| 1. |
- Aftab, Umair, et al.
(author)
-
The chemically reduced CuO-Co3O4 composite as a highly efficient electrocatalyst for oxygen evolution reaction in alkaline media
- 2019
-
In: Catalysis Science & Technology. - : ROYAL SOC CHEMISTRY. - 2044-4753 .- 2044-4761. ; 9:22, s. 6274-6284
-
Journal article (peer-reviewed)abstract
- The fabrication of efficient, alkaline-stable and nonprecious electrocatalysts for the oxygen evolution reaction is highly needed; however, it is a challenging task. Herein, we report a noble metal-free advanced catalyst, i.e. the chemically reduced mixed transition metal oxide CuO-Co3O4 composite, with outstanding oxygen evolution reaction activity in alkaline media. Sodium borohydride (NaBH4) was used as a reducing agent for the mixed transition metal oxide CuO-Co3O4. The chemically reduced composite carried mixed valence states of Cu and Co, which played a dynamic role in driving an excellent oxygen evolution reaction process. The X-ray photo-electron spectroscopy (XPS) study confirmed high density of active sites in the treated sample with a large number of oxygen vacancies. The developed electrocatalyst showed the lowest overpotential of 144.5 mV vs. the reversible hydrogen electrode (RHE) to achieve the current density of 40 mA cm(-2) and remained stable for 40 hours throughout the chronoamperometry test at the constant potential of 1.39 V vs. RHE. Moreover, the chemically reduced composite was highly durable. Electrochemical impedance spectroscopy (EIS) confirmed the low charge transfer resistance of 13.53 ohms for the chemically reduced composite, which was 50 and 26 times smaller than that of Co3O4 and untreated CuO-Co3O4, respectively. The electrochemically active surface area for the chemically reduced composite was found to be greater than that for pristine CuO, Co3O4 and untreated pristine CuO-Co3O4. These findings reveal the possibility of a new gateway for the capitalization of a chemically reduced sample into diverse energy storage and conversion systems such as lithium-ion batteries and supercapacitors.
|
|
| 2. |
- Hassaan, Muhammad Umair, et al.
(author)
-
Highly Efficient Energy Transfer in Light Emissive Poly(9,9-dioctylfluorene) and Poly(p-phenylenevinylene) Blend System
- 2018
-
In: ACS Photonics. - : AMER CHEMICAL SOC. - 2330-4022. ; 5:2, s. 607-613
-
Journal article (peer-reviewed)abstract
- A polymer blend system F8(1-x):SYx based on poly(9,9-dioctylfluorene) (F8) from the family of polyfluorenes (PFO) and a poly(para-phenylenevinylene) (PPV) derivative superyellow (SY) shows highly efficient energy transfer from F8 host to SY guest molecules. This has been realized due to a strong overlap between F8 photoemission and SY photoabsorption spectra and negligibly low self-absorption. The steady-state and time-correlated spectroscopic measurements show an increased photo-luminescence quantum efficiency (PLQE) and lifetime (tau) of SY, with an opposite trend of decreasing PLQE and tau of F8 excitons with increasing SY concentration, suggesting the Forster resonance energy transfer (FRET) to be the main decay pathway in the proposed system. The systematic study of the exciton dynamics shows a complete energy transfer at 10% of SY in the F8 host matrix and a Forster radius of similar to 6.3 nm. The polymer blend system exhibits low laser and amplified spontaneous emission thresholds. An ultrahigh efficiency (27 cd.A(-1)) in F8(1-x):SYx based light emitting diodes (LED) has been realized due to the intrinsic property of a well-balanced charge transport within the emissive layer. The dual pathway, that is, the efficient energy transfer between the blended molecules via resonance energy transfer, and the charge-traps-assisted balanced transport makes the system promising for achieving highly efficient devices and a potential candidate for lasing applications.
|
|
| 3. |
- Mugheri, Abdul Qayoom, et al.
(author)
-
An advanced and efficient Co3O4/C nanocomposite for the oxygen evolution reaction in alkaline media
- 2019
-
In: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 9:59, s. 34136-34143
-
Journal article (peer-reviewed)abstract
- The design of efficient nonprecious catalysts for the hydrogen evolution reaction (HER) or the oxygen evolution reaction (OER) is a necessary, but very challenging task to uplift the water-based economy. In this study, we developed a facile approach to produce porous carbon from the dehydration of sucrose and use it for the preparation of nanocomposites with cobalt oxide (Co3O4). The nanocomposites were studied by the powder X-ray diffraction and scanning electron microscopy techniques, and they exhibited the cubic phase of cobalt oxide and porous structure of carbon. The nanocomposites showed significant OER activity in alkaline media, and the current densities of 10 and 20 mA cm(-2) could be obtained at 1.49 and 1.51 V versus reversible hydrogen electrode (RHE), respectively. The impedance study confirms favorable OER activity on the surface of the prepared nanocomposites. The nanocomposite is cost-effective and can be capitalized in various energy storage technologies.
|
|
| 4. |
- Mugheri, Abdul Qayoom, et al.
