Xiao Chen | Beijing Normal University (original) (raw)

Papers by Xiao Chen

Ceramics International, 2017

Sandwich-structured TiN/CrAlN films were rationally designed using metallic Ti and Al-Cr alloy ta... more Sandwich-structured TiN/CrAlN films were rationally designed using metallic Ti and Al-Cr alloy targets by RF-pulsed magnetron sputtering. After obtained films were annealed at diverse temperatures at atmospheric pressure for 1 h, the hardness reveals an apparent decrease evolution from 29.2 to 15.7 GPa and H/E* ratio declines below 0.1 with increasing annealing temperature. Meanwhile, the grain size gradually becomes larger from 16.3 to 130.0 nm with increasing annealing temperature. Interestingly, it is observed that cracking behavior of sandwich-structured composite TiN/CrAlN films at elevated temperature is originated from the top of the blisters where main component is alumina on the surface, in virtue of intrinsically induced stress during oxidation, thermal expansion mismatch and phase transformation of the oxide layer. No cracks, nevertheless, are yielded in the film between any two blisters. Herein, these findings provide some beneficial references for preparing high quality films and coatings in high temperature service.

Ceramics International, 2018

The thermal failure mechanism of multilayer brittle TiN/CrAlN films at high annealing temperature... more The thermal failure mechanism of multilayer brittle TiN/CrAlN films at high annealing temperature has been investigated. Firstly, multilayer brittle TiN/CrAlN films (about 2.1 µm thick) were deposited on high speed steel by using metallic Ti and Al-Cr alloy (Al/Cr at% ratio=70:30) targets by RF-pulsed magnetron sputtering. Then, the multilayer TiN/CrAlN films were subjected to large heating-cooling shock during the high temperature process. The thermal expansion mismatch between the substrate-film, film-film and oxide-nitride interfaces causes large thermal stress. Finally, large thermal stress results in crack initiation, where the defects are the preferential sites for crack nucleation. During the heating-cooling process, the deformation results in stress concentration and strain mismatch, generates surface cracks and interface cracks due to the different mechanical properties between the substrate and multilayer films. The propagation of the interface cracks ultimately brings about the film delamination and loses thermal protection capability under high temperature service. Additionally, multiple surface cracks, to some extent, cause a reduction of the driving force for interface crack nucleation via relieving some tensile stress, thus inhibiting interface crack propagation and delamination failure.

Chemical Physics, 2018

A novel interface-facilitated synthesis of graphene-like carbon nanosheets from P123 is reported.... more A novel interface-facilitated synthesis of graphene-like carbon nanosheets from P123 is reported. The morphology and structure of the carbon nanosheets were characterized though FESEM, TEM, AFM, XRD, Raman and FTIR. The formation mechanism of the graphene-like carbon nanosheets is proposed. P123 serves a dual function of structure-directing agent and carbon precursor, which first assembles at the toluene-HCl interface and then is in situ carbonized to carbon nanosheets. This process shows several advantages such as mild condition, simple procedure and low cost. In addition, the obtained carbon nanosheets can be effectively confined at the interface and self-organize into film with high uniformity.

ChemCatChem, 2020

Photocatalytic CO2 reduction can reduce greenhouse gas emissions and convert CO2 into value-added... more Photocatalytic CO2 reduction can reduce greenhouse gas emissions and convert CO2 into value-added chemical feedstocks and fuels. P25 is one of the most popular photocatalyst, but its high photoinduced charge recombination rate and low CO2 adsorption ability hinder its application in photocatalytic CO2 reduction due to the limited anatase/rutile interface and small specific surface area. Herein, a paragenetic anatase/rutile interface is in-situ formed in one crystal grain via calcination of NH2-MIL-125 in argon atmosphere and the obtained N doped porous carbon layer endows its high specific surface area. The in situ XRD and HRTEM characterization proved the anatase/rutile interface is in situ formed by the phase transformation from anatase (211) plane to rutile (211) plane. The charge separation efficiency of the photocatalyst with N-doped carbon coating paragenetic heterostructure is proved to be enhanced compared with N-doped carbon coating anatase or rutile single phase catalyst. The optimized catalyst S750Ar with paragenetic anatase/rutile structure shows a 7.6 folds enhanced CO conversion rate than that of P25. These findings provide an in-situ transition strategy to regulate charge transfer between phases at the interface and promote the application of heterogeneous catalysts.

