Subsequent Thermal Annealing Research Articles

Flexible electrospun iron compounds/carbon fibers: Phase transformation and electrochemical properties

Flexible electrodes are currently widely studied for applications in energy storage, due to their elasticity and lightweight. Here we describe the fabrication of flexible electrodes obtained by embedding different iron-compound nanoparticles in carbon fibers. The composites are prepared by electrospinning followed by subsequent thermal annealing. We elucidate the phase evolution process of iron compounds in the carbon fibers, i.e., Fe3O4, Fe3O4/Fe3C and Fe3C being produced in the carbon fibers at 450 °C, 620 °C and 800 °C, respectively. In addition, we investigate the electrochemical performance of Fe3O4/carbon fibers (Fe3O4/CF), Fe3O4/Fe3C/carbon fibers (Fe3O4/Fe3C/CF) and Fe3C/carbon fibers (Fe3C/CF). When used as anode materials for lithium-ion batteries (LIBs), Fe3O4/CF, Fe3O4/Fe3C/CF and Fe3C/CF electrodes exhibit discharge capacities of 255.3, 478.1 and 169.2 mAh g−1 after 650 cycles at 1 A g−1, corresponding to 50.2%, 99.3% and 39.3% of the capacities after the second cycle, respectively. Compared with Fe3O4/CF and Fe3C/CF electrodes, the Fe3O4/Fe3C/CF electrode delivers higher capacity and better cycling stability. The excellent electrochemical performance of Fe3O4/Fe3C/CF is attributed to the high theoretical specific capacity of Fe3O4 and the excellent catalytic activity of Fe3C. Amorphous carbon fibers can buffer large volume changes during the lithium-ion insertion/extraction process. Finally, we evaluate the lithium storage properties of Fe3O4/CF and Fe3C/CF. Our work provides insights on the phase evolution and lithium storage mechanisms for iron-compound nanoparticles embedded in carbon fibers.

Direct writing of divacancy centers in silicon carbide by femtosecond laser irradiation and subsequent thermal annealing

Divacancy (VSiVC) centers in silicon carbide (SiC) have potential applications in quantum communication and sensing due to their attractive optical and spin properties. To realize many of these divacancy-based quantum applications, it is vital that they are created in prescribed locations with high accuracy. Here, we describe the production of arrays of divacancy centers in 4H polytype SiC (4H-SiC) by femtosecond laser irradiation and subsequent thermal annealing. We optically characterized these divacancy centers by photoluminescence (PL) confocal mapping using a custom-built confocal microscope. The created divacancy centers show a bright stable emission that depends on the pulse energy of the femtosecond laser. PL spectra of the divacancy centers were collected using micro-Raman spectroscopy at the low temperature of 4.2 K and room temperature. The effect of thermal annealing was studied at various temperatures from 500 °C to 1000 °C and showed that the maximum divacancy center PL intensity was achieved at 800 °C. These and the aforementioned measurements show that the femtosecond laser writing method enables divacancy centers to be accurately positioned in 4H-SiC.

Phase transformations in composite films of the system Se-Cu, obtained using explosive crystallization and thermal annealing

The results of experimental studies of the phase transformation in composite films of the Se-Cu system obtained in vacuum as a result of the sequential thermal deposition of selenium and copper on a glass substrate are presented. At a fixed thickness of the selenium layer (45 nm), the effect of the thickness of the copper layer (40-115 nm) on the phase composition of the synthesized films formed as a result of explosive crystallization occurring during the interaction of hot copper clusters with low-melting selenium was studied. It was found that the subsequent thermal annealing of the synthesized films is accompanied by a significant change in their phase composition and optical transmission spectra. Keywords: phase transformations, composite films of the Se-Cu system, explosive crystallization, thermal annealing, optical properties.

Фазовые превращения в композитных пленках системы Se-Cu, полученных взрывной кристаллизацией и термическим отжигом

The results of experimental studies of the phase transformation in composite films of the Se-Cu system obtained in vacuum as a result of the sequential thermal deposition of selenium and copper on a glass substrate are presented. At a fixed thickness of the selenium layer (45 nm), the effect of the thickness of the copper layer (40 - 115 nm) on the phase composition of the synthesized films formed as a result of explosive crystallization occurring during the interaction of hot copper clusters with low-melting selenium was studied. It was found that the subsequent thermal annealing of the synthesized films is accompanied by a significant change in their phase composition and optical transmission spectra.

