Academic Journals

PbS x Se 1−x thin films from the thermal decomposition of lead(II) dodecylxanthate and bis ( N , N -diethyl- N ′-naphthoylselenoureato)lead(II) precursors

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

Thin films of PbS x Se(1−x) (0 ≤ x ≤ 1) have been deposited by spin coating of bis(dodecylxanthato)lead(II) (1) and/or bis(N,N-diethyl-N′-naphthoylselenoureato)lead(II) (2) complexes onto glass substrates followed by heating. The mole fraction of the selenium precursor in the coating mixture was varied from 0 to 1 by mixing the S and Se precursors. The as-prepared thin films were then heated at temperatures ranging from 250 to 400 °C. Powder X-ray diffraction showed all films were of the halite structure with preferred orientation along (200) plane. The PbS films showed a closely packed network of nanorods, each comprised of smaller nanoparticles. The nanorods were about 500 nm in length and 25 nm in width; the adhered particles had ca. 30 nm sides. The PbSe nanoparticles were also cubic. The alloys showed an intermediate morphology between the rods and cubes depending on the precursor ratio in the coating mixture. The band gaps estimated from Tauc plots for the films heated at 250 °C for 30 min were 1.03 and 0.79 eV for PbS and PbSe, respectively. The alloyed PbS x Se(1−x) thin films exhibited band gaps between those of PbS and PbSe. The band gaps and lattice parameters of the alloys varied in a Vegardian manner and could be closely correlated with the composition of the precursor mixture.

Categories: Academic Journals

Co 3 O 4 polyhedrons with enhanced electric conductivity as efficient water oxidation electrocatalysts in alkaline medium

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

It is a great challenge to develop Co3O4-based electrocatalysts of excellent performance for oxygen evolution reaction, because of its poor electrical conductivity. In this paper, we have prepared pristine Co3O4 (P-Co3O4) and Co3O4-C polyhedrons via two different calcination strategies. Then we have also displayed a simple and green reduction method to synthesize reduced Co3O4 (R-Co3O4) polyhedron with abundant surface oxygen vacancies. Oxygen vacancies and the doping of carbon species can enhance conductivity of electrocatalysts, thus, improving their electrocatalytic activities obviously. R-Co3O4 and Co3O4-C polyhedrons show lower overpotentials of 380 and 420 mV, respectively, compared to P-Co3O4 polyhedron (520 mV) at the current density of 10 mA cm−2 in 1 M KOH solution (pH 13.7). And they also have smaller Tafel slopes of 86 and 78 mV dec−1 than that of P-Co3O4 polyhedron (93 mV dec−1), respectively. The integrated strategy reported here provides the way to design high-performance electrocatalysts for water oxidation.

Categories: Academic Journals

Experimental investigation on the effect of carbon nanotube additive on the field-induced viscoelastic properties of magnetorheological elastomer

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

The additives improve the properties of magnetorheological elastomer by modifying the surface of ferromagnetic filler particles or by varying the properties of a host polymer matrix. In this study, effect of carbon nanotube additive on the viscoelastic properties of magnetorheological elastomer reinforced with optimum quantity of ferromagnetic filler is studied. Room temperature vulcanizing silicone elastomer-based test samples are prepared by mixing the elastomer with the carbon nanotube and carbonyl iron powder blend obtained from ultrasonication. Viscoelastic properties are measured by adopting the dynamic blocked transfer stiffness method. The results revealed that the properties of magnetorheological elastomer vary significantly with the inclusion of carbon nanotube. With the addition of 0.5 wt% carbon nanotube, the zero field dynamic stiffness of magnetorheological elastomer is enhanced by 36.7% and the loss factor is increased by 17.2%. The enhancement in zero field properties led to the least field-induced enhancement for magnetorheological elastomer doped with 0.5 wt% carbon nanotube. A relatively larger flexibility of pure magnetorheological elastomer samples had resulted in the maximum field-induced enhancement of 48.04%. Among the prepared test samples with carbon nanotube addition, the sample loaded with 0.25 wt% carbon nanotube exhibited a pronounced stiffness enhancement and lower loss factor. This substantiated the existence of an optimum limit for carbon nanotube additive. The present study also confirmed the feasibility of developing MRE tailor-made to suit the particular application by selecting a proper composition of matrix, filler and the additives.

