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2017 Volume 33 Issue 9
2017, 33(9):
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2017, 33(9): 1721-1722
doi: 10.3866/PKU.WHXB201705193
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2017, 33(9): 1723-1723
doi: 10.3866/PKU.WHXB201705224
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2017, 33(9): 1724-1725
doi: 10.3866/PKU.WHXB201705225
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2017, 33(9): 1726-1727
doi: 10.3866/PKU.WHXB201705243
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2017, 33(9): 1728-1729
doi: 10.3866/PKU.WHXB201705291
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2017, 33(9): 1730-1751
doi: 10.3866/PKU.WHXB201705042
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Halide perovskites have recently emerged as promising materials for low-cost, high-efficiency solar cells. The efficiency of perovskite-based solar cells has increased rapidly, from 3.8% in 2009 to 22.1% in 2016, with the use of all-solid-state thin-film architecture and by engineering cell structures with mixed-halide perovskites. The emergence of perovskite solar cells has revolutionized the field not only because of their rapidly increased efficiency, but also their flexibility in material growth and architecture. The superior performance of the perovskite solar cells suggested that perovskite materials possess intrinsically unique properties. In this review, we summarize recent theoretical investigations into the structural, electrical, and optical properties of halide perovskite materials in terms of their applications in solar cells. We also discuss some current challenges of using perovskites in solar cells, along with possible theoretical solutions.
Halide perovskites have recently emerged as promising materials for low-cost, high-efficiency solar cells. The efficiency of perovskite-based solar cells has increased rapidly, from 3.8% in 2009 to 22.1% in 2016, with the use of all-solid-state thin-film architecture and by engineering cell structures with mixed-halide perovskites. The emergence of perovskite solar cells has revolutionized the field not only because of their rapidly increased efficiency, but also their flexibility in material growth and architecture. The superior performance of the perovskite solar cells suggested that perovskite materials possess intrinsically unique properties. In this review, we summarize recent theoretical investigations into the structural, electrical, and optical properties of halide perovskite materials in terms of their applications in solar cells. We also discuss some current challenges of using perovskites in solar cells, along with possible theoretical solutions.
2017, 33(9): 1752-1764
doi: 10.3866/PKU.WHXB201704273
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A simplified mechanism of methyl decanoate and n-heptane blend was developed for a homogeneous charge compression ignition engine built from a previously reported detailed mechanism of a methyl decanoate and n-heptane. The simplified mechanism with 113 species and 306 reactions was developed using path flux and temperature sensitivity analyses. The simplified mechanism was validated against the experimental data of ignition delay time, in-cylinder pressure, and CO emissions. Results show that the simplified mechanism not only coincides with the ignition delay time of the methyl decanoate and n-heptane, but also the CO emissions, and can reproduce the variation of in-cylinder pressure. The simplified mechanism can be further validated by comparison with the detailed mechanism, which shows that the simplified mechanism can coincide with the in-cylinder pressure and temperature, and can reproduce the variation tendency of the core components. Thus, the reduced mechanism is a reasonable one.
A simplified mechanism of methyl decanoate and n-heptane blend was developed for a homogeneous charge compression ignition engine built from a previously reported detailed mechanism of a methyl decanoate and n-heptane. The simplified mechanism with 113 species and 306 reactions was developed using path flux and temperature sensitivity analyses. The simplified mechanism was validated against the experimental data of ignition delay time, in-cylinder pressure, and CO emissions. Results show that the simplified mechanism not only coincides with the ignition delay time of the methyl decanoate and n-heptane, but also the CO emissions, and can reproduce the variation of in-cylinder pressure. The simplified mechanism can be further validated by comparison with the detailed mechanism, which shows that the simplified mechanism can coincide with the in-cylinder pressure and temperature, and can reproduce the variation tendency of the core components. Thus, the reduced mechanism is a reasonable one.
2017, 33(9): 1765-1772
doi: 10.3866/PKU.WHXB201705102
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In this work, first-principles calculations were performed to study the effect of the adsorption of Fe atoms on the structure and properties of the WS2 monolayer. It was found that the most stable adsorption site for an Fe atom on WS2 at low coverage (< 0.0625 ML) of the monolayer lies directly above the W atom and the atomic adsorption energy is ca. 1.84 eV. The interaction between the Fe and substrate atoms weakens the nearest W-S bonds which increases their bond length by ca. 0.011 nm. The orbital occupation of the adsorbed Fe atoms also undergoes redistribution. The 3d orbitals of Fe are fully occupied with the exception of the spin down channel of dyz and dxz orbitals. The magnetic interactions of Fe-Fe are mainly believed to involve super-exchange interactions which are mediated by the substrate. Thus the ferromagnetic order is unstable at low coverage. However, at high coverage, the distance between Fe-Fe decreases and the states close to the Fermi energy level induce magnetic interactions between the local magnetic moment and the itinerant electron, which are identified as RKKY interactions. In this manner, the ferromagnetic order is more stable at high coverage of the monolayer. The Density of state and band-structure calculations show that the spin polarization of Fe-WS2 near the Fermi energy level is about 100%. The spin up channel acts as an indirect band gap semiconductor, while the another one acts as a metal. These calculations indicate that the Fe-WS2 layer at high coverage could be half metallic, which can be potentially used to develop spin-based electronic materials.