Journal of Alloys and Compounds, 2015

Multilayer brittle TiN/CrAlN films were prepared on polished silicon and high speed steel by RF m... more Multilayer brittle TiN/CrAlN films were prepared on polished silicon and high speed steel by RF magnetron sputtering technology with various substrate bias voltages ranging from 0 to À150 V. In this study, the main attention is targeting the correlation between the substrate bias voltage and the resulting mechanicaletribological properties. It is revealed that the films become much denser and more compact with increasing substrate bias, meanwhile, hardness and elastic modulus are correspondingly elevated. However, relatively decreased adhesion emerges when reaching the bias voltage of À150 V. The wear resistance is progressively enhanced while the deposition rate gradually declines as the substrate bias increases. Additionally, the mean values of dry friction coefficients sliding against Si 3 N 4 are in the range of 0.57e0.42, and the wear volumes are ranging from 23.97 Â 10 À3 to 13.93 Â 10 À3 mm 3. Thus, it can be drawn that the film maintains more excellent mechanical and tribological properties, which is sputtered at the moderate substrate bias of À100 V.

Journal of Alloys and Compounds, 2018

A Sisal-Like TiO 2 /Graphene-Like Carbon Sheets (SL-TiO 2 /GLCSs) composite was fabricated via a ... more A Sisal-Like TiO 2 /Graphene-Like Carbon Sheets (SL-TiO 2 /GLCSs) composite was fabricated via a facile one-pot self-assembling route at a two-phase interface. The ingenious P123 was introduced to serve a dual function of carbon precursor and structure-directing agent, which first assembled at the water/oil interfaces and subsequently was in situ carbonized to GLCSs. Then the sisal-like TiO 2 grew gradually on the GLCSs along the preferred direction. This process shows several advantages such as simple processes, mild condition, low cost and good combination of SL-TiO 2 and GLCSs. The combination of SL-TiO 2 with GLCSs significantly helps the adsorption of substrates as well as promotes electron-hole pair separation, exhibiting good photocatalytic activity towards degradation of methylene blue (MB) compared to the pristine SL-TiO 2 and commercial P25. This strategy opens up new perspectives for fabricating novel composites of nanooxides/GLCSs.

Electrochimica Acta, 2020

Hierarchical nanostructure with hollow feature can greatly promote electrocatalytic activity by f... more Hierarchical nanostructure with hollow feature can greatly promote electrocatalytic activity by facilitating the diffusion of active species and accelerating the contact between catalyst and electrolyte. In this paper, we report the preparation of hierarchical hollow NiFe hydroxide nanospheres assembled from ultrathin nanosheets as the OER electrocatalyst via a simple and gentle self-templating strategy, which includes two steps: the synthesis of Ni(OH) 2 nanospheres precursor and its further transformation to the final hollow-spheres after the introduction of Fe 3 + via a mild hydrothermal method. The hollow NiFe hydrox-ide nanospheres were proven to be composed of ultrathin nanosheets which formed porous walls. This unique structure achieved numerous mass transfer channels for electrolytes, ideal pathways for ions and electrons, and a high specific surface area, leading to the improved performance for the product during the electrocatalytic reaction. In addition, the charge transfer rate and structural stability of the architecture have been greatly improved after the addition of Fe 3 + , which guaranteed high electrochemical performance toward OER. The tafel plot for NiFe-190 without any conductive agents is 60 mV dec −1 and the overpotential needed to reach a current density of 10 mA cm −2 is a 270 mV.

