Direct liquid fuel cells are among the most promising energy conversion devices for sustainable e... more Direct liquid fuel cells are among the most promising energy conversion devices for sustainable energy applications, especially as portable energy sources. The two most effective fuels are methanol and formic acid (FA), and even though methanol has higher energy content, it is toxic, non-renewable, and has high fuel crossover. However, FA can be produced easily from biomass and it is non-toxic and has a higher open circuit potential among other factors1. Usually, FA can be oxidized through two pathways, a direct pathway that is most desirable and directly produces CO2 2. While the indirect pathway produces CO as an intermedia that can adsorb to the catalyst surface deactivating it (poisoning effect)3. Palladium is known to be the most active catalyst for FA oxidation in acidic media4 but it is also easily poisoned by CO accumulation on its surface. The increase in FA concentration to get higher energy density would make the indirect oxidation pathway more favorable lowering the effi...
Host-guest systems such as hematite/SnO2 have attracted a great deal of interest as photoanodes f... more Host-guest systems such as hematite/SnO2 have attracted a great deal of interest as photoanodes for photoelectrochemical water splitting. In the present work we form an ordered porous tin oxide layer formed by self-organizing anodization of Sn films on a FTO substrate. Subsequently the anodic tin oxide nanostructure is doped with antimony (ATO) by a simple impregnation and annealing treatment, and then decorated with hematite using anodic deposition. Photoelectrochemical water splitting experiments show that compared to conventional SnO2 nanostructures, using a Sb doped nanochannel SnO2 as a host leads to a drastic increase of the water splitting photocurrent response up to 1.5 mA cm(-2) at 1.6 V (vs. RHE) in 1 M KOH under AM 1.5 (100 mW cm(-2) ) conditions compared to 0.04 mA cm(-2) for the non-Sb doped SnO2 scaffold.
Theoretical models were used to predict dielectric permittivities of the thermosetting polyimide ... more Theoretical models were used to predict dielectric permittivities of the thermosetting polyimide (PI) matrix nanocomposite films loading with BaTiO3 (BT) nanoparticles prepared by the alkoxide route. The observed dielectric permittivities are in good agreement with calculated values using Jayasundere equation and effective medium theory when the interactions of nanoparticle-nanoparticle and nanoparticle-polymer are considered. Additionally, temperature dependence of dielectric permittivity of the BT/PI nanocomposite films at 103 Hz was also studied for both heating from −50 to 150 °C and cooling from 150 to −50 °C. The transformation in crystal phase of BT and changes of free volume in PI were considered to be the main factors influencing the dielectric permittivities of the BT/PI nanocomposite films.
International Journal of Hydrogen Energy, Dec 1, 2017
Abstract The generation of renewable solar fuel through photoelectrochemical water splitting is h... more Abstract The generation of renewable solar fuel through photoelectrochemical water splitting is hindered by the inability to identify the right material with the optimum optical, electrical and chemical characteristics. Herein, we demonstrate the ability to fabricate TiO2 hollow porous spheres (HPS)/graphene (Gr) hybrid composite photoanodes for use in solar fuel generation cells. The fabricated materials were characterized by X-ray diffraction, Raman spectroscopy, UV–Vis diffuse reflectance spectroscopy, photoluminescence (PL), scanning electron microscopy and electrochemical techniques. Upon the use of the TiO2 HPS/Gr photoanodes to split water photoelectrochemically under AM 1.5 illumination in 1.0 M KOH aqueous electrolyte, the performance increased with increasing the Gr content, showing a ten-fold increase in the photocurrent for the photoanode containing 5% Gr (1.449 mA cm−2) as compared to bare TiO2 HPS (0.143 mA cm−2). This enhancement is attributed to the effect of Gr in suppressing the recombination of charge carriers, as supported by the PL measurements and the decrease in the dark current upon the addition of Gr, which acts as an electron acceptor and transports electrons more efficiently. Moreover, the transient photocurrent (J–t) tests confirm the stability of the hybrid photoanodes.
Abstract Developing innovative energy storage platforms with long-lasting stability and high ener... more Abstract Developing innovative energy storage platforms with long-lasting stability and high energy and power densities is a substantial endeavor that is urgently needed. To this end, supercapacitors are very promising candidates for such needs. However, supercapacitors still provide energy density that is below the required threshold for long-term applications mainly due to the lack to identify the optimum materials. Transition metal sulfides are a class of materials that can provide high energy density using different current collectors. However, most of the currently used current collectors are rigid, hindering their use in flexible supercapacitor devices. Herein, we report on one-pot electrodeposition of Mn-Ni-Co-S binder-free nanosheets on carbon cloth as a flexible substrate as confirmed via FESEM, XPS, and EDS analyses. The electrochemical characterization revealed that the electrodes exhibited a unique specific capacity of 2451 C g−1 (3771 F g−1) at 1 A/g with excellent stability over a wide range of current densities. The Ni-Mn-Co-S/CC was used in an asymmetric device as the positive electrode with a graphene hydrogel negative electrode providing power density and energy density at 1.0 A/g of 800 W/Kg and 49.55 Wh/Kg, respectively. The constructed device showed 100% Columbic efficiency with 86.5% capacitance retention after 12,000 cycles.
