Umakant M. Patil

High-performance supercapacitor electrode based on a polyaniline nanofibers/3D graphene framework as an efficient charge transporter

The current paper describes chemically grown polyaniline (PANI) nanofibers on porous three dimensional graphene (PANI/3D graphene) as a supercapacitor electrode material with enhanced electrochemical performance. The chemical and structural properties of the electrode are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy with confirmation of a semi-crystalline nature. The homogeneous growth of PANI on the 3D graphene network is visualized by field emission scanning electron microscopy (FESEM) and shows a nanofibers-based morphology. The maximum specific capacitance of the PANI/3D graphene electrode is found to be ∼1024 F g−1 in 1 M H2SO4 within the potential window of −150 to 800 mV vs. Ag/AgCl at 10 mV s−1 scan rate (∼1002 F g−1 at 1 mA cm−2 discharge current density). The high surface area offered by the conducting, porous 3D graphene framework stimulates effective utilization of the deposited PANI and improves electrochemical charge transport and storage. This signifies that the 3D graphene framework is a proficient contender for high-performance capacitor electrodes in energy storage applications.

Enhanced Supercapacitive Performance of Chemically Grown Cobalt–Nickel Hydroxides on Three-Dimensional Graphene Foam Electrodes

Chemical growth of mixed cobalt-nickel hydroxides (CoxNi1-x(OH)2), decorated on graphene foam (GF) with desirable three-dimensional (3D) interconnected porous structure as electrode and its potential energy storage application is discussed. The nanostructured CoxNi1-x(OH)2 films with different Ni:Co (x) compositions on GF are prepared by using the chemical bath deposition (CBD) method. The structural studies (X-ray diffraction and X-ray photoelectron spectroscopy) of electrodes confirm crystalline nature of CoxNi1-x(OH)2/GF and crystal structure consists of Ni(OH)2 and Co(OH)2. The morphological properties reveal that nanorods of Co(OH)2 reduce in size with increases in nickel content and are converted into Ni(OH)2 nanoparticles. The electrochemical performance reveals that the Co0.66Ni0.33(OH)2/GF electrode has maximum specific capacitance of ∼1847 F g(-1) in 1 M KOH within a potential window 0 to 0.5 V vs Ag/AgCl at a discharge current density of 5 A g(-1). The superior pseudoelectrochemical properties of cobalt and nickel are combined and synergistically reinforced with high surface area offered by a conducting, porous 3D graphene framework, which stimulates effective utilization of redox characteristics and communally improves electrochemical performance with charge transport and storage.

Hierarchical MnCo-layered double hydroxides@Ni(OH)2 core–shell heterostructures as advanced electrodes for supercapacitors

Rational assembly and hetero-growth of hybrid structures consisting of multiple components with distinctive features are a promising and challenging strategy to develop materials for energy storage applications. Herein, we propose a supercapacitor electrode comprising a three-dimensional self-supported hierarchical MnCo-layered double hydroxides@Ni(OH)2 [MnCo-LDH@Ni(OH)2] core–shell heterostructure on conductive nickel foam. The resultant MnCo-LDH@Ni(OH)2 structure exhibited a high specific capacitance of 2320 F g−1 at a current density of 3 A g−1, and a capacitance of 1308 F g−1 was maintained at a high current density of 30 A g−1 with a superior long cycle lifetime. Moreover, an asymmetric supercapacitor was successfully assembled using MnCo-LDH@Ni(OH)2 as the positive electrode and activated carbon (AC) as the negative electrode. The optimized MnCo-LDH@Ni(OH)2//AC device with a voltage of 1.5 V delivered a maximum energy density of 47.9 W h kg−1 at a power density of 750.7 W kg−1. The energy density remained at 9.8 W h kg−1 at a power density of 5020.5 W kg−1 with excellent cycle stability.

