Pseudocapacitive effects of multi-walled carbon nanotubes-functionalised spinel copper manganese oxide

Spinel copper manganese oxide nanoparticles combined with acid-treated multi-walled carbon nanotubes (CuMn2O4/MWCNTs) were used in the development of electrodes for pseudocapacitor applications. The CuMn2O4/MWCNTs preparation involved initial synthesis of Mn3O4 and CuMn2O4 precursors followed by an energy efficient reflux growthmethod for the CuMn2O4/MWCNTs. The CuMn2O4/MWCNTs in a three-electrode cell assembly and in 3 M LiOH aqueous electrolyte exhibited a specific capacitance of 1652.91 F g1 at 0.5 A g1 current load. Similar investigation in 3 M KOH aqueous electrolyte delivered a specific capacitance of 653.41 F g1 at 0.5 A g1 current load. Stability studies showed that after 6000 cycles, the CuMn2O4/MWCNTs electrode exhibited a higher capacitance retention (88%) in LiOH than in KOH (64%)

High power asymmetric supercapacitor based on activated carbon/reduced graphene oxide electrode system

We synthesized Graphene oxide (GO) using the modified Hummers method and further reduced to reduced graphene oxide (rGO) using hydrazine monohydrate and ammonia solution. The prepared materials were interrogated using different characterization techniques to determine which of them is more suitable for supercapacitor application. High resolution scanning electron microscopy (HRSEM) revealed a sheet-like morphology of separated thin sheets and wrinkled edges for GO, whereas rGO consist of thinner sheets with smaller pores than GO. The structural studies as elucidated from X-ray diffraction (XRD) shows that the GO has more interlayer spacing due to a higher oxygen content as compared to the rGO. The oxygen containing functional groups seen in GO either disappear or are greatly reduced in intensity in rGO as evidenced from the Fourier transform infrared spectroscopy (FTIR) of the materials. The electrochemical studies indicate that the rGO gave a higher current response compared to GO and a specific capacitance of 105.3 and 56.7 F g 1 respectively was delivered by rGO and GO at a scan rate of 10 mV s 1 in a three-electrode set-up. Asymmetric supercapacitor cells using GO and rGO as positive electrodes and activated carbon as the negative electrodes gave the highest specific capacitance value of 94.3 F g 1 for the AC//rGO cell and 59.6 F g 1 for the AC//GO cell at a current load of 0.25 A g 1. The specific capacitance obtained from the AC//rGO is comparable to most recorded values for rGO electrodes. A high specific power of 6411.7 W kg 1 was obtained at a specific energy of 22.6 W h kg 1 while at a specific energy of 25.7 W h kg 1, a specific power of 700.1 W kg 1 was obtained for the AC//rGO. This is due to the more porous and thinner sheet of the rGO. The overall results showed that the rGO gave better supercapacitive properties than the GO

High stability asymmetric supercapacitor cell developed with novel microwave-synthesized graphene-stabilized ruthenium antimonide nanomaterial

Ruthenium antimony oxide (RuSbO), and ruthenium antimony oxide graphene (RuSbO-G) nanomaterial was synthesized via the microwave-assisted method for the first time and tested as a possible electrode material for an asymmetric supercapacitor device. The formation of the nanocomposites was confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images where the RuSbO material showed randomly distributed spherically shaped nanoparticles, and the RuSbO-G showed ruthenium and antimony nanoparticles scattered randomly on the graphene sheets. The SEM-electron dispersion X-ray spectroscopy (SEMEDS) showed significant proof for nanoparticle formation with the elemental composition, while the X-ray photoelectron spectroscopy confirmed the oxidation states of the elements present. Both materials were further characterized in a three-electrode cell setup using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) and their electrochemical properties were compared to establish their suitability for energy storage purposes. From the result, different double layer properties were shown by the RuSbO and RuSbO-G in the 1 M Li2SO4 electrolyte. When compared to the RuSbO electrode, the composite had greater energy storage capabilities with a maximum capacitance of 289.47 F g 1 at 0.1 A g 1 current load. An efficiency of ~100 % was reached at a current density of 0.5 A g 1. Subsequently, both materials were used to fabricate a portable asymmetric supercapacitor. The RuSbO-G device yielded a maximum specific capacitance of 167.96 F g 1, resulting in an energy density of 75.58.0 W h kg 1 at a power density of 360 W kg 1 at 0.1 A g 1 current load, with ~100 % charge retention after 4900 cycles. This study turns a new research light on RuSbO based materials as an energy storage material for supercapacitors

A fumonisins immunosensor based on polyanilino-carbon nanotubes doped with palladium telluride quantum dots

