Pseudocapacitive Electrode Research Articles

Achieved advanced wastewater phosphate removal via improved ionic interference resistance in a migration-electric-field assisted electrocoagulation (MEAEC) system with modified-biochar pseudocapacitor electrode

The capacitive deionization-assisted electrocoagulation system has promising application potential in advanced phosphate removal of its low electricity consumption and sacrificial anode material. Phosphate removal in wastewater is crucial since excess phosphate might lead to eutrophication. However, the complex ion composition in raw wastewater can influence the effective phosphate removal by competing with the precipitable metal ions during electrocoagulation. In this study, a novel migration electric-field assisted electrocoagulation (MEAEC) with an assisted capacitive electrode made of N-doped and Fe-La co-modified biochar (LFNB) to achieve specific phosphate electro-adsorption for effective advanced phosphate removal. The LFNB-MEAEC achieved ultrahigh phosphate removal with the effluent of 0.1 mg/L in synthetic and raw municipal wastewater and met the first Grade A standard of total phosphate in the discharge standard of pollutants for municipal wastewater treatment plant (DSPMWTP) in China. The commonly observed coexisting ions in wastewater and a pH range of 2–12 did not significantly fluctuate the phosphate removal of LFNB-MEAEC. Cyclic voltammetry and charging-discharging tests confirmed the high phosphate affinity and excellent durability of LFNB in ion-interference circumstances. The MEAEC assisted with selective-adsorption capacitive electrodes and provided an effective and practical method for advanced phosphate removal from low-phosphorus-contaminated wastewater. The MEAEC with a selective-adsorbed capacitive electrode improved phosphate removal by 21 % (from 74 ± 1.7% to 95 ± 1.0%), reduced the energy consumption by 65.7% (0.012 kWh m−3-wastewater), and saved the sacrificial anode material by 67.5% (from 200 to 65 g m−3-wastewater) than those of MEAEC without phosphate-selective electrode in the same period (Sacrificial anode working time 200 s).

Plasma-Activated Solutions Regulate Surface-Terminating Groups Enhancing Pseudocapacitive Ti3C2Tx Electrode Performance.

2D transition metal carbides and nitrides (MXenes) are actively pursued as pseudocapacitive materials for supercapacitors owing to their advantages in electronic conductivity and surface reactivity. Increasing the fraction of ─O terminal groups in Ti3C2Tx is a promising approach to improve the pseudocapacitive charge storage in H2SO4 electrolytes, but it suffers from a lack of effective functionalization methods and stability of the groups in practical operation. Here a low-temperature and environment-friendly approach via the interaction of nonequilibrium plasmas with Ti3C2Tx dispersion is demonstrated to generate abundant and stable surface-terminating O groups. The impact of the discharge environment (Ar, O2, and H2) on the structural characteristics and electrochemical performance of Ti3C2Tx nanosheets is studied. The Ti3C2Tx modified in Ar and H2 maintains their original morphology but a significantly lower F content. Consequently, an extraordinarily high content (78.5%) of surface-terminating O groups is revealed by the high-resolution X-ray photoelectron spectroscopy spectra for the Ti3C2Tx samples modified in H2 plasma-treated solutions. Additionally, the Ti3C2Tx treated using H2 plasmas exhibits the best capacitive performance of 418.3 F g-1 at 2mV s-1, which can maintain 95.88% capacity after 10000 cycles. These results contribute to the development of advanced nanostructured pseudocapacitive electrode materials for renewable energy storage applications.

Controlled assembly of NiCo-LDH nanosheets into diverse superstructures via concentration-dependent solvothermal method for advanced supercapacitors

The tunable layer structure, composition, and diverse morphologies of layered double hydroxides (LDHs) make them a favorable choice as pseudocapacitive electrode materials for supercapacitors. However, the severe agglomeration and low conductivity of nanosheets are detrimental to obtaining excellent electrochemical performance. In this work, a controllable assembly of nanosheets was achieved by adjusting the concentrations of Ni and Co salt solutions, resulting in a series of 3D-shaped NiCo-LDHs superstructures with diverse morphologies. The prepared structures were found to significantly reduce aggregation and electron transport distance. The results approved that the diameter, thickness and interlayer space of NiCo-LDHs nanosheets and the morphologies of their self-assembled superstructures were subtly controlled, and significantly impacted their electrochemical performance. A stretch trumpet shaped flower-like superstructure in NiCo-LDH-2 was constructed by the large and ultrathin nanosheets with much more accessible active sites and larger interlayer space, which can rapidly promote electron transfer and show the highest specific capacitance of 2265 F g−1 at 1 A g−1 and retention of 86.5% at 20 A g−1. The NiCo-LDHs//AC ASC based on NiCo-LDH-2 and active carbon (AC) reveals a high specific capacitance of 298 F g−1 at 1 A g−1 and an excellent energy density of 105.0 Wh kg−1 at the power density of 820.1 W kg−1. The current work presents a simple way for controlling the nanostructure of NiCo-LDHs in the development of high-performance supercapacitors.