In this work, first-principles calculations were performed to study the effect of the adsorption of Fe atoms on the structure and properties of the WS2 monolayer. It was found that the most stable adsorption site for an Fe atom on WS2 at low coverage (< 0.0625 ML) of the monolayer lies directly above the W atom and the atomic adsorption energy is ca. 1.84 eV. The interaction between the Fe and substrate atoms weakens the nearest W-S bonds which increases their bond length by ca. 0.011 nm. The orbital occupation of the adsorbed Fe atoms also undergoes redistribution. The 3d orbitals of Fe are fully occupied with the exception of the spin down channel of dyz and dxz orbitals. The magnetic interactions of Fe-Fe are mainly believed to involve super-exchange interactions which are mediated by the substrate. Thus the ferromagnetic order is unstable at low coverage. However, at high coverage, the distance between Fe-Fe decreases and the states close to the Fermi energy level induce magnetic interactions between the local magnetic moment and the itinerant electron, which are identified as RKKY interactions. In this manner, the ferromagnetic order is more stable at high coverage of the monolayer. The Density of state and band-structure calculations show that the spin polarization of Fe-WS2 near the Fermi energy level is about 100%. The spin up channel acts as an indirect band gap semiconductor, while the another one acts as a metal. These calculations indicate that the Fe-WS2 layer at high coverage could be half metallic, which can be potentially used to develop spin-based electronic materials.
2017, 33(9): 1773-1780
doi: 10.3866/PKU.WHXB201705087
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Based on molecular dynamics simulations, the plastic deformation of silver nanowires under uniaxial tension has been studied systematically. In this paper, the mechanical properties of [111]-oriented twin nanowires with different hole sizes have been studied. The existence of holes has no effect on the elastic deformation stage. The hole on the twin boundary has two main roles in the plastic deformation stage. During the initial stages of plastic deformation, the main function of the hole is to produce new dislocations as dislocation sources at small hole sizes.Upon increasing the hole size, the main effect changes to stop dislocation slip. During the late stages of plastic deformation, the two functions of the hole complement each other, upon increasing the hole size, the function of the hole as dislocation sources becomes obvious, leading to weakening of the plasticity of the nanowires.
Based on molecular dynamics simulations, the plastic deformation of silver nanowires under uniaxial tension has been studied systematically. In this paper, the mechanical properties of [111]-oriented twin nanowires with different hole sizes have been studied. The existence of holes has no effect on the elastic deformation stage. The hole on the twin boundary has two main roles in the plastic deformation stage. During the initial stages of plastic deformation, the main function of the hole is to produce new dislocations as dislocation sources at small hole sizes.Upon increasing the hole size, the main effect changes to stop dislocation slip. During the late stages of plastic deformation, the two functions of the hole complement each other, upon increasing the hole size, the function of the hole as dislocation sources becomes obvious, leading to weakening of the plasticity of the nanowires.
2017, 33(9): 1781-1788
doi: 10.3866/PKU.WHXB201705041
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Ni-rich layered oxides are the preferred cathode materials for high-energy-density lithium-ion batteries currently used in electric vehicles. In this paper, we present a systematic first-principles evaluation of the deintercalation process in the Li1-xNiO2-ySy. The partial density of states (PDOS) characters of the electrons near the Fermi level, redox behaviors, and thermal stability have been investigated within the GGA+U scheme. The results show that the introduction of sulfur alleviates the lattice distortion during charging, suppresses nickel migration, and enhances the stability of oxygen according to the contribution of sulfur anion redox to the charge compensation for the overcharged Li1-xNiO2-ySy. This study provides a new insight on improving the stability of Ni-rich cathode materials by tuning of the electrochemical behaviors based on sulfur anion redox.
Ni-rich layered oxides are the preferred cathode materials for high-energy-density lithium-ion batteries currently used in electric vehicles. In this paper, we present a systematic first-principles evaluation of the deintercalation process in the Li1-xNiO2-ySy. The partial density of states (PDOS) characters of the electrons near the Fermi level, redox behaviors, and thermal stability have been investigated within the GGA+U scheme. The results show that the introduction of sulfur alleviates the lattice distortion during charging, suppresses nickel migration, and enhances the stability of oxygen according to the contribution of sulfur anion redox to the charge compensation for the overcharged Li1-xNiO2-ySy. This study provides a new insight on improving the stability of Ni-rich cathode materials by tuning of the electrochemical behaviors based on sulfur anion redox.
2017, 33(9): 1789-1795
doi: 10.3866/PKU.WHXB201705082
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This work describes the characteristics of benzobisthiadiazole analogues with different heteroatom substitution patterns as electronwithdrawing anchoring groups in dye-sensitized solar cells (DSSCs). In order to provide a systematic analysis of the effect of the designed anchoring groups, the widely used anchor cyanoacrylic acid was used as the reference. Theoretical calculations show that the newly designed anchors are capable of displaying a decent level of light absorption covering the entire visible range up to the near-IR region of 1000 nm. More importantly, an ultrafast electron injection is observed from the dyes SPN and SPS into the TiO2 surface. The quantum dynamics of the interfacial electron transfer (IET) reveal that SPN and SPS anchors provide efficient IET performance. About 90% of the electron injection occurs in the first 15 fs, and is complete after ~100 fs. Furthermore, the pathway of electron injection is direct, leading to very efficient transfer of the wavepacket through the TiO2 semiconductor. Therefore, the performances of both the anchors, SPN and SPS, are equivalent and even superior to that of cyanoacrylic acid. These findings are important in the context of providing guidelines for the design of metal-free organic dye sensitizers for high efficient DSSCs.
This work describes the characteristics of benzobisthiadiazole analogues with different heteroatom substitution patterns as electronwithdrawing anchoring groups in dye-sensitized solar cells (DSSCs). In order to provide a systematic analysis of the effect of the designed anchoring groups, the widely used anchor cyanoacrylic acid was used as the reference. Theoretical calculations show that the newly designed anchors are capable of displaying a decent level of light absorption covering the entire visible range up to the near-IR region of 1000 nm. More importantly, an ultrafast electron injection is observed from the dyes SPN and SPS into the TiO2 surface. The quantum dynamics of the interfacial electron transfer (IET) reveal that SPN and SPS anchors provide efficient IET performance. About 90% of the electron injection occurs in the first 15 fs, and is complete after ~100 fs. Furthermore, the pathway of electron injection is direct, leading to very efficient transfer of the wavepacket through the TiO2 semiconductor. Therefore, the performances of both the anchors, SPN and SPS, are equivalent and even superior to that of cyanoacrylic acid. These findings are important in the context of providing guidelines for the design of metal-free organic dye sensitizers for high efficient DSSCs.