Inorganic Chemistry, 2019

Novel 3D self-supported porous NiO@NiMoO 4 core−shell nanosheets are grown on nickel foam through... more Novel 3D self-supported porous NiO@NiMoO 4 core−shell nanosheets are grown on nickel foam through a facile stepwise hydrothermal method. Ultrathin NiO nanosheets on the nickel foam cross-linked to each other are used as the core, and tiny NiMoO 4 nanosheets are further engineered to be immobilized uniformly on the NiO nanosheets to form the shell. This step-by-step construction of the architecture composed of ultrathin primary and secondary nanosheets efficiently avoids the agglomeration problems of individual ultrathin nanosheets. The ingenious architecture possesses the advantages of numerous diffusion channels for electrolyte ions, ideal pathways for electrons, and a large interfacial area for electrochemical reaction. The introduction of the NiMoO 4 secondary nanosheets on the NiO primary nanosheets not only endows the heterostructure with high electrical conductivity and a large active area but also promotes an increase in oxygen vacancy content, which favors the improvement of electrocatalytic properties for the oxygen evolution reaction. The Tafel plot for the NiO@NiMoO 4 core−shell architecture is as low as 32 mV dec −1 , and the overpotential needed to reach 10 mA·cm −2 for NiO@NiMoO 4 nanosheets is only 0.28 V.

Chemical Engineering Science, 2020

The direct pyrolysis of metal organic frameworks (MOFs) has recently provided an effective method... more The direct pyrolysis of metal organic frameworks (MOFs) has recently provided an effective method to prepare various metal-incorporated composite carbon materials. In this work, hierarchical Coembedded N-doped porous carbon microspheres were synthesized by controlled pyrolysis of bimetallic Zn-Co Prussian blue analogues (PBAs), in which the metallic Zn component served as thermally removable template and ligand [Co(CN)6]3 served as both Co and N sources. When devoted to catalyzing the reduction of 4-nitrophenol (4-NPh) into 4-aminophenol (4-APh), the optimized catalyst exhibited a large apparent rate constant of 1.35 min1 and high turnover frequency (TOF) of 0.0204 s1, which was superior to the majority of noble-metal-based catalysts. Besides, a home-made continuous flow catalysis system was readily constructed. Control experiments confirmed that both partially uncovered and totally inbuilt active metallic Co species acted as catalytically active sites. This work might provide a further understanding of the identification of active sites within metal-incorporated carbon-based catalysts.

Journal of Power Sources, 2019

A template-free hydrothermal method is employed to construct 3D-scaffold structure. Defect-rich T... more A template-free hydrothermal method is employed to construct 3D-scaffold structure. Defect-rich TiO 2 (B) nanosheets-based free-standing film is successfully obtained. The defect-rich nanosheets-based electrode exhibits outstanding cycling stability. A R T I C L E I N F O Keywords: Self-assembly Scaffolds TiO 2 (B) nanosheets Free-standing films Lithium-ion batteries A B S T R A C T Nanosheets with large exposed surface and high chemical activity are of paramount significance for catalysis, gas sensing and energy storage. However, assembling them into large-area free-standing films and preventing ag-gregation of individual nanosheets remain a great challenge. Herein, an efficient strategy is proposed to assemble defect-rich TiO 2 (B) nanosheets into a 3D-scaffold structured free-standing film, which can preserve high chemical activity and prevent their aggregation. The inherent pores of Teflon lining are employed as load-bearing base to construct 3D scaffolds, and then, a rapid dissolution-recrystallization hydrothermal process is developed to fabricate defect-rich TiO 2 (B) nanosheets (~5 nm in thickness) on the 3D scaffolds. The numerous defects are crucial for boosting high rate performance within LIBs. The hierarchical 3D-scaffold structure endows the nanosheets-based electrode with outstanding cycling stability (96.1% retention after 6000 cycles at 6.7 A g À 1), which hits a record high in terms of capacity retention for TiO 2 (B) nanosheets at high rate. The strategy for fabricating and assembling defect-rich TiO 2 (B) nanosheets paves the way for high performance LIBs.

