Search

The use of easy synthesis methodology, high performance, and stable electrode materials is mandatory while developing potential energy storage devices on a mass scale. In the present work, room-tem...

Emerging energy storage electrodes synthesized with controlled morphology are of great importance to enhance supercapacitor properties including specific capacitance (SC). In this study, polycrystalline orthorhombic alpha-molybdenum trioxide (α-MoO3) thin films of different morphologies are deposited over a fluorine-tin oxide (FTO) 3D conducting substrate at various deposition temperatures using spray pyrolysis chemical method. The electrochemical properties of the α-MoO3 thin film electrode supercapacitors were performed using cyclic voltammetry and galvanostatic charge/discharge curves recorded at different scan rates and applied current densities. The nanosheet-type α-MoO3 electrode material prepared at 400 °C on envisaging in supercapacitor applications has endowed a specific capacitance (SC) of 1249.2 F g−1 and cycling stability of 85% even after 5000 cycles, suggesting the importance of the α-MoO3 electrode material in energy storage supercapacitor devices. This work affords a morphology engineering method for supercapacitor applications, which can be extended for implications in other technologies including gas sensors, solar cells, and catalysis.

Layered double hydroxides (LDHs) have drawn significant interest as emerging active materials for advanced energy storage devices; however, their low electric and ionic conductivity limit their applications. In this study, we report sulfur (S) and phosphorus (P) co-doped NiCo LDH nanoarrays prepared via a facile phosphor–sulfurization process to impart diverse co-doping effects. Combining the benefits of their unique hierarchical structure and reduced charge transfer resistance, the S and P co-doped NiCo LDH (NiCo LDH-SP) nanoarrays realize faster and more efficient redox reactions and achieve enhanced surface reactivity, thereby resulting in a performance superior to that of pristine NiCo LDH. Therefore, a NiCo LDH-SP shows an ultra-high specific capacitance of 3844.8 F g−1 at a current density of 3 A g−1 and maintains a specific capacitance of 2538.8 F g−1 at a high current density of 20 A g−1. Additionally, an asymmetric supercapacitor, assembled with the NiCo LDH-SP as the cathode and activated carbon (AC) as the anode (NiCo LDH-SP//AC), shows a high energy density of 74.5 W h kg−1 at a power density of 0.8 kW kg−1 and outstanding cycling stability, thereby retaining ∼81.3% of its initial specific capacitance after 5000 cycles. This study presents a facile and promising strategy for developing LDH-based electrode materials with excellent electrochemical performance for advanced energy storage applications.

A promising electrode for hydrogen evolution reaction (HER) has been prepared via a reduction process to form NiF2 nanorod arrays directly grown on a 3D nickel foam. We reveal NiF2@Ni nanorod arrays for a stable hydrogen evolution reaction (HER) application. The computational analysis for H2O, OH and H and experimentally in aqueous KOH endow considerable shift in Fermi levels for Ni (111) unlike for NiF2 (110) on account of an effective coalition of p-orbitals of fluorine and d-orbitals of Ni in NiF2, NiF2 under pinning the reduced overpotential of 172 mV at 10 mA cm−2 compared to Ni (242 mV) in same electrolyte. The electrocatalytic mechanism has been proposed using density functional theory (DFT) and is found in well accordance with the experimental findings of the present study. The preparation of self-grown porous nanostructured electrodes on the 3D nickel foam via a displacement reaction is possibly valuable for other metal halides for energy storage and conversion applications as these materials have inherently smaller overpotentials.

A simple, room-temperature operable, glycerol-supported single beaker-inspired, and binder-free soft-chemical protocol has been developed to synthesize 3-D dandelion flower-type nickel chloride (NiCl2) supercapattery (supercapacitor + battery) nanostructured electrode material from solid 3-D nickel‐foam (NiF). The dandelion flower-type NiCl2@NiF labeled as B electrode, demonstrates a battery-type electrochemical performance as obtained 1551 F·g−1 specific capacitance (SC) and 95% cyclability over 50,000 cycles is higher than that of a setaria viridis-type NiCl2@NiF electrode, prepared without glycerol labeled as A electrode. As a commercial market product, assembled NiCl2@NiF@ (cathode)// BiMoO3 (anode) pouch-type asymmetric supercapacitor energy storage device demonstrates moderate energy density and power density (28 Wh·kg−1 and 845 W·kg−1). By utilizing three devices in series, three different colored LEDs can be operated at full brightness. The as-proposed low temperature protocol impeccably effective and efficient on account of the low-cost, easy synthesis methodology for scalability, and high crytallinity as well as solvent-free and non-toxic as pyrolated gases were used while synthesis processing.