Suppresses Dissolution and Enhanced Conductivity in Core–Shell VO2@Ni3N as a High‐Capacitance and Improved Cycling Anode Materials for Supercapacitor

Vanadium dioxide, as one of superior pseudocapacitive electrode candidates in supercapacitors, suffers from the detrimental dissolution in aqueous electrolytes and poor intrinsic electronic conductivity. Herein, an ultrathin Ni3N shell is deposited on the VO2 surfaces (VO2@Ni3N) to inhibit the inevitable dissolution during charge/discharge processes. Meanwhile, the Ni3N coating layer also provides sufficient electron transport pathways for the rapid surface faradic reactions of VO2, promoting the electrochemical reaction kinetics. The designed VO2@Ni3N anode exhibits significant energy storage ability, especially at large current density (2058 F g−1 at 1 A g−1, 711 F g−1 at 7 A g−1), and the considerable cycling lifespans (capacitance retention of 91.3% after 5000 cycles). The asymmetric supercapacitor presents an energy density of 41.73 Wh kg−1 at a power density of 1176.7 W kg−1. This study may enlighten the design of advanced pseudocapacitive materials for practical electrochemical energy storage technologies.

Hydrothermal synthesis of Ni,Co hydroxide nanosheet array on vertically suspended Ni foam for high performance supercapacitors

Ni(OH)2 have attracted great attention as pseudocapacitor electrode materials due to its high theoretical capacitance. However, the intrinsic disadvantaged in low electronic conductivity and sluggish ion diffusion kinetics of Ni(OH)2 limit its performance and practical application. Herein, we report a simple hydrothermal method to synthesize Co doped Ni(OH)2 and NiOOH array structure on vertical hanging Ni foam. Compared with traditional hydrothermal methods, vertical hanging Ni foam provide sufficient reaction sites and ensure fully growth of array structure, leading to large mass loading of active materials. The array structure and the wide interlayer spacing due to interlayer embedded CH3COO− together build an effcient ion diffusion path. Morevoer, strong electron exchange between Ni(OH)2 or NiOOH and Ni provide high electrical conductivity at the interface, forming the fast and complete electron transport channel inside the electrode. As a result of robust electrochemical kinetics, NiCoLDH@vNF-12 shows a high capacitive and outstanding rate performance of 952.9 C g−1 at 1 A g−1 and 660.0 C g−1 even at 50 A g−1.

Ion selective electrosorption by two pseudocapacitive intercalating nanocomposite electrodes

Two ion intercalating electrodes were in an ion selectivity study for capacitive deionization (CDI). One has MXene (Ti3C2Tx) and reduced graphene oxide (rGO) as MG. The second involved rod-shaped NTO (Na8Ti5O14) and rGO as NG. An ion selectivity study of mono- and divalent cations in binary and ternary solutions was conducted. The results suggested that the ion selectivity was influenced by the hydrated radius, the valence state of the ions, and the intrinsic charge of the electrode materials. In a binary solution, both electrodes exhibited higher selectivity for K+ ions over Li+ ions due to their smaller hydration radius. In a ternary solution, the order of ion selectivity was Ca2+ ≈ Mg2+ > Li+ and Ca2+ ≈ Mg2+ > K+ respectively. The NG electrode demonstrated a higher selectivity for divalent ions over monovalent ions (Mg2+/Li+ and Ca2+/Li+) due to stronger intrinsic negative charge. The specific adsorption capacities (SACs) of MG electrode with well-organized interlayer spaces were found to be higher than NG electrode as 105, 130, 122 mg/g for MG, and 99, 102, 90 mg/g for NG. A pseudo-second-order model was found to describe the kinetics of diffusion-controlled intercalation. These findings are valuable for developing selective electrosorption water treatment systems.

Intensifying Electrochemical Activity of Ti3C2Tx MXene via Customized Interlayer Structure and Surface Chemistry.