Although transition metal hydroxides are promising candidates as advanced supercapattery material... more Although transition metal hydroxides are promising candidates as advanced supercapattery materials, they suffer from poor electrical conductivity. In this regard, previous studies have typically analyzed separately the impacts of defect engineering at the atomic level and the conversion of hydroxides to phosphides on conductivity and the overall electrochemical performance. Meanwhile, this paper uniquely studies the aforementioned methodologies simultaneously inside an all-in-one simple plasma treatment for nickel cobalt carbonate hydroxide, examines the effect of altering the nickel-to-cobalt ratio in the binder-free defect-engineered bimetallic Ni-Co system, and estimates the respective quantum capacitance. Results show that the concurrent defect-engineering and phosphidation of nickel cobalt carbonate hydroxide boost the amount of effective redox and adsorption sites and increase the conductivity and the operating potential window. The electrodes exhibit ultra-high-capacity of 1462 C g-1, which is among the highest reported for a nickel-cobalt phosphide/phosphate system. Besides, a hybrid supercapacitor device was fabricated that can deliver an energy density of 48 Wh kg-1 at a power density of 800 W kg-1, along with an outstanding cycling performance, using the best performing electrode as the positive electrode and graphene hydrogel as the negative electrode. These results outperform most Ni-Co-based materials, demonstrating that plasma-assisted defect-engineered Ni-Co-P/POx is a promising material for use to assemble efficient energy storage devices.
We demonstrate the fabrication of binder-free electrospun nickel-manganese oxides embedded into c... more We demonstrate the fabrication of binder-free electrospun nickel-manganese oxides embedded into carbon-shell fibrous electrodes. The morphological and structural properties of the assembled electrode materials were elucidated by high-resolution transmission electron microscopy (HR-TEM), field-emission scanning electron microscopy, and glancing-angle X-ray diffraction. The fibrous structure of the electrodes was retained even after annealing at high temperatures. The X-ray photoelectron spectroscopy and HR-TEM analyses revealed the formation of nickel and manganese oxides in multiple oxidation states (Ni2+, Ni3+, Mn2+, Mn3+, and Mn4+) embedded in the carbon shell. The embedded nickel-manganese oxides into the carbon matrix fibrous electrodes exhibit an excellent capacitance (1082 F/g) in 1 M K2SO4 at 1 A/g and possess a high rate capability of 73% at 5 A/g. The high rate capability and capacitance can be attributed to the presence of carbon cross-linked channels, the binder-free nature of the electrodes, and various oxidation states of the Ni-Mn oxides. The asymmetric supercapacitor device constructed of the as-fabricated nanofibers and the bio-derived microporous carbon as the positive and negative electrodes, respectively, sustains up to 1.9 V with a high specific capacitance at 1.5 A/g of 108 F/g. The nanofibrous//bio-derived device exhibits an outstanding specific energy of 54.2 W h/kg with a high specific power of 1425 W/kg. Interestingly, the tested device maintains a high capacitive retention of 92% upon cycling over 10,000 charging/discharging cycles.
Abstract Herein, we report on a facile one pot synthesis of polyoxometalates encapsulated zeolite... more Abstract Herein, we report on a facile one pot synthesis of polyoxometalates encapsulated zeolite imidazolate framework cages (PMo10V2@ZIF-67). The morphological and structural properties of the as synthesized materials were investigated via FESEM, EDS, XRD and FTIR techniques. Moreover, N2 adsorption/desorption isotherms and XPS measurements were carried out to elucidate the textural properties and composition of the fabricated materials. Upon their use as supercapacitor electrodes, the PMo10V2@ZIF-67 electrode exhibited a maximum specific capacitance of 765 F/g at a scan rate of 5 mV/s. Furthermore, a supercapacitor device was assembled using activated carbon as the negative electrode and PMo10V2@ZIF-67 as the positive electrode, delivering a specific power of 702 W/kg and a corresponding specific energy of 20.9 Wh/kg at a charging current density of 1 A/g. In addition, the device shows an excellent long term stability and high Columbic efficiency over 5000 charging and discharging cycles at a charging and discharging current density of 5 A/g.