Controlled electrochemical growth of Co(OH)2 flakes on 3D multilayered graphene foam for high performance supercapacitors

The present research describes successful enchase of Co(OH)2 microflakes by the potentiodynamic mode of electro-deposition (PED) on porous, light weight, conducting 3D multilayered graphene foam (MGF) and their synergistic effect on improving the supercapacitive performance. Structural and morphological analyses reveal uniform growth of Co(OH)2 microflakes with an average flake width of ∼30 nm on the MGF surface. Moreover, electrochemical capacitive measurements of the Co(OH)2/MGF electrode exhibit a high specific capacitance of ∼1030 F g−1 with ∼37 W h kg−1 energy and ∼18 kW kg−1 power density at 9.09 A g−1 current density. The superior pseudoelectrochemical properties of cobalt hydroxide are synergistically decorated with high surface area offered by a conducting, porous 3D graphene framework, which stimulates the effective utilization of redox characteristics and mutually improves electrochemical capacitive performance with charge transport and storage. This work evokes scalable electrochemical synthesis with the enhanced supercapacitive performance of the Co(OH)2/MGF electrode in energy storage devices.

Controllable sulfuration engineered NiO nanosheets with enhanced capacitance for high rate supercapacitors

NiO has been intensively studied as a promising electrode material for supercapacitors because of its high theoretical specific capacitance, well-defined redox behavior, and good chemical compatibility with nickel foam. However, it still suffers from inferior rate capability and cycling stability because of the simple component and random structural integration. Herein, we report a tunable sulfuration process of NiO nanosheets constructed on porous nickel foam for supercapacitor applications. The resulting NiO/Ni3S2 with distinct structural features exhibits an ultra-high specific capacitance of 2153 F g−1 at a current density of 1 A g−1, and the capacitance is retained at 1169 F g−1 even at a current density as high as 30 A g−1. An asymmetric supercapacitor device fabricated with NiO/Ni3S2 as the positive electrode and activated carbon as the negative electrode delivers high energy and power densities (52.9 W h kg−1 at 1.6 kW kg−1; 26.3 W h kg−1 at 6.4 kW kg−1), and good cycling stability (a capacitance retention of 92.9% over 5000 cycles).

Post-heating effects on the physical and electrochemical capacitive properties of reduced graphene oxide paper

We report combined electrochemical double-layer capacitance (EDLC) and pseudocapacitance in reduced graphene oxide (rGO) thick film like paper due to annealing temperature variations. The influence of annealing temperature (from room temperature (RT) to 1000 °C) on the structural, morphological, electrical, and electrochemical properties of rGO paper was evaluated. Upon increasing the annealing temperature, shifting of the dominant (002) X-ray diffraction (XRD) peak to a higher degree, volume expansion, and red-shifting of the G band in Raman spectra were observed. High-resolution transmission electron microscopy (HRTEM) images showed a reduction in the interlayer distance in rGO sheets from 0.369 to 0.349 nm as the annealing temperature increased from RT to 1000 °C; these results were congruent with the XRD results. According to X-ray photoelectron spectroscopy (XPS), the presence of hydroxyl, carboxyl, and other oxygen-containing groups decreased in samples annealed at higher temperatures. The attached functional groups, the electrical conductivity, and the supercapacitance of rGO papers were found to be mutually interrelated and could be tuned by varying the annealing temperature. The rGO paper annealed at 200 °C in a 1 M H2SO4 electrolyte at a scan rate of 50 mV s−1 exhibited a maximum specific capacitance of 198 F g−1.

Radio frequency based label-free detection of glucose

We investigated the frequency based mediator-free glucose sensor in the radio-frequency (RF) range. Frequency dependent power signal showed clear dependence on the glucose concentration with free enzymatic condition. Also, the passive electrical components such as the resistance, inductance, shunt conductance, and capacitance were extracted based on the transmission line model for further analysis. These various parameters proposed by the signal processing provided more effective verification for instant multi-components in-situ readings without any added supporters. Additionally the residual signal (RS), impedance (Z), and propagation constant (γ) were also calculated from measured S-parameters for glucose analysis. These parameters basically showed amplitude variation and interestingly, some parameters such as inductance and impedance showed frequency shift of resonance dip. The results support that the frequency based sensing technique including the parameter based analysis can enable effective multi-dimensional detection of glucose. Moreover, this technique showed that glucose sensing is also possible over a diabetic patients serum.