MXene, a new intercalation pseudocapacitive electrode material, possesses a high theoretical capacitance for supercapacitor application. However, limited accessible interlayer space and active sites are major challenges to achieve this high capacitance in practical application. In order to stimulate the electrochemical activity of MXene to a greater extent, herein, a method of hydrothermal treatment in NaOH solution with reducing reagent-citric acid is first proposed. After this treatment, the gravimetric capacitance of MXene exhibits a significant enhancement, about 250% of the original value, reaching 543 F g-1 at 2 mV s-1. This improved electrochemical performance is attributed to the tailoring of an interlayer structure and surface chemistry state. An expanded and homogenized interlayer space is created, which provides enough space for electrolyte ions storage. The -F terminations are replaced with O-containing groups, which enhances the hydrophilicity, facilitating the electrolyte's accessibility to MXene's surface, and makes MXene show stronger adsorption for electrolyte ion-H+, providing sufficient electrochemical active sites. The change in terminations further leads to the increase in Ti valence, which becomes more prone to reduction. This work establishes full knowledge of the rational MXene design for electrochemical energy storage applications.

Topochemically prepared tungsten disulfide nanostructures as a novel pseudocapacitive electrode for high performance supercapacitor

The topochemical preparation of nanostructured materials (NMs) has received significant attention in recent years due to the exceptional electrochemical properties exhibited by the resulting NMs. This work focuses on the preparation of two-dimensional tungsten di-sulfide (WS2) nanostructures through the topochemical conversion of tungsten trioxide (WO3) nanostructures and also evaluates their potential applications as electrode materials for supercapacitors (SCs). The X-ray diffraction and photoelectron studies conducted in this research reveal the conversion of hexagonal WO3 into hexagonal WS2 nanosheets, accompanied by changes in oxidation states. The FE-SEM and HR-TEM studies confirm the formation of WS2 in the sheet-like morphologies with lateral dimensions of 100 × 100 nm. The electrochemical investigation, using techniques such as CV, galvanostatic CD, and EIS, confirmed the presence of intercalation pseudocapacitance in the WS2 electrode, with a higher electrode-specific-capacitance (260 F g−1) than that of WO3 electrode. The WS2 symmetric SC delivered high device capacitance (59.17 F g−1), energy density (8.21 Wh kg−1) and power density (3,750 W kg−1) with better cyclic stability over 5000 cycles. These experimental findings show that the topochemically synthesized WS2as novel supercapacitor electrodes might be useful for the advancement of future-generation energy storage devices.

MXene/biomass/chitosan carbon aerogel (MBC) with shared cathode and anode for the construction of high-efficiency asymmetric supercapacitor

Despite the rapid development of biomass-based carbon aerogels research and specific outcomes have been accomplished, the preparation process requires to be developed further compared with other porous media such as activated carbon and graphene, and there are still many obstacles to overcome before reaching industrial production and practical applications since the competitiveness in terms of mechanical strength, adsorption capacity, and structural stability is weaker. Via using electro-static self-assembly between the negatively charged MXene nanosheets and the positively charged radish flakes infiltrated with salt solution, a strategy is proposed for the in-situ preparation of flexible MXene/biomass/chitosan aerogel (MBC) pseudo-capacitive electrode by hydrothermal methods. The electrode was drived according to the principle of concentration difference permeation (CDP) between MXene nanosheets and radish cells. Under both driving forces, the MXene nanosheets are embedded inside the radish cells. Importantly, the MBC pseudocapacitive electrode doping 6% (MBC-6) by lyophilization annealing exhibits a volumetric specific capacitance of 1801.4 mF/cm3 at a scan rate of 2 mV/s. In addition, the assembled binder-free asymmetrical supercapacitor exhibits an ultra-high volume energy density of 33.4 Wh/L, a capacitance retention rate of 82% and a long cycle life of 50,000 times at a high current density of 10 mA/cm3. A plausible approach for creating energy storage devices with a high energy density and voltage window is presented in this study.