(author)
-
Efficient tri-metallic oxides NiCo2O4/CuO for the oxygen evolution reaction
- 2019
-
In: RSC ADVANCES. - : ROYAL SOC CHEMISTRY. - 2046-2069. ; 9:72, s. 42387-42394
-
Journal article (peer-reviewed)abstract
- In this study, a simple approach was used to produce nonprecious, earth abundant, stable and environmentally friendly NiCo2O4/CuO composites for the oxygen evolution reaction (OER) in alkaline media. The nanocomposites were prepared by a low temperature aqueous chemical growth method. The morphology of the nanostructures was changed from nanowires to porous structures with the addition of CuO. The NiCo2O4/CuO composite was loaded onto a glassy carbon electrode by the drop casting method. The addition of CuO into NiCo2O4 led to reduction in the onset potential of the OER. Among the composites, 0.5 grams of CuO anchored with NiCo2O4 (sample 2) demonstrated a low onset potential of 1.46 V vs. a reversible hydrogen electrode (RHE). A current density of 10 mA cm(-2) was achieved at an over-potential of 230 mV and sample 2 was found to be durable for 35 hours in alkaline media. Electrochemical impedance spectroscopy (EIS) indicated a small charge transfer resistance of 77.46 ohms for sample 2, which further strengthened the OER polarization curves and indicates the favorable OER kinetics. All of the obtained results could encourage the application of sample 2 in water splitting batteries and other energy related applications.
|
|
| 5. |
- Mugheri, Abdul Qayoom, et al.
(author)
-
Facile efficient earth abundant NiO/C composite electrocatalyst for the oxygen evolution reaction Electronic supplementary information (ESI) available. See DOI: 10.1039/c8ra10472g
- 2019
-
In: RSC Advances. - : ROYAL SOC CHEMISTRY. - 2046-2069. ; 9:10, s. 5701-5710
-
Journal article (peer-reviewed)abstract
- Due to the increasing energy consumption, designing efficient electrocatalysts for electrochemical water splitting is highly demanded. In this study, we provide a facile approach for the design and fabrication of efficient and stable electrocatalysts through wet chemical methods. The carbon material, obtained by the dehydration of sucrose sugar, provides high surface area for the deposition of NiO nanostructures and the resulting NiO/C catalysts show higher activity towards the OER in alkaline media. During the OER, a composite of NiO with 200 mg C can produce current densities of 10 and 20 mA cm(-2) at a bias of 1.45 V and 1.47 V vs. RHE, respectively. Electrochemical impedance spectroscopy experiments showed the lowest charge transfer resistance and the highest double layer capacitance in the case of the NiO/C composite with 200 mg C. The presence of C for the deposition of NiO nanostructures increases the active centers and consequently a robust electrocatalytic activity is achieved. The obtained results in terms of the low overpotential and small Tafel slope of 55 mV dec(-1) for non-precious catalysts are clear indications for the significant advancement in the field of electrocatalyst design for water splitting. This composite material based on NiO/C is simple and scalable for widespread use in various applications, especially in supercapacitors and lithium-ion batteries.
|
|
| 6. |
- Qayoom Mugheri, Abdul, et al.
(author)
-
Co3O4/ NiO bifunctional electrocatalyst for water splitting
- 2019
-
In: Electrochimica Acta. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0013-4686 .- 1873-3859. ; 306
-
Journal article (peer-reviewed)abstract
- The development of noble metal free and active bifunctional catalysts for water splitting in alkaline media is highly demanded but very challenging. Herein, synergetic effects developed between two nonprecious metal oxides, Co3O4 and NiO, are reported, with the resulting composite showing promising properties as a catalyst for alkaline water electrolysis. The activity of the composite material towards both the HER and the OER was enhanced and the dynamic potential decreased, as compared with its counterparts. Importantly, low Tafel slopes of 101 and 61 mVdec(-1) are found for the composite catalyst for OER and HER respectively. EIS measurements revealed a decreased impedance response of the composite dominated by the intermediate frequency relaxation, related to the adsorption of intermediates. Moreover, based on the structural features the improved catalytic activity of the composite is also due to high electroactive surface area, swift electron transfer kinetics, and excellent electrical chemical coupling between Co3O4 and NiO. (c) 2019 Elsevier Ltd. All rights reserved.
|
|
| 7. |
|
|
| 8. |
- Tahira, Aneela, et al.