2017, 33(9): 1796-1802
doi: 10.3866/PKU.WHXB201705081
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First-principles calculations based on density functional theory (DFT) have been used to investigate how Ni doping in the supporter impacts CH4/CO2 reforming over Ni/MgO catalysts. Ni8 clusters supported on different NixMgyO27(100) slabs (x+y= 27) have been selected to model Ni/MgO catalysts with different Ni : Mg ratio. The CH4/CO2 reforming mechanisms on different Ni8/NixMgyO27(100) slabs indicate that the energy barriers of CH4 dissociated adsorption and CHx oxidation both increase with an increase in the Ni : Mg ratio of the supporter. CH would be easily generated from the pyrolytic carbon. The electron structure analysis shows that the direction of electron transfer changes to “between metal and supporter” with increasing Ni : Mg ratio of the supporter, but not to “from supporter to metal” on pure Ni/MgO. When the Ni cluster is negative, electron transfer occurs between adsorbed species and Ni atoms in the surface layer of the Ni cluster, and CH2 is the main species for CHx oxidation. When the Ni cluster is positive, its Hirshfeld is stable, electron transfer occurs between adsorbed species and Ni atoms in the surface layer of the NiO-MgO solid solution, and CH is the main oxidative species. The electron deficiency of the Ni cluster is the reason for the poor catalytic performance of Ni/MgO with a high Ni doping ratio.
First-principles calculations based on density functional theory (DFT) have been used to investigate how Ni doping in the supporter impacts CH4/CO2 reforming over Ni/MgO catalysts. Ni8 clusters supported on different NixMgyO27(100) slabs (x+y= 27) have been selected to model Ni/MgO catalysts with different Ni : Mg ratio. The CH4/CO2 reforming mechanisms on different Ni8/NixMgyO27(100) slabs indicate that the energy barriers of CH4 dissociated adsorption and CHx oxidation both increase with an increase in the Ni : Mg ratio of the supporter. CH would be easily generated from the pyrolytic carbon. The electron structure analysis shows that the direction of electron transfer changes to “between metal and supporter” with increasing Ni : Mg ratio of the supporter, but not to “from supporter to metal” on pure Ni/MgO. When the Ni cluster is negative, electron transfer occurs between adsorbed species and Ni atoms in the surface layer of the Ni cluster, and CH2 is the main species for CHx oxidation. When the Ni cluster is positive, its Hirshfeld is stable, electron transfer occurs between adsorbed species and Ni atoms in the surface layer of the NiO-MgO solid solution, and CH is the main oxidative species. The electron deficiency of the Ni cluster is the reason for the poor catalytic performance of Ni/MgO with a high Ni doping ratio.
2017, 33(9): 1803-1810
doi: 10.3866/PKU.WHXB201705104
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[4]Cyclo-9,9-dimethyl-2,7-fluorenylene ([4]CF) was used as a model compound to explore the steric strain effect on the structures and photoelectrical properties of materials. A series of strained cyclic polyfluorene materials, [n]CFs (n=3-8), was designed. It was found that the strain energy decreased and the energy gap increased as the number of n and ring diameter increased. The ionization potential and electronic affinity tended to increase and decrease as the strain energy decreased at the same number of [n]CFs, respectively. With a balance between hole and electron reorganization energies in the system, these compounds demonstrated great potential as ambipolar materials. It was also found that [n]CFs showed an obvious blue shift in their emission spectra wavelengths (λem2) as the strain energy decreased. Steric strain provides a powerful tool for the design of multifunctional semiconductors in organic optoelectronics.
[4]Cyclo-9,9-dimethyl-2,7-fluorenylene ([4]CF) was used as a model compound to explore the steric strain effect on the structures and photoelectrical properties of materials. A series of strained cyclic polyfluorene materials, [n]CFs (n=3-8), was designed. It was found that the strain energy decreased and the energy gap increased as the number of n and ring diameter increased. The ionization potential and electronic affinity tended to increase and decrease as the strain energy decreased at the same number of [n]CFs, respectively. With a balance between hole and electron reorganization energies in the system, these compounds demonstrated great potential as ambipolar materials. It was also found that [n]CFs showed an obvious blue shift in their emission spectra wavelengths (λem2) as the strain energy decreased. Steric strain provides a powerful tool for the design of multifunctional semiconductors in organic optoelectronics.
2017, 33(9): 1811-1821
doi: 10.3866/PKU.WHXB201704264
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Development of high-efficiency and low-cost electrocatalysts for large-scale oxygen reduction reaction (ORR) remains a challenge. In this study, we employed melamine, trithiocyanuric acid, and cobaltous nitrate to fabricate a novel ORR electrocatalyst with cobalt and cobalt carbide supported on carbon co-doped with nitrogen and sulfur (hereafter referred to as MTC-0.1-900) by two-step pyrolysis. The MTC-0.1-900 was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) specific surface area analysis, and X-ray photoelectron spectroscopy (XPS). The electrochemical performance for ORR was investigated by cyclic voltammetry and linear sweep voltammetry in 0.1 mol·L-1 KOH solutions. The results showed that the onset potential and half-wave potential of MTC-0.1-900 were 29 and 5 mV superior to the commercial Pt/C catalyst, respectively. After 12000 s operation at the potential of -0.3 V (vs Ag/AgCl), the current retention capacities of MTC-0.1-900 and Pt/C were 97.1% and 76.7%, respectively. MTC-0.1-900 also showed better methanol tolerance than Pt/C. These unique properties of MTC-0.1-900 provide us with an alternative for replacing or reducing the use of Pt catalyst in metal-air battery cathode materials.
