Different silicidation processes are employed to form NiSi,and the NiSi/Si interface corresponding to each process is studied by cross-section transmission electron microscopy （XTEM）. With the sputter deposition of ...Different silicidation processes are employed to form NiSi,and the NiSi/Si interface corresponding to each process is studied by cross-section transmission electron microscopy （XTEM）. With the sputter deposition of a nickel thin film,nickel silicidation is realized on undoped and doped （As and B） Si（001） substrates by rapid ther mal processing （RTP）. The formation of NiSi is demonstrated by X-ray diffraction and Raman scattering spectros- copy. The influence of the substrate doping and annealing process （one-step RTP and two-step RTP） on the NiSi! Si interface is investigated. The results show that for one-step RTP the silicidation on As-doped and undoped Si substrates causes a rougher NiSi/Si interface,while the two-step RTP results in a much smoother NiSi/Si interface. High resolution XTEM study shows that axiotaxy along the Si（111） direction forms in all samples, in which specific NiSi planes align with Si（111） planes in the substrate. Axiotaxy with spacing mismatch is also discussed.展开更多
This study of the thermal decomposition kinetics of various average diameter nano-particles of cal-cium carbonate by means of TG-DTA(thermogravimetry and differential thermal analysis) showed that the thermal decompos...This study of the thermal decomposition kinetics of various average diameter nano-particles of cal-cium carbonate by means of TG-DTA(thermogravimetry and differential thermal analysis) showed that the thermal decomposition kinetic mechanisms of the same crystal type of calcium carbonate samples do not vary with decreasing of their average diameters ; their pseudo-active energy Ea; and that the top-temperature of decom-position Tp decreases gently in the scope of micron-sized diameter, but decreases sharply when the average di-ameter decreases from micron region to nanometer region. The extraordinary properties of nano-particles were explored by comparing the varying regularity of the mechanisms and kinetic parameters of the solid-phase reac-tions as well as their structural characterization with the variation of average diameters of particles. These show that the aggregation, surface effect as well as internal aberrance and stress of the nano-particles are the main reason causing both Ea and Tp to decline sharply with the decrease of the average diameter of nano-particles.展开更多
La（0.6）Sr（0.4）Co（0.2）Fe（0.8）O（3-δ）（LSCF） anodes were infiltrated by Gd（0.2）Ce（0.8）O（1.9）GDC） nanoparticles to improve the oxygen evolution reaction（OER） performance of solid oxide electrolysis ce...La（0.6）Sr（0.4）Co（0.2）Fe（0.8）O（3-δ）（LSCF） anodes were infiltrated by Gd（0.2）Ce（0.8）O（1.9）GDC） nanoparticles to improve the oxygen evolution reaction（OER） performance of solid oxide electrolysis cells（SOECs） in CO2 electroreduction. The effect of GDC loading was investigated, and 10 wt% GDC nanoparticle infiltration of the LSCF（10 GDC/LSCF） anode results in the highest OER performance. Electrochemical impedance spectra measurements indicate that the infiltration by GDC nanoparticles greatly decreases the polarization resistance of the SOECs with the 10 GDC/LSCF anodes. The following distribution of relaxation time analysis suggests that four individual electrode processes are involved in the OER and that all of them are accelerated on the 10 GDC/LSCF anode. Three phase boundaries, surface oxygen vacancies, and bulk oxygen mobility increased, based on scanning electron microscopy and temperature-programmed desorption of O2 characterizations, and contributed to the enhancement of the four electrode processes of the OER and electrochemical performance of SOECs.展开更多
The carbon nanotubes(CNTs) reinforced Al-Cu matrix composites were prepared by hot pressing sintering and hot rolling, and the effects of Cu content on the interfacial reaction between Al and CNTs, the precipitation b...The carbon nanotubes(CNTs) reinforced Al-Cu matrix composites were prepared by hot pressing sintering and hot rolling, and the effects of Cu content on the interfacial reaction between Al and CNTs, the precipitation behavior of Cu-containing precipitates, and the resultant mechanical properties of the composites were systematically investigated. The results showed that the increase of Cu content can not only increase the number and size of Cu-containing precipitate generated during the composite fabrication processes, but also promote the interfacial reaction between CNTs and Al matrix, leading to the intensified conversion of CNTs into Al_(4)C_(3). As a result, the composite containing 1 wt.% Cu possesses the highest strength, elastic modulus and hardness among all composites, due to the maintenance of the original structure of CNTs. Moreover, the increase of Cu content can change the dominant strengthening mechanisms for the enhanced strength of the fabricated composites.展开更多