(author)
-
An efficient bifunctional electrocatalyst based on a nickel iron layered double hydroxide functionalized Co3O4 core shell structure in alkaline media
- 2019
-
In: Catalysis Science & Technology. - : Royal Society of Chemistry. - 2044-4753 .- 2044-4761. ; 9:11, s. 2879-2887
-
Journal article (peer-reviewed)abstract
- Developing highly active nonprecious metal and binder free bifunctional electrocatalysts for water splitting is a challenging task. In this study, we used a simple strategy to deposit a nickel iron layered double hydroxide (NiFeLDH) onto cobalt oxide (Co3O4) nanowires. The cobalt oxide nanowires are covered with thin nanosheets of NiFeLDH forming a core shell structure. The Co3O4 nanowires contain the mixed oxidation states of Co2+ and Co3+, and the surface modification of Co3O4 nanowires has shown synergetic effects due to there being more oxygen defects, catalytic sites, and enhanced electronic conductivity. Further, the core shell structure of Co3O4 nanowires demonstrated a bifunctional activity for water splitting in 1 M KOH aqueous solution. From the hydrogen evolution reaction (HER), a current density of 10 mA cm - 2 is achieved at a potential of - 0.303 V vs. reversible hydrogen electrode (RHE). Meanwhile for the case of the oxygen evolution reaction (OER), a current density of 40 mA cm - 2 is measured at a potential of 1.49 V vs. RHE. Also, this electrocatalyst has shown a considerable long- term stability of 15 h for both the HER and the OER. Importantly, electrochemical impedance spectroscopy has shown that the NiFeLDH integration onto cobalt oxide exhibited around 3 fold decrease of charge transfer resistance for both the HER and the OER in comparison with pristine cobalt oxide films, which reveals an excellent electrocatalytic activity for both faradaic processes. All these results confirm that the proposed electrocatalyst can be integrated into an efficient water splitting system.
|
|
| 9. |
- Umair Hassan, Muhammad, et al.
(author)
-
Low Thresholds for a Nonconventional Polymer Blend-Amplified Spontaneous Emission and Lasing in F8(1-x):SYx System
- 2016
-
In: Journal of Polymer Science Part B. - : WILEY-BLACKWELL. - 0887-6266 .- 1099-0488. ; 54:1, s. 15-21
-
Journal article (peer-reviewed)abstract
- A mixture of two polymer materials, poly (9,9-dioctylfluorene) (F8), and one of the poly(para-phenylenevinylene) derivatives, superyellow (SY) have been used to make F8(1-x):SYx polymer blend system. Under a 3-5 ns pulsed-laser excitation, this system showed excellent optical properties with low threshold values of approximate to 14 mJ/cm(2) and approximate to 8 mJ/cm(2) for amplified spontaneous emission and optically pumped lasing, respectively. The proposed system was also electroluminescent and an interesting candidate for future research on polymer injection lasers. (C) 2015 Wiley Periodicals, Inc.
|
|
| 10. |
- Umair, Muhammad, et al.
(author)
-
Positronium-dipole induced resonances in e(+)-H and e(+)-alkali systems
- 2017
-
In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 50:4
-
Journal article (peer-reviewed)abstract
- We derive general universal scaling relations governing resonances induced by the dipole moment of excited positronium interacting with atomic ions. A single non-universal parameter, which contains all the system-dependent information, is defined. Our results are compared to numerical calculations, using complex scaling, for S, P, and D-wave resonances below the positronium n. =. 2 threshold in the e(+)-(H, Li, Na, K) systems. The energy and width ratios of the successive resonances are found to agree well with the analytically derived scaling law.
|
|
| 11. |
- Umair, Muhammad, et al.
(author)
-
Resonances in a positron-lithium (e+−Li) system
- 2016
-
In: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 93:5
-
Journal article (peer-reviewed)abstract
- The method of complex scaling is used to calculate S- and P-wave resonance energies and widths below the Li(3s, 3p, 4s, 4p) excitation thresholds and positronium n = 2 formation threshold in the positron-lithium system. We use two different types of model potentials to determine the interaction between the core and the valence electron. Explicitly correlated Gaussian basis functions are used to represent the correlation effects between the valence electron, the positron, and the Li+ core. A dipole series of resonances are found under the positronium n = 2 threshold. Furthermore, these resonances are found to agree well with an analytically derived scaling law. The present results are compared with those in the literature.
|
|
| 12. |
- Umair, Muhammad, et al.