Journal of Energy Chemistry, 2018

Electrochemical reduction of water to hydrogen holds great promise for clean energy, while its wi... more Electrochemical reduction of water to hydrogen holds great promise for clean energy, while its widespread application relies on the development of efficient catalysts with large surface area, abundant exposed active sites and superior electron conductivity. Herein, we report a facile strategy to configure an electrocatalyst composed of cobalt phosphide and rhodium uniformly anchored on reduced graphene oxide for hydrogen generation. The hybrids effectively integrate the exposed active sites, electron conductivity and synergistic effect of the catalyst. Electrochemical tests exhibit that the catalyst shows superior hydrogen evolution reaction catalytic activity and stability, with a small Tafel slope of 43 mV dec −1. Over-potentials as low as 29 and 72 mV are required to achieve current densities of 2 and 10 mA cm −2 in 0.5M H 2 SO 4 , respectively. The hybrid constitution with highly active sites on conductive substrate is a new strategy to synthesize extremely efficient electrocatalysts. Especially, the efficient synergistic effect among cobalt phosphide, rhodium and reduced graphene oxide provides a novel approach for configuring electrocatalysts with high electron efficiency.

Solar Energy Materials and Solar Cells, 2019

In this study, shape-stabilized composite phase change materials were fabricated by the impregnat... more In this study, shape-stabilized composite phase change materials were fabricated by the impregnation method based on dodecanoic acid (DA) as energy storage material and graphene as a supporting matrix. The supporting material was prepared via in-situ filling with Na 2 CO 3 cores from solid sodium acetate and showed large specific surface area, high thermal stability, and large PCM loading ratio (81.1%), favorable pore characteristics and green and economical related to conventional graphene, carbon nanotubes and other 1D and/or 2D-carbon matrixes. The as-prepared composites were investigated by various characterization techniques to evaluate the performance of thermo-chemical and physicochemical properties. The resulted composite demonstrated an enhanced energy storage capacity of 157.6 kJ/kg, which was up to 101.4% higher than that of expected energy storage capacity with the reduced supercooling phenomenon. Due to supporting material that assisted the DA to nucleate heterogeneously. In addition, the composite revealed enhanced photo-thermal conversion about 78% and thermal conductivity up to 159.1% compared to that of pristine PCM with high reliability after 100 times thermal cycling, chemical compatibility and shape stability above the normal melting temperature of pristine DA. This signified that the composite is a promising material for practical applications like building heat preservation , air conditioning, and solar energy storage.

Solar Energy Materials and Solar Cells, 2020

Three-dimensional (3D) graphene-reinforced structural materials with excellent solar-thermal conv... more Three-dimensional (3D) graphene-reinforced structural materials with excellent solar-thermal conversion, mechanical and thermal transfer properties present attractive prospects for the fabrication of high-performance composite phase change materials (PCMs). Herein, multifunctional 3D continuous sponge frameworks wrapping with reduced graphene oxide (rGO) are facilely prepared via simply circular impregnation and in-suit reduction process. Further, the stable combination of 3D support material and phase change matrix through vacuum melting infiltration can successfully obtain the rGO@sponge framework/paraffin wax (rGO@SF/PW) composite shape-stabilized PCMs. As an advanced energy conversion and storage PCMs, the rGO@SF/PW achieves efficient solar-thermal conversion effciency of 85%, excellent energy storage properties (phase-change enthalpy of 170.4 J/g for the loading amount of 90 wt%), high thermal transfer performance and good cycling thermal stability. Based on the comprehensive performances of the rGO@SF/PW, domestic storage systems for solar-thermal water are designed to broaden the application of PCMs in the solar-thermal energy area.

Advanced Electronic Materials, 2020

Electro-thermal phase-change materials (PCMs) enable continuous operation of heating-related proc... more Electro-thermal phase-change materials (PCMs) enable continuous
operation of heating-related processes, which is urgently required for
modern thermal-management devices. Driven by the unmet needs to
develop promising electro-thermal PCMs with low operation voltage and
high electro-thermal storage efficiency simultaneously, unique ZIF@MOFderived carbon-nanotube (CNT)-penetrated porous carbon supports for electro-thermal PCMs are introduced. The network structure of the support decreases the resistivity of the composite and ensures a low operation voltage. Furthermore, abundant CNT cores in porous carbon shells facilitate interfacial interaction between the PCMs and the support and realize a rapid heat transformation. It is noted that low thermal conductive porous carbon shells prevent convective heat dissipation at the CNT-air interface to a great degree which leads to enhanced electro-thermal storage efficiency. Consequently, the obtained electro-thermal PCMs exhibit a low operation voltage of 1.1 V and a record-high electro-thermal storage efficiency of 94.5%, which shows great potential in thermal management of electronic devices.