Direct liquid fuel cells are among the most promising energy conversion devices for sustainable e... more Direct liquid fuel cells are among the most promising energy conversion devices for sustainable energy applications, especially as portable energy sources. The two most effective fuels are methanol and formic acid (FA), and even though methanol has higher energy content, it is toxic, non-renewable, and has high fuel crossover. However, FA can be produced easily from biomass and it is non-toxic and has a higher open circuit potential among other factors1. Usually, FA can be oxidized through two pathways, a direct pathway that is most desirable and directly produces CO2 2. While the indirect pathway produces CO as an intermedia that can adsorb to the catalyst surface deactivating it (poisoning effect)3. Palladium is known to be the most active catalyst for FA oxidation in acidic media4 but it is also easily poisoned by CO accumulation on its surface. The increase in FA concentration to get higher energy density would make the indirect oxidation pathway more favorable lowering the effi...
Host-guest systems such as hematite/SnO2 have attracted a great deal of interest as photoanodes f... more Host-guest systems such as hematite/SnO2 have attracted a great deal of interest as photoanodes for photoelectrochemical water splitting. In the present work we form an ordered porous tin oxide layer formed by self-organizing anodization of Sn films on a FTO substrate. Subsequently the anodic tin oxide nanostructure is doped with antimony (ATO) by a simple impregnation and annealing treatment, and then decorated with hematite using anodic deposition. Photoelectrochemical water splitting experiments show that compared to conventional SnO2 nanostructures, using a Sb doped nanochannel SnO2 as a host leads to a drastic increase of the water splitting photocurrent response up to 1.5 mA cm(-2) at 1.6 V (vs. RHE) in 1 M KOH under AM 1.5 (100 mW cm(-2) ) conditions compared to 0.04 mA cm(-2) for the non-Sb doped SnO2 scaffold.
Theoretical models were used to predict dielectric permittivities of the thermosetting polyimide ... more Theoretical models were used to predict dielectric permittivities of the thermosetting polyimide (PI) matrix nanocomposite films loading with BaTiO3 (BT) nanoparticles prepared by the alkoxide route. The observed dielectric permittivities are in good agreement with calculated values using Jayasundere equation and effective medium theory when the interactions of nanoparticle-nanoparticle and nanoparticle-polymer are considered. Additionally, temperature dependence of dielectric permittivity of the BT/PI nanocomposite films at 103 Hz was also studied for both heating from −50 to 150 °C and cooling from 150 to −50 °C. The transformation in crystal phase of BT and changes of free volume in PI were considered to be the main factors influencing the dielectric permittivities of the BT/PI nanocomposite films.
International Journal of Hydrogen Energy, Dec 1, 2017
Abstract The generation of renewable solar fuel through photoelectrochemical water splitting is h... more Abstract The generation of renewable solar fuel through photoelectrochemical water splitting is hindered by the inability to identify the right material with the optimum optical, electrical and chemical characteristics. Herein, we demonstrate the ability to fabricate TiO2 hollow porous spheres (HPS)/graphene (Gr) hybrid composite photoanodes for use in solar fuel generation cells. The fabricated materials were characterized by X-ray diffraction, Raman spectroscopy, UV–Vis diffuse reflectance spectroscopy, photoluminescence (PL), scanning electron microscopy and electrochemical techniques. Upon the use of the TiO2 HPS/Gr photoanodes to split water photoelectrochemically under AM 1.5 illumination in 1.0 M KOH aqueous electrolyte, the performance increased with increasing the Gr content, showing a ten-fold increase in the photocurrent for the photoanode containing 5% Gr (1.449 mA cm−2) as compared to bare TiO2 HPS (0.143 mA cm−2). This enhancement is attributed to the effect of Gr in suppressing the recombination of charge carriers, as supported by the PL measurements and the decrease in the dark current upon the addition of Gr, which acts as an electron acceptor and transports electrons more efficiently. Moreover, the transient photocurrent (J–t) tests confirm the stability of the hybrid photoanodes.
Abstract Developing innovative energy storage platforms with long-lasting stability and high ener... more Abstract Developing innovative energy storage platforms with long-lasting stability and high energy and power densities is a substantial endeavor that is urgently needed. To this end, supercapacitors are very promising candidates for such needs. However, supercapacitors still provide energy density that is below the required threshold for long-term applications mainly due to the lack to identify the optimum materials. Transition metal sulfides are a class of materials that can provide high energy density using different current collectors. However, most of the currently used current collectors are rigid, hindering their use in flexible supercapacitor devices. Herein, we report on one-pot electrodeposition of Mn-Ni-Co-S binder-free nanosheets on carbon cloth as a flexible substrate as confirmed via FESEM, XPS, and EDS analyses. The electrochemical characterization revealed that the electrodes exhibited a unique specific capacity of 2451 C g−1 (3771 F g−1) at 1 A/g with excellent stability over a wide range of current densities. The Ni-Mn-Co-S/CC was used in an asymmetric device as the positive electrode with a graphene hydrogel negative electrode providing power density and energy density at 1.0 A/g of 800 W/Kg and 49.55 Wh/Kg, respectively. The constructed device showed 100% Columbic efficiency with 86.5% capacitance retention after 12,000 cycles.