Categories: Academic Journals

Investigation of the molecular dynamics of restricted water in wood by broadband dielectric measurements

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

Dielectric measurements are one of the most reliable techniques for investigating the molecular dynamics of water in moist materials. However, dielectric measurements of moist wood have not yet been carried out in a wide frequency range that can be used to evaluate the molecular dynamics of water in wood. We performed dielectric measurements of a deciduous tree, Zelkova serrata, along the fiber direction in the frequency range of 40 Hz to 10 GHz at room temperature around the fiber saturation point of wood to investigate the molecular dynamics of water in wood. Cole–Cole-type relaxation process reflecting the molecular dynamics of the water is observed in the GHz region. The water content dependences of the relaxation time and strength of this process are similar to those of the relaxation process of free water observed in polymer–water mixtures. However, the τ − β CC diagram of this process markedly deviates from that of the relaxation process of free water in polymer–water mixtures. The molecular mechanism of this characteristic relaxation process is interpreted as the formation of the local structure of water restricted in the void spaces of wood. The water molecules adsorbed on the inner walls of the void spaces form a local structure, and the local structure grows in the length direction along the walls of the void spaces with increasing water content of wood. The molecular dynamics of these water molecules is strongly restricted between the inner walls of the void spaces and air spaces, and the strongly restricted molecular dynamics of the water leads to the characteristic relaxation process observed in the GHz region. We give molecular descriptions of the strongly restricted water adsorbed on the inner walls of the void spaces of wood around the fiber saturation point.

Categories: Academic Journals

High-temperature oxidation of yttrium silicides

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

Current silicon melt-infiltrated (SMI) ceramic matrix composites (CMCs) are limited by the melting temperature of silicon (1414 °C) and the volatility of the thermally grown SiO2 scale in high-temperature water vapor environments. Replacement of the melt-infiltrated (MI) silicon with a rare-earth silicide offers the potential to address both limitations of SMI CMCs. This study focuses on the ability of yttrium silicides to form yttrium silicates (phases with greater stability in high-temperature water vapor than SiO2) in high-temperature oxidizing environments. Yttrium silicides with compositions of 41, 67 and 95 at.% Si–Y were fabricated using arc melting and oxidized in air at 1000 and 1200 °C for up to 24 h. Oxidation resulted in the rapid formation of a non-protective Y2O3 scale and rejected Si. Additional minor oxide phases of Y–Si–O, Y2SiO5, Y2Si2O7 and SiO2 were observed to form on and beneath the specimen surface. Characterization of the microstructural evolution with time and temperature helped elucidate the diffusion mechanisms that control oxide growth rates. Replacement of MI silicon with a MI yttrium silicide would significantly compromise the high-temperature performance of a CMC due to Y2O3 CTE mismatch with SiC, high oxygen permeability and the large volume change associated with its rapid subsurface formation. Results are utilized to examine the viability of other rare-earth silicides as MI materials for CMCs.

Categories: Academic Journals

Investigation of suitable binder combination and electrochemical charge transfer dynamics of vanadium carbide nanoparticles-based counter electrode in Pt-free dye-sensitized solar cell

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

We have fabricated vanadium carbide counter electrode (CE), and we have investigated suitable binder combination (conductive carbon/N-methyl pyrrolidone (CC/NMP), NMP, CC/IPA (isopropanol)) material for increasing bonding strength, crack-free coated films, high conductivity and highly catalytic activity functions on the fluorine-doped tin oxide (FTO) glass substrate for the redox reaction at the counter electrode of dye-sensitized solar cells (DSSCs). The power conversion efficiency of 3.9% is obtained for vanadium carbide–CC/NMP binder, comparable performance to the traditional Pt-based CE (4.0%). Based on the electrochemical investigation and current–voltage measurement, the comparable efficiency was achieved by the higher current density (J sc) and lower charge transfer resistance (R ct) due to the CC/NMP binder which is increasing bonding strength between CE materials and FTO. The present investigations open promising ways to the further movement for substantial amount of production of traditional Pt-free DSSC.

