Fabrication of g-C3N4 Nanomesh-Anchored Amorphous NiCoP2O7: Tuned Cycling Life and the Dynamic Behavior of a Hybrid Capacitor

Optimum iron-pyrophosphate electronic coupling to improve electrochemical water splitting and charge storage

Tuning the electronic properties of transition metals using pyrophosphate (P2O7) ligand moieties can be a promising approach to improving the electrochemical performance of water electrolyzers and supercapacitors, although such a material's configuration is rarely exposed. Herein, we grow NiP2O7, CoP2O7, and FeP2O7 nanoparticles on conductive Ni-foam using a hydrothermal procedure. The results indicated that, among all the prepared samples, FeP2O7 exhibited outstanding oxygen evolution reaction and hydrogen evolution reaction with the least overpotential of 220 and 241 mV to draw a current density of 10 mA/cm2. Theoretical studies indicate that the optimal electronic coupling of the Fe site with pyrophosphate enhances the overall electronic properties of FeP2O7, thereby enhancing its electrochemical performance in water splitting. Further investigation of these materials found that NiP2O7 had the highest specific capacitance and remarkable cycle stability due to its high crystallinity as compared to FeP2O7, having a higher percentage composition of Ni on the Ni-foam, which allows more Ni to convert into its oxidation states and come back to its original oxidation state during supercapacitor testing. This work shows how to use pyrophosphate moieties to fabricate non-noble metal-based electrode materials to achieve good performance in electrocatalytic splitting water and supercapacitors.

Carbon Nitride Coupled Co3O4: A Pyrolysis-Based Approach for High-Performance Hybrid Energy Storage

Graphitic carbon nitride (CN) is a cost-effective and easily synthesized supercapacitor electrode material. However, its limited specific capacity has hindered its practical use. To address this, we developed a binary nanostructure by growing nanosized Co3O4 particles on CN. The CN-Co-2 composite, synthesized via thermal decomposition, exhibited a remarkable specific capacity of 280.64 C/g at 2 A/g. Even under prolonged cycling at 10.5 A/g, the retention rate exceeded 95%, demonstrating exceptional stability. In an asymmetric capacitor device, the CN-Co composite delivered 20.84 Wh/kg at 1000 W/kg, with a retention rate of 99.97% over 20,000 cycles, showcasing outstanding cycling stability. Controlled cobalt source adjustments yielded high-capacity electrode materials with battery-like behavior. This optimization strategy enhances energy density by retaining battery-like properties. In summary, the CN-Co composite is a promising, low-cost, easily synthesized electrode material with a high specific capacity and remarkable cycling stability, making it an attractive choice for energy storage applications.

Salts-assistant synthesis of g-C3N4/Prussian-blue analogue/nickel foam with hierarchical structures as binder-free electrodes for supercapacitors

The exploitation of high-performance electrode materials is significant to develop supercapacitors with satisfied energy and power output properties. In this study, a g-C₃N₄/Prussian-blue analogue (PBA)/Nickel foam (NF) with hierarchical micro/nano structures was developed by a simple salts-directed self-assembly approach. In this synthetic strategy, NF acted as both 3D macroporous conductive substrate and Ni source for PBA formation. Moreover, the incidental salt in molten salt-synthesized g-C₃N₄ nanosheets could regulate the combination mode between g-C₃N₄ and PBA to generate interactive networks of g-C₃N₄ nanosheets-covered PBA nano-protuberances on NF surfaces, which further expended the electrode/electrolyte interfaces. Based on the merits from this unique hierarchical structure and the synergy effect of PBA and g-C₃N₄, the optimized g-C₃N₄/PBA/NF electrode exhibited a maximum areal capacitance of 3366 mF cm^-2 at current of 2 mA cm^-2, as well as 2118 mF cm^-2 even under large current of 20 mA cm^-2. The solid-state asymmetric supercapacitor using g-C₃N₄/PBA/NF electrode possessed an extended working potential window of 1.8 V, prominent energy density of 0.195 mWh cm^-2 and power density of 27.06 mW cm^-2. Compared to the device with pure NiFe-PBA electrode, a better cyclic stability with capacitance retention rate of 80% after 5000 cycles was also achieved due to the protective effect of g-C₃N₄ shells on the etching of PBA nano-protuberances in electrolyte. This work not only builds a promising electrode material for supercapacitors, but also provide an effective way to apply molten salt-synthesized g-C₃N₄ nanosheet without purification.

