Surfactant-free hydrothermal synthesis of hierarchically structured spherical CuBi2O4 as negative electrodes for Li-ion hybrid capacitors

Preparation of a High-Performance Asymmetric Supercapacitor by Recycling Aluminum Paper and Filter Components of Heated Tobacco

In this study, Al paper and cellulose acetate (CA) filters derived from heated tobacco waste were successfully converted into current collectors and active materials for a supercapacitor device. Typically, heated tobacco contains electrically discontinuous Al paper. First, Al was extracted from the tobacco waste using HCl to produce Lewis acid (AlCl3). This acid was then used in an Al electrodeposition process utilizing the chloroaluminate ionic liquid reaction between the acid and the base (RCl) at room temperature. To enhance the conductivity, a supplementary coating of Al metal was applied to the Al paper through electrodeposition, thus re-establishing the electrical continuity of the discontinuous parts and forming an Al-coated current collector. Moreover, the CA filters were carbonized under a nitrogen atmosphere, yielding carbon precursors (C-CA) for the supercapacitor electrodes. To further enhance the electrochemical performance, nickel oxide (NiO) was incorporated into C-CA, resulting in C-CA@NiO with pseudocapacitance. The specific surface area of CA increased with carbonization and the subsequent incorporation of NiO. The as-synthesized C-CA and C-CA@NiO materials were applied to an Al-coated current collector to obtain C-CA- and C-CA@NiO-based electrodes, exhibiting stable electrochemical behavior in the voltage range of -1.0 to 0 V and 0 to 1.0 V, respectively. An asymmetric supercapacitor (ASC) device was assembled with C-CA@NiO and C-CA as the positive and negative electrodes, respectively. This ASC device demonstrated a high specific capacitance of 40.8 F g-1, while widening the operating voltage window to 2.0 V. The high electrochemical performance of the device is attributed to the successful Al electrodeposition, which facilitates the electrical conductivity and increased porosity of the C-CA@NiO and C-CA materials. To the best of our knowledge, this is a pioneering study in regards to the conversion of biomass waste into current collectors and active materials to fabricate a practical ASC device. Our findings highlight the potential of reusing Al paper and CA filters from heated tobacco waste as essential components of energy storage devices.

An ab initio DFT perspective on experimentally synthesized CuBi2O4

Here we present a comprehensive density functional theory (DFT) based ab initio study of copper bismuth oxide CuBi₂O₄ (CBO) in combination with experimental observations. The CBO samples were prepared following both solid-state reaction (SCBO) and hydrothermal (HCBO) methods. The P4/ncc phase purity of the as-synthesized samples was corroborated by Rietveld refinement of the powdered X-ray diffraction measurements along with Generalized Gradient Approximation of Perdew-Burke-Ernzerhof (GGA-PBE) and the Hubbard interaction U corrected GGA-PBE+U relaxed crystallographic parameters. Scanning and field emission scanning electron micrographs confirmed the particle size of the SCBO and HCBO samples to be ∼250 and ∼60 nm respectively. The GGA-PBE and GGA-PBE+U derived Raman peaks are in better agreement with that of the experimentally observed ones when compared to local density approximation based results. The DFT derived phonon density of states conforms with the absorption bands in Fourier transform infrared spectra. Both structural and dynamic stability criteria of the CBO are confirmed by elastic tensor and density functional perturbation theory-based phonon band structure simulations respectively. The CBO band gap underestimation of GGA-PBE as compared to UV-vis diffuse reflectance derived 1.8 eV was eliminated by tuning the U and the Hartree-Fock exact-exchange mixing parameter α_HF in GGA-PBE+U and Heyd-Scuseria-Ernzerhof (HSE06) hybrid functionals respectively. The HSE06 with α_HF = 14% yields the optimum linear optical properties of CBO in terms of the dielectric function, absorption, and their derivatives as compared to that of GGA-PBE and GGA-PBE+U functionals. Our as-synthesized HCBO shows ∼70% photocatalytic efficiency in degrading methylene blue dye under 3 h optical illumination. This DFT-guided experimental approach to CBO may help to gain a better understanding of its functional properties.