Categories: Academic Journals

Transition metal oxide nanostructures: premeditated fabrication and applications in electronic and photonic devices

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

Transition metal oxide (TMO) nanomaterials possess both novel nanoeffects and excellent semiconductor properties that make them promising materials for electronics and photonics. Great expectations have been placed on TMO nanomaterials to deal with the global challenges in many fields, especially portable equipment and energy issues. In the last decades, extensive research work concentrated on the synthesis, microstructure, and macro-performance of TMO nanomaterials. A comprehensive understanding of both growth mechanism and underlying relationship between microstructure and physical properties can lead to performance enhancements of TMO nanomaterials in electronics and photonics, which in turn enables the fabrication TMO nanostructures based on anticipated design strategies. At present, TMO nanostructures do not satisfactorily meet the technical criteria for direct practical applications in electronics and photonics. In this paper, recent developments in synthesis, characterization, and prominent applications of TMO nanomaterials are reviewed from a structural perspective, which serves as a stepping stone to develop novel nanostructures with superior performances and provides a necessary guidance for transformation of scientific achievements into practical applications.

Categories: Academic Journals

A novel biomimetic catalyst constructed by axial coordination of hemin with PAN fiber for efficient degradation of organic dyes

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

A novel biomimetic catalyst was synthesized by supporting hemin onto the amidoximated polyacrylonitrile (PAN) fiber and then used for the oxidative degradation of organic dyes by H2O2 activation. SEM, FTIR and XPS results suggested that the OH and NH2 in amidoxime groups were responsible for hemin immobilization through axial coordination bonds. The fibrous support significantly enhanced the catalytic activity and pH tolerance of pure hemin, and the prepared catalyst also exhibited excellent recycling capability. In addition, the effect of axial ligands on the catalytic mechanism was clarified by employing the modified PAN fiber with amidrazones groups as the support of hemin, and the possible catalytic mechanism was proposed and discussed based on the ESR measurement combined with a series of designed experiments. It is found that OH and NH2 as axial ligands of hemin might induce H2O2 activation through two different pathways, corresponding to the generation of Fe(IV)=O and ·OH species, respectively.

Categories: Academic Journals

Enhanced stability of lead-free perovskite heterojunction for photovoltaic applications

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

A low-cost and simple solution-based method is employed to prepare cesium tin tri-iodide (CsSnI3) thin films. The as-prepared dense CsSnI3 thin films are confirmed belong to orthorhombic structure (black-γ phase) of CsSnI3 (B-γ-CsSnI3), which deposited via spin coating technique at 3000 r/min. X-ray photoelectron spectroscopy (XPS) results reveal that Sn is + 2 valence and no other states of Sn can be observed in the thin film. Hall effect measurements of the B-γ-CsSnI3 thin film indicate that it is a p-type direct band gap semiconductor with carrier density at room temperature of ~ 1019 cm−3 and a hole mobility increases from ~ 2 to 19 cm2 V−1s−1 with the film thickness increasing from 200 to 800 nm. Moreover, the n-type Cs2SnI6, a kind allotrope of CsSnI3, is deposited on B-γ-CsSnI3 thin film to form a p–n heterojunction, and the photoelectric conversion efficiency (PCE) of this lead-free device reaches 1.1%. Although the PCE is low, the Cs2SnI6 layer effectively prevents the degradation of the B-γ-CsSnI3 thin film, and 90% of the initial performance is retained after the device stored in ambient air for 20 h, which significantly enhanced the stability of lead-free B-γ-CsSnI3-based perovskite solar cells (PSCs).

Categories: Academic Journals

PbS x Se 1−x thin films from the thermal decomposition of lead(II) dodecylxanthate and bis ( N , N -diethyl- N ′-naphthoylselenoureato)lead(II) precursors

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

Thin films of PbS x Se(1−x) (0 ≤ x ≤ 1) have been deposited by spin coating of bis(dodecylxanthato)lead(II) (1) and/or bis(N,N-diethyl-N′-naphthoylselenoureato)lead(II) (2) complexes onto glass substrates followed by heating. The mole fraction of the selenium precursor in the coating mixture was varied from 0 to 1 by mixing the S and Se precursors. The as-prepared thin films were then heated at temperatures ranging from 250 to 400 °C. Powder X-ray diffraction showed all films were of the halite structure with preferred orientation along (200) plane. The PbS films showed a closely packed network of nanorods, each comprised of smaller nanoparticles. The nanorods were about 500 nm in length and 25 nm in width; the adhered particles had ca. 30 nm sides. The PbSe nanoparticles were also cubic. The alloys showed an intermediate morphology between the rods and cubes depending on the precursor ratio in the coating mixture. The band gaps estimated from Tauc plots for the films heated at 250 °C for 30 min were 1.03 and 0.79 eV for PbS and PbSe, respectively. The alloyed PbS x Se(1−x) thin films exhibited band gaps between those of PbS and PbSe. The band gaps and lattice parameters of the alloys varied in a Vegardian manner and could be closely correlated with the composition of the precursor mixture.

