Hierarchical Fe2O3 hexagonal nanoplatelets anchored on SnO2 nanofibers for high-performance asymmetric supercapacitor device

Tailoring a facile electronic and ionic pathway to boost the storage performance of Fe3O4 nanowires as negative electrode for supercapacitor application

Today, high-energy applications are devoted to boosting the storage performance of asymmetric supercapacitors. Importantly, boosting the storage performance of the negative electrodes is a crucial topic. Fe3O4-based active materials display a promising theoretical storage performance as a negative electrode. Thus, to get a high storage performance of Fe3O4, it must be tailored to have a higher ionic and electronic conductivity and outstanding stability. Functionalized graphite felt (GF) is an excellent candidate for tailoring Fe3O4 with a facile ionic and electronic pathway. However, the steps of the functionalization of GF are complex and time-consuming as well as the energy loss during this step. Thus, the in-situ functionalization of the GF surface throughout the synthesis of Fe3O4 active materials is proposed herein. Fe3O4 is electrodeposited at the in-situ functionalized GF surface with the crystalline nanowires-like structure as revealed from the various analyses; SEM, TEM, Mapping EDX, XPS, XRD, wettability test, and Raman analysis. Advantageously, the synthetic approach introduces full homogeneous and uniform coverage of the large surface area of the GF. Thus, Fe3O4 nanowires with high ionic and electronic conductivity are characterized by a higher storage performance. Interestingly, Fe3O4/GF possesses a high specific capacity of 1418 mC cm-2 at a potential scan rate of 10 mV s-1 and this value retained to 54% at a potential scan rate of 50 mV s-1 at an extended potential window of 1.45 V. Remarkably, the diffusion-controlled reaction is the main contributor of the storage of Fe3O4/GF electrode as revealed by the mechanistic studies.

Rational Design of CoOOH/α-Fe2O3/SnO2 for Boosted Photoelectrochemical Water Oxidation: The Roles of Underneath SnO2 and Surface CoOOH

Hematite (α-Fe2O3) photoanode is a promising candidate for efficient PEC solar energy conversion. However, the serious charge recombination together with the sluggish water oxidation kinetics of α-Fe2O3 still restricts its practical application in renewable energy systems. In this work, a CoOOH/α-Fe2O3/SnO2 photoanode was fabricated, in which the ultrathin SnO2 underlayer is deposited on the fluorine-doped tin oxide (FTO) substrate, α-Fe2O3 nanorod array is the absorber layer, and CoOOH nanosheet is the surface modifier, respectively. The resulting CoOOH/α-Fe2O3/SnO2 exhibited excellent PEC water splitting with a high photocurrent density of 2.05 mA cm-2 at 1.23 V vs RHE in the alkaline electrolyte, which is ca. 3.25 times that of bare α-Fe2O3. PEC characterizations demonstrated that SnO2 not only could block hole transport from α-Fe2O3 to FTO substrate but also could efficiently enhance the light-harvesting property and reduce the surface states by controlling the growth process of α-Fe2O3, while the CoOOH overlayer as cocatalysts could rapidly extract the photogenerated holes and provide catalytic active sites for water oxidation. Benefiting from the synergistic effects of SnO2 and CoOOH, the efficiency of the charge recombination and the overpotential for water oxidation of α-Fe2O3 are obviously decreased, resulting in the boosted PEC efficiency for water oxidation. The rational design and simple fabrication strategy display great potentials to be used for other PEC systems with excellent efficiency.

Novel electrospun bead-like Ag2MoO4 nanofibers coated on Ni foam for visible light-driven heterogeneous photocatalysis and high-performance supercapacitor electrodes

Novel Ag2MoO4 nanocomposite fibers were designed to enhance the photocatalytic response and supercapacitor performance of MoO3 grown via the sol-gel electrospinning technique. The Ag2MoO4 nanocomposite fibers exhibit a high specific surface area of 49.3 m2 g-1 comprising nanobeads that aggregate in the fibrous structure. The photodegradation efficiency of Ag2MoO4 was evaluated as 62% under visible light irradiation which improved to 71% with heterogeneous photocatalysis. The Ag2MoO4@Ni foam exhibited a low Rct of 19.6 Ω, and an enhanced specific capacitance of 1445 F g-1 was obtained at 1 A g-1, with 93% of its initial capacitance remaining after 5000 cycles. In addition, the Ag2MoO4//activated carbon asymmetric supercapacitor possesses an excellent energy density of 76.6 W h kg-1 at 743.2 W kg-1 and a noteworthy cycling durability of 91% after 5000 cycles. Our findings demonstrate that the electrospun Ag2MoO4@Ni foam is an important and inexpensive electrode material for supercapacitor applications and visible light-driven heterogeneous photocatalysis, drawing on the synergic effects of Ag and Mo to exhibit much better performance.

