach to develop carbon micro-tubes from bulk biomass for high-power SIB anodes.

Hybrid and Asymmetric Supercapacitors: Achieving Balanced Stored Charge across Electrode Materials.

An electrochemical capacitor configuration extends its operational potential window by leveraging diverse charge storage mechanisms on the positive and negative electrodes. Beyond harnessing capacitive, pseudocapacitive, or Faradaic energy storage mechanisms and enhancing electrochemical performance at high rates, achieving a balance of stored charge across electrodes poses a significant challenge over a wide range of charge-discharge currents or sweep rates. Consequently, fabricating hybrid and asymmetric supercapacitors demands precise electrochemical evaluations of electrode materials and the development of a reliable methodology. This work provides an overview of fundamental aspects related to charge-storage mechanisms and electrochemical methods, aiming to discern the contribution of each process. Subsequently, the electrochemical properties, including the working potential windows, rate capability profiles, and stabilities, of various families of electrode materials are explored. It is then demonstrated, how charge balancing between electrodes falters across a broad range of charge-discharge currents or sweep rates. Finally, a methodology for achieving charge balance in hybrid and asymmetric supercapacitors is proposed, outlining multiple conditions dependent on loaded mass and charge-discharge current. Two step-by-step tutorials and model examples for applying this methodology are also provided. The proposed methodology is anticipated to stimulate continued dialogue among researchers, fostering advancements in achieving stable and high-performance supercapacitor devices.

Pseudocapacitive Kinetics in Synergistically Coupled MoS2-Mo2N Nanowires with Enhanced Interfaces toward All-Solid-State Flexible Supercapacitors.

Pseudocapacitive kinetics in rationally engineered nanostructures can deliver higher energy and power densities simultaneously. The present report reveals a high-performance all-solid-state flexible symmetric supercapacitor (FSSC) based on MoS2-Mo2N nanowires deposited directly on stainless steel mesh (MoS2-Mo2N/SSM) employing DC reactive magnetron co-sputtering technology. The abundance of synergistically coupled interfaces and junctions between MoS2 nanosheets and Mo2N nanostructures across the nanocomposite results in greater porosity, increased ionic conductivity, and superior electrical conductivity. Consequently, the FSSC device utilizing poly(vinyl alcohol)-sodium sulfate (PVA-Na2SO4) hydrogel electrolyte renders an outstanding cell capacitance of 252.09 F·g-1 (44.12 mF·cm-2) at 0.25 mA·cm-2 and high rate performance within a wide 1.3 V window. Dunn's and b-value analysis reveals significant energy storage by surface-controlled capacitive and pseudocapacitive mechanisms. Remarkably, the symmetric device boosts tremendous energy density ∼10.36 μWh·cm-2 (59.17 Wh·kg-1), superb power density ∼6.5 mW·cm-2 (37.14 kW·kg-1), ultrastable long cyclability (∼93.7% after 10,000 galvanostatic charge-discharge cycles), and impressive mechanical flexibility at 60°, 90°, and 120° bending angles.

Rare Earth metal oxide nanoparticle-infused polymer nanocomposites for enhanced supercapacitor electrodes

