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1. chinaXiv:201803.01543 [pdf]

Ultrafine nickel nanoparticles modified reduced graphene oxide as efficient non-platinum catalysts for methanol oxidation

Hongmei Sun; Jun Liu; Zhenfei Tian; Yixing Ye; Changhao Liang
Subjects: Physics >> Interdisciplinary Physics and Related Areas of Science and Technology

Synthesis of low-cost, highly-active and durable non-platinum metal catalysts for methanol oxidation reaction (MOR) is always full of challenge. Here, Ni nanoparticles modified reduced graphene oxide (Ni/rGO) as an efficient non-platinum catalyst were synthesized by laser ablation of Ni target in graphene oxide (GO) solution and the following in situ reduction process. It found that GO played an important role to restrict the growth and aggregation of ultrafine nickel colloids (< 5 nm) in the process of laser ablation. The resulting Ni/rGO catalyst showed advantageous in active sites and charge transport resulting from the small particle size, uniform dispersion and electronic effect arising from the electron interactions between reduced graphene oxide (rGO) and Ni. The obtained Ni/rGO exhibited the ultrahigh catalytic mass activity of 1600 mA/mg, methanol saturation concentration (4 M), which was superior to that of the reported Ni-based catalysts. Remarkably the mass activities of Ni/rGO before and after 1000 cycles exceed that of the commercial Pt/C catalyst, indicating excellent catalytic activity and stability.

submitted time 2018-03-30 Hits2575Downloads1282 Comment 0

2. chinaXiv:201803.01545 [pdf]

Site-specifically Immobilize Pt Nanocrystals on NiFe Layered Double Hydroxide: Old Catalysts with Enhanced Stability Through strong Fe3+-O(H)-Pt Interfacial Contact

Yechuang Han; Pengfei Li; Jun Liu; Shouliang Wu ; Yixing Ye; Zhenfei Tian; Changhao Liang
Subjects: Physics >> Interdisciplinary Physics and Related Areas of Science and Technology

Agglomeration-triggered deactivation of supported platinum electrocatalysts markedly hinders their application in methanol oxidation reaction (MOR). In this study, graphene-supported nickel–iron layered double hydroxide (NiFe–LDH/rGO), in which Fe3+ was introduced to replace Ni2+ partially in the Ni(OH)2 lattice to provide stronger metal–support bonding sites, was utilized to immobilize Pt nanoparticles (NPs). Given the optimized metal–support interfacial contact (Fe3+–O(H)–Pt) between Pt NPs and NiFe–LDH/rGO nanosheets for Pt/NiFe–LDH/rGO electrocatalysts, the Pt/NiFe–LDH/rGO electrocatalysts displayed dramatically enhanced durability than that of Pt/Ni(OH)2/rGO counterpart as well as commercial Pt/C, and 86.5% of its initial catalytic activity can be maintained even after 1200 cycles of cyclic voltammetry (CV) tests during MOR. First-principle calculations toward the resultant M–O(H)–Pt (M = Fe3+, Ni2+) interfacial structure further corroborates that the NiFe–LDH nanosheets can provide stronger bonding sites (via the Fe3+–O(H)–Pt bonds) to immobilize Pt NPs than those of Ni(OH)2 nanosheets (via the Ni2+–O(H)–Pt bonds).

submitted time 2018-03-30 Hits2485Downloads1167 Comment 0

3. chinaXiv:201803.01552 [pdf]

Fe-N-doped mesoporous carbon loaded on reduced graphene oxides with dual active sites for efficient oxygen reduction catalysts

Chao Zhang; Jun Liu; Zabeada Aslam; Rik Drummond-Brydson; Changhao Liang
Subjects: Physics >> Interdisciplinary Physics and Related Areas of Science and Technology

Transition metal/nitrogen/carbon (M-N/C) catalysts are considered as one of the most promising candidates to replace Pt/C catalysts for oxygen reduction reactions (ORR). Here, we have designed novel reduced graphene oxides (rGO) supported Fe-N-doped carbon (Fe-N-C/rGO) catalysts via simple pyrolysis of polypyrrole(Ppy)-FeO-GO composites. The as-prepared catalysts induced an onset potential of 0.94 V, a half-wave potential of 0.81 V in alkaline solutions, which is much better than that of the counterpart N-C and N-C/rGO catalysts, and comparable to that of Pt/C catalysts. Moreover, the Fe-N-C/rGO catalysts showed improved durability and higher tolerance against methanol crossover than Pt/C in alkaline solutions. This superior ORR perfomance can be ascribed to the combined catalytic effect of both Fe-based nanoparticles (Fe3O4, Fe4C) and Fe-Nx sites, as well as fast mass transfer and accessible active sites benefitting from the mesporous structure and high specific surface area. This work provides new insight for synthesis of a more promising non-platinum electrocatalyst for metal-air batteries and fuel-cell applications.

submitted time 2018-03-30 Hits1926Downloads910 Comment 0

4. chinaXiv:201711.00002 [pdf]