Development of high-efficiency and low-cost electrocatalysts for large-scale oxygen reduction reaction (ORR) remains a challenge. In this study, we employed melamine, trithiocyanuric acid, and cobaltous nitrate to fabricate a novel ORR electrocatalyst with cobalt and cobalt carbide supported on carbon co-doped with nitrogen and sulfur (hereafter referred to as MTC-0.1-900) by two-step pyrolysis. The MTC-0.1-900 was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) specific surface area analysis, and X-ray photoelectron spectroscopy (XPS). The electrochemical performance for ORR was investigated by cyclic voltammetry and linear sweep voltammetry in 0.1 mol·L-1 KOH solutions. The results showed that the onset potential and half-wave potential of MTC-0.1-900 were 29 and 5 mV superior to the commercial Pt/C catalyst, respectively. After 12000 s operation at the potential of -0.3 V (vs Ag/AgCl), the current retention capacities of MTC-0.1-900 and Pt/C were 97.1% and 76.7%, respectively. MTC-0.1-900 also showed better methanol tolerance than Pt/C. These unique properties of MTC-0.1-900 provide us with an alternative for replacing or reducing the use of Pt catalyst in metal-air battery cathode materials.
2017, 33(9): 1822-1827
doi: 10.3866/PKU.WHXB201705022
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Polyaniline was synthesized on the surface of flexible graphene paper by pulse voltage method. The composite material was used as free-standing and binder-free electrode and catalyst support in methanol fuel cells with deposited Pd nanoparticles via cyclic voltammetry. The surface morphology and chemical composition of the material were analyzed by scanning electron microscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy, and the electrocatalytic performance of the electrode was investigated. The results show that graphene paper is flexible, that this fabrication procedure is efficient, and that polyaniline on the surface of the graphene paper is homogeneous. The existence of polyaniline can improve catalytic efficiency since the methanol oxidation peak current density increased from 3 mA·mg-1 to 67 mA·mg-1 with the addition of polyaniline. The lifespan of the catalyst is also prolonged according to If/Ib value (the oxidation peak current density ratio of forward scan and reverse scan) reaching 5.7.
Polyaniline was synthesized on the surface of flexible graphene paper by pulse voltage method. The composite material was used as free-standing and binder-free electrode and catalyst support in methanol fuel cells with deposited Pd nanoparticles via cyclic voltammetry. The surface morphology and chemical composition of the material were analyzed by scanning electron microscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy, and the electrocatalytic performance of the electrode was investigated. The results show that graphene paper is flexible, that this fabrication procedure is efficient, and that polyaniline on the surface of the graphene paper is homogeneous. The existence of polyaniline can improve catalytic efficiency since the methanol oxidation peak current density increased from 3 mA·mg-1 to 67 mA·mg-1 with the addition of polyaniline. The lifespan of the catalyst is also prolonged according to If/Ib value (the oxidation peak current density ratio of forward scan and reverse scan) reaching 5.7.
2017, 33(9): 1828-1837
doi: 10.3866/PKU.WHXB201705089
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A new three-dimensional (3D) porous graphene thin film named rGO-Fe was prepared through chemical reduction from Fe3+ ions cross-linking graphene oxide hydrogel, and a 3D porous graphene/titanium-containing conjugated polymer composite film named rGO-Fe/P(EDOT:P3C)-1-Ti was further prepared via electrochemical polymerization on the rGO-Fe substrate. As a new composite film, rGO-Fe/P(EDOT:P3C)-1-Ti film with average thickness of 3 μm can withstand the tensile load 0.97 N which is better than that of rGO-Fe (0.76 N). We compared the electrochemical properties of these film materials, and prepared self-supporting electrodes and a flexible all-solid-state supercapacitor based on rGO-Fe/P(EDOT:P3C)-1-Ti. Galvanostatic charge-discharge test results showed that the as prepared flexible supercapacitor delivered a gravimetric specific capacitance of 71.13 F·g-1 (18.14 F·g-1) and an area specific capacitance of 101 mF·cm-2 (25.8 mF·cm-2) at 0.1 A·g-1 (0.6 A·g-1).
A new three-dimensional (3D) porous graphene thin film named rGO-Fe was prepared through chemical reduction from Fe3+ ions cross-linking graphene oxide hydrogel, and a 3D porous graphene/titanium-containing conjugated polymer composite film named rGO-Fe/P(EDOT:P3C)-1-Ti was further prepared via electrochemical polymerization on the rGO-Fe substrate. As a new composite film, rGO-Fe/P(EDOT:P3C)-1-Ti film with average thickness of 3 μm can withstand the tensile load 0.97 N which is better than that of rGO-Fe (0.76 N). We compared the electrochemical properties of these film materials, and prepared self-supporting electrodes and a flexible all-solid-state supercapacitor based on rGO-Fe/P(EDOT:P3C)-1-Ti. Galvanostatic charge-discharge test results showed that the as prepared flexible supercapacitor delivered a gravimetric specific capacitance of 71.13 F·g-1 (18.14 F·g-1) and an area specific capacitance of 101 mF·cm-2 (25.8 mF·cm-2) at 0.1 A·g-1 (0.6 A·g-1).
2017, 33(9): 1838-1845
doi: 10.3866/PKU.WHXB201705052
Abstract:
A series of nanocatalysts consisting of acid treated carbon nanotubes (CNTs) with different diameters (8-15, 20-30, 30-50, >50 nm) supporting platinum (Pt) nanoparticles (Pt/CNTs) were synthesized via a microwave-assisted ethylene glycol method. The as-synthesized catalysts were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). Their catalytic performances in the oxygen reduction reaction (ORR) were evaluated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The experimental results showed that the diameter of the CNTs influences the particle size, loading, and dispersion of Pt NPs. Furthermore, the Pt/CNTs having different CNT diameters displayed different catalytic activities in the ORR. The catalyst Pt/CNT8, which was prepared by using CNTs with diameters ranging between 8-15 nm as the support, exhibited the highest Pt loading, catalytic activity, and stability in the ORR. The mass activity of Pt/CNT8 was determined to be 0.188 A·mg-1 at 0.9 V, which is folds higher than that of the commercially available JM Pt/C catalyst. After testing the stability for 5000 potential cycles, the negative shift (~7 mV) of the half-wave potential for Pt/CNT8 was found to be significantly lesser than that for the JM Pt/C catalyst (~32 mV), indicating superior catalytic stability.