Photoelectrochemical Performance of a CuBi2O4 Photocathode with H2O2 as a Scavenger

Photoelectrochemical (PEC) water splitting is an eco-friendly method for producing clean and sustainable hydrogen fuels. Compared with the fabrication of solar hydrogen using n-type metal oxide semiconductor photoanodes, that of solar hydrogen using p-type metal oxide semiconductor photocathodes has not been researched as thoroughly. Therefore, this study investigated the effect of drop casting time on the PEC performance of a prepared CuBi2O4 photocathode. XPS, HRTEM, UV-DRS, Raman spectroscopy, XRD, and SEM analyses were used to characterize the prepared CuBi2O4 photocathode. Owing to the high charge separation and transfer, the photocurrent density of the CuBi2O4 photocathode was ~0.6 mA cm−2 at 0.3 V vs. RHE. The nanoporous CuBi2O4 photocathode exhibited a high photocurrent density of up to 1.2 mA cm−2 at 0.3 V vs. RHE with H2O2 as a sacrificial agent. Mott–Schottky and impedance measurements were also performed on the CuBi2O4 photocathode to estimate its acceptor density and charge-transfer resistance.

Nanointerface engineering Z-scheme CuBiOS@CuBi2O4 heterojunction with OS interpenetration for enhancing photocatalytic hydrogen peroxide generation and accelerating chromium(VI) reduction

Designing a core-shell nanointerface is beneficial for enhancing the photocatalytic performance of hydrogen peroxide (H₂O₂) production. Hence, a direct Z-scheme one-dimensional (1 D) CuBiOS@CuBi₂O₄ nanorods with a core (oxide)-shell (sulfide) nanostructure and OS interpenetrated nanointerface was controllably synthesized through in-situ anion exchange. The formation of OS interpenetration at the heterogeneous interface with surface oxygen vacancies could effectively boost light absorption, reduce the interface contact resistance, facilitate band bending, and thus enhance charge separation and transfer as a "bridge". The as-prepared catalyst with tunable OS nanointerface greatly improved the photocatalytic performances in the H₂O₂ production with a yield of 201.9 μmol·L^-1 and the in-situ generated H₂O₂ effectively accelerated the reduction of chromium(VI) (Cr(VI), 95.4% within 15 min). The excellent performances were due to the OS interpenetration with rich oxygen vacancies and unique shell-core structure with intimate contact inter-doping nanointerface. Moreover, the photocatalytic mechanism was discussed in detail. This work might provide a guideline in the design and construction of high-performance catalysts with well-defined nanointerface for various applications.

Uplifting the charge carrier separation and migration in Co-doped CuBi2O4/TiO2 p-n heterojunction photocathode for enhanced photoelectrocatalytic water splitting

Here, cobalt-doped copper bismuth oxide (Co-CuBi₂O₄) was synthesized via a facile hydrothermal method for photoelectrocatalytic (PEC) hydrogen production. The results disclosed that the 5% Co-doped CuBi₂O₄ has better PEC activity which is ∼3 fold higher than pristine CuBi₂O₄. The doping of cobalt in CuBi₂O₄ improves the interfacial charge transfer at an electrode/electrolyte interface and reduces the recombination rate of photogenerated electron-hole pairs. This higher performed 5% Co-doped CuBi₂O₄ photocathode further modified with TiO₂-P25 to form a Co-CuBi₂O₄/TiO₂ p-n heterojunction. This Co-CuBi₂O₄/TiO₂ photocathode displayed a photocurrent density of 330 μA cm^-2 at +0.5 V vs. RHE which was ∼2 fold higher than Co-CuBi₂O₄. Because this p-n junction affords inner electric field in the space charge region that helps for further minimization of electron-hole recombination, which facilitate efficient charge separation and transport thereby enhance the PEC water reduction.