ACS Appl. Mater. Interfaces, 2018

Phase change enthalpy and thermal conductivity are the two essential parameters for practical app... more Phase change enthalpy and thermal conductivity are the two essential parameters for practical applications of shape-stabilized phase change materials (ss-PCMs). Herein, hierarchical three-dimensional (3D) reduced graphene porous carbon support PCMs have been successfully synthesized by carbonizing a graphene oxide@metal−organic framework (GO@MOF) template, which simultaneously realizes large phase change enthalpy and high thermal conductivity. During the carbonization process, MOFs were converted into hierarchical porous carbons, whereas GO was reduced to high-thermal-performance reduced graphene (rGO). Thus, a hierarchical 3D porous carbon structure with high porosity and large specific surface area was obtained, which provided a suitable condition for encapsulating PCMs. Furthermore, the pores of carbon stabilized the PCMs by capillary force and surface tension. The interaction between the PCM molecule and rGO significantly decreased the interfacial thermal resistance and made the composites reveal high thermal conductivity. Furthermore, the 3D network structure promoted the stretching and crystallization characteristics of the stearic acid molecule in the confined pore space, which enhanced the heat release efficiency. Compared with the rGO/MOF-5-C support, the hierarchical 3D structure of rGO@MOF-5-C revealed a thermal conductivity of 0.60 ± 0.02 W m −1 K −1 , which was 27.7% improvement, with large phase change latent heat of 168.7 J g −1 , which increased by 18.5%. Additionally, the obtained ss-PCMs showed transient thermal response and good durability, indicating its promising potential in thermal energy storage application.

Applied Energy, 2017

• Core-sheath CNT@PC with 3D network structure was synthesized. • The carbon sheath was conductiv... more • Core-sheath CNT@PC with 3D network structure was synthesized. • The carbon sheath was conductive to the stability of network structure. • The CNTs provide heat transfer paths for ss-PCMs. • The hierarchical porous carbon sheath reduced interfacial thermal resistance. • The ss-PCMs exhibited excellent thermal storage capability (up to 99.9%). A B S T R A C T Energy storage capacity and heat transfer ability are two important indexes for shape-stabilized phase change materials (ss-PCMs). In this paper, a core-sheath CNT@PC was prepared via carbonation of CNT@ZIF-8, simultaneously 3D structural supports were obtained due to the porous carbon (PC) sheath stabilized the CNT@PC network structure. Porous carbon (PC), derived from carbonized metal organic frameworks (MOFs), exhibited high porosity and large specific surface area. PCMs, absorbed by capillary force of porous structure, was stabilized in the pores of PC sheath. Further, the interaction between PCMs and CNTs reduced the interfacial thermal resistance greatly. Carbon nanotubes (CNTs), acting as heat transfer pathways, provided continuous channels for phonons transfer and realized rapid heat transformation between ss-PCMs and external environment. The obtained SA/CNT@PC ss-PCMs exhibited excellent thermal conductivity (1.023 W/mK), large phase change enthepy (155.7 J g −1) and high thermal storage capabilities (99.9%). The thermal conductivity of SA/ CNT@PC was improved 222.6% and phase change enthalpy was increased 92.6% over SA/PC ss-PCM. SA/ CNT@PC with large energy storage density, flexible designation, simple operation and near-constant temperature properties during phase change process shows great potential in waste heat utilization.

Chemical Engineering Journal, 2020

Regulation of the electronic structure of metal oxo clusters in metal organic frameworks (MOFs) i... more Regulation of the electronic structure of metal oxo clusters in metal organic frameworks (MOFs) is a promising way to modulate charge transfer efficiency and photocatalytic performance. Herein, a series of Ni2+ doped NH2-MIL-125-Ti (NH2-MIL-125-Nix/Ti) with different Ni2+/Ti4+ molar ratio (x = 0.5%–1.5%) are prepared via an
in-situ doping method. Correlations between the electronic structure of (Ti/Ni)8O8(OH)4 nodes and charge transfer efficiency, bandgap and energy position of band edges of the NH2-MIL-125-Nix/Ti are systematically investigated based on experimental and computational method. The doped Ni2+ was confirmed to be an efficient mediator to promote the electron transfer from photoexcited terephthalate ligand to the (Ti/Ni)8O8(OH)4 nodes in NH2-MIL-125-Nix/Ti. The NH2-MIL-125-Ni1%/Ti exhibited the highest CO2 conversion rate with 98.6% CO selectivity and the factors affecting the photocatalytic CO2 reduction performance are also studied. It provides some guidance for developing MOFs photocatalyst with targeted performance via modification of the electronic structure of metal oxo clusters.