A series of nanocatalysts consisting of acid treated carbon nanotubes (CNTs) with different diameters (8-15, 20-30, 30-50, >50 nm) supporting platinum (Pt) nanoparticles (Pt/CNTs) were synthesized via a microwave-assisted ethylene glycol method. The as-synthesized catalysts were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). Their catalytic performances in the oxygen reduction reaction (ORR) were evaluated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The experimental results showed that the diameter of the CNTs influences the particle size, loading, and dispersion of Pt NPs. Furthermore, the Pt/CNTs having different CNT diameters displayed different catalytic activities in the ORR. The catalyst Pt/CNT8, which was prepared by using CNTs with diameters ranging between 8-15 nm as the support, exhibited the highest Pt loading, catalytic activity, and stability in the ORR. The mass activity of Pt/CNT8 was determined to be 0.188 A·mg-1 at 0.9 V, which is folds higher than that of the commercially available JM Pt/C catalyst. After testing the stability for 5000 potential cycles, the negative shift (~7 mV) of the half-wave potential for Pt/CNT8 was found to be significantly lesser than that for the JM Pt/C catalyst (~32 mV), indicating superior catalytic stability.
2017, 33(9): 1846-1854
doi: 10.3866/PKU.WHXB201705051
Abstract:
In this research, the wetting behavior of nonionic surfactant Triton X-100 on wheat leaf surfaces at different developmental stages has been investigated based on the surface free energy, contact angle, adhesion tension, and liquid-solid interfacial tension. The results show that the contact angle remains constant with low adsorption at the liquid-air (ΓLV) and liquid-solid (Γ'SL) interfaces at low concentration, and the wetting state is in the Cassie-Baxter state. On increasing the concentration, the contact angle decreases sharply and the ratio of Γ'SL/ΓLV becomes more than 1. Meanwhile, the droplet overcomes the pinning effect to displace the air among three-dimensional wax layers and is in the Wenzel state. When the concentration becomes over critical micelle concentration (CMC), a saturated adsorption film forms at the interfaces, and the hemiwicking process occurs among micro/nano structures because of the capillary effect, then the contact angle remains constant.
In this research, the wetting behavior of nonionic surfactant Triton X-100 on wheat leaf surfaces at different developmental stages has been investigated based on the surface free energy, contact angle, adhesion tension, and liquid-solid interfacial tension. The results show that the contact angle remains constant with low adsorption at the liquid-air (ΓLV) and liquid-solid (Γ'SL) interfaces at low concentration, and the wetting state is in the Cassie-Baxter state. On increasing the concentration, the contact angle decreases sharply and the ratio of Γ'SL/ΓLV becomes more than 1. Meanwhile, the droplet overcomes the pinning effect to displace the air among three-dimensional wax layers and is in the Wenzel state. When the concentration becomes over critical micelle concentration (CMC), a saturated adsorption film forms at the interfaces, and the hemiwicking process occurs among micro/nano structures because of the capillary effect, then the contact angle remains constant.
2017, 33(9): 1855-1864
doi: 10.3866/PKU.WHXB201704282
Abstract:
Octahedral layered birnessite (denoted as OL) was synthesized by the oxidation-reduction method and a series of Cux/OL catalysts were prepared by the ion exchange method with various Cu loadings. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption-desorption, hydrogen temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), thermogravimetric (TG) and.oxygen temperature-programmed desorption (O2-TPD) techniques, and their catalytic activities for CO and ethyl acetate oxidation were evaluated. The results show that OL is a typical octahedral layered structure, and the doping of Cu hardly affects the structure of OL. Moreover, Cux/OL samples had different reducibility, oxygen mobility, and atomic ratio of Cu2+/CuO, (Mn2++Mn3+)/Mn4+, and Oads/Olatt after the addition of Cu to OL. Among the Cux/OL samples, the Cu5/OL sample showed the best activity for the catalytic oxidation of CO and ethyl acetate (T50=70 and T90=100℃ for CO oxidation; T50=160℃ and T90=200℃ for ethyl acetate oxidation). Cu5/OL showed the best reducibility, most isolated Cu2+ species, highest surface (Mn2++Mn3+)/Mn4+ atomic ratio, highest chemisorbed oxygen species, and lowest O2 desorption temperature. Hence, factors such as the strong interaction between copper and manganese, good reducibility, and oxygen mobility were responsible for the excellent catalytic activity of Cu5/OL.
Octahedral layered birnessite (denoted as OL) was synthesized by the oxidation-reduction method and a series of Cux/OL catalysts were prepared by the ion exchange method with various Cu loadings. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption-desorption, hydrogen temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), thermogravimetric (TG) and.oxygen temperature-programmed desorption (O2-TPD) techniques, and their catalytic activities for CO and ethyl acetate oxidation were evaluated. The results show that OL is a typical octahedral layered structure, and the doping of Cu hardly affects the structure of OL. Moreover, Cux/OL samples had different reducibility, oxygen mobility, and atomic ratio of Cu2+/CuO, (Mn2++Mn3+)/Mn4+, and Oads/Olatt after the addition of Cu to OL. Among the Cux/OL samples, the Cu5/OL sample showed the best activity for the catalytic oxidation of CO and ethyl acetate (T50=70 and T90=100℃ for CO oxidation; T50=160℃ and T90=200℃ for ethyl acetate oxidation). Cu5/OL showed the best reducibility, most isolated Cu2+ species, highest surface (Mn2++Mn3+)/Mn4+ atomic ratio, highest chemisorbed oxygen species, and lowest O2 desorption temperature. Hence, factors such as the strong interaction between copper and manganese, good reducibility, and oxygen mobility were responsible for the excellent catalytic activity of Cu5/OL.