Categories: Academic Journals

Co 3 O 4 polyhedrons with enhanced electric conductivity as efficient water oxidation electrocatalysts in alkaline medium

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

It is a great challenge to develop Co3O4-based electrocatalysts of excellent performance for oxygen evolution reaction, because of its poor electrical conductivity. In this paper, we have prepared pristine Co3O4 (P-Co3O4) and Co3O4-C polyhedrons via two different calcination strategies. Then we have also displayed a simple and green reduction method to synthesize reduced Co3O4 (R-Co3O4) polyhedron with abundant surface oxygen vacancies. Oxygen vacancies and the doping of carbon species can enhance conductivity of electrocatalysts, thus, improving their electrocatalytic activities obviously. R-Co3O4 and Co3O4-C polyhedrons show lower overpotentials of 380 and 420 mV, respectively, compared to P-Co3O4 polyhedron (520 mV) at the current density of 10 mA cm−2 in 1 M KOH solution (pH 13.7). And they also have smaller Tafel slopes of 86 and 78 mV dec−1 than that of P-Co3O4 polyhedron (93 mV dec−1), respectively. The integrated strategy reported here provides the way to design high-performance electrocatalysts for water oxidation.

Categories: Academic Journals

Experimental investigation on the effect of carbon nanotube additive on the field-induced viscoelastic properties of magnetorheological elastomer

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

The additives improve the properties of magnetorheological elastomer by modifying the surface of ferromagnetic filler particles or by varying the properties of a host polymer matrix. In this study, effect of carbon nanotube additive on the viscoelastic properties of magnetorheological elastomer reinforced with optimum quantity of ferromagnetic filler is studied. Room temperature vulcanizing silicone elastomer-based test samples are prepared by mixing the elastomer with the carbon nanotube and carbonyl iron powder blend obtained from ultrasonication. Viscoelastic properties are measured by adopting the dynamic blocked transfer stiffness method. The results revealed that the properties of magnetorheological elastomer vary significantly with the inclusion of carbon nanotube. With the addition of 0.5 wt% carbon nanotube, the zero field dynamic stiffness of magnetorheological elastomer is enhanced by 36.7% and the loss factor is increased by 17.2%. The enhancement in zero field properties led to the least field-induced enhancement for magnetorheological elastomer doped with 0.5 wt% carbon nanotube. A relatively larger flexibility of pure magnetorheological elastomer samples had resulted in the maximum field-induced enhancement of 48.04%. Among the prepared test samples with carbon nanotube addition, the sample loaded with 0.25 wt% carbon nanotube exhibited a pronounced stiffness enhancement and lower loss factor. This substantiated the existence of an optimum limit for carbon nanotube additive. The present study also confirmed the feasibility of developing MRE tailor-made to suit the particular application by selecting a proper composition of matrix, filler and the additives.

Categories: Academic Journals

Investigation of the molecular dynamics of restricted water in wood by broadband dielectric measurements

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

Dielectric measurements are one of the most reliable techniques for investigating the molecular dynamics of water in moist materials. However, dielectric measurements of moist wood have not yet been carried out in a wide frequency range that can be used to evaluate the molecular dynamics of water in wood. We performed dielectric measurements of a deciduous tree, Zelkova serrata, along the fiber direction in the frequency range of 40 Hz to 10 GHz at room temperature around the fiber saturation point of wood to investigate the molecular dynamics of water in wood. Cole–Cole-type relaxation process reflecting the molecular dynamics of the water is observed in the GHz region. The water content dependences of the relaxation time and strength of this process are similar to those of the relaxation process of free water observed in polymer–water mixtures. However, the τ − β CC diagram of this process markedly deviates from that of the relaxation process of free water in polymer–water mixtures. The molecular mechanism of this characteristic relaxation process is interpreted as the formation of the local structure of water restricted in the void spaces of wood. The water molecules adsorbed on the inner walls of the void spaces form a local structure, and the local structure grows in the length direction along the walls of the void spaces with increasing water content of wood. The molecular dynamics of these water molecules is strongly restricted between the inner walls of the void spaces and air spaces, and the strongly restricted molecular dynamics of the water leads to the characteristic relaxation process observed in the GHz region. We give molecular descriptions of the strongly restricted water adsorbed on the inner walls of the void spaces of wood around the fiber saturation point.