Ni/Mn metal-organic framework decorated bacterial cellulose (Ni/Mn-MOF@BC) and nickel foam (Ni/Mn-MOF@NF) as a visible-light photocatalyst and supercapacitive electrode

Recently, metal-organic frameworks (MOFs) and hybrids with biomaterial are broadly investigated for a variety of applications. In this work, a novel dual-phase MOF has been grown on bacterial cellulose (BC) as a biopolymer nano-fibrous film (Ni/Mn-MOF@BC), and nickel foam (Ni/Mn-MOF@NF) using a simple reflux method to explore their potential for photocatalyst and energy storage applications. The studies showed that the prepared Mn and Ni/Mn-MOFs display different structures. Besides, the growth of MOFs on BC substantially changed the morphology of the samples by reducing their micro sized scales to nanoparticles. The nanosized MOF particles grown on BC served as a visible-light photocatalytic material. Regarding the high surface area of BC and the synergistic effect of two metal ions, Ni/Mn-MOF@BC with a lower band gap demonstrates remarkable photocatalytic degradation efficiency (ca. 84% within 3 h) against methylene blue (MB) dye under visible light, and the catalyst retained 65% of its initial pollutant removal properties after four cycles of irradiation. Besides, MOF powders deposited on nickel foam have been utilized as highly capacitive electrochemical electrodes. There, Ni/Mn-MOF@NF electrode also possesses outstanding electrochemical properties, showing a specific capacitance of 2769 Fg-1 at 0.5 Ag-1, and capacity retention of 94% after 1000 cycles at 10 Ag-1.

Boosted electrochemical performance of magnetic caterpillar-like Mg0.5Ni0.5Fe2O4 nanospinels as a novel pseudocapacitive electrode material

Ni-incorporated MgFe₂O₄ (Mg_0.5Ni_0.5Fe₂O₄) porous nanofibers were synthesized using the sol-gel electrospinning method. The optical bandgap, magnetic parameters, and electrochemical capacitive behaviors of the prepared sample were compared with pristine electrospun MgFe₂O₄ and NiFe₂O₄ based on structural and morphological properties. XRD analysis affirmed the cubic spinel structure of samples and their crystallite size is evaluated to be less than 25 nm using the Williamson-Hall equation. FESEM images demonstrated interesting nanobelts, nanotubes, and caterpillar-like fibers for electrospun MgFe₂O₄, NiFe₂O₄, and Mg_0.5Ni_0.5Fe₂O₄, respectively. Diffuse reflectance spectroscopy revealed that Mg_0.5Ni_0.5Fe₂O₄ porous nanofibers possess the band gap (1.85 eV) between the calculated value for MgFe₂O₄ nanobelts and NiFe₂O₄ nanotubes due to alloying effects. The VSM analysis revealed that the saturation magnetization and coercivity of MgFe₂O₄ nanobelts were enhanced by Ni²⁺ incorporation. The electrochemical properties of samples coated on nickel foam (NF) were tested by CV, GCD, and EIS analysis in a 3 M KOH electrolyte. The Mg_0.5Ni_0.5Fe₂O₄@Ni electrode disclosed the highest specific capacitance of 647 F g^-1 at 1 A g^-1 owing to the synergistic effects of multiple valence states, exceptional porous morphology, and lowest charge transfer resistance. The Mg_0.5Ni_0.5Fe₂O₄ porous fibers showed superior capacitance retention of 91% after 3000 cycles at 10 A g^-1 and notable Coulombic efficiency of 97%. Moreover, the Mg_0.5Ni_0.5Fe₂O₄//Activated carbon asymmetric supercapacitor divulged a good energy density of 83 W h Kg^-1 at a power density of 700 W Kg^-1.

Hydrothermal assisted synthesis of hierarchical SnO2 micro flowers with CdO nanoparticles based membrane for energy storage applications

Hierarchical nanostructures with appropriate morphology and surface functionalities are highly desired to achieve an optimized electrochemical property for active electrode materials. This work renders the facile hydrothermal synthesis of CdO, SnO₂, and CdO-SnO₂ nanocomposite, and their capacitive performance was tested. The formation of the pure samples and their composite was committed by low-temperature Raman spectroscopy and x-ray diffraction studies which revealed the tetragonal and cubic structures of CdO and SnO₂ powder samples with good crystallinity and purity. The morphological postmortem reveals the formation of nanoparticles morphology of CdO with a highly smooth surface appearance. Besides, the SnO₂ illustrates the morphology of the micro flowers composed of ultrathin nanosheets. More specifically, the electrochemical properties indicate the pseudocapacitive charge storage mechanism based on cyclic voltammetry and chronopotentiometry analysis. The CdO-SnO₂ composite electrode displayed a higher capacitance due to additional pores/space offered for active sites and continuously allowed electrolyte ions to interact with the inner/outer surface of the electrode. These exciting findings led us to design and fabricate battery hybrid supercapacitors (BHSC) from CdO-SnO_2, and activated carbon (AC), referred to as CdO-SnO₂//AC BHSC, attains a high power delivery (5717 W/kg), and a maximum energy density of 42 Wh/kg at low discharge rate. Noteworthy, a stable cycling performance was obtained with only 91.3% retention after 8000 cycling at a large discharge current of 10 A/g, denoting the magnificent durability of the active electrode material.