2017, 33(9): 1865-1874
doi: 10.3866/PKU.WHXB201704285
Abstract:
Rh-Mn-based catalysts are promising for ethanol synthesis from syngas. In this work, a carbon fiber (CF)-supported Rh-Mn catalyst, with highly dispersed Rh and close contact Rh-Mn species, has been prepared by a new in situ polymerization route using citric acid and ethylene glycol interaction. The structure and physicochemical properties of both the calcined and reduced samples have been characterized by TPR, XRD, TEM, EDS, CO-TPD, H2 chemisorption, and XPS techniques and the catalytic performance for ethanol synthesis from syngas has been evaluated. The results show that the new method is beneficial in forming close contact Rh-Mn species than that obtained with the conventional impregnation method. This can enhance the dispersion and sintering resistance of Rh and effectively improve the activity of CO hydrogenation and the selectivity to ethanol in ethanol synthesis from syngas.
Rh-Mn-based catalysts are promising for ethanol synthesis from syngas. In this work, a carbon fiber (CF)-supported Rh-Mn catalyst, with highly dispersed Rh and close contact Rh-Mn species, has been prepared by a new in situ polymerization route using citric acid and ethylene glycol interaction. The structure and physicochemical properties of both the calcined and reduced samples have been characterized by TPR, XRD, TEM, EDS, CO-TPD, H2 chemisorption, and XPS techniques and the catalytic performance for ethanol synthesis from syngas has been evaluated. The results show that the new method is beneficial in forming close contact Rh-Mn species than that obtained with the conventional impregnation method. This can enhance the dispersion and sintering resistance of Rh and effectively improve the activity of CO hydrogenation and the selectivity to ethanol in ethanol synthesis from syngas.
2017, 33(9): 1875-1883
doi: 10.3866/PKU.WHXB201705088
Abstract:
S doping in Fe/N/C non-precious metal catalysts is an effective approach to further improve their catalytic activity for the oxygen reduction reaction (ORR). However, the enhancement mechanism is not yet clear. Here, we synthesized an Fe/N/C catalyst using melamine-formaldehyde resin as the N and C precursors, CaCl2 as the template, and FeCl3 as the Fe precursor. The effects of S doping on the morphology, textural property, composition, and ORR catalytic activity were investigated by adding various amounts of KSCN as a precursor. Transmission electron microscopy (TEM) and N2 adsorption- desorption isotherm results revealed that S prevented the growth of Fe-containing nanoparticles, and facilitated the formation of a porous structure, which increased both the catalyst surface area and mass transfer rate. X-ray photoelectron spectroscopy (XPS) results indicated that a suitable amount of S precursor led to a high doping level of S and provided the highest ORR activity. However, too much S in the precursor decreased the doping levels of both Fe and S, due to the formation of FeS, which could be completely removed by acid leaching. Density functional theory (DFT) calculations showed that the addition of S in an Fe-N4 macrocycle could enhance the interaction strength of the Fe―O bond between the O2 molecule or the intermediate OOHspecies and Fe in the Fe-N4 structure, resulting in a significant decrease in the O―O bond energy, and may help in bond breaking in subsequent reactions, facilitating the ORR process.
S doping in Fe/N/C non-precious metal catalysts is an effective approach to further improve their catalytic activity for the oxygen reduction reaction (ORR). However, the enhancement mechanism is not yet clear. Here, we synthesized an Fe/N/C catalyst using melamine-formaldehyde resin as the N and C precursors, CaCl2 as the template, and FeCl3 as the Fe precursor. The effects of S doping on the morphology, textural property, composition, and ORR catalytic activity were investigated by adding various amounts of KSCN as a precursor. Transmission electron microscopy (TEM) and N2 adsorption- desorption isotherm results revealed that S prevented the growth of Fe-containing nanoparticles, and facilitated the formation of a porous structure, which increased both the catalyst surface area and mass transfer rate. X-ray photoelectron spectroscopy (XPS) results indicated that a suitable amount of S precursor led to a high doping level of S and provided the highest ORR activity. However, too much S in the precursor decreased the doping levels of both Fe and S, due to the formation of FeS, which could be completely removed by acid leaching. Density functional theory (DFT) calculations showed that the addition of S in an Fe-N4 macrocycle could enhance the interaction strength of the Fe―O bond between the O2 molecule or the intermediate OOHspecies and Fe in the Fe-N4 structure, resulting in a significant decrease in the O―O bond energy, and may help in bond breaking in subsequent reactions, facilitating the ORR process.
2017, 33(9): 1884-1890
doi: 10.3866/PKU.WHXB201705084
Abstract:
A CoTenanocatalyst has been successfully synthesized via a template-free hydrothermal method. Inorganic reactants were used so as not to introduce carbon residue contamination. The as-prepared sample was characterized by many techniques, including X-ray diffraction, scanning electron microscopy, ultraviolet-visible light absorption spectroscopy, and X-ray photoelectron spectroscopy. The obtained sample was found to be sponge-like CoTe with a hexagonal structure, which exhibited visible-light (λ> 420 nm) photocatalytic activity. Photoreduction of CO2 over CoTe is believed to have undergone via the carbene pathway. The CO2 was photocatalytically reduced into CH4 with a low yield when N,N-dimethylacetamide (DMA) or water was used as the solvent. When the sacrificial agent triethanolamine (TEOA) was introduced into the photocatalytic system, however, the product was CO instead. These results indicated that both the solvent and sacrificial agent can influence the photoreduction of CO2 over the CoTenanocatalyst. Usually, the solubility of CO2 in an organic solvent such as DMA is higher than that in the pure water, leading to a larger product yield. The presence of TEOA may change the adsorption characteristics of CO onto the surface of the CoTe catalyst, as well as enhance the separation efficiency of photogenerated charge carriers, resulting in a change in the activity and selectivity of CO2 photoreduction.