Formation of Carbon-Incorporated NiO@Co3O4 Nanostructures via a Direct Calcination Method and Their Application as Battery-Type Electrodes for Hybrid Supercapacitors

Nickel and cobalt oxides are promising electrode materials for supercapacitors, but their poor conductivity and sluggish kinetics seriously hinder their application. Herein, a simple one-step calcination method was proposed to prepare carbon-incorporated NiO@Co₃O₄ (denoted as CNC) using a NiCo Prussian blue analogue (NiCo-PBA) as a precursor. The effect of calcination temperature on the electrochemical behavior of CNC was investigated. Benefiting from the relatively large specific surface area and porous structure characteristics, when used as an electrode for supercapacitors, the CNC obtained at 400 °C shows the typical features of a battery-type electrode, with a good specific capacitance of 208.5 F g^-1 at 1 A g^-1 and a rate capability of 70.8% at 30 A g^-1. The hybrid supercapacitor (HSC) constructed with the optimum CNC electrode can provide a high energy density of 32.6 Wh kg^-1 at the corresponding power density of 750.0 W kg^-1 and an excellent cycling stability of 87.1% over 5000 cycles. This study provides a simple calcination method for preparing MOF-derived high-conductivity mixed metal oxide electrode materials for supercapacitors.

Electro-oxidation of heavy metals contaminated water using banana waste-derived activated carbon and Fe3O4 nanocomposites

The main objective of this study was to banana waste-derived activated carbon (BWAC) make a high pore surface area was prepared and composited with Fe₃O₄ via a facile hydrothermal method. Various physiochemical characteristics of the prepared samples were evaluated using XRD, FTIR, FESEM, Raman Spectroscopy and XPS analysis. In addition, cyclic voltammetry and electrochemical impedance spectroscopy analyses were performed to determine the electrochemical properties of the prepared samples. The Fe₃O₄/BWAC sample showed a higher capacitance (285 F g^-1) than BWAC at the same scan rate of 10 mV s^-1. The capacitive deionization (CDI) cell configuration was varied, and its electro-sorption and defluoridization efficiencies were analyzed during the lead (Pb²⁺) removal 90%. An asymmetric combination of electrodes in the CDI cell exhibited better heavy metal removal performance, possibly due to the synergistic effect of the high surface area and the balance between the active adsorption site and the overlapping effect of the EDL. As a result, Fe₃O₄/BWAC could be a potential resource for supercapacitors and CDI electrodes, and the novel Fe₃O₄/BWAC nanocomposites outstanding performance suggests that they could be helpful for future energy storage and environmental applications.

Augmenting the Photocatalytic Performance of Direct Z-Scheme Bi2O3/g-C3N4 Nanocomposite

Huge demands for photocatalytically efficient visible-light-induced catalysts have spurred widespread interest in building adaptable heterojunctions. Here, we used in situ thermal polymerization to synthesise the Z-scheme Bi2O3/g-C3N4 heterojunction. The optical, structural, chemical, compositional and photocatalytic behaviours of the samples were analysed through various analytical techniques and photocatalytic methylene blue (MB) dye degradation reaction. Among the various ratios of Bi2O3/g-C3N4 heterojunction composites, the 1:1 ratio showed improved visible-light-induced catalytic activity, which attained 91.2% degradation efficiency after 120 min of visible-light exposure. The dye degradation efficiency was calculated under various environmental conditions by varying the dye concentration, solution pH and catalyst dosage. A improved Z-scheme photocatalytic mechanism was proposed in light of the results. A potential mechanism was suggested to explain the photocatalytic activity, and trapping experiments supported it. Last but not least, this strategy might be helpful to prepare the heterojunction photocatalyst for the degradation of organic pigments.

Intimately coupled gC3N4 photocatalysis and mixed culture biofilm enhanced detoxification of sulfamethoxazole: Elucidating degradation mechanism and toxicity assessment

In recent years, wide spread of antibiotic-resistant microorganisms and genes emerging globally, an eco-friendly method for efficient degradation of antibiotics from the polluted environment is essential. Intimately coupled photocatalysis and biodegradation (ICPB) using gC₃N₄ for enhanced degradation of sulfamethoxazole (SMX) was investigated. The gC₃N₄ were prepared and coated on the carbon felt. The mixed culture biofilm was developed on the surface as a biocarrier. The photocatalytic degradation showed 74%, and ICPB exhibited 95% SMX degradation efficiency. ICPB showed superior visible light adsorption, photocatalytic activity, and reduced charge recombination. The electron paramagnetic resonance spectrum confirms that the generation of •OH and O₂• radicals actively participated in the degradation of SMX into biodegradable intermediated compounds, and then, the bacterial communities present in the biofilm mineralized the biodegradable compound into carbon dioxide and water. Moreover, the addition of NO₃^-, PO₄^-, and Cl^- significantly enhanced the degradation efficiency by trapping the surface electron. Stability experiments confirmed that gC₃N₄ biohybrid can maintain 85% SMX degradation efficiency after 5 consecutive recycling. Extracellular polymeric substances characterization results show that biohybrid contains 47 mg/L, 14 mg/L, and 13 mg/L protein, carbohydrate, and humic acid, respectively, which can protect the bacterial communities from the antibiotic toxicity and reactive oxygen species. Furthermore, biotoxicity was investigated using degradation products on E.coli and results revealed 83% detoxification efficiency. Overall, this study suggested that gC₃N₄ photocatalyst in an ICPB can be used as a promising eco-friendly method to degrade sulfamethoxazole efficiently.