Simultaneous Cu Doping and Growth of TiO2Nanocrystalline Array Film as a Glucose Biosensor.pdf

Yunyu Cai; Yixing Ye; Shouliang Wu; Jun Liu; Changhao Liang
Subjects: Materials Science >> Materials Chemistry

Doping additional ions into semiconductor is a potential strategy to modify the electronic structure of semiconductor materials. By using a highly reactive colloidal Cu clusters as doping precursor, we present here the successful doping of Cu ions into TiO2 nanocrystalline that simultaneously transformed from amorphous anodic TiO2 nanotubes during a dissolution and recrystallization process. The Cu-doped TiO2 nanoparticles (Cu-TNPs) film was characterized by X-ray diffraction, scanning and transmission electron microscopy and Raman spectroscopy. The Cu-TNPs show a rugby-like shape with exposed active {101}, {001} facets and the long-axis parallel to [001] lattice direction. The substitutional Cu2+ ions dopants in TiO2 nanocrystals caused the swelling of the crystalline unit cell. Such efficient doping design facilitate the improvement of nanostructured TiO2 as a potential biosensor for glucose molecules.

submitted time 2017-11-01 Hits16026Downloads1434 Comment 0

5. chinaXiv:201711.00003 [pdf]

Highly-dispersed ultrafine Pt nanoparticles on reduced graphene oxide nanosheets In situ sacrificial template synthesis and superior electrocatalytic performance for methanol oxidation.pdf

Shouliang Wu; Jun Liu ; Zhenfei Tian; Yunyu Cai; Yixing Ye; Qinglin Yuan; Changhao Liang
Subjects: Materials Science >> Materials Chemistry

We report a simple and environment-friendly route to prepare platinum/reduced graphene oxide (Pt/rGO) nanocomposites (NCs) with highly reactive MnOx colloids as reducing agents and sacrificial templates. The colloids are obtained by laser ablation of a metallic Mn target in graphene oxide (GO)-containing solution. Structural and morphological investigations of the as-prepared NCs revealed that ultrafine Pt nanoparticles (NPs) with an average size of 1.8 (± 0.6) nm are uniformly dispersed on the surfaces of rGO nanosheets. Compared with commercial Pt/C catalysts, Pt/rGO NCs with highly electrochemically active surface areas show remarkably improved catalytic activity and durability toward methanol oxidation. All of these superior characteristics can be attributed to the small particle size and uniform distribution of the Pt NPs, as well as the excellent electrical conductivity and stability of the rGO catalyst support. These findings suggest that Pt/rGO electrocatalysts are promising candidate materials for practical use in fuel cells.

submitted time 2017-11-01 Hits16181Downloads1522 Comment 0

6. chinaXiv:201711.00004 [pdf]

Co-doped Ni hydroxide and oxide nanosheet networks Laser-Assisted Synthesis Effective Doping, and Ultrahigh Pseudocapacitor Performance.pdf

Dewei Liang; Shouliang Wu; Jun Liu; Zhenfei Tian; Changhao Liang
Subjects: Materials Science >> Materials Chemistry

Morphology control and impurity doping are two widely applied strategies to improve the electrochemical performance of nanomaterials. Herein, we report an environmentally friendly approach to obtain Co-doped Ni(OH)2 nanosheet networks using a laser-induced cobalt colloid as a doping precursor followed by an aging treatment in a hybrid medium of nickel ions. The shape and specific surface area of the doped Ni(OH)2 can be successfully adjusted by changing the concentration of sodium thiosulfate. Furthermore, a Co-doped Ni(OH)2 nanosheet network was further converted into Co-doped NiO with its pristine morphology retained via facile thermal decomposition in air. The structure and electrochemical performance of the as-prepared samples are investigated with scanning and transmission electron microscopy, energy dispersive x-ray analysis, x-ray diffraction, Fourier transform infrared spectroscopy, the nitrogen adsorption-desorption isotherm technique, and electrochemical measurements. The Co-doped Ni(OH)2 electrode shows an ultrahigh specific capacitance of 1421 F/g at a current density of 6 A/g, and a good retention level of 76% after 1000 cycles, in sharp contrast with only a 47% retention level of the pure Ni(OH)2 electrode at the same current density. In addition, the Co-doped NiO electrode exhibits a capacitance of 720 F/g at 6 A/g and 92% retention after 1000 cycles, which is also superior to those values for relevant pure NiO electrodes. The Co2+ partially substitutes for Ni2+ in the metal hydroxide and oxide, resulting in an increase of free holes in the valence band, and, therefore, enhancement of the p-type conductivity of Ni(OH)2 and NiO. Moreover, such novel mesoporous nanosheet network structures are also able to enlarge the electrode-electrolyte contact area and shorten the path length for ion transport. The synergetic effect of these two results is responsible for the observed ultrahigh pseudocapacitor performance.