J. Mater. Chem. A, 2020

Owing to the high abundance, good conductivity and excellent tolerance to harsh environment, carb... more Owing to the high abundance, good conductivity and excellent tolerance to harsh environment, carbon host materials have recently attracted considerable research interest in the fields of electrochemical hydrogen evolution reaction (HER). However, the deficiency of intrinsic active sites within the carbon host materials substantially gives rise to an inferior HER performance. In this work, atomically dispersed ruthenium active sites are deliberately introduced into the carbon host structure by controlled pyrolysis of Ru-doped ZIF-8. With atomic Ru sites on a unique whisker-like secondary microstructure and a favorable porous texture, the optimal product exhibits a high intrinsic activity as well as robust durability, which especially outperforms the Pt/C benchmarking in alkaline media. A combination of control experiments and theoretical calculations demonstrates that atomically dispersed Ru sites within the carbon host matrix serve as the dominant catalytically active sites, and remarkably optimize the free energy of water molecule dissociation during the Volmer step, thus boosting the HER performance.

Nano Energy, 2018

Using phase change materials (PCMs) for thermal energy storage is an effective technique of energ... more Using phase change materials (PCMs) for thermal energy storage is an effective technique of energy management to address the mismatch problems between energy supply and demand. Shape-stabilized composite PCMs could efficiently solve their leakage problem during the solid-liquid phase change process, which have been widely used and extensively reviewed in literature. However, those reviews mainly focused on microencapsulated PCMs and the broad properties and applications of composite PCMs but paid little attention to the nanoporous shape-stabilized composite PCMs. The nanoporous shape-stabilized composite PCMs do solve the leakage problem and show excellent chemical stability and thermal cycling stability, but most of their enthalpy values were much lower than that of the pure PCMs component. So in this review we have highlighted recent progress in the research of nanoporous shape-stabilized PCMs, such as the design concept of porous support, fabrication and characterization techniques, and especially the nanoconfinement effects of the porous support on the thermal properties of the PCMs confined in the nanopores. Finally, we have provided a brief outlook of the future challenges and potential prospects of nanoporous shape-stabilized composite PCMs. This review paper will help to explore and develop better nanoporous shape-stabilized composite PCMs for practical applications and offer basic understanding of nanoconfinement effects on thermal properties.

Composites Part B: Engineering, 2020

Currently, numerous studies are devoted to the pursuit of thermal conductivity enhancement of pha... more Currently, numerous studies are devoted to the pursuit of thermal conductivity enhancement of phase change materials (PCMs). On the contrary, few researches are reported to reduce the thermal conductivity of PCMs. Generally, the PCMs with reduced thermal conductivity have great potential in thermal protection application. Herein, we propose a novel in situ one-step strategy to facilely prepare monolithic silica aerogel-based composite PCMs. The silica aerogels possess low thermal conductivity and are used to encapsulate PCMs to prepare composite PCMs, such as polyethylene glycol (PEG) or octadecanol. Compare with PEG2000@silica aerogel, the resulting monolithic octadecanol@silica aerogel have low thermal conductivity (0.12 W m 1 K 1), high latent heat (127.73 J/g), large compressive strength (11 MPa), good hydrophobicity (contact angle 124�) and superior thermal cycling stability. This monolithic silica aerogel-based composite PCMs could prolong heat preservation duration due to the synergistic effect between low thermal conductivity and high latent heat of composite PCMs, showing potential promise for direct application to the thermal insulation and thermal protection device. More importantly, this in situ one-step synthesis strategy is universal for different types of PCMs.