Uniform Li deposition assisted by dual carbon-confined CoO-NiO nanoparticles for dendrite-free Li metal anode

Li metal has been considered as one of the most promising anodes for next-generation rechargeable batteries. However, the growth of Li dendrites and the huge volume change limit its practical application. Herein, we have developed a CoO-NiO nanoparticles embedded in carbon polyhedral matrix (CPM) and reduced graphene oxide (rGO) sheets electrode with lithiophilic properties for a Li metal anode via a simple hydrothermal method followed by freeze-drying process and subsequent thermal annealing. The homogeneously distributed CoO-NiO nanoparticles serve as nucleation sites to effectively reduce the overpotential for Li nucleation. Moreover, CPM and rGO sheets lead to the double carbon-confined hierarchical composites with strong coupling effect, providing sufficient void space to withstand the volume expansion during Li deposition. As a result, the as-obtained composite delivers enhanced Columbic efficiency (~98.7% after 300 cycles) along with negligible nucleation overpotential. The symmetric cell can operate stably over 800 h at 1 mA cm−2 and even 120 h under 3 mA cm−2 with a fixed capacity of 1 mAh cm−2. Moreover, remarkable rate capability and long-term cycling stability (92.6% capacity retention after 300 cycles at 1 C) are obtained in full cells paired with a LiFePO4 cathode.

Ultrahigh nitrogen-vacancy center concentration in diamond

High concentration of negatively charged nitrogen-vacancy (NV−) centers was created in diamond single crystals containing approximately 100 ppm nitrogen using electron and neutron irradiation and subsequent thermal annealing in a stepwise manner. Continuous-wave electron paramagnetic resonance (EPR) was used to determine the transformation efficiency from isolated N atoms to NV− centers in each production step and its highest value was as high as 17.5%. Charged vacancies are formed after electron irradiation as shown by EPR spectra, but the thermal annealing restores the sample quality as the defect signal diminishes. We find that about 25% of the vacancies form NVs during the annealing process. The large NV− concentration allows observing orientation dependent spin-relaxation times and also determining the hyperfine and quadrupole coupling constants with high precision using electron spin echo (ESE) and electron-nuclear double resonance (ENDOR). We also observed the EPR signal associated with the so-called W16 centers, whose spectroscopic properties might imply a nitrogen dimer-vacancy center for its origin.

Synthesis of porous silicon, nickel and carbon layers by vapor phase dealloying

Porous thin films have various application fields, e.g., for energy conversion in fuel cells , energy storage in lithium ion batteries or supercapacitors as well for catalysis, filtration and sensing. We synthesized porous thin films by co-evaporating a low-vapor-pressure material (e.g., Si, Ni or C) together with zinc and depositing a compact layer of resulting composite. High-rate deposition process up to 100 nm/s was realized by electron beam physical vapor deposition (EB-PVD) of the materials from two graphite crucibles with a fast deflected electron beam in high vacuum. Immediately after deposition, the coated substrates were heated up in vacuum to a temperature above 500 °C and thereby zinc is removed selectively. Due to its higher vapor pressure against that of remaining component, zinc is expelled from the layer and vacancies are generated by so called vapor phase dealloying (VPD). We investigated the feasibility of VPD process for the elements silicon, nickel and carbon. The elemental composition and the morphology of the layers prior and after thermal annealing were analyzed by scanning electron microscopy, by energy-dispersive X-ray spectrometry and by X-ray diffraction. • High-rate deposition of compact multiphase layers by co-evaporation of Zn together with Si/Ni/C • Layer morphology can be adjusted by deposition parameters. • Subsequent thermal annealing in vacuum for expelling zinc and generating pores • Porous structure can be adjusted by layer morphology and annealing parameters.