Deposition and Characterization of Innovative Bulk Heterojunction Films Based on CuBi2O4 Nanoparticles and Poly(3,4 ethylene dioxythiophene):Poly(4-styrene sulfonate) Matrix

This work presents the deposition and study of the semiconductor behavior of CuBi2O4 nanoparticles (NPs) with an average crystallite size of 24 ± 2 nm embedded in poly(3,4 ethylene dioxythiophene):poly(4-styrene sulfonate) (PEDOT:PSS) films. The CuBi2O4 NP bandgap was estimated at 1.7 eV, while for the composite film, it was estimated at 2.1 eV, due to PEDOT:PSS and the heterojunction between the polymer and the NPs. The charge transport of the glass/ITO/PEDOT:PSS-CuBi2O4 NP/Ag system was studied under light and dark conditions by means of current–voltage (I–V) characteristic curves. In natural-light conditions, the CuBi2O4 NPs presented electric behavior characterized by three different mechanisms: at low voltages, the behavior follows Ohm’s law; when the voltage increases, charge transport occurs by diffusion between the NP–polymer interfaces; and at higher voltages, it occurs due to the current being dominated by the saturation region. Due to their crystalline structure, their low bandgap in films and the feasibility of integrating them as components in composite films with PEDOT:PSS, CuBi2O4 NPs can be used as parts in optoelectronic devices.

Energy storage electrochromic devices in the era of intelligent automation

The current intelligent automation society faces increasingly severe challenges in achieving efficient storage and utilization of energy. In the field of energy applications, various energy technologies need to be more intelligent and efficient to produce, store, transform and save energy. In addition, many smart electronic devices facing the future also require newer, lighter, thinner and even transparent multi-functional power supplies. The unique properties of electrochromic energy storage devices (ECESDs) have attracted widespread attention. In the field of energy applications, they have high potential value and competitiveness. This review focuses on the electrochromic basic principles, and the latest technological examples of ECESDs, which are related to materials and device structures. Simultaneously, this review makes a detailed comparison and summary of example performances. Moreover, the review compares the current mainstream energy storage devices: lithium batteries and supercapacitors, and the main challenges of ECESDs are discussed. Finally, the future development directions in the field of electrochromic energy storage are predicted.

Eco-friendly synthesis of self-regenerative low-cost biosorbent by the incorporation of CuO: a photocatalyst sensitive to visible light irradiation for azo dye removal

Acid pretreated biomass Lemna minor (BM-H3PO4) was used as support for CuO nanoparticles loading, to investigate the dye biosorption capacity and the photocatalytic performance under artificial visible light. The surface morphology, crystal structure, elemental composition, and the bandgap of modified biomass have been determined using FE-SEM, XRD, EDX, XPS, FTIR, and UV-DR analysis. The results showed that NH2 and P-O functional groups of (BM-H3PO4) can attract the copper ions (Cu2+), which can facilitate the loading of CuO nanoparticles hence, smaller nanoparticles with an average diameter of 21 nm was obtained. It was also found that when the CuO was incorporated in BM-H3PO4 in a proper mass ratio of 0.4, the biosorption efficiency was enhanced to 3 times compared with BM-H3PO4 and reached a maximum of 91%, at a dye concentration of 20 mg/L, solution pH equal to 5, and an ambient temperature of 25 °C. Furthermore, CuO-modified BM-H3PO4 exhibits a better photocatalytic activity than pure CuO in the presence of H2O2 and visible light irradiation, where the dye was completely removed and mineralized after 240 min, evidenced by COD measurement. The photocatalytic regeneration also shows that the biosorption efficiency was maintained at 91% over 3 cycles, indicating the significant self-regenerative capacity of the biosorbent.