Solid-aqueous interfaces and phenomena occurring at those interfaces are ubiquitously found in a plethora of chemical systems.When it comes to heterogeneous catalysis,however,our understanding of chemical transformati...Solid-aqueous interfaces and phenomena occurring at those interfaces are ubiquitously found in a plethora of chemical systems.When it comes to heterogeneous catalysis,however,our understanding of chemical transformations at solid-aqueous interfaces is relatively limited and primitive.This review phenomenologically describes a selection of water-engendered effects on the catalytic behavior for several prototypical acid-base-catalyzed reactions over solid catalysts,and critically assesses the general and special roles of water molecules,structural moieties derived from water,and ionic species that are dissolved in it,with an aim to extract novel concepts and principles that underpin heterogeneous acid-base catalysis in the aqueous phase.For alcohol dehydration catalyzed by solid Bronsted acids,rate inhibition by water is most typically related to the decrease in the acid strength and/or the preferential solvation of adsorbed species over the transition state as water molecules progressively solvate the acid site and form extended networks wherein protons are mobilized.Water also inhibits dehydration kinetics over most Lewis acid-base catalysts by competitive adsorption,but a few scattered reports reveal substantial rate enhancements due to the conversion of Lewis acid sites to Brønsted acid sites with higher catalytic activities upon the introduction of water.For aldol condensation on catalysts exposing Lewis acid-base pairs,the addition of water is generally observed to enhance the rate when C–C coupling is rate-limiting,but may result in rate inhibition by site-blocking when the initial unimolecular deprotonation is rate-limiting.Water can also promote aldol condensation on Brønsted acidic catalysts by facilitating inter-site communication between acid sites through hydrogen-bonding interactions.For metallozeolite-catalyzed sugar isomerization in aqueous media,the nucleation and networking of intrapore waters regulated by hydrophilic entities causes characteristic enthalpy-entropy tradeoffs as these water moieties interact with kinetically relevant hydride transfer transition states.The discussed examples collectively highlight the utmost importance of hydrogen-bonding interactions and ionization of covalently bonded surface moieties as the main factors underlying the uniqueness of water-mediated interfacial acid-base chemistries and the associated solvation effects in the aqueous phase or in the presence of water.A perspective is also provided for future research in this vibrant field.展开更多
Nonprecious metal-based oxygen reduction reaction(ORR)electrocatalysts with high efficiency in both alkaline and acidic media are being intensively studied for the purpose of replacing expensive Pt-based catalysts;how...Nonprecious metal-based oxygen reduction reaction(ORR)electrocatalysts with high efficiency in both alkaline and acidic media are being intensively studied for the purpose of replacing expensive Pt-based catalysts;however,it is still a challenge to achieve superior ORR performances,especially in acidic media.Herein,by pyrolysis of mixed precursors of diammonium phosphate,melamine and hemin,we prepared a nanocomposite catalyst(denoted as FeP@PGL)composed of nitrogen-doped carbon nanosheets with embedded FeP nanoparticles(NPs),which were encapsulated by in-situ formed phosphorus-doped graphene layers.It is found that phosphorous was preferentially doped in the coating layers on FeP NPs,instead of in the carbon nanosheets.The FeP@PGL catalyst exhibited excellent ORR performance,with the onset and half-wave potential up to 1.01 and 0.90 V vs.the reversible hydrogen electrode(RHE)in alkaline media,and0.95 and 0.81 V vs.RHE in acidic media,respectively.By thorough microscopy and spectroscopy characterizations,the interfacial charge transfer between the encapsulated FeP NPs and P-doped graphene layers was identified,and the local work function of the catalyst surface was also reduced by the interfacial interaction.The interfacial synergy between the encapsulated FeP and phosphorus-doped graphene layers was essential to enhance the ORR performance.This study not only demonstrates the promising ORR properties of the encapsulated-FeP-based nanocomposite catalyst,but also provides direct evidence of the interfacial charge transfer effect and its role in ORR process.展开更多
Ru has recently been regarded as a promising catalyst for hydrogen oxidation reaction(HOR) and hydrogen evolution reaction(HER) due to its similar binding energy towards *H but lower price compared to Pt.Nevertheless,...Ru has recently been regarded as a promising catalyst for hydrogen oxidation reaction(HOR) and hydrogen evolution reaction(HER) due to its similar binding energy towards *H but lower price compared to Pt.Nevertheless, the quest of high-efficiency Ru-based catalysts for HOR and HER is driven by the current disadvantages including low activity and unsatisfactory stability. Herein, we have fabricated and engineered two-dimensional(2D) Ru-based snow-like nanosheets with Ru/Ru O2interface(Ru/Ru O2SNSs)via a post-annealing treatment. Detailed characterizations and theoretical calculations indicate that the interfacial synergy, which is dependent on the temperature for annealing, can alter the hydrogen binding energy(HBE) and hydroxide binding energy(OHBE), as a result of the enhanced HOR and HER performance. Impressively, the optimal Ru/RuO_(2) SNSs display a mass activity of 9.13 A mgRu^(–1) at an overpotential of 50 m V in 0.1 mol L^(–1) KOH for HOR, which is 65, 304, and 21 times higher than those of Ru SNSs(0.14 A mg_(