3D yolk–shell NiGa2S4 microspheres confined with nanosheets for high performance supercapacitors

Recent advances in the development of two-dimensional transition-metal chalcogenides (2D TMCs) have opened up new avenues for supercapacitor applications. However, they still suffer from limited specific capacitance and poor rate capability due to their poor interfacial properties and simple geometry. Here, we propose a facile strategy for the synthesis of yolk–shell NiGa2S4 microspheres comprising crumpled nanosheets supported on nickel foam. The robust structure not only highly facilitates the electron and charge transportation but also efficiently alleviates the volume expansion during redox reactions, contributing to excellent electrochemical behaviors in terms of specific capacitance and rate capability. Significantly, an asymmetric supercapacitor based on the prepared NiGa2S4 as the positive electrode and N,S-codoped graphene/Fe2O3 (N,S-G/Fe2O3) as the negative electrode delivers a high energy density of 43.6 W h kg−1 at a power density of 961 W kg−1 and retains an energy density of 22.2 W h kg−1 even at 15974 W kg−1. These impressive results may provide a new perspective to develop high energy and power density storage systems for practical applications.

A binder free synthesis of 1D PANI and 2D MoS2 nanostructured hybrid composite electrodes by the electrophoretic deposition (EPD) method for supercapacitor application

A facile, binder-free approach is applied, along with the electrophoretic deposition (EPD) method, to fabricate large-scale, hybrid 2D MoS2 nanosheets and 1D polyaniline (PANI) nanowires based electrodes on a conducting substrate for supercapacitor electrode material. The entire substrate surface is uniformly decorated by electrophoretically assembled MoS2 2D nanosheets and 1D nanowires of PANI, revealed by structural and morphological analysis. The electrochemical capacitive measurements of the MoS2/PANI hybrid electrode exhibit a specific capacitance of ∼485 F g−1 at a low charging–discharging current density (1 mA cm−2). The MoS2:PANI composition ratio was varied as 1:1, 1:2 and 1:3 to achieve high supercapacitive performance. The maximum supercapacitive performance (∼812 F g−1) was obtained for a 1:2 ratio of MoS2 and PANI, with high energy density (112 W h kg−1) and power density (0.6 kW kg−1). Synergistic interactions between conductive 1D PANI and 2D MoS2 nanosheets with high surface area lead to a high supercapacitive performance. A binder approach to the direct synthesis of hybrid electrode by the EPD method eradicates the drawbacks offered by conventional electrodes prepared by the general slurry coating technique with resistive binders.

PolyHIPE Derived Freestanding 3D Carbon Foam for Cobalt Hydroxide Nanorods Based High Performance Supercapacitor

The current paper describes enhanced electrochemical capacitive performance of chemically grown Cobalt hydroxide (Co(OH)2) nanorods (NRs) decorated porous three dimensional graphitic carbon foam (Co(OH)2/3D GCF) as a supercapacitor electrode. Freestanding 3D porous GCF is prepared by carbonizing, high internal phase emulsion (HIPE) polymerized styrene and divinylbenzene. The PolyHIPE was sulfonated and carbonized at temperature up to 850 °C to obtain graphitic 3D carbon foam with high surface area (389 m2 g−1) having open voids (14 μm) interconnected by windows (4 μm) in monolithic form. Moreover, entangled Co(OH)2 NRs are anchored on 3D GCF electrodes by using a facile chemical bath deposition (CBD) method. The wide porous structure with high specific surface area (520 m2 g−1) access offered by the interconnected 3D GCF along with Co(OH)2 NRs morphology, displays ultrahigh specific capacitance, specific energy and power. The Co(OH)2/3D GCF electrode exhibits maximum specific capacitance about ~1235 F g−1 at ~1 A g−1 charge-discharge current density, in 1 M aqueous KOH solution. These results endorse potential applicability of Co(OH)2/3D GCF electrode in supercapacitors and signifies that, the porous GCF is a proficient 3D freestanding framework for loading pseudocapacitive nanostructured materials.