Sub-micro photocatalytic TiO2 particles for a water depollution: Comparable removal efficiency to commercial P25 and easy separation via a simple sedimentation

The sub-micrometer sized TiO2 particles (100–200 nm) were synthesized by a sol-gel and subsequent thermal annealing. The particle size, surface area, pore structure, and crystallinity were varied upon the annealing temperatures (450, 550, 650 °C). The photocatalytic activities of three TiO2 particles annealed at various temperatures (450-, 550-, and 650-TiO2) were examined by performing photocatalytic depollution of three organic model pollutants (methylene blue, methyl orange, and phenol) from aqueous solutions under the UV light irradiation. Among three samples, 550-TiO2 (~200 nm) exhibited the highest photocatalytic activity towards the removals of all three model pollutants. Photocatalytic activity of the 550-TiO2 was compared with a commercial TiO2 (P25, Evonik) at various conditions of loading amounts of particles dispersed in MB solution. Light scattering by dispersed particles at high sample loading conditions was less pronounced in the case of 550-TiO2. Therefore, the sub-micro 550-TiO2 particles can exhibit comparable activity to P25 at high sample loading conditions (2–4 g/L). In addition, the bigger size of 550-TiO2 made it possible to separate them via a simple sedimentation process, showing a potential of sub-micro TiO2 particles as an efficient photocatalysts for water depollution.

Influence of precursor solvent and confined environment on the polymorphic transition in electrospun Poly(l-lactide) fibers

The present study examined the thermal and crystallization properties of poly(l-lactide) (PLLA) chains confined in electrospun fibers. The heat of fusion and crystallite sizes decreased with a decrease in fiber diameter because of the confinement effect. The crystal structure of PLLA fibers exhibited α′ and α forms, which comprised loosely and closely packed chains, respectively. As-electrospun PLLA fibers exhibited an unstable α′ phase because of the rapid solidification of polymer chains during electrospinning. Subsequent thermal annealing at a temperature higher than 140 °C induced a polymorphic transition from the α′ phase to the stable α phase. This finding differed from that observed in bulk PLLA, which exhibited α crystals regardless of annealing temperature. Furthermore, the polymorphic transition of α′ crystals to α crystals in fibers fabricated with 95:5 chloroform/trifluoroethanol solvent occurred with lower annealing temperatures or shorter annealing times relative to those fabricated with 60:40 chloroform/trifluoroethanol solvent. This behavior was attributed to the low entanglement content in the PLLA chains in fibers fabricated with 95:5 chloroform/trifluoroethanol solvent; the low entanglement content increased chain mobility, thereby accelerating polymorphic transition.

Study of color centers in radiation-modified diamonds

We report on the optical properties of He-related color centers created by He-ion implantation and subsequent thermal annealing in natural diamonds, including the temperature (300–700 K) and excitation power (1–1800 kW/cm2)-dependent photoluminescence (PL) measurements. The prospects for the use of He-implanted diamonds for temperature sensing are discussed. The effect of fast neutron irradiation on the optical properties of Si-V color centers in CVD diamonds were also examined.

Study of phase transformation dynamics, structural and optical properties of ferroelectric SrTiO3 ceramics

In this work, ferroelectrics of the SrTiO3 type were obtained using solid-phase synthesis method and subsequent thermal annealing. Using the X-ray diffraction method, the dynamics of phase transformations of the TiO2/Sr2Ti6O13/Sr3Ti2O7 → TiO2/Sr2Ti6O13/Sr3Ti2O7/SrTiO3 → SrTiO3/Ti3O5 type was established. According to the data obtained, it was found that thermal annealing in the range of 200–1100 °C allows obtaining both complex multiphase ceramics and SrTiO3 ceramics with a perovskite structure. As a result of determination of the optical properties, it was found that an increase in the structural ordering degree and the formation of a stable SrTiO3 phase, a broad induced absorption band appears in the region of 3.0–3.3 eV, with a maximum of 3.14 eV. During the determination of ferroelectric characteristics, it was found that the formation of a stable SrTiO3 phase in ceramics structure leads to a sharp increase in dielectric constant and a decrease in Curie-Weiss temperature from 125-130 °C to 105–110 °C.

Photodeposited Polyamorphous CuOx Hole-Transport Layers in Organic Photovoltaics

Hole-selective charge-transport layers are an important part of modern thin-film electronics, serving to direct electron flow and prevent leakage current. Crystalline metal-oxide hole-transport layers (HTLs) such as NiO and CuOx exhibit high performance and stability. However, they are traditionally not amenable to scalable and sustainable solution-processing techniques. Conversely, amorphous metal oxides are much more readily prepared by low-temperature solution processing methods but often lack the charge-transport properties of crystalline semiconductors. Herein, we report the fabrication of amorphous a-CuOx thin films from commercially available starting materials using a simple UV-based thin-film deposition method. Subsequent thermal annealing of the a-CuOx induces an amorphous-to-amorphous phase transition, resulting in p-type semiconducting behavior. The resulting thin films were used as HTLs in organic photovoltaic devices with power conversion efficiencies comparable to those fabricated with PEDOT:PSS.