One Step Synthesis of Tetragonal-CuBi2O4/Amorphous-BiFeO3 Heterojunction with Improved Charge Separation and Enhanced Photocatalytic Properties

Tetragonal CuBi₂O₄/amorphous BiFeO₃ (T-CBO/A-BFO) composites are prepared via a one-step solvothermal method at mild conditions. The T-CBO/A-BFO composites show expanded visible light absorption, suppressed charge recombination, and consequently improved photocatalytic activity than T-CBO or A-BFO alone. The T-CBO/A-BFO with an optimal T-CBO to A-BFO ratio of 1:1 demonstrates the lowest photoluminescence signal and highest photocatalytic activity. It shows a removal rate of 78.3% for the photodegradation of methylene orange under visible light irradiation for 1 h. XPS test after the cycle test revealed the reduction of Bi³⁺ during the photocatalytic reaction. Moreover, the as prepared T-CBO/A-BFO show fundamentally higher photocatalytic activity than their calcinated counterparts. The one-step synthesis is completed within 30 min and does not require post annealing process, which may be easily applied for the fast and cost-effective preparation of photoactive metal oxide heterojunctions.

Short-Time Hydrothermal Synthesis of CuBi2O4 Nanocolumn Arrays for Efficient Visible-Light Photocatalysis

In this article, a short-time hydrothermal method is developed to prepare CuBi₂O₄ nanocolumn arrays. By using Bi(NO₃)₃·5H₂O in acetic acid and Cu(NO₃)₂·3H₂O in ethanol as precursor solutions, tetragonal CuBi₂O₄ with good visible light absorption can be fabricated within 0.5 h at 120 °C. Tetragonal structured CuBi₂O₄ can be formed after 15 min hydrothermal treatment, however it possesses poor visible light absorption and low photocatalytic activity. Extending the hydrothermal treatment duration to 0.5 h results in a significant improvement invisible light absorption of the tetragonal CuBi₂O₄. The CuBi₂O₄ obtained through 0.5 h hydrothermal synthesis shows a band gap of 1.75 eV and exhibits the highest photocatalytic performance among the CuBi₂O₄ prepared with various hydrothermal time. The removal rate of methylene blue by the 0.5 h CuBi₂O₄ reaches 91% under visible light irradiation for 0.5 h. This study proposes a novel strategy to prepare photoactive CuBi₂O₄ nanocolumn arrays within 0.5 h at a moderate temperature of 120 °C. The hydrothermal method provides a facile strategy for the fast synthesis of metal-oxide-based photocatalysts at mild reaction conditions.

Ag3PO4 Deposited on CuBi2O4 to Construct Z-Scheme Photocatalyst with Excellent Visible-Light Catalytic Performance Toward the Degradation of Diclofenac Sodium

CuBi₂O₄/Ag₃PO₄ was synthesized through a combination of hydrothermal synthesis and an in situ deposition method with sodium stearate as additives, and their textures were characterized with XRD, XPS, SEM/HRTEM, EDS, UV-Vis, and PL. Then, the photodegradation performance of CuBi₂O₄/Ag₃PO₄ toward the degradation of diclofenac sodium (DS) was investigated, and the results indicate that the degradation rate of DS in a CuBi₂O₄/Ag₃PO₄ (1:1) system is 0.0143 min⁻¹, which is 3.6 times that in the blank irradiation system. Finally, the photocatalytic mechanism of CuBi₂O₄/Ag₃PO₄ was discussed, which follows the Z-Scheme theory, and the performance enhancement of CuBi₂O₄/Ag₃PO₄ was attributed to the improved separation efficiency of photogenerated electron–hole pairs.

A facile strategy for the synthesis of three-dimensional heterostructure self-assembled MoSe2 nanosheets and their application as an anode for high-energy lithium-ion hybrid capacitors