The contemporary energy shortage has spurred scientists to explore other options. In this regard, there's significant interest in utilizing electrochemical energy sources for converting and storing energy. Here, a fresh endeavor involves utilizing a set of semiconducting rare earth Gd2O3/conducting polymers (CP) (CP= polypyrrole, polyindole) for energy storage purposes. The synthesis method involves the straightforward oxidative polymerization of either indole or pyrrole to produce Gd2O3/PIn or Gd2O3/PPy, respectively. The integrity of the garnets synthesized was verified through XRD, Raman, XPS, FESEM, and TEM analysis, ensuring their phase purity and morphology. The scanning electron microscopy (SEM) analysis reveals the particle morphology, with sizes ranging from 100 to 800 nanometers. FTIR and Raman spectroscopy further validate the integration of Gd2O3 into the conducting polymer matrix. XRD shows broad peaks for amorphous structures in Gd2O3/PPy and Gd2O3/PIn nanocomposites. To evaluate its performance in supercapacitors, cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and impedance spectroscopy (EIS) were employed using a three-electrode configuration. The rectangular CV curves indicate the pseudo-capacitance mechanism of the Gd2O3/CP nanocomposite-coated carbon fiber electrode in an H2SO4 electrolyte. Specific capacitance (SC) values for Gd2O3/PPy and Gd2O3/PIn binary nanocomposite electrodes are determined as 341.61 F/g and 305.56 F/g, respectively, from GCD curves. In hybrid energy systems, especially electric automobiles, the Gd2O3/PPy and Gd2O3/PIn nanocomposite-coated carbon fiber electrode has a potential of up to 1.8 V and short charging and discharging durations, implying fast-charging and extended lifespan. The easy oxidative polymerization process utilized to produce gadolinium oxide/conducting polymer nanocomposites for supercapacitors is the main breakthrough of this research.

Scalable fabrication of two-dimensional Bi2Se3 for high-performance supercapacitors

Although having an advantageous charge–discharge rate, supercapacitors, in terms of energy density, are still dwarfed by their battery counterparts, thereby hindering their industrial use. Two-dimensional (2D) Bi2Se3, which is characterized by high electrical conductivity, possesses a large theoretical specific capacity that has not been experimentally realized. In this study, we employed scalable electrochemical exfoliation to fabricate high-quality Bi2Se3 nanosheets with a yield of over 95 %. These nanosheets were then applied as anode materials with the hitherto highest specific capacitance of 662.5 F/g at 1A/g to assemble asymmetric supercapacitors (ASCs) of Bi2Se3//NiCo2S4. The supercapacitors demonstrated an extraordinary energy density of 48 Wh/kg at a power density of 800 W/kg and efficiently drove devices such as perovskite-LEDs. This study reveals the huge potential of 2D Bi2Se3 as an efficient supercapacitor electrode via a primary Faradaic pseudocapacitive storage mechanism. The scalable production of this material is expected to stimulate its widespread and practical use.

Facile synthesis and modification of Fe2O3 nanorod arrays on carbon paper as efficient negative electrodes for supercapacitors

In this research, Fe2O3 nanorod arrays grown on carbon fiber paper were studied, and carbon-coated Fe2O3 (Fe2O3 @C) and sulfurized Fe2O3 @C (Fe2O3 @C-S) were fabricated by carbon coating and sulfurization processes. To promote the application of these materials in supercapacitors, their electrochemical properties were systematically investigated. Based on the results, the materials obtained utilized a pseudocapacitive mechanism for energy storage. Specifically, Fe2O3 exhibited a moderate specific capacitance and extraordinary cycling stability, and no degradation was observed after 10,000 cycles. Impressively, sulfurization greatly enhanced the rate capability and specific capacitance of the sample. As a result, Fe2O3 @C-S attained a specific capacitance of 976.4 mF cm–2 at 4 mA cm–2 and a robust rate capability of 97.30% at 20 mA cm–2, outperforming Fe2O3 @C (84.39%) and Fe2O3 (70.55%) and demonstrating good cycling stability (92.9%). Notably, Fe2O3 @C-S was active as a positive electrode material; thus, a symmetric supercapacitor was assembled, which yielded a volumetric energy density of 1.46 mWh cm–3 at 16.71 mW cm–3 and maintained an energy density of 0.91 mWh cm–3 even at 145.63 mW cm–3. Moreover, the device exhibited good cycling stability with a capacity retention of 88.3% after 10,000 cycles at 10 mA cm–2. The integration of Fe2O3 nanorod arrays on conductive substrates, coupled with the above modifications, strongly promoted the material’s energy storage performance. Our study emphasized the significant potential of Fe2O3 @C-S as an efficient electrode material for supercapacitors.