Co-precipitation synthesis of pseudocapacitive λ-MnO2 for 2D MXene (Ti3C2Tx) based asymmetric flexible supercapacitor

The rapid growth of wearable/portable electronics imposes a development of flexible, lightweight and highly efficient energy storage devices. In this work, we have synthesized λ-MnO2 nanoplates through one step co-precipitation method and used for flexible asymmetric supercapacitor (SC). The structural, morphological and electrochemical properties of synthesized λ-MnO2 were systematically investigated. The optical and electronic properties of λ-MnO2 were studied using UV–vis spectroscopy and density functional theory (DFT) calculations. The pseudocapacitive λ-MnO2 nanoplates-like electrode showed a maximum specific capacitance of 288.5 F g−1 at the scan rate of 5 mV s−1. To check the practicability, symmetric (λ-MnO2//λ-MnO2) as well as asymmetric (λ-MnO2//AC and λ-MnO2//Ti3C2Tx MXene) SCs were fabricated and their performances were compared. The asymmetric λ-MnO2//Ti3C2Tx MXene SC demonstrated a maximum energy density of 15.5 Wh kg−1 at the power density 1100 W kg−1 along with 86.3 % of capacitive retention after 5000 cycles. Besides, to confirm the suitability of these electrodes for flexible energy storage, a flexible λ-MnO2//Ti3C2Tx asymmetric SC was fabricated using PVA: Na2SO4 gel polymer electrolyte that operated in the potential window of 2 V and supplies high areal energy density of 39.9 μWh cm−2 at a power density of 8586 μW cm−2. Therefore, the λ-MnO2 prepared with a simple and scalable co-precipitation method may play a promising role in flexible energy storage.

Flexible ultrathin Nitrogen-Doped carbon mediates the surface charge redistribution of a hierarchical tin disulfide nanoflake electrode for efficient capacitive deionization

Constructing pseudocapacitive electrodes with high specific capacities is indispensable for increasing the large-scale application of capacitive deionization (CDI). However, the insufficient CDI rate and cycling performance of pseudocapacitive-based electrodes have led to a decline in their use due to the corresponding volumetric expansion and contraction that occurs during long-term CDI processes. Herein, hierarchical porous SnS2 nanoflakes are encapsulated inside an N-doped carbon (NC) matrix to achieve efficient CDI. Benefiting from the synergistic properties of the pseudocapacitive SnS2 nanoflakes and few-layered N-doped carbon, the heterogeneous interface simultaneously provides more available vigorous sites and demonstrates rapid charge-transfer kinetics, resulting in a superior desalination capability (49.86 mg g−1 at 1.2 V), rapid desalination rate (1.66 mg g−1 min−1) and better cyclic stability. Computational research reveals a work function-induced surface charge redistribution of the SnS2@NC heterojunction, which can lead to an auspicious surface electronic structure that reduces the adsorption energy to improve the diffusion kinetics toward sodium adsorption. This work contributes to providing a thoughtful understanding of the interface engineering between transition metal dichalcogenides and NC to construct high-performance CDI electrode materials for further industrialization.

Assembly and pseudocapacitive electrode materials application of octamolybdates based coordination polymers

AbstractA new octamolybdates based Cu‐organic polymer, [Cu2(mbix)2]2[Mo8O26] (mbix=1,3‐bis(imidazol‐1‐ylmethyl) benzene), abbreviated as Cu‐Mo8, was hydrothermally synthesized and characterized by routine method. Single‐crystal X‐ray diffraction analysis shows that {Mo8} as template and linker induce and promote the formation and connection of quadcore planetary loop (Cu4mbix4) to form the 2D planetary plane, then are stacked by van der Waals forces to stabilize the whole structure. Electrochemical results show that compound Cu‐Mo8 as electrode materials for supercapacitors exhibits the better supercapacitor performance of ca. 592.2 F g−1 at 1 A g−1, along with great cycling stability, which enriches POMs chemistry in the supercapacitor field.

Preparation of sustainable and binder-free electrode materials for high energy asymmetric supercapacitor applications: A cleaner alternative

Herein, we demonstrate a pioneering method for repurposing one of the most abundant and noxious weeds (Parthenium hysterophorus or PH) derived ultrahigh surface area carbon as capacitive electrode and design high performance asymmetric supercapacitor with leveraging ternary metal oxides (TMO) (Ni–Co–Mn–O or TMO-1 and Ni–Co–Zn–O or TMO-2) as binder-free pseudocapacitive positive electrodes to improve the performance and efficiency of supercapacitors. Furthermore, the ternary metal oxides (TMO-1 and TMO-2) were synthesized using a one-pot hydrothermal method, followed by annealing. In a three-electrode configuration, both TMO-1 and TMO-2 exhibited remarkable capacitances. At a current density of 0.5 A/g, a total stored charge of 557.23 C/g and 628.22 C/g was obtained for the TMO-1 and TMO-2, respectively. The asymmetric construction using PH-900-K as the negative electrode and TMO-1 or TMO-2 as the positive electrode demonstrated a maximum energy density of 49.29 Wh/kg for the TMO-1//PH-900-K configuration. While the TMO-2//PH-900-K configuration exhibited a maximum energy density of 70.86 Wh/kg.