The high demand for long-lasting and portable energy storage devices with enhanced energy and power densities has attracted researcher's interest globally. The three-dimensional (3D) nickel foam is a promising electrode material for storing energy in various devices because they possess large surface area, are very conductive and enjoy a continuous permeable 3D system. This article provides a review and detailed information on the uses of 3D nickel foam-based electrodes with metal oxides/hydroxides of different morphologies for high-performance pseudocapacitors. We assess the limitations and future prospects of 3D nickel foam-based electrodes with metal oxides/hydroxides for industrial application towards enhancing pseudocapacitors' energy storage capability.

In recent years, interest in nanostructured electrode materials for use in supercapacitors has been on the rise. Nickel oxide has been reported as a good candidate for supercapacitor applications due to its high theoretical capacitance and low cost. However, its poor electrical conductivity has resulted in actual poor specific capacitance and cycling ability. Over the years, researchers have studied various techniques to modify the structure and composition of NiO with the aim of improving its electrochemical performance. In this review, we opine that NiO-based electrodes can be fabricated using different approaches and different composite forms in order to obtain cells of high efficiency and specific capacitances. We discuss the recent advances in NiO-based electrodes fabricated using different approaches.

The different temperature drying processes were carried out at −60 °C, 15 °C, and 60 °C to control the nanosheet morphology of MXene matrix. The MXene electrode prepared at −60 °C (denoted as LT-Ti3C2Tx) produced more nanosheet arrays than those with drying temperatures of 15 °C and 60 °C (denoted as RT-Ti3C2Tx and HT-Ti3C2Tx MXene electrodes, respectively). The results of BET and electrochemical measurements show that the specific surface area and capacitance initially decrease and then increase with the change in nanosheet layers in MXene. Among these prepared electrodes, LT-Ti3C2Tx, with a well-controlled nanosheet array, showed outstanding specific capacitance (Cs) of 467.4 F g−1 at current density of 0.5 A g−1, and 98.13% stability after 5000 cycles. Furthermore, an LT-Ti3C2Tx // LT-Ti3C2Tx symmetric supercapacitor device (SSD) was assembled, employing the LT-Ti3C2Tx with a well-controlled nanosheet acting as both anode and cathode. The SSD exhibited high energy density of 5.67 Wh kg−1 at power density of 589.09 W kg−1, and long cycle life electrochemical stability of 99.9% after 5000 cycles. These promising results show that MXene electrodes prepared by low-temperature drying (i.e. –60 °C) may be useful for supercapacitor applications.

Room-temperature (27 °C) synthesis and carbon dioxide (CO2)-gas-sensor applications of bismuth oxide (Bi2O3) nanosensors obtained via a direct and superfast chemical-bath-deposition method (CBD) with different surface areas and structures, i.e., crystallinities and morphologies including a woollen globe, nanosheet, rose-type, and spongy square plate on a glass substrate, are reported. Moprhologies of the Bi2O3 nanosensors are tuned through polyethylene glycol, ethylene glycol, and ammonium fluoride surfactants. The crystal structure, type of crystallinity, and surface appearance are determined from the X-ray diffraction patterns, X-ray photoelectron spectroscopy spectra, and high-resolution transmission electron microscopy images. The room-temperature gas-sensor applications of these Bi2O3 nanosensors for H2, H2S, NO2, SO2, and CO2 gases are monitored from 10 to 100 ppm concentrations, wherein Bi2O3 nanosensors of different physical properties demonstrate better performance and response/recovery time measurement for CO2 gas than those for the other target gases employed. Among various sensor morphologies, the nanosheet-type Bi2O3 sensor has exhibited at 100 ppm concentration of CO2 gas, a 179% response, 132 s response time, and 82 s recovery time at room-temperature, which is credited to its unique surface morphology, high surface area, and least charge transfer resistance. This suggests that the importance of the surface morphology, surface area, and crystallinity of the Bi2O3 nanosensors used for designing room-temperature operable CO2 gas sensors for commercial benefits.