(author)
-
Resonances in positron-potassium ($e^{+}$-K) system with natural and unnatural parities
- 2016
-
In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 49:1
-
Journal article (peer-reviewed)abstract
- We present an investigation of resonances with natural and unnatural parities in the positron-potassium system using the complex scaling method. A model potential is used to represent the interaction between the core and the valence electron. Explicitly correlated Gaussian wave functions are used to represent the correlation effects between the valence electron, the positron and the K+ core. Resonance energies and widths for two partial waves (S- and P-wave) below the K(4p, 5s, 5p, 4d, 4f) excitation thresholds and positronium n = 2 formation threshold are calculated for natural parity. Resonance states for P-e below the K(4d) excitation threshold and positronium n = 2, 3 formation thresholds are calculated for unnatural parity which has not been previously reported. Below both positronium thresholds we have found a dipole series of resonances, with binding energies scaling in good agreement with exceptions from an analytical calculation. The present results are compared with those in the literature.
|
|
| 13. |
- Umair, Muhammad, 1984-
(author)
-
Resonances in Three-Body Systems
- 2016
-
Doctoral thesis (other academic/artistic)abstract
- Three particles interacting via Coulomb forces represent a fundamental problem in quantum mechanics with no known exact solution. We have investigated resonance states composed of three particles interacting via Coulombic and more general potentials in non-relativistic quantum mechanics, using the complex scaling method. Our calculations have been applied to three different systems.(i) An investigation of resonances in the positron-alkali (Li, Na, K) systems has been conducted. Some calculations have previously been reported on the resonances in positron-alkali systems; however, most of the work was limited to the lower partial wave, such as S-wave resonances. In this thesis, we have extended the calculations to higher partial waves and extracted the resonance positions and widths using the more accurate complex scaling method. A dipole series of resonances has been found under positronium n = 2 threshold, for natural parity and n = 3 threshold for unnatural parity states. Furthermore, these resonances were found to agree well with an analytically derived scaling law. This series in the positron-alkali system are caused by the attractive potential formed by the dipole moment of positronium (the bound state of an electron and a positron). This dipole moment is a hydrogen-like system, and hence its energy levels are degenerate with respect to orbital angular momentum. We have also predicted several new resonances.(ii) A calculation of resonances in positron-hydrogen scattering, which shows that we can represent this system with the accuracy needed for future scattering calculations. Such cross sections are of interest since this is a way to form anti-hydrogen.(iii) A search for possible resonances in the pµe system, which has been suggested as a possible reason for unexpected results from a recent measurement of the proton radius in muonic hydrogen. We have ruled out the possibility of such resonances.In all calculations we used the Couple Rearrangement Channel Method, where the wave function is represented by Gaussians expressed in Jacobi coordinates. Thus effects due to mass polarization are automatically.
|
|
| 14. |
- Umair, Muhammad, et al.
(author)
-
Resonances with natural and unnatural parities in positron-sodium scattering
- 2015
-
In: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 92:1
-
Journal article (peer-reviewed)abstract
- We present an investigation of resonances in positron-sodium scattering using the complex scaling method. For the target sodium atoms, the interaction between the core and outer electron is treated using two different types of analytical model potentials. Explicitly correlated Gaussian wave functions are used to represent the correlation effects between the outer electron, the positron, and the Na+ core. S-, P-, and D-wave resonances with natural parity have been calculated for energies extending up to the positronium n = 2 formation threshold. Resonance states for unnatural parities Pe and D0 have been calculated for energies extending up to the positronium n = 3 threshold. Below both positronium thresholds we have for each symmetry identified a dipole series of resonances, with binding energies scaling in good agreement with expectations from an analytical calculation. The presented results are compared with other theoretical calculations.
|
|
| 15. |
- Yamashita, Takuma, et al.
(author)
-
Bound and resonance states of positronic copper atoms
- 2017
-
In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 50:20
-
Journal article (peer-reviewed)abstract
- We report a theoretical calculation for the bound and S-wave resonance states of the positronic copper atom (e(+) Cu). A positron is a positively charged particle; therefore, a positronic atom has an attractive correlation between the positron and electron. A Gaussian expansion method is adopted to directly describe this correlation as well as the strong repulsive interaction with the nucleus. The correlation between the positron and electron is much more important than that between electrons in an analogous system of Cu-, although the formation of a positronium (Ps) in e(+) Cu is not expressed in the ground state structure explicitly. Resonance states are calculated with a complex scaling method and identified above the first excited state of the copper atom. Resonance states below Ps (n = 2) + Cu+ classified to a dipole series show agreement with a simple analytical law. Comparison of the resonance energies and widths of e(+) Cu with those of e(+) K, of which the potential energy of the host atom resembles that of e(+) Cu, reveals that the positions of the resonance for the e(+) Cu dipole series deviate equally from those of e(+) K.
|
|