Investigations of flexible pseudocapacitive electrodes consisting of ternary V2O5/PEDOT/rGO hybrids in Li-ion containing aqueous and organic electrolytes

Investigations of flexible pseudocapacitive electrodes consisting of ternary V2O5/PEDOT/rGO hybrids in Li-ion containing aqueous and organic electrolytes

Fabrication of High-Performance Asymmetric Supercapacitors Using Rice Husk-Activated Carbon and MnFe2O4 Nanostructures

To meet the growing demand for efficient and sustainable power sources, it is crucial to develop high-performance energy storage systems. Additionally, they should be cost-effective and able to operate without any detrimental environmental side effects. In this study, rice husk-activated carbon (RHAC), which is known for its abundance, low cost, and excellent electrochemical performance, was combined with MnFe2O4 nanostructures to improve the overall capacitance of asymmetric supercapacitors (ASCs) and their energy density. A series of activation and carbonization steps are involved in the fabrication process for RHAC from rice husk. Furthermore, the BET surface area for RHAC was determined to be 980 m2 g−1 and superior porosities (average pore diameter of 7.2 nm) provide abundant active sites for charge storage. Additionally, MnFe2O4 nanostructures were effective pseudocapacitive electrode materials due to their combined Faradic and non-Faradic capacitances. In order to assess the electrochemical performance of ASCs extensively, several characterization techniques were employed, including galvanostatic charge –discharge, cyclic voltammetry, and electrochemical impedance spectroscopy. Comparatively, the ASC demonstrated a maximum specific capacitance of ~420 F/g at a current density of 0.5 A/g. The as-fabricated ASC possesses remarkable electrochemical characteristics, including high specific capacitance, superior rate capability, and long-term cycle stability. The developed asymmetric configuration retained 98% of its capacitance even after 12,000 cycles performed at a current density of 6A/g, demonstrating its stability and reliability for supercapacitors. The present study demonstrates the potential of synergistic combinations of RHAC and MnFe2O4 nanostructures in improving supercapacitor performance, as well as providing a sustainable method of using agricultural waste for energy storage.

Revealing High‐Rate and High Volumetric Pseudo‐Intercalation Charge Storage from Boron‐Vacancy Doped MXenes

AbstractThe design of pseudocapacitive electrodes that exhibit high‐rate and high volumetric capacitances is a big challenge, since it requires subtle modulation of ion‐intercalation structures that are able to achieve high electrochemical activity, fast ion transport, and facilitated electron transfer, simultaneously. Herein, controllable and selective etching of B atoms from B‐doped Ti3AlC2 precursors is reported, which generates boron‐vacancy doped MXene (B‐V‐MXene) nanosheets with finely‐regulated, ion‐intercalation structures. Electrochemical studies and density‐functional‐theory calculations demonstrate that Ti around vacancies possess higher surface‐redox activity with protons than those on pristine MXenes for the improvement of capacitances. In addition, interlayer spacing can be optimized on B‐V‐MXenes in promoting proton intercalation. More importantly, the dopant B atoms can increase the electron density on Ti, facilitating the adsorption of the intercalated protons; and further, B 2p‐Ti 3d hybridized band sits closer to the Fermi energy than that of C 2p bands, which bridges the energy gap for electron transfer in the pseudo‐capacitive reaction. With synergy of all these effects, the novel B‐V‐MXene compact electrodes can deliver the previously unmatched high volumetric capacitances of 807 F cm−3 at 1,000 mV s−1 and 1,815 F cm−3 at 5 mV s−1, with excellent cycle stability over 10,000 cycles.