Microstructure of a new ODS Cu–0.7wt-%Cr–0.11wt-%Zr material produced by a novel powder metallurgical method

ABSTRACT A new oxide dispersion strengthened Cu–0.7wt-%Cr–0.11wt-%Zr material was processed via mechanical alloying (MA) and hot isostatic pressing (HIP). A fine dispersion of yttria particles (Y2O3) was incorporated to the Cu matrix via the addition of yttrium (III) acetate tetrahydrate (C6H9O6Y·4H2O) powder (Y3ATH), which decomposed during thermomechanical processing and subsequent thermal annealing. The microstructure after consolidation by HIP revealed the coexistence of zones with a low and high density of precipitates/particles, LDPZ and HDPZ, respectively. The HDPZ were characterized by fine grains with an average size of ∼300 nm and fine Y–O rich particles (∼40 nm) and Cr rich coarse particles (∼215 nm), homogenously distributed in the Cu matrix. However, the LDPZ contained coarse grains containing 60°/〈111〉 (Σ3) twins’ boundaries.

Tuning Defects in the MoS2/Reduced Graphene Oxide 2D Hybrid Materials for Optimizing Battery Performance

Rechargeable aqueous zinc ion batteries (AZIB) are an emerging topic in the battery research due to the high volumetric capacity of the zinc anode (5855 mAh/cm3), low cost, environmental friendliness and safety. But the development of the zinc ion batteries has been hindered by the slow insertion/extraction kinetics of the multivalent Zn2+ ions in the host structure mainly due to the larger ionic radii of the hydrated zinc ion (~4.60 Å) and stronger electrostatic interaction of the divalent metal cation with the host structure that monovalent Li+ ions. These factors make the existing Li-ion battery (LIB) cathode materials unfit for the intercalation/deintercalation of Zn2+ ion. Transition metal dichalcogenides like Molybdenum disulfide (MoS2) have caught the attention as a host for both monovalent and divalent ion storage due to their two-dimensional layered structure and high theoretical specific capacity for Li-ion storage (670 mAh g-1). The MoS2 structure consists of a two-dimensional (2D) layered structure with a layer of molybdenum atoms covalently bonded between two layers of sulfur atoms. The triatomic layers of MoS2 are linked by weak van der Waals forces similar to graphene, which can effectively accommodate the volume expansion to facilitate reversible intercalation/deintercalation of metal ions. Despite the advantages, MoS2 suffers from low electrical conductivity and pulverization of the structure after few intercalation/deintercalation cycles which causes rapid capacity fading. These problems can be mitigated by modifying the structure through (1) increasing the interlayer spacing (2) introducing active defects in the MoS2 structure to enhance Zn2+ ion adsorption, and (3) forming a hybrid structure with carbonaceous materials to improve the electrical conductivity, mechanical strength, and structural stability of MoS2 layers. Among which, defect engineering has been recently explored as an effective approach to enhancing the specific capacity of MoS2 towards the storage of monovalent and divalent ions including Li+, Na+, Zn2+ ions.In this work, the preparation of a set of hybrid materials consisting of Molybdenum disulfide (MoS2) nanopatches on reduced graphene oxide (rGO) nanosheets with controllable defect density and its impact on the storage of Li+ and Zn2+ ions will be presented and discussed. The MoS2/rGO hybrid materials are synthesized by applying the novel microwave specific heating of graphene oxide and molecular molybdenum precursors followed by a thermal annealing in 3% H2 and 97% Ar. The microwave process converts graphene oxide to ordered rGO nanosheets that are sandwiched between uniform thin layers of amorphous Molybdenum trisulfide (MoS3). The subsequent thermal annealing converts the intermediate layers into MoS2 nanopatches with 2D layered structures whose defect density is tunable by controlling the annealing temperature at 250°C (MoS2/rGO-250), 325°C (MoS2/rGO-325) and 600°C (MoS2/rGO-600), respectively. The defect-free MoS2/rGO-600 material performs well as an anode for Li+ ion intercalation with a high specific capacity of 519 mAh gMoSx -1 (~3.1 Li+ ions per MoS2). Other samples show comparable results, indicating the insignificant effect by the defects. In contrast, the Zn-ion storage properties strongly depend on the defects in the MoS2 adlayer. The highly defective MoS2/rGO-250 hybrid prepared by annealing at 250°C shows the highest initial Zn-ion storage capacity of ~300 mAh gMoSx -1 (~1.8 Zn2+ per MoS2) and close to 100% coulombic efficiency after 3 cycles, which is dominated by pseudocapacitive surface reactions at the edges or defects in the MoS2 nanopatches. The fast fading in initial cycles can be mitigated by applying higher charge/discharge currents or extended cycles. These results provide critical insights to improve metal ion storage properties by defect engineering of the MoS2 in the MoS2/rGO hybrid materials.