In this study, MnO2 nanowires are electrochemically grown over a 3D nickel foam (NF) substrate using cyclic-voltammetry at 27°C; furthermore, their potential for applications in supercapacitors and oxygen evolution reactions (OERs) is explored. The as-obtained MnO2@NF nanowire-type electrode has demonstrated a specific capacitance (SC) of 641 F g−1 and a capacitance retention of 97%. The as-assembled MnO2//MnO2 symmetric supercapacitor device has endowed a maximum energy density of 25 W h kg−1 at power and current densities of 588 W kg−1 and 2 A g−1, respectively, which has successfully activated three different-colored LEDs with moderate light intensity. Furthermore, a small overpotential of 260 mV is obtained when the MnO2 electrode was used for OERs, highlighting its potential as an efficient catalyst. The use of MnO2 nanowires in supercapacitors and OERs has several advantages, such as (a) accessibility of several active sites, (b) easy charge transfer with reduced diffusion resistance, and (c) smooth and fast percolation of electrolyte ions responsible for optimum redox reactions. Therefore, the design of a hybrid system, containing both energy storage and water splitting applications, can be featured using only the MnO2 electrode material.

The surface characteristics of electrodes vary depending on the solvent used. Furthermore, electrochemical performance varies depending on the surface morphology of the electrode. In this study, we grew 3D binary NiCu-based composites on Ni foam, via a binder-free hydrothermal method, for use as a cathode in high-performance supercapacitors. We employed different solvents to prepare the electrodes by adjusting the ratio of deionized water (DI water) to methanol. The electrode prepared using DI water as the solvent had the largest surface area with a nanowire structure. This morphology allowed for good electrical performance by greatly improving the electrode and electrolyte contact area and shortening the ion diffusion path. The optimized deposition of NiCu(CO3)(OH)2 nanowires (50 mL of DI water as solvent) showed an excellent maximum specific capacity of 758.9 mA h g−1 at a current density of 3 A g−1, as well as outstanding cycling performance with 87.2% retention after 5000 cycles. In this work, we focused on the large specific surface area and suitable electrochemical properties of NiCu(CO3)(OH)2 electrodes with various solvents. As a result, the asymmetric supercapacitor (ASC) using the NiCu(CO3)(OH)2 electrode prepared with 50 ml of DI water as the solvent as the positive electrode and graphene as the negative electrode, exhibited an energy density of 26.7 W h kg−1 at a power density of 2534 W kg−1, and excellent cycling stability with 91.3% retention after 5000 cycles. The NiCu(CO3)(OH)2//graphene ASC could turn on an LED light and demonstrated better electrical performance than most previously reported nickel- and copper-based carbonate hydroxide ASCs. In addition, in the present scenario where many nanoscale studies are conducted, a method of controlling the nanostructure of a material through facile solvent control will be of great help to many researchers.

A self-grown copper sulfide@copper oxide (CuS@Cu2O) positrode synthsis by a hydrothermal method followed by 2 h of air annealing method (at 300 °C) from copper-foam (Cu-F) is envisaged as supercapattery electrode material in 0.1 M KOH electrolyte solution where remarkable capacities of 145, 134, 125, and 112 mA h g−1 at current densities of 1, 2, 3, and 4 A g−1, respectively, with about 80% retention ability after 2000 redox cycles, are obtained. The electrochemical performance obtained for self-grown CuS@Cu2O positrode is better than those reported previously for self-gown CuS, Cu(OH)2, and CuO electrode materials. An asymmetric supercapattery device fabricate using CuS@Cu2O as a positrode with Bi2O3 as negatrode, i.e., CuS@Cu2O//Bi2O3, demonstrates an energy density of 52 Wh kg−1 at a power density of 750 W kg−1 at 0.5 A g−1 which, when connected in series with another similar device, lightens a LED with its full-bright intensity, confirming a commercial potential of designed electrochemical supercapattery device.

Soft chemical synthesis is used to obtain a hydrangea-type bismuth molybdate (Bi2MoO6) supercapattery electrode that demonstrates considerable energy/power density and cycling life. Structure and m...