Riboflavin-functionalized activated carbon delivering high energy storage performance and electrochemical stability assisted by potential control

Pseudocapacitive materials are used to increase the energy density of supercapacitors, but their rate performance and cycling stability are frequently unsatisfactory. Herein, we report a riboflavin-functionalized activated carbon (AC/VB2) as a negative electrode with high specific capacitance (419.1 F g−1) and outstanding rate performance. The potent combination of VB2 and AC renders VB2 insoluble in alkaline liquids and fully exploits its redox characteristics. VB2 contributes additional redox reactions to AC and its reaction plateau is from −0.65 to −0.9 V (vs. Hg/HgO), favoring the storage of large amounts of energy. Based on the detailed analysis of the surface state of the material during the reaction, a strategy to improve cycling stability by controlling the charge/discharge potential window is proposed, which can effectively inhibit the desorption and overreaction of VB2, thus greatly enhancing cycling stability. The electrode can be operated stably for 100,000 cycles without any decline at high current densities. An AC/VB2(–)||LDH(+, Co-doped Ni(OH)2) device delivered a high energy density of 58.6 Wh kg−1 at a power density of 686 W kg−1 and a high power density of 27,410 W kg−1 at an energy density of 13.2 Wh kg−1. This work offers a practical manual for making high–energy pseudocapacitive negative electrodes and enhancing their cycling stability.

Understanding the Degradation Mechanisms of Conducting Polymer Supercapacitors.

Conducting polymers like polyaniline (PANI) are promising pseudocapacitive electrode materials, yet experience instability in cycling performance. Since polymers often degrade into oligomers, short chain length anilines have been developed to improve the cycling stability of PANI-based supercapacitors. However, the capacitance degradation mechanisms of aniline oligomer-based materials have not been systematically investigated and are little understood. Herein, two composite electrodes based on aniline trimers (AT) and carbon nanotubes (CNTs) are studied as model systems and evaluated at both pre-cycling and post-cycling states through physicochemical and electrochemical characterizations. The favorable effect of covalent bonding between AT and CNTs is confirmed to enhance cycling stability by preventing the detachment of aniline trimer and preserving the electrode microstructure throughout the charge/discharge cycling process. In addition, higher porosity has a positive effect on electron/ion transfer and the adaptation to volumetric changes, resulting in higher conductivity and extended cycle life. This work provides insights into the mechanism of enhanced cycling stability of aniline oligomers, indicating design features for aniline oligomer electrode materials to improve their electrochemical performance.

Synthesis of Low-Crystalline MnO2/MXene Composites for Capacitive Deionization with Efficient Desalination Capacity

MXene has drawn widespread attention as a potential material for electrode use in capacitive deionization (CDI). However, the applications of MXene are limited by its property of low electrical capacity. Herein, a MnO2/MXene composite was firstly evaluated in a capacitive deionization system, in which the MnO2 acts as intercalation-type pseudocapacitive electrodes to enhance the electrical capacity, and MXene provides an electron conduction highway network that improves the charge transfer of the MnO2. The result showed that the low-crystallinity MnO2 with irregular particles was well-distributed on the surface of the MXene. The desalination capacity of 30.5 mg·g−1 is achieved at a voltage window of 1.2 V, which was higher than that of the reported pure MXene and MnO2. The electrical double-layer (EDL) capacitive and the diffusion-controlled processes are the main charge storage mechanisms, and the EDL contribution provides 50.3% to the total capacitance. This result suggests a promising direction for further applying a MnO2/MXene composite in CDI.

Fabrication of Assembled FeS2 Nanosheet and Application for High-Performance Supercapacitor Electrodes.

To overcome the low-energy-density limitation of supercapacitors, we aimed to achieve a material with a high specific capacitance by manipulating the nanostructure of FeS2, which comprises the most abundant and affordable elements. In this study, nanosheet-assembled FeS2 (NSA-FeS2) was fabricated using a novel method. Sub-micron droplets of sulfur particles stabilized with polyvinylpyrrolidone were formed in silicone oil medium, and Fe(CO)5 was absorbed and reacted on the surface to form core-shell particles, ES/[Fe], with a sulfur core and an iron-containing outer shell. The high temperature treatment of ES/[Fe] produced NSA-FeS2, in which pyrite FeS2 nanosheets grew and were partially interconnected. In a three-electrode system, the as-prepared NSA-FeS2 and NSA-FeS2/polyaniline (PANI) composites exhibited specific capacitances of 763 and 976 Fg-1, respectively, at a current density of 0.5 Ag-1, with corresponding capacitance retentions of 93 and 96% after 3000 charge-discharge cycles. The capacitance retention of the NSA-FeS2/PANI composites was 49% when the current density was increased from 0.5 to 5 Ag-1. Notably, the obtained specific capacitances exhibited the highest values in pure FeS2 and FeS2-based composites, indicating the significant potential for the utilization of iron sulfide in pseudocapacitive electrode materials.