submitted time 2017-11-01 Hits16277Downloads1463 Comment 0

7. chinaXiv:201710.00078 [pdf]

Laser irradiation-induced Au-ZnO nanospheres with enhanced sensitivity and stability in ethanol sensing.pdf

Hao Zhang; Shouliang Wu; Jun Liu; Yunyu Cai; Changhao Liang
Subjects: Materials Science >> Materials Chemistry

Incorporating noble metal nanoparticles on the surface or inner side of semiconductors to form a hybrid nanostructure is an effective route to improve the gas sensing performance of these semiconductors. In this study, we present novel Au-decorated ZnO nanospheres (Au-ZnO NSs) obtained by laser irradiation of liquids. Structural characterization indicated that the Au-ZnO NSs consisted of single crystalline ZnO NSs with few Au nanoparticles decorated on their surfaces and abundant encapsulated Au nanoparticles with relatively small sizes. Laser irradiation-induced heating–melting–evaporating processes are responsible for the formation of unique Au-ZnO NSs. Gas sensing properties of the Au-ZnO NSs, as gas sensing materials, were investigated and compared with those of pure ZnO NSs. The former showed lower working temperature, higher sensitivity, better selectivity, and good reproducibility. The response values of Au-ZnO NSs and pure ZnO NSs sensors to ethanol of 100 ppm were 252 and 75 at working temperature of 320 °C and 360 °C, respectively. The significant enhancements in gas sensing performance should be attributed to the electronic sensitization induced by the depleted layers between encapsulated Au nanoparticles and ZnO and chemical sensitization originating from the catalytic effects of Au nanoparticles decorated on the surfaces that dissociated molecular oxygen.

submitted time 2017-10-31 Hits15934Downloads1373 Comment 0

8. chinaXiv:201710.00079 [pdf]

A general strategy toward transition metal carbidecarbon coreshell nanospheres and their application for supercapacitor electrode.pdf

Hemin Zhang; Jun Liu; Zhenfei Tian; Yixing Ye; Yunyu Cai; Changhao Liang; Kazuya Terabe
Subjects: Materials Science >> Materials Chemistry

A general and straightforward strategy was developed for fabricating transition metal carbide (TMC)/carbon (C) core/shell nanospheres (NSs) by laser ablation of transition metals in acetone/ethanol liquid. Various TMC/C core/shell NSs such as TaC/C, NbC/C, HfC/C, and MoC/C core/shell NSs were successfully fabricated, highlighting the generality of this method. Crucially, this approach is green, facile, catalyst-free, and especially can be operated under ambient environments. Interestingly, all of the as-synthesized TMCs in the NS cores showed a cubic phase and structures similar to that of NaCl-type. The cores were further encapsulated by amorphous carbon shell with different thickness. As an example of the functional properties of these compound materials, the TaC/C core/shell NSs obtained were investigated as a supercapacitor electrode, which showed a large specific capacitance, excellent rate capability and remarkable cycling ability, revealing that the NSs could be used as new electrode materials for electrochemical energy storage. The photoluminescence of TaC/C core/shell NSs exhibited strong emission under the specific excitation wavelength at room temperature, showing potential biomedical applications due to the good biocompatibility of carbon shell. Besides, the basic physical and chemical reactions involved in the unique formation mechanism under highly nonequilibrium states induced by ultrafast laser ablation were discussed.

submitted time 2017-10-31 Hits16377Downloads1523 Comment 0

9. chinaXiv:201710.00080 [pdf]

Recent Advances in Ligand-Free, Charged and Defect-Rich Catalysts Developed by Laser Ablation and Processing in Liquids.pdf

Dongshi Zhang; Jun Liu,; Pengfei Li; Zhenfei Tian; Changhao Liang
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Catalysts are the foundation of sustainable and renewable energies to address the depletion of natural fossil fuels problem. Because the catalysts’ activity is surface chemistry dependent, those “naked”, so-called ligand-free catalysts with more active sites exposing to the reactants are more preferable. With ligand-free, highly surface charged nanomaterials as the innate products, a newly emerging technique―laser synthesis and processing in liquids―is gaining increasing attention. The priority of laser-synthesized ligand-free metallic catalysts over chemically-synthesized counterparts has been confirmed by increasing groups through comparative studies on their catalytic activities. Besides the ligand-free metallic catalysts, this technique also excels at synthesis of bimetallic-alloy, core-shell and defect-rich semiconductor catalysts, and show good compatibility with other techniques (e.g., hydrothermal treatment and electrophoresis) to develop advanced catalysts such as ternary oxide, doped semiconductor, supported composite, nanoparticle-polymer matrix and film catalysts. Following the concept of why to choose, how to synthesize and where to use, in this review, we first introduce the advantages of this technique and the synthesized catalysts, secondly show how to develop complex catalysts using the laser-generated particles as the building blocks, and finally present the exciting application examples for photodegradation, water splitting and fuel cells.

submitted time 2017-10-31 Hits1418Downloads799 Comment 0

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