As energy storage devices, lithium-ion hybrid capacitors (LIHCs) are currently favored by researchers, because they combine the high energy density of lithium-ion batteries and the high power density as well as the long cycle life of electric double-layer capacitors. However, the reason that LIHCs are problematic for researchers and cannot be applied practically is the slow dynamic behavior of the battery type anode that leads to low magnification and cycle performance of the anode, furthermore, causing a dynamic imbalance between the Faraday embedded electrode and the capacitive electrode. Hence, it is imperative to find an anode material that can quickly intercalate/de-intercalate lithium. In this study, a novel anode material, MoSe2 nanoflowers, for LIHCs was incorporated through a facile solvothermal technique. The MoSe2 nanoflowers with a small volume change after Li+ insertion, conducive to a rapid kinetic layered heterostructure, result in extraordinary electrochemical performance. The prepared MoSe2 nanoflowers exhibit very good invertible capacity (641.4 mA h g-1 at 0.1 A g-1 after 200 cycles), superior velocity performance (380.3 mA h g-1 at 5 A g-1) and long-term cycling stability (214.6 mA h g-1 even after 1000 cycles at 1 A g-1) as anode materials for LIHCs. Benefiting from the reasonable nanometer size effect, locally fine charge transfers and low energy diffusion barriers, MoSe2 nanoflowers possess high rate pseudocapacitive behavior. In addition, the assembled MoSe2//AC (AC, activated carbon) LIHCs deliver a high energy density (78.75-39.1 W h kg-1) and high-power characteristic (150-3600 W kg-1). Besides, after 5000 cycles, the capacity retention rate is 70.28% under a broad potential window (0.5-3.5 V). This LIHC based on a transition metal selenide as an anode shows great potential for application in the fields of new energy electric vehicles and smart electronic products.

Formation of high-density CuBi2O4 thin film photocathodes with polyvinylpyrrolidone-metal interaction

We present a polymer-assisted spin coating process used to fabricate high-density p-type CuBi₂O₄ (CBO) thin films. Polyvinylpyrrolidone (PVP) is introduced in the precursor solutions in order to promote uniform nucleation of CBO and prevent formation of the secondary phase, such as Bi₂O_3, by Bi³⁺ ion hydrolysis. Slow PVP molecule decomposition during the two-step annealing process, with a 1 M/0.5 M (Bi³⁺/Cu²⁺) metal ion concentration, enables optimum contact at the CBO/substrate interface by avoiding formation of voids. This resulted in the formation of non-porous, compact CBO thin films. The highest current density of the photoelectrochemical (PEC) oxygen reduction reaction is obtained with non-porous, compact CBO thin films due to unimpeded charge transport through the CBO bulk, as well as across the interface. When combined with silicon, the high-density CBO thin film investigated in this work is expected to provide new PEC tandem cell options to use for solar applications.

Fabrication of nanocomposite photocatalyst CuBi2O4/Bi3ClO4 for removal of acid brown 14 as water pollutant under visible light irradiation

In the present study, CuBi₂O₄/Bi₃ClO₄ nanocomposites have been fabricated via an improved Pechini sol-gel process using the mixtures of various gelling agents and polybasic acids. This work shows that by controlling the reaction conditions such as kind of polybasic acids, gelling agents, pH and mole ratio of polybasic acid to total metals, the CuBi₂O₄/Bi₃ClO₄ nanocomposites with ultrafine sphere-like, irregular polyhedral-like, plate-like and cubic-like morphologies were prepared. The phase, elemental composition, morphology and optical characteristics of as-synthesized CuBi₂O₄/Bi₃ClO₄ nanostructures were analyzed utilizing UV-Vis, FESEM, TEM, HRTEM, FT-IR, XRD, TOC and EDS techniques. Furthermore, the CuBi₂O₄/Bi₃ClO₄ nanocomposites exhibited excellent TOC removal (75%) and photocatalytic activity (92%) to photodegradation of acid brown 14 azo dye as water pollutants under visible light irradiation. The excellent degradation activity of CuBi₂O₄/Bi₃ClO₄ photocatalyst can be attributed to the strong visible light absorption, high charge separation efficiency, fine particle size distribution and proper band gap of the nanocomposite. In addition, the reliable photocatalytic mechanism was discussed on the basis of the radical trapping study, which revealed the h⁺ and O₂^- radicals were the prevailing active species in the photocatalytic process.