A CoTenanocatalyst has been successfully synthesized via a template-free hydrothermal method. Inorganic reactants were used so as not to introduce carbon residue contamination. The as-prepared sample was characterized by many techniques, including X-ray diffraction, scanning electron microscopy, ultraviolet-visible light absorption spectroscopy, and X-ray photoelectron spectroscopy. The obtained sample was found to be sponge-like CoTe with a hexagonal structure, which exhibited visible-light (λ> 420 nm) photocatalytic activity. Photoreduction of CO2 over CoTe is believed to have undergone via the carbene pathway. The CO2 was photocatalytically reduced into CH4 with a low yield when N,N-dimethylacetamide (DMA) or water was used as the solvent. When the sacrificial agent triethanolamine (TEOA) was introduced into the photocatalytic system, however, the product was CO instead. These results indicated that both the solvent and sacrificial agent can influence the photoreduction of CO2 over the CoTenanocatalyst. Usually, the solubility of CO2 in an organic solvent such as DMA is higher than that in the pure water, leading to a larger product yield. The presence of TEOA may change the adsorption characteristics of CO onto the surface of the CoTe catalyst, as well as enhance the separation efficiency of photogenerated charge carriers, resulting in a change in the activity and selectivity of CO2 photoreduction.
2017, 33(9): 1891-1897
doi: 10.3866/PKU.WHXB201705111
Abstract:
CuS fabricated by an element-reaction route using copper and sulfur powders was loaded on WO3 in situ at a low temperature. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller analysis, and UV-visible diffuse reflectance spectra were used to characterize the crystalline phase, morphology, particle size, and optical properties of the CuS-WO3 samples. CuS modification had no obvious influence on the crystalline phase, particle size, and surface area of WO3. However, it led to the enhancement of the utilization of light energy for WO3. CuS-WO3 composites were utilized as photocatalysts for the degradation of Rhodamine B. The CuS-WO3 photocatalysts showed higher photocatalytic activity than pure WO3 or CuS under visible light irradiation. CuS content had a significant influence on the photocatalytic activity of CuS-WO3. CuS-WO3 with 7% (w, mass fraction) CuS content exhibited the highest photocatalytic degradation activity (91.3%). Based on analysis of the band structure of CuS and WO3, photoluminescence results, and active species trapping, a “direct Z-scheme” mechanism for the enhanced photocatalytic activity of CuS-WO3 was proposed. The “direct Z-scheme” results in effective charge separation, leading to increased photocatalytic activity compared to that of CuS and WO3.
CuS fabricated by an element-reaction route using copper and sulfur powders was loaded on WO3 in situ at a low temperature. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller analysis, and UV-visible diffuse reflectance spectra were used to characterize the crystalline phase, morphology, particle size, and optical properties of the CuS-WO3 samples. CuS modification had no obvious influence on the crystalline phase, particle size, and surface area of WO3. However, it led to the enhancement of the utilization of light energy for WO3. CuS-WO3 composites were utilized as photocatalysts for the degradation of Rhodamine B. The CuS-WO3 photocatalysts showed higher photocatalytic activity than pure WO3 or CuS under visible light irradiation. CuS content had a significant influence on the photocatalytic activity of CuS-WO3. CuS-WO3 with 7% (w, mass fraction) CuS content exhibited the highest photocatalytic degradation activity (91.3%). Based on analysis of the band structure of CuS and WO3, photoluminescence results, and active species trapping, a “direct Z-scheme” mechanism for the enhanced photocatalytic activity of CuS-WO3 was proposed. The “direct Z-scheme” results in effective charge separation, leading to increased photocatalytic activity compared to that of CuS and WO3.
2017, 33(9): 1898-1904
doi: 10.3866/PKU.WHXB201705112
Abstract:
Polar groups in the skeletons of conjugated microporous polymers (CMPs) play an important role in determining their porosity and gas sorption performance. Understanding the effect of the polar group on the properties of CMPs is essential for further advances in this field. To address this fundamental issue, we used benzene, the simplest aromatic system, as a monomer for the construction of two novel CMPs with multi-carboxylic acid groups in their skeletons (CMP-COOH@1 and CMP-COOH@2). We then explored the profound effect the amount of free carboxylic acid in each polymer had on their porosity, isosteric heat, gas adsorption, and gas selectivity. CMP-COOH@1 and CMP-COOH@2 showed Brunauer-Emmett-Teller (BET) surface areas of 835 and 765 m2·g-1, respectively, displaying high potential for carbon dioxide storage applications. CMP-COOH@1 and CMP-COOH@2 exhibited CO2 capture capabilities of 2.17 and 2.63 mmol·g-1 (at 273 K and 1.05 × 105 Pa), respectively, which were higher than those of their counterpart polymers, CMP-1 and CMP-2, which showed CO2 capture capabilities of 1.66 and 2.28 mmol·g-1, respectively. Our results revealed that increasing the number of carboxylic acid groups in polymers could improve their adsorption capacity and selectivity.
Polar groups in the skeletons of conjugated microporous polymers (CMPs) play an important role in determining their porosity and gas sorption performance. Understanding the effect of the polar group on the properties of CMPs is essential for further advances in this field. To address this fundamental issue, we used benzene, the simplest aromatic system, as a monomer for the construction of two novel CMPs with multi-carboxylic acid groups in their skeletons (CMP-COOH@1 and CMP-COOH@2). We then explored the profound effect the amount of free carboxylic acid in each polymer had on their porosity, isosteric heat, gas adsorption, and gas selectivity. CMP-COOH@1 and CMP-COOH@2 showed Brunauer-Emmett-Teller (BET) surface areas of 835 and 765 m2·g-1, respectively, displaying high potential for carbon dioxide storage applications. CMP-COOH@1 and CMP-COOH@2 exhibited CO2 capture capabilities of 2.17 and 2.63 mmol·g-1 (at 273 K and 1.05 × 105 Pa), respectively, which were higher than those of their counterpart polymers, CMP-1 and CMP-2, which showed CO2 capture capabilities of 1.66 and 2.28 mmol·g-1, respectively. Our results revealed that increasing the number of carboxylic acid groups in polymers could improve their adsorption capacity and selectivity.