An impedimetric immunosensor for fumonisins was developed based on poly(2,5-dimethoxyaniline)-multi-wall carbon nanotubes doped with palladium telluride quantum dots onto a glassy carbon surface. The composite was assembled by a layer-by-layer method to form a multilayer film of quantum dots (QDs) and poly(2,5-dimethoxyaniline)- multi-wall carbon nanotubes (PDMA-MWCNT). Preparation of the electrochemical immunosensor for fumonisins involved drop-coating of fumonisins antibody onto the composite modified glassy carbon electrode. The electrochemical impedance spectroscopy response of the FB1 immunosensor (GCE/PT-PDMA-MWCNT/anti-Fms-BSA) gave a linear range of 7 to 49 ng L−1 and the corresponding sensitivity and detection limits were 0.0162 kΩ L ng−1 and 0.46 pg L−1 , respectively, hence the limit of detection of the GCE/PT-PDMA-MWCNT immunosensor for fumonisins in corn certified material was calculated to be 0.014 and 0.011 ppm for FB1, and FB2 and FB3, respectively. These results are lower than those obtained by ELISA, a provisional maximum tolerable daily intake (PMTDI) for fumonisins (the sum of FB1, FB2, and FB3) established by the Joint FAO/WHO expert committee on food additives and contaminants of 2 μg kg−1 and the maximum level recommended by the U.S. Food and Drug Administration (FDA) for protection of human consumption (2–4 mg L−1 )

Novel heterojunction superstrate Cu2ZnInS4−x (CZIS) thin film kesterite solar cell with vertical arrays of hexagonal ZnO nanorods window layer

Quaternary Cu2ZnInS4−x (CZIS) thin films have been prepared by a facile and cheap sol-gel spin coating technique. Low-temperature solution-based methods were used to fabricate a heterojunction solar cell in the superstrate architecture with CZIS thin film as the absorber, vertically aligned ZnO nanorod arrays, and CdS as the window and buffer layers respectively. ZnO nanorod arrays were prepared by hydrothermal technique and nanocrystal layer deposition technique were employed for the deposition of CdS-coated ZnO nanorod arrays. CZIS absorber layer was spin coated on the CdS-coated ZnO nanorod arrays and annealed at different temperatures. The vertically aligned ZnO nanorod arrays, and uniformly distributed CdS shell layer were confirmed from morphological studies. The device had a final configuration of Glass/ITO/ZnO NRs/CdS/ CZIS/Ag. HRSEM revealed a nanoflake-like morphology and a band gap between 1.5 and 1.77 eV for the CZIS thin films. CZIS superstrate solar cell had a power conversion efficiency of ∼ 0.61%, an open circuit voltage of ∼ 0.8 V, a short circuit current of ∼ 0.95 mA cm−2 and a fill factor of ∼ 61.35%. This method demonstrates a novel, facile and eco-friendly technique for synthesizing nanocrystalline CZIS thin films with promising photo response from the fabricated device indicating a proof of principle that this material can find application in solar cells.University of the Western Cap

Development of high performance composite lithium ion battery cathode systems with carbon nanotubes functionalised with bimetallic inorganic nanocrystal alloys

Philosophiae Doctor - PhDLithium ion cathode systems based on composites of lithium iron phosphate (LiFePO₄), iron-cobalt-derivatised carbon nanotubes (FeCo-CNT) and polyaniline (PA) nanomaterials were developed. The FeCo-functionalised CNTs were obtained through in-situ reductive precipitation of iron (II) sulfate heptahydrate (FeSO₄.7H₂O) and cobalt (II) chloride hexahydrate (CoCl₂.6H₂O) within a CNT suspension via sodium borohydrate (NaBH₄) reduction protocol. Results from high Resolution Transmission Electron Microscopy (HRTEM) and Scanning Electron Microscopy (SEM) showed the successful attachment FeCo nanoclusters at the ends and walls of the CNTs. The nanoclusters provided viable routes for the facile transfer of electrons during lithium ion deinsertion/insertion in the 3-D nanonetwork formed between the CNTs and adjacent LiFePO₄ particles

Photoluminescence quenching of a novel electroconductive poly(Propylene thiophenoimine)-co-poly(ethylenedioxy thiophene) star copolymer