Optical and structural analysis of the charge transfer of Ce3++ e- →Ce4+ ion in the cerium oxide (CeO2)

Cerium oxide (CeO2(s)) is prepared by Chemical Bath Deposition (green chemistry) at ~23.0 °C and subsequent thermal annealing treated (TAT) at ~1000 °C. This manuscript continues with previous research examining the spectra situated at UV–Vis-region to investigate the 4fds→4fds electronic intra-transitions of CeO2. The in-plane and out-of-plane strains are located at εc ~1.1 × 10−3, ~− 3.0 × 10−4 and εa ~− 1.2 ×10−3, ~4.0 × 10−4, dislocation density were ~3.87×1014 lines/m2 and ~4.31×1016 lines/m2 for the As-grown and the CeO2-TAT nanocrystals, respectively. As a first approximation, we consider that the inorganic nanomaterial has intrinsic native crystalline defects. It is supposed that the strain is caused by native point defects (vacancies and interstices). According to the d(DO)/dE equation, absorption band associated at Ce3+ + e-→Ce4+, assigned to 5d→4f electronic intra-transitions (~2.48 eV) at Vis-region. Deconvolution of the observed absorbance spectra shows that the emissions bands originating from the F0 centers prevail over those of F+ centers of V0. For CeO2-TAT nanocrystals, the band gap energy was at ~289 nm (~4.29 eV), whereas the As-grown was found at ~304 nm (~4.07 eV). In As-grown nanocrystals, three optical signals can be seen ~277 nm (~4.47 eV), ~330 nm (~3.75 eV), and ~393 nm (~3.15 eV). The absorption band at ~3.15 eV is relatively narrow and assigned to Ce3+ + e-→Ce4+ charge transfer. Calculations of Urbach energy were Eu~1.54 eV for As-grown and Eu~0.52 eV for CeO2-TAT nanocrystals, respectively.

Si-based light emitters synthesized with Ge+ ion bombardment

The photoluminescence (PL) of Ge/Si nanostructures synthesized by using Ge+ ion bombardment is studied. The structure represents a Si substrate with GeSi nanoclusters created by 80 keV Ge implantation with a fluence of ∼1015 ions/cm2 and subsequent thermal annealing. The PL measurements confirm the advantage of Ge/Si structures synthesized using Ge+ ion bombardment over the usual epitaxial structures with GeSi quantum dots. The presence of defects produced by Ge implantation results in pronounced PL at telecom wavelengths up to room temperature. The results provide a basis for creating efficient light emitters compatible with the existing Si technology.

Radiation defects in NaCl matrix with reduced lattice symmetry caused by light cation doping and elastic uniaxial deformation

The processes of radiation defect creation and radiative relaxation of electronic excitations under applied local or/and uniaxial elastic deformation have been studied in NaCl crystals by means of optical absorption, luminescence and thermoactivation spectroscopy methods. In NaCl:Li at 80 K, X-ray-induced absorption bands peaked around 3.35 and 4.6 eV have been detected and ascribed to interstitial halide atoms located nearby Li impurity cations, HA(Li) centres. Subsequent thermal annealing of HA(Li) centres leads to the formation of polyhalide centres responsible for the absorption band at 5.35 eV. In an X-irradiated and stressed NaCl:Li crystal (degree of uniaxial elastic deformation of ε = 0.9%), the peak of thermally stimulated luminescence at ~115 K is composed of the ~2.7-eV emission appearing, in our opinion, due to the recombination of the electron, thermally released from an F′ centre, with a hole-type HA(Li) centre. The applied uniaxial elastic stress facilitates the self-trapping of anion excitons in regular regions of a NaCl lattice and impedes the energy transfer by mobile excitons to impurities/defects and, in turn, attenuates the Br-related luminescence peaked at 3.95 eV with respect to the π-emission of self-trapped excitons (~3.35 eV). The 3.95 eV emission has been detected in a natural NaCl crystal containing homologous Br impurity ions.