2017, 33(9): 1905-1914
doi: 10.3866/PKU.WHXB201704274
Abstract:
Alzheimer's disease (AD) is mainly caused by the aggregation of amyloid-β (Aβ) protein. Development of inhibitors to prevent Aβ aggregation is the most efficient method to devise a cure for AD. Aβ aggregation has been found to be inhibited by the affibody protein ZAβ3, selected via phage display. However, the molecular basis of affinity interactions between Aβ and ZAβ3, the interaction region, and important residues of Aβ and ZAβ3 remain unclear. Herein, molecular dynamics simulations and free energy calculation and decomposition using the molecular mechanics-Poisson-Boltzmann surface area method (MM-PBSA) were coupled to investigate the molecular mechanism underlying interactions between Aβ and ZAβ3. Interactions between the β-strand of ZAβ3 and Aβ16-40 were found to contribute greatly to their binding free energy, while that between the α-helix of ZAβ3 and ZAβ3 has a smaller contribution. Based on the free energy decomposition, hotspot residues of ZAβ3 are E15, I16, V17, Y18, L19, P20, N21, and L22 and those of Aβ16-40 include F19, F20, A21, E22, D23, K28, I31, I32, G33, L34, M35, V36, G38, and V40. ZAβ3 stabilizes the β-sheet by burying the two mostly nonpolar faces of the Aβ hairpin within a large hydrophobic tunnel-like cavity formed by the α-helix. The identified binding motif can be used as a starting point for rational design of protein inhibitors with high affinity for Aβ to prevent Aβ aggregation. The three key characteristics of efficient protein inhibitors are the presence of a high-affinity site (β-strand), a large accessory structure (α-helix), and a stable conformation owing to disulfide bonds. The high-affinity site can competitively bind to the Aβ monomer, and the large accessory structure can block other Aβ monomers; both these elements require a stable conformation via disulfide bonds. These three characteristics of a protein inhibitor can be employed together to suppress Aβ aggregation.
Alzheimer's disease (AD) is mainly caused by the aggregation of amyloid-β (Aβ) protein. Development of inhibitors to prevent Aβ aggregation is the most efficient method to devise a cure for AD. Aβ aggregation has been found to be inhibited by the affibody protein ZAβ3, selected via phage display. However, the molecular basis of affinity interactions between Aβ and ZAβ3, the interaction region, and important residues of Aβ and ZAβ3 remain unclear. Herein, molecular dynamics simulations and free energy calculation and decomposition using the molecular mechanics-Poisson-Boltzmann surface area method (MM-PBSA) were coupled to investigate the molecular mechanism underlying interactions between Aβ and ZAβ3. Interactions between the β-strand of ZAβ3 and Aβ16-40 were found to contribute greatly to their binding free energy, while that between the α-helix of ZAβ3 and ZAβ3 has a smaller contribution. Based on the free energy decomposition, hotspot residues of ZAβ3 are E15, I16, V17, Y18, L19, P20, N21, and L22 and those of Aβ16-40 include F19, F20, A21, E22, D23, K28, I31, I32, G33, L34, M35, V36, G38, and V40. ZAβ3 stabilizes the β-sheet by burying the two mostly nonpolar faces of the Aβ hairpin within a large hydrophobic tunnel-like cavity formed by the α-helix. The identified binding motif can be used as a starting point for rational design of protein inhibitors with high affinity for Aβ to prevent Aβ aggregation. The three key characteristics of efficient protein inhibitors are the presence of a high-affinity site (β-strand), a large accessory structure (α-helix), and a stable conformation owing to disulfide bonds. The high-affinity site can competitively bind to the Aβ monomer, and the large accessory structure can block other Aβ monomers; both these elements require a stable conformation via disulfide bonds. These three characteristics of a protein inhibitor can be employed together to suppress Aβ aggregation.
2017, 33(9): 1915-1922
doi: 10.3866/PKU.WHXB201705083
Abstract:
Sulfur and nitrogen co-doped porous carbon (SNDPC) was successfully synthesized using one-step microwave-assisted pyrolysis of ionic liquid. The structure and morphology of the pyrolysis products were characterized by Fourier-transform infrared (FT-IR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), electron microscopy, and X-ray photoelectron spectroscopy (XPS). The pyrolysis mechanism of the ionic liquid 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide (EMImNTf2) under microwave irradiation was discussed. Microwave irradiation was found to accelerate the pyrolysis of EMImNTf2. The cation of EMImNTf2 works as the precursor of the carbon backbone of the porous carbon, while the anion acts as sulfur source and porosity-directing regulator. The SNDPC was obtained at 320 ℃ and exhibited graphitic structure with numerous surface defects. The atomic percentages of N and S in SNDPC were 12.84% and 1.07%, respectively. The N atoms mainly substitute the C sites in the graphitic carbon matrix, whereas the S atoms mainly bond to the ledges and defects of the carbon matrix.
Sulfur and nitrogen co-doped porous carbon (SNDPC) was successfully synthesized using one-step microwave-assisted pyrolysis of ionic liquid. The structure and morphology of the pyrolysis products were characterized by Fourier-transform infrared (FT-IR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), electron microscopy, and X-ray photoelectron spectroscopy (XPS). The pyrolysis mechanism of the ionic liquid 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide (EMImNTf2) under microwave irradiation was discussed. Microwave irradiation was found to accelerate the pyrolysis of EMImNTf2. The cation of EMImNTf2 works as the precursor of the carbon backbone of the porous carbon, while the anion acts as sulfur source and porosity-directing regulator. The SNDPC was obtained at 320 ℃ and exhibited graphitic structure with numerous surface defects. The atomic percentages of N and S in SNDPC were 12.84% and 1.07%, respectively. The N atoms mainly substitute the C sites in the graphitic carbon matrix, whereas the S atoms mainly bond to the ledges and defects of the carbon matrix.