Latest advances in supercapacitors: from new electrode materials to novel device designs

Notably, many significant breakthroughs for a new generation of supercapacitors have been reported in recent years, related to theoretical understanding, material synthesis and device designs. Herein, we summarize the state-of-the-art progress toward mechanisms, new materials, and novel device designs for supercapacitors. Firstly, fundamental understanding of the mechanism is mainly focused on the relationship between the structural properties of electrode materials and their electrochemical performances based on some in situ characterization techniques and simulations. Secondly, some emerging electrode materials are discussed, including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), MXenes, metal nitrides, black phosphorus, LaMnO₃, and RbAg₄I₅/graphite. Thirdly, the device innovations for the next generation of supercapacitors are provided successively, mainly emphasizing flow supercapacitors, alternating current (AC) line-filtering supercapacitors, redox electrolyte enhanced supercapacitors, metal ion hybrid supercapacitors, micro-supercapacitors (fiber, plane and three-dimensional) and multifunctional supercapacitors including electrochromic supercapacitors, self-healing supercapacitors, piezoelectric supercapacitors, shape-memory supercapacitors, thermal self-protective supercapacitors, thermal self-charging supercapacitors, and photo self-charging supercapacitors. Finally, the future developments and key technical challenges are highlighted regarding further research in this thriving field.

Heterogeneous activation of peroxymonosulfate by hierarchical CuBi2O4 to generate reactive oxygen species for refractory organic compounds degradation: morphology and surface chemistry derived reaction and its mechanism

Activation of peroxymonosulfate (PMS) by a novel hierarchical CuBi₂O₄ generated reactive oxygen radical for degradation refractory organic compounds in aqueous solution, which would be controlled by the morphology and surface chemistry of solid catalyst. It's found that the activation ability of CuBi₂O₄ toward PMS was highly dependent on the morphology and surface hydroxyl group, as using rhodamine B (RhB) as the model compound. The spherical CuBi₂O₄, which possessed higher density of surface hydroxyl group, exhibited better catalytic activity in RhB degradation than scattered cluster CuBi₂O₄, and as-prepared CuBi₂O₄ could efficiently activated PMS to degrade RhB within a wide pH range as an absolute heterogeneous process. The emerging organic chemicals, including bisphenol A, 1H-benzotriazole, and carbamazepine, could also be effectively removed in this novel CuBi₂O₄/PMS. Furthermore, activation mechanism of PMS by as-prepared CuBi₂O₄ was proposed, the existence of surface hydroxyl group bonded with Cu(II), and inward electron transfer cycling reaction between Cu(II)/Cu(I) facilitated the effective activation of PMS to generate SO₄^·- and ·OH. In addition, the intermediates of RhB formed in this process were identified by silylation derivatation-GC-MS and LC-high-resolution MS/MS, and degradation pathway was proposed.

Carbon nanofibers (CNFs) supported cobalt- nickel sulfide (CoNi2S4) nanoparticles hybrid anode for high performance lithium ion capacitor

Lithium ion capacitors possess an ability to bridge the gap between lithium ion battery and supercapacitor. The main concern of fabricating lithium ion capacitors is poor rate capability and cyclic stability of the anode material which uses sluggish faradaic reactions to store an electric charge. Herein, we have fabricated high performance hybrid anode material based on carbon nanofibers (CNFs) and cobalt-nickel sulfide (CoNi₂S₄) nanoparticles via simple electrospinning and electrodeposition methods. Porous and high conducting CNF@CoNi₂S₄ electrode acts as an expressway network for electronic and ionic diffusion during charging-discharging processes. The effect of anode to cathode mass ratio on the performance has been studied by fabricating lithium ion capacitors with different mass ratios. The surface controlled contribution of CNF@CoNi₂S₄ electrode was 73% which demonstrates its excellent rate capability. Lithium ion capacitor fabricated with CNF@CoNi₂S₄ to AC mass ratio of 1:2.6 showed excellent energy density of 85.4 Wh kg⁻¹ with the power density of 150 W kg⁻¹. Also, even at the high power density of 15 kW kg⁻¹, the cell provided the energy density of 35 Wh kg⁻¹. This work offers a new strategy for designing high-performance hybrid anode with the combination of simple and cost effective approaches.

Hierarchical CuBi2O4 microspheres as lithium-ion battery anodes with superior high-temperature electrochemical performance

Hierarchical CuBi₂O₄ microspheres as anode materials for Li-ion batteries show superior high-temperature electrochemical performance due to its multilevel structure and outstanding thermostability.