Although transition metal hydroxides are promising candidates as advanced supercapattery material... more Although transition metal hydroxides are promising candidates as advanced supercapattery materials, they suffer from poor electrical conductivity. In this regard, previous studies have typically analyzed separately the impacts of defect engineering at the atomic level and the conversion of hydroxides to phosphides on conductivity and the overall electrochemical performance. Meanwhile, this paper uniquely studies the aforementioned methodologies simultaneously inside an all-in-one simple plasma treatment for nickel cobalt carbonate hydroxide, examines the effect of altering the nickel-to-cobalt ratio in the binder-free defect-engineered bimetallic Ni-Co system, and estimates the respective quantum capacitance. Results show that the concurrent defect-engineering and phosphidation of nickel cobalt carbonate hydroxide boost the amount of effective redox and adsorption sites and increase the conductivity and the operating potential window. The electrodes exhibit ultra-high-capacity of 1462 C g-1, which is among the highest reported for a nickel-cobalt phosphide/phosphate system. Besides, a hybrid supercapacitor device was fabricated that can deliver an energy density of 48 Wh kg-1 at a power density of 800 W kg-1, along with an outstanding cycling performance, using the best performing electrode as the positive electrode and graphene hydrogel as the negative electrode. These results outperform most Ni-Co-based materials, demonstrating that plasma-assisted defect-engineered Ni-Co-P/POx is a promising material for use to assemble efficient energy storage devices.
We demonstrate the fabrication of binder-free electrospun nickel-manganese oxides embedded into c... more We demonstrate the fabrication of binder-free electrospun nickel-manganese oxides embedded into carbon-shell fibrous electrodes. The morphological and structural properties of the assembled electrode materials were elucidated by high-resolution transmission electron microscopy (HR-TEM), field-emission scanning electron microscopy, and glancing-angle X-ray diffraction. The fibrous structure of the electrodes was retained even after annealing at high temperatures. The X-ray photoelectron spectroscopy and HR-TEM analyses revealed the formation of nickel and manganese oxides in multiple oxidation states (Ni2+, Ni3+, Mn2+, Mn3+, and Mn4+) embedded in the carbon shell. The embedded nickel-manganese oxides into the carbon matrix fibrous electrodes exhibit an excellent capacitance (1082 F/g) in 1 M K2SO4 at 1 A/g and possess a high rate capability of 73% at 5 A/g. The high rate capability and capacitance can be attributed to the presence of carbon cross-linked channels, the binder-free nature of the electrodes, and various oxidation states of the Ni-Mn oxides. The asymmetric supercapacitor device constructed of the as-fabricated nanofibers and the bio-derived microporous carbon as the positive and negative electrodes, respectively, sustains up to 1.9 V with a high specific capacitance at 1.5 A/g of 108 F/g. The nanofibrous//bio-derived device exhibits an outstanding specific energy of 54.2 W h/kg with a high specific power of 1425 W/kg. Interestingly, the tested device maintains a high capacitive retention of 92% upon cycling over 10,000 charging/discharging cycles.
Abstract Herein, we report on a facile one pot synthesis of polyoxometalates encapsulated zeolite... more Abstract Herein, we report on a facile one pot synthesis of polyoxometalates encapsulated zeolite imidazolate framework cages (PMo10V2@ZIF-67). The morphological and structural properties of the as synthesized materials were investigated via FESEM, EDS, XRD and FTIR techniques. Moreover, N2 adsorption/desorption isotherms and XPS measurements were carried out to elucidate the textural properties and composition of the fabricated materials. Upon their use as supercapacitor electrodes, the PMo10V2@ZIF-67 electrode exhibited a maximum specific capacitance of 765 F/g at a scan rate of 5 mV/s. Furthermore, a supercapacitor device was assembled using activated carbon as the negative electrode and PMo10V2@ZIF-67 as the positive electrode, delivering a specific power of 702 W/kg and a corresponding specific energy of 20.9 Wh/kg at a charging current density of 1 A/g. In addition, the device shows an excellent long term stability and high Columbic efficiency over 5000 charging and discharging cycles at a charging and discharging current density of 5 A/g.
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Papers by Nashaat Ahmed