Surface morphology and mechanical properties changes induced in Ti3InC2 (M3AX2) thin nanocrystalline films by irradiation of 100 keV Ne+ ions

We report on the structure of the Ti3InC2 (M3AX2) thin nanocrystalline films (TNCFs) produced by ion beam sputtering of the Ti, In, and C targets with subsequent thermal annealing, and irradiation by 100 keV Ne+ ions with two different fluences of 1 · 1014 cm−2 and 1 · 1016 cm−2. The Ti3InC2 TNCFs were characterized by a set of microscopic techniques (AFM, STEM/EDS, and HRTEM) as well ion beam analytical methods RBS and NRA. The STEM/EDS analysis revealed that the structure and chemical composition of the Ti3InC2 TNCF remained intact after irradiation with the lower fluence of 1 · 1014 cm−2 Ne+. However, a significant morphological instability was observed after irradiation with the higher fluence of 1 · 1016 cm−2 Ne+. The simulation of the nanobeam electron diffraction (NBED) patterns by using CrystalMaker code has pointed at the existence of new ε-Ti2C0.06 (MXene) structures and separation of Indium (In) from the Ti3InC2 matrix. The analysis by nanoindentation showed that the irradiated Ti3InC2 TNCFs exhibited promising mechanical properties considering Young's modulus and hardness even for the locally disordered structure. M3AX2 TNCFs are a new type of 2D materials designed for applications in extreme environments, such as nuclear facilities with intensive radiation fields. However, the research is still in its infancy and requires further study on the synthesis of high-quality, dense, and homogeneous M3AX2 TNCFs. This work is an initial study related to the radiation resistance of Ti3InC2 TNCFs.

Vacuum‐Assisted Preparation of High‐Quality Quasi‐2D Perovskite Thin Films for Large‐Area Light‐Emitting Diodes

AbstractRecent years have witnessed marked progress in the electroluminescence efficiency of perovskite‐based light emitting diodes (PeLEDs). Nevertheless, the majority of highly efficient devices feature only several square millimeters with the perovskite emitting layers deposited by nonscalable methods, which hinders their intriguing application in large‐area lightings and displays. Here, a robust crystallization protocol is devised for the deposition of high‐quality perovskite emitting layers by blade coating. Central to this method is the deployment of a vacuum process to the freshly coated precursor film, thereby achieving controllable crystallization kinetics by decoupling precursor deposition and the subsequent thermal annealing. Accordingly, dense and uniform perovskite thin films with efficient energy funneling among the evenly distributed 2D and 3D phases are obtained. PeLED devices based on the vacuum‐processed quasi‐2D cesium lead tribromide layers achieve high external quantum efficiencies of 8.24% and 6.12% on active areas of 0.12 and 1 cm2, respectively. The scalability of the technology is further demonstrated by fabricating a 3.5 × 3.5 cm2 device with bright and uniform emitting characteristic. This work offers a viable approach for further advancing the performance of large‐area PeLEDs by scalable methods.

N‐Doped FeS2 Achieved by Thermal Annealing of Anodized Fe in Ammonia and Sulfur Atmosphere: Applications for Supercapacitors

Iron pyrite (FeS2) has attracted intense research interest for low-cost supercapacitor applications due to its improved electrical conductivity in comparison with its oxide counterpart. Herein, we demonstrate a novel strategy for the facile synthesis of N-doped FeS2 nanosphere films on iron substrate, which includes anodization of Fe and subsequent thermal annealing treatment. The rod-like ferrous oxalate films are obtained by anodization of Fe in an oxalic acid electrolyte. Then, nanosphere-like N-doped FeS2 films can be readily achieved through thermal annealing of ferrous oxalate films under ammonia (NH3) atmosphere in the presence of sulfur powder. The N-doped FeS2 electrode fabricated without the need for any binder shows superior rate capability and enhanced specific capacitance compared to the pristine FeS2. The prepared N-doped FeS2 nanosphere electrode displays a high specific capacitance of 238.2 mF cm−2 at 3 mA cm−2 over a potential range of −1.2 to 0 V and good cycling stability with a capacitance retention of 84.3% after 5000 cycles.