Categories: Academic Journals

High-temperature oxidation of yttrium silicides

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

Current silicon melt-infiltrated (SMI) ceramic matrix composites (CMCs) are limited by the melting temperature of silicon (1414 °C) and the volatility of the thermally grown SiO2 scale in high-temperature water vapor environments. Replacement of the melt-infiltrated (MI) silicon with a rare-earth silicide offers the potential to address both limitations of SMI CMCs. This study focuses on the ability of yttrium silicides to form yttrium silicates (phases with greater stability in high-temperature water vapor than SiO2) in high-temperature oxidizing environments. Yttrium silicides with compositions of 41, 67 and 95 at.% Si–Y were fabricated using arc melting and oxidized in air at 1000 and 1200 °C for up to 24 h. Oxidation resulted in the rapid formation of a non-protective Y2O3 scale and rejected Si. Additional minor oxide phases of Y–Si–O, Y2SiO5, Y2Si2O7 and SiO2 were observed to form on and beneath the specimen surface. Characterization of the microstructural evolution with time and temperature helped elucidate the diffusion mechanisms that control oxide growth rates. Replacement of MI silicon with a MI yttrium silicide would significantly compromise the high-temperature performance of a CMC due to Y2O3 CTE mismatch with SiC, high oxygen permeability and the large volume change associated with its rapid subsurface formation. Results are utilized to examine the viability of other rare-earth silicides as MI materials for CMCs.

Categories: Academic Journals

Investigation of suitable binder combination and electrochemical charge transfer dynamics of vanadium carbide nanoparticles-based counter electrode in Pt-free dye-sensitized solar cell

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

We have fabricated vanadium carbide counter electrode (CE), and we have investigated suitable binder combination (conductive carbon/N-methyl pyrrolidone (CC/NMP), NMP, CC/IPA (isopropanol)) material for increasing bonding strength, crack-free coated films, high conductivity and highly catalytic activity functions on the fluorine-doped tin oxide (FTO) glass substrate for the redox reaction at the counter electrode of dye-sensitized solar cells (DSSCs). The power conversion efficiency of 3.9% is obtained for vanadium carbide–CC/NMP binder, comparable performance to the traditional Pt-based CE (4.0%). Based on the electrochemical investigation and current–voltage measurement, the comparable efficiency was achieved by the higher current density (J sc) and lower charge transfer resistance (R ct) due to the CC/NMP binder which is increasing bonding strength between CE materials and FTO. The present investigations open promising ways to the further movement for substantial amount of production of traditional Pt-free DSSC.

Categories: Academic Journals

Transition metal oxide nanostructures: premeditated fabrication and applications in electronic and photonic devices

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

Transition metal oxide (TMO) nanomaterials possess both novel nanoeffects and excellent semiconductor properties that make them promising materials for electronics and photonics. Great expectations have been placed on TMO nanomaterials to deal with the global challenges in many fields, especially portable equipment and energy issues. In the last decades, extensive research work concentrated on the synthesis, microstructure, and macro-performance of TMO nanomaterials. A comprehensive understanding of both growth mechanism and underlying relationship between microstructure and physical properties can lead to performance enhancements of TMO nanomaterials in electronics and photonics, which in turn enables the fabrication TMO nanostructures based on anticipated design strategies. At present, TMO nanostructures do not satisfactorily meet the technical criteria for direct practical applications in electronics and photonics. In this paper, recent developments in synthesis, characterization, and prominent applications of TMO nanomaterials are reviewed from a structural perspective, which serves as a stepping stone to develop novel nanostructures with superior performances and provides a necessary guidance for transformation of scientific achievements into practical applications.