We report water-splitting application of chemically stable self-grown nickel sulfide (Ni x S y ) electrocatalysts of different nanostructures including rods, flakes, buds, petals, etc., synthesized by a hydrothermal method on a three-dimensional Ni foam (NiF) in the presence of different sulfur-ion precursors, e.g., thioacetamide, sodium thiosulfate, thiourea, and sodium sulfide. The S2- ions are produced after decomposition from respective sulfur precursors, which, in general, react with oxidized Ni2+ ions from the NiF at optimized temperatures and pressures, forming the Ni x S y superstructures. These Ni x S y electrocatalysts are initially screened for their structure, morphology, phase purity, porosity, and binding energy by means of various sophisticated instrumentation technologies. The as-obtained Ni x S y electrocatalyst from sodium thiosulfate endows an overpotential of 200 mV. The oxygen evolution overpotential results of Ni x S y electrocatalysts are comparable or superior to those reported previously for other self-grown Ni x S y superstructure morphologies.

Polycrystalline and mesoporous bismuth oxide (Bi2O3) micro-sponge-balls of 4–7 μm in diameter comprising of 58–65 (±2) nm upright standing petals, separated by 100–700 (±50) nm crevices, are synthesized directly onto 3D Ni-foam at room-temperature (27 °C) using Tritonx-100 surfactant-mediated soft wet chemical method. After knowing the phase purity, surface area, pore-size distribution, micro-sponge-ball-type surface morphology, elemental analysis and binding energy confirmations of Bi2O3, a material with quasi-faradaic redox reactions responsible for supercapattery type behavior, are measured and explored. At a low scan rate, the specific capacitance of Bi2O3 sponge-ball electrode, measured from 0.4 to 1.80 A g−1 current density, decreases from 559 to 211 F g−1 which is equivalent to a capacity from 155 to 58 mAh.g−1. An asymmetric supercapacitor (ASC) device assembly of Bi2O3 sponge-ball electrode with graphite i.e. Bi2O3//graphite demonstrates excellent electrochemical properties with 8 Wh kg−1 energy density at 2040 W kg−1 power density, and about 80% cycling retention over 5000 redox cycle operations. A demonstration of LED with full-bright intensity during discharge process of the Bi2O3//graphite ASC device suggests its practical potentiality and industrial viability.

Sulphur source-inspired self-grown polycrystalline and mesoporous nickel sulfide (Ni xS y) superstructures with vertically aligned nanomorphologies viz. rods, flakes, buds, and petals, synthesized at elevated temperatures and moderate pressures by a facile one-pot hydrothermal method on a three-dimensional Ni foam demonstrate remarkable areal specific capacitances of 7152, 4835, and 2160 F cm-2 at current densities of 1, 2, and 5 mA cm-2, respectively, with a cycling stability of 94% for a battery-type electrochemical supercapacitor when used as an electrode material in a supercapacitor. The Ni xS y//Bi2O3 asymmetric supercapacitor assembly exhibits an energy density of 41 W h·kg-1 at a power density of 1399 W kg-1 for 1 A g-1 and was used in a three-cell series combination to operate a "GFHIM" display panel (our research institute name, Global Frontier R & D Center for Hybrid Interface Materials) composed of nearly 50 differently colored light-emitting diodes with high intensity in 1 M KOH water-alkali electrolyte. The electrochemical supercapacitor results obtained for the Ni xS y superstructures because of a combination of catalytically active amorphous and high mobility polycrystalline are highly comparable to those reported previously for salt-mediated and self-grown Ni xS y structures and morphologies.