A generation 1 poly(propylene thiophenoimine)-co-poly(ethylenedioxy thiophene) (G1PPT-co-PEDOT) star copolymer, which exhibits a strong optical absorption over a broad range in the ultraviolet–visible (UV-Vis) region and with good electro/conductive properties, was chemically prepared for the first time. Synthesis of the star copolymer, G1PPT-co-PEDOT was confirmed by spectroscopic studies. Indeed, the disappearance of the very high intensity bands, C–H bending at α-position (687 cm−1), and C=N stretching (1620 cm−1) in the Fourier transform infrared spectroscopy (FTIR) of G1PPT-co-PEDOT, which were initially present in the spectrum of the thiolated starting material, G1PPT, confirmed copolymerization. Furthermore, a large bathochromic shift in the onset wavelength of the UV-Vis absorbance spectra from 367 nm in G1PPT to 674 nm in G1PPT-co-PEDOT further attests of successful copolymerization. The electrochemical analysis of G1PPT-co-PEDOT achieved a highest occupied molecular orbital (HOMO) energy level value of 5.3 eV, which is reminiscent of the value for an ideal electron-donor material. Photoluminescence quenching of up to 82% was observed in solution blends of the G1PPT-co-PEDOT star copolymer and N,N′-diisopropyl naphthalene diimide (NDI)

Palladium-Gold Nanoalloy Surface Modified LiMn2O4 Cathode for Enhanced Li-Ion Battery

Au with Pd nanoparticles were synthesized and coated onto the spinel LiMn2O4 via a coprecipitation calcination method with the objective to improve the microstructure, conductivity, and electrochemical activities of pristine LiMn2O4. The novel LiPdAuxMn2-xO4 composite cathode had high phase purity, well crystallized particles, and more regular morphological structures with narrow size distributions. At enlarged cycling potential ranges the LiPdAuxMn2-xO4 sample delivered 90 mAh g−1 discharge capacity compared to LiMn2O4 (45 mAh g−1). It was concluded that even a small amount of the Pd and Au enhanced both the lithium diffusivity and electrochemical conductivity of the host sample due to the beneficial properties of their synergy

Pseudocapacitive Effects of Multi-Walled Carbon Nanotubes-Functionalised Spinel Copper Manganese Oxide

Spinel copper manganese oxide nanoparticles combined with acid-treated multi-walled carbon nanotubes (CuMn2O4/MWCNTs) were used in the development of electrodes for pseudocapacitor applications. The CuMn2O4/MWCNTs preparation involved initial synthesis of Mn3O4 and CuMn2O4 precursors followed by an energy efficient reflux growth method for the CuMn2O4/MWCNTs. The CuMn2O4/MWCNTs in a three-electrode cell assembly and in 3 M LiOH aqueous electrolyte exhibited a specific capacitance of 1652.91 F g−1 at 0.5 A g−1 current load. Similar investigation in 3 M KOH aqueous electrolyte delivered a specific capacitance of 653.41 F g−1 at 0.5 A g−1 current load. Stability studies showed that after 6000 cycles, the CuMn2O4/MWCNTs electrode exhibited a higher capacitance retention (88%) in LiOH than in KOH (64%). The higher capacitance retention and cycling stability with a Coulombic efficiency of 99.6% observed in the LiOH is an indication of a better charge storage behaviour in this electrolyte than in the KOH electrolyte with a Coulombic efficiency of 97.3%. This superior performance in the LiOH electrolyte than in the KOH electrolyte is attributed to an intercalation/de-intercalation mechanism which occurs more easily in the LiOH electrolyte than in the KOH electrolyte

Photoluminescence Quenching of a Novel Electroconductive Poly(propylene thiophenoimine)-co-Poly(ethylenedioxy thiophene) Star Copolymer

A generation 1 poly(propylene thiophenoimine)-co-poly(ethylenedioxy thiophene) (G1PPT-co-PEDOT) star copolymer, which exhibits a strong optical absorption over a broad range in the ultraviolet–visible (UV-Vis) region and with good electro/conductive properties, was chemically prepared for the first time. Synthesis of the star copolymer, G1PPT-co-PEDOT was confirmed by spectroscopic studies. Indeed, the disappearance of the very high intensity bands, C–H bending at α-position (687 cm−1), and C=N stretching (1620 cm−1) in the Fourier transform infrared spectroscopy (FTIR) of G1PPT-co-PEDOT, which were initially present in the spectrum of the thiolated starting material, G1PPT, confirmed copolymerization. Furthermore, a large bathochromic shift in the onset wavelength of the UV-Vis absorbance spectra from 367 nm in G1PPT to 674 nm in G1PPT-co-PEDOT further attests of successful copolymerization. The electrochemical analysis of G1PPT-co-PEDOT achieved a highest occupied molecular orbital (HOMO) energy level value of 5.3 eV, which is reminiscent of the value for an ideal electron-donor material. Photoluminescence quenching of up to 82% was observed in solution blends of the G1PPT-co-PEDOT star copolymer and N,N′-diisopropyl naphthalene diimide (NDI). This demonstrates the occurrence of photoinduced intermolecular charge transfer (PICT) from the electron-donating G1PPT-co-PEDOT to the electron accepting NDI, a good property, beneficial for optoelectronic and photovoltaic applications