In Situ Synthesis of CoCeSx Bimetallic Sulfide Nanoparticles on a Bi-Pyrene Terminated Molecular Wire Modified Graphene Surface for Supercapacitors

The excellent electrical conductivity of graphene is due to its highly-conjugated structures. Manipulation of the electronic and mechanical properties of graphene can be achieved by controlling the destruction of its in-sheet conjugation system. Herein, we report the preparation of CoCeS_x -SA@BPMW@RGO through π-π stacking interactions at the molecular level. In this study, sodium alginate was reacted with Co²⁺ and Ce³⁺ , and the composite was loaded onto a graphene surface. The graphene sheets were prepared using a bi-pyrene terminated molecular wire (BPMW) to avoid re-stacking of the grapheme sheets, thereby forming nanoscale spaces between sheets. The angle between the BPMW coplanar pyrene group and the phenyl group was 33.2°, and the graphene layer is supported in an oblique direction. Finally, a three-dimensional porous composite was obtained after annealing and vulcanization. The obtained CoCeS_x -SA@BPMW@RGO exhibited excellent electrical conductivity and remarkable cycle stability. When the current density was 1 A g^-1 , its specific capacitance was as high as 1004 F g^-1 . BPMW modifies graphene through the synergistic effect of π-π stacking interaction and special structure to obtain excellent electrochemical performance. Moreover, a solid-state asymmetric supercapacitor device was fabricated based on the synthesized CoCeS_x -SA@BPMW@RGO hybrid, which exhibited a power density of 979 W kg^-1 at an energy density of 23.96 Wh kg^-1 .

Controlled synthesis of a hierarchical CuNi2O4@SnS nanocauliflower-like structure on rGO as a positive electrode material for an asymmetric supercapacitor

Hierarchical CuNi2O4@SnS@rGO/NF is a promising electrode material for building up an impressive supercapacitor.

A binder-free Ni2P2O7/Co2P2O7 nanograss array as an efficient cathode for supercapacitors

Binder-free Ni₂P₂O₇/Co₂P₂O₇ cathode of nanograss morphology, delivered an energy and power density of 33.2 W h kg⁻¹ and 257.8 W kg⁻¹ respectively. Through power law, the contribution of each type of mechanism in charge storage process was calculated.

Interfacial synthesis of micro-cuboid Ni0.55Co0.45C2O4 solid solution with enhanced electrochemical performance for hybrid supercapacitors

Efficient charge and energy storage relies essentially on the development of innovative electrode materials with enhanced electrochemical kinetics. Herein, Ni_0.55Co_0.45C₂O₄ solid solution was successfully synthesized by a liquid-liquid interfacial reaction. The observation of the morphologies of Ni_0.55Co_0.45C₂O₄ depicts a peculiar micro-cuboid structure composed of nanoparticles in the size range of 13 to 23 nm, benefiting the increase in the contribution of surface-controlled reactions to charge storage processes. The results from X-ray diffraction and thermogravimetric analysis demonstrate the similarity of the crystal structure and thermal decomposition behavior between Ni_0.55Co_0.45C₂O₄ and CoC₂O₄, and indicate that the CoC₂O₄ lattice plays a role as the fundamental framework in the solid solution instead of NiC₂O₄. The electrochemical measurements show that Ni_0.55Co_0.45C₂O₄ achieves a higher specific capacity of 562 C g^-1 at a current density of 1 A g^-1 than its counterpart NiC₂O₄/CoC₂O₄ hybrids, due to this the alternative arrangement of nickel and cobalt species in the solid solution expedites the diffusion process of active ions during the electrochemical reaction. Depending on the enhancement of the electrochemical stability in the solid solution, Ni_0.55Co_0.45C₂O₄ electrodes retain 87.4% of the initial capacity after 4000 cycles. The assembled Ni_0.55Co_0.45C₂O₄//AC hybrid supercapacitor attains an energy density of 38.5 W h kg^-1 at a power density of 799 W kg^-1 with a long cycling life (80% of the initial capacitance after 10 000 cycles). The excellent electrochemical performance suggests that Ni_0.55Co_0.45C₂O₄ is a promising candidate electrode material for supercapacitors.