In the current study, we have explored the coupling of Bi2O3 negative electrode and MnO2 positive electrode materials as an asymmetric faradaic assembly for a high-performance hybrid electrochemical energy storage device (HEESD). Aiming at a low-cost device, both the electrodes have been synthesized by a simple, scalable, and cost-effective chemical synthesis method. After their requisite structure-morphological confirmation and correlation, these electrodes were separately examined for their electrochemical performance in a three-electrode configuration. The results obtained confirm that Bi2O3 and MnO2 exhibit 910 C g−1 and 424 C g−1 specific capacity, respectively, at 2 A g−1 current density. Notably, the performance of both electrodes has been analyzed using Dunn's method to highlight the distinct nature of their faradaic properties. Afterwards, the asymmetric faradaic assembly of both electrodes, when assembled as a HEESD (MnO2//Bi2O3), delivered 411 C g−1 specific capacity at 1 A g−1 current density due to the inclusive contribution from the capacitive as well as the non-capacitive faradaic quotient. Consequently, the assembly offers an excellent energy density of 79 W h kg−1 at a power density of 702 W kg−1, with a magnificent retention of energy density up to 21.1 W h kg−1 at 14 339 W kg−1 power density. Moreover, it demonstrates long-term cycling stability at 10 A g−1, retaining 85.2% of its initial energy density after 5000 cycles, which is significant in comparison with the previously reported literature. Additionally, to check the performance of the device in real time, two HEESDs were connected in series to power a light-emitting diode. The results obtained provide significant insight into hybrid coupling, where two different faradaic electrodes can be combined in a synergistic combination for a high-performance HEESD.

A promising electrode for hydrogen evolution reaction (HER) has been prepared via a reduction process to form NiF2 nanorod arrays directly grown on a 3D nickel foam. We reveal NiF2@Ni nanorod arrays for a stable hydrogen evolution reaction (HER) application. The computational analysis for H2O, OH and H and experimentally in aqueous KOH endow considerable shift in Fermi levels for Ni (111) unlike for NiF2 (110) on account of an effective coalition of p-orbitals of fluorine and d-orbitals of Ni in NiF2, NiF2 under pinning the reduced overpotential of 172 mV at 10 mA cm-2 compared to Ni (242 mV) in same electrolyte. The electrocatalytic mechanism has been proposed using density functional theory (DFT) and is found in well accordance with the experimental findings of the present study. The preparation of self-grown porous nanostructured electrodes on the 3D nickel foam via a displacement reaction is possibly valuable for other metal halides for energy storage and conversion applications as these materials have inherently smaller overpotentials.

The organic and eco-friendly materials are extended to prevail over the worldwide energy crisis where bio-inspired carbonaceous electrode materials are being prepared from biogenic items and wastes. Here, coconut water is sprayed over three-dimensional (3D) nickel foam for obtaining a carbonaceous electrode material, i.e., C@Ni-F. The as-prepared C@Ni-F electrode has been used for structural elucidation and morphology evolution studies. Field emission scanning electron microscopy analysis confirms the vertically grown nanosheets of the C@Ni-F electrode, which is further employed in the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), where excellent OER and HER performances with small overpotentials of 219 and 122 mV and with stumpy Tafel slopes, i.e., 27 and 53 mV dec-1, are respectively obtained, suggesting a bifunctional potential of the sprayed electrode material. Moreover, sustainable bifunctional performance of C@Ni-F proves considerable chemical stability and moderate mechanical robustness against long-term operation, suggesting that, in addition to being a healthy drink to mankind, coconut water can also be used for water splitting applications.

We introduce a simple room-temperature (25-27°C) solution process-inspired approach for obtaining sharp-edged nanoshapes like nanocubes, nanorods and nanoparticles of molybdenum oxide (MoO3) on a stainless-steel (SS) substrate for supercapacitor and electrocatalysis applications. The nanoshape of MoO3 has been strikingly changed from nanocubes to nanopaticles dependig on HCl concentration. The MoO3 electrodes of different morphologies are systematically characterized by various characterization techniques for confirming phase, structure, and surface elemental composition. The electrochemical studies show significant enhancement in specific capacitance and oxygen evolution reaction (OER) activity for MoO3 nanorod structures. The specific capacitance of 2561.53 F g−1 for MoO3 nanorods is much higher than 608.20 F g−1 and 400.28 F g−1 for nanocubes and nanoparticles, respectively. Besides, with the 98.59% capacitance retention up to 2000 cycles, the electrode consisting nanorods is found to be highly stable. In the commercial point of view, the as-fabricated MoO3//MoO3 symmetric device adduces excellent energy/power density (69.06 Wh kg-1)/(1336.63 W Kg-1) at current density of 1 A g-1. The laboratory panel, Center for Nanomaterials and Energy Devices (CNED), containing nearly 42 LEDs was ignited with full intensity using MoO3//MoO3 symmetric device as the practical demonstration of electrode material. From supercapacitor study, the MoO3 nanorod-based electrode endows excellent OER activity (overpotential of 246 mV; Tafel slope of 36 mV dec-1). In both cases, the MoO3 nanorod-based electrode produces excellent chemical and cyclic stability. Overall electrochemical results demonstrate that the MoO3 nanorod-based electrode would be excellent electrode material for supercapacitor as well as OER applications. The proposed room-temperature solution synthesis process is valuable and well effective in view of trouble-free, cost-effective, and scalability for commercial benefits.