Categories: Academic Journals

A novel biomimetic catalyst constructed by axial coordination of hemin with PAN fiber for efficient degradation of organic dyes

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

A novel biomimetic catalyst was synthesized by supporting hemin onto the amidoximated polyacrylonitrile (PAN) fiber and then used for the oxidative degradation of organic dyes by H2O2 activation. SEM, FTIR and XPS results suggested that the OH and NH2 in amidoxime groups were responsible for hemin immobilization through axial coordination bonds. The fibrous support significantly enhanced the catalytic activity and pH tolerance of pure hemin, and the prepared catalyst also exhibited excellent recycling capability. In addition, the effect of axial ligands on the catalytic mechanism was clarified by employing the modified PAN fiber with amidrazones groups as the support of hemin, and the possible catalytic mechanism was proposed and discussed based on the ESR measurement combined with a series of designed experiments. It is found that OH and NH2 as axial ligands of hemin might induce H2O2 activation through two different pathways, corresponding to the generation of Fe(IV)=O and ·OH species, respectively.

Categories: Academic Journals

Enhanced stability of lead-free perovskite heterojunction for photovoltaic applications

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

A low-cost and simple solution-based method is employed to prepare cesium tin tri-iodide (CsSnI3) thin films. The as-prepared dense CsSnI3 thin films are confirmed belong to orthorhombic structure (black-γ phase) of CsSnI3 (B-γ-CsSnI3), which deposited via spin coating technique at 3000 r/min. X-ray photoelectron spectroscopy (XPS) results reveal that Sn is + 2 valence and no other states of Sn can be observed in the thin film. Hall effect measurements of the B-γ-CsSnI3 thin film indicate that it is a p-type direct band gap semiconductor with carrier density at room temperature of ~ 1019 cm−3 and a hole mobility increases from ~ 2 to 19 cm2 V−1s−1 with the film thickness increasing from 200 to 800 nm. Moreover, the n-type Cs2SnI6, a kind allotrope of CsSnI3, is deposited on B-γ-CsSnI3 thin film to form a p–n heterojunction, and the photoelectric conversion efficiency (PCE) of this lead-free device reaches 1.1%. Although the PCE is low, the Cs2SnI6 layer effectively prevents the degradation of the B-γ-CsSnI3 thin film, and 90% of the initial performance is retained after the device stored in ambient air for 20 h, which significantly enhanced the stability of lead-free B-γ-CsSnI3-based perovskite solar cells (PSCs).

Categories: Academic Journals

A cobalt porphyrin-based metal organic framework/multi-walled carbon nanotube composite electrocatalyst for oxygen reduction and evolution reactions

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

We report the synthesis of a composite from cobalt porphyrin-based metal organic framework (MOF) and multi-walled carbon nanotube (MWCNT), possessing good catalytic activity toward oxygen reduction (OR) and oxygen evolution (OE) processes. A 3-D porous coordination network (PCN) with 3-D nanochannels was synthesized using ultrastable Zr6 clusters and tetrakis(4-carboxyphenyl)porphyrin cobalt(II). Located in the backbone of MOF, cobalt porphyrins as the active centers are easily accessible to the reactants. The composite exhibits smaller overpotentials and higher current for OR and OE reactions compared to the commercial Pt/C catalyst. A proton-coupled electron transfer mechanism has been suggested due to the pH dependence of water oxidation on the electrocatalyst. Furthermore, the stability of the catalyst has been verified by various techniques. Our designed heterogeneous, inexpensive, and stable electrocatalyst is a proper candidate for acidic fuel cells and water splitting devices under near neutral condition without requirement of pyrolysis process.

Categories: Academic Journals

High-temperature stress-dependent piezoelectric and dielectric coefficient of soft Pb(Zr,Ti)O 3

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

The dielectric constant and the direct piezoelectric coefficient as well as the macroscopic ferroelastic behavior of co-doped Pb(Zr,Ti)O3 were characterized from 25 to 350 °C as a function of uniaxial compressive stress. Experimental results show a decrease in the small signal piezoelectric coefficient and the permittivity with stress, although there exists a uniaxial compressive stress that significantly reduces the variation of the piezoelectric coefficient with increasing temperature, making it a possible method for sensors that operate over a large temperature range. In the vicinity of the depolarization temperature, the piezoelectric response rapidly decreases. This temperature, however, was observed well below the temperature at maximum permittivity. Experimental results reveal that uniaxial compressive stress shifts the temperature at maximum permittivity, giving insight into the effect of stress on the phase transition behavior in Pb(Zr,Ti)O3, but does not apparently influence the depolarization temperature.

Categories: Academic Journals

Pages

Subscribe to Kentucky Association for Behavior Analysis aggregator - Academic Journals