Recently, the 2021 United nations climate change conference (COP26) have again stressed on the need of carbon neutral economy. To cope up with the power hunger of industrial and/ technological world of hybrid electric vehicles and portable electronic devices it is imperative to search the environment friendly novel materials with property tailoring abilities. In this connection, we have deposited Co1-xCuxS/CoCuS (0.025 ≤ x ≤ 0.1) thin-films via chemical route as an alternative material for supercapacitor application. To asses the suitability of as-deposited thin films, we have characterized thin films using variety of characterization techniques. X-ray photoelectron spectroscopy was used to examine and confirm the chemical states of Co, Cu, and S. Surface morphology of as-deposited CoCuS film (x = 0.075, sample-C3) showed a crumpled flower-like microstructure. Uniform distribution of hillocks and valleys was observed using atomic force microscopy. The topographical outcomes obtained from electrostatic force microscopy and Kelvin probe force microscopy confirmed that the sample-C3 (x = 0.075) is suitable for energy storage applications. Sample-C3 demonstrated excellent supercapcitive performance with a high specific capacitance of 907.55 F g-1 at 5 mV s-1, remarkable rate capability, and ~ 90% of capacitive retention after 5000 cycles in a 1 M KOH electrolyte. Better supercapacitive behavior and cycling stability of the CoCuS samples may offer a perspective for various mixed metal sulfide thin films with hierarchical architectures as an viable alternative for the efficient energy storage devices.

Nickel oxide-graphene oxide (NiO-GO), zinc oxide-graphene oxide (ZnO-GO) and bismuth oxide-graphene oxide (Bi2O3-GO) metal oxide-graphene oxide nanocomposite (MO-GO NC) sensors, operable at room temperature, were synthesized via a simple and cost-effective microwave-assisted combustion method for chemiresistive gas sensor applications. From the measured structural, morphological, and elemental detection properties, the sensors are found capable of detecting various gases. The Bi2O3-GO NC sensor exhibited excellent response over NiO-GO (~20 at 50 ppm) and ZnO-GO NC (~60 at 50 ppm) sensors for detecting NH3. The response of the Bi2O3-GO NC sensor at 50 ppm NH3 in just 14 s operation duration was ~81.23, which is improved 25-fold and 13-fold compared to pristine GO sensors. Additionally, the as-developed Bi2O3-GO NC sensor demonstrates outstanding repeatability and recovery kinetics, attributed to porosity and the combined effects of MO and GO. The sensing mechanism of the Bi2O3-GO NC gas sensors is proposed herein. The superior sensing performance, including quick response and recovery of the Bi2O3-GO NC sensor is attributed to favorable charge transfer across the Bi2O3 and GO interface. The significance of relative humidity on sensing potential of the Bi2O3-GO NC sensor has also been studied and the sensor is confirmed to be unaffected by relative humidity.

A simple, room-temperature operable, glycerol-supported single beaker-inspired, and binder-free soft-chemical protocol has been developed to synthesize 3-D dandelion flower-type nickel chloride (NiCl

Ferrite materials are being widely envisaged in magnetic, electronic, and microwave devices. They exhibit high resistivity and low eddy current losses which make them a better choice over metals. Apart from their promising magnetic properties, ferrite nanostructures have great impact on next generation needs for designing energy storage devices such as hybrid electric vehicles, mobiles, etc. This chapter presents applications of ferrites in diverse fields from magnetic devices to energy storage devices. Their role in electrical properties such as charge storage arises from the fast-reversible surface faradaic reactions occurring at electrode/electrolyte interface. The rate of redox reaction can control the electrical charge transport of pseudo materials. Recently, the interest in the development of high performance electrode materials for supercapacitors has increased intensively. In particular, the negative electrodes with high specific capacitance, wide range of operating potential, high redox activity, low cost, abundant availability, and ecofriendliness are highly desirable to obtain scalable supercapacitors. Ferrites have proved to be promising negative electrodes in supercapacitors, and in this chapter we have briefed the recent developments of composites with special architectures such as unitary, binary, mixed, and composite ferrite structures, which are considered to be a promising approach to improve charge transfer reaction kinetics. A separate section signifying future perspectives is also provided with various thoughts at the end of the chapter.

The constraints over efficiency improvements in Cu2ZnSn(S, Se)4 photovoltaic cells have prompted the search for alternative replacements. The simultaneous incorporation of (Cu, Zn, S) in the CdSe host lattice with different stoichiometry can be an attractive approach to circumventing the difficulties associated with CZTSSe. This paper reports the non-vacuum deposition technique of a new chalcogenide semiconductor material, Cd1-x-yZnxCuySzSe1-z (0 ≤ x + y ≤ z ≤ 0.15) sample-0 to 3), for photoelectrochemical (PEC) solar cell applications. Compositional studies detected Cd, Cu, Zn, Se, and S in the deposits, and chemical analysis identified Cd2+, Cu2+, Zn2+, S2- and Se2- in the deposits. Surface micrographs revealed a cauliflower-like morphology having a high surface area, which can provide additional reactive sites for the effective percolation of electrolyte ions. The AFM study showed uniformly distributed hillocks and valleys with the maximum surface to area ratio. The highest efficiency of 1.60 % was achieved for Cd1-x-yZnxCuySzSe1-z solar cells (sample -3). These results highlight this new material for further studies.

A dual phase bismuth oxyiodide (BiOI/Bi9I2) nanostructure battery type supercapacitor electrode is synthesized using chemical bath deposition (CBD) and the capacitance and energy/power density (ED/PD) reported. The supercapacitor electrode BiOI/Bi9I2 exhibited a specific capacitance of 515.5 F g-1 (capacity value 143 mA h g-1) at a current density of 2 A g-1, with 80% of the original capacitance retained, even at a high current density of 4 A g-1 over 5000 cycles. A pouch-type symmetric supercapacitor (PSS) device was created, based on BiOI/Bi9I2//BiOI/Bi9I2 electrodes (acting as anode and cathode electrodes) with 6 M KOH as the aqueous electrolyte and with an extended voltage up to 1.5 V. The ED value was 38.2 W h kg-1 at a current density of 2 A g-1, and the PD was 2280.4 W·kg-1. Three PSS type BiOI/Bi9I2//BiOI/Bi9I2 devices were connected in series and used to illuminate a red LED for 20 min with full brightness, confirming potential use as an energy storage device. The above summarized results indicate that BiOI/Bi9I2//BiOI/Bi9I2 could be a potential electrode for battery type supercapacitor applications.

A electrode for energy storage cells is possible directly on Ni foam, using a simple reduction process to form NiF2 nanorod arrays (NA). We demonstrate NiF2@Ni NA for a symmetric electrochemical supercapattery electrode. With an areal specific capacitance of 51 F cm–2 at 0.25 mA cm–2 current density and 94% cycling stability, a NiF2@Ni electrode can exhibit supercapattery behavior, a combination of supercapacitor and battery-like redox. The symmetric electrochemical supercapattery delivers 31 W h m–2 energy density and 797 W m–2 power density with 83% retention in a 1 M KOH electrolyte, constituting a step toward manufacturing a laboratory-scale energy storage device based on metal halides. Producing self-grown hierarchically porous nanostructured electrodes on three-dimensional metal foams by displacement reactions may be useful for other metal halides as electrodes for supercapacitors, supercapatteries, and lithium-ion batteries.

The interesting and multifunctional properties of alpha-manganese dioxide (α-MnO2) are considered to be highly sensitive and selective to nitrogen dioxide (NO2) chemresistive gas sensors. The α-MnO2 mesoporous interlocked micro-cubes composed of several interconnected nanocrystals synthesized by a facile and low-cost hydrothermal method on soda-lime glass substrate are envisaged as selective and sensitive NO2 gas sensors. Phase-purity and surface area with pore-size distribution are initially screened. The three-dimensional α-MnO2 mesoporous-cube-based gas sensors tested for NO2 gas from room-temperature (27 °C) to 250 °C have demonstrated 33% response for 100 ppm NO2 levels at 150 °C. The response and recovery time values of the α-MnO2 sensor are found to be 26 s and recovery 91 s, respectively, with high selectivity, good sensitivity, and considerable chemical and environmental stabilities, confirming the gas sensor applications potentiality of α-MnO2 morphology which is a combination of interlocked mesoporous micro-cubes and well-connected nanocrystals.

Since the discovery of two-dimensional (2D) graphene, a new class of 2D materials with excellent electrical conductivity has recently been attracting attention in studying promising electrode materials in energy storage applications. Herein, bismuth oxychloride nanosheets-immobilised Ti3C2Tx MXene material (TCBOC) is synthesised by a facile and cost-effective chemical bath deposition (CBD) route. The bismuth oxychloride (BiOCl) nanosheets are grown and immobilised on surfaces of Ti3C2Tx-MXene flakes. An electrode based on the TCBOC nanocomposite exhibited a remarkably volumetric specific capacitance of 396.5 F cm-3 at 1 A g−1 and 228.0 F cm-3 at 15 A g−1. Furthermore, a symmetric supercapacitor (SSC) assembled using TCBOC material proves to have a high energy density of 15.2 Wh kg−1 at a power density of 567.4 W kg−1 compared to SSCs using previously reported Ti3C2Tx MXene materials. The SSC shows cycle life retention of 85.0% after 5000 cycles (at 5 A g−1). The enhanced capacitive performance is attributed to the increased surface area due to BiOCl nanosheets anchored on a 2D MXene surface, the activities of BiOCl sheets, and the excellent conductivity of a Ti3C2Tx MXene material.

Superfast (≤10 min) room-temperature (300 K) chemical synthesis of three-dimensional (3-D) polycrystalline and mesoporous bismuth(III) oxide (Bi2O3) nanostructured negatrode (as an abbreviation of negative electrode) materials, viz., coconut shell, marigold, honey nest cross section and rose with different surface areas, charge transfer resistances, and electrochemical performances essential for energy storage, harvesting, and even catalysis devices, are directly grown onto Ni foam without and with poly(ethylene glycol), ethylene glycol, and ammonium fluoride surfactants, respectively. Smaller diffusion lengths, caused by the involvement of irregular crevices, allow electrolyte ions to infiltrate deeply, increasing the utility of inner active sites for the following electrochemical performance. A marigold 3-D Bi2O3 electrode of 58 m2·g–1 surface area has demonstrated a specific capacitance of 447 F·g–1 at 2 A·g–1 and chemical stability of 85% even after 5000 redox cycles at 10 A·g–1 in a 6 M KOH electroly...

The acetone gas sensor and electrochemical supercapacitor applications of bismuth oxide (Bi2O3) nanostructures, synthesised using a facile and cost-effective quaternary-beaker mediated successive ion transfer wet chemical method and deposited onto soda-lime-glass (SLG) and Ni-foam substrates, respectively, are explored. The as-deposited Bi2O3 nanostructures on these substrates exhibit polycrystalline nature and a slight change in their surface appearance (i.e. upright-standing nanoplates on SLG and a curvy nanosheet structure on Ni-foam), suggesting the importance of the deposition substrate in developing Bi2O3 morphologies. The Bi2O3 nanoplate gas sensor on the SGL demonstrated a room temperature sensitivity of 41%@100 ppm for acetone gas, whereas the nanosheet structure of Bi2O3 on the Ni-foam elucidated a specific capacitance of 402 F g−1 at 2 mA cm−2, long-term cyclability, and rate capability with moderate chemical and environmental stability in a 6 M KOH electrolyte solution. The Bi2O3//graphite pencil-type asymmetric supercapacitor device revealed a specific capacitance as high as 43 F g−1, and an energy density of 13 W h kg−1 at 793 W kg−1 power density, turning a light emitting diode ON, with considerable full-brightness light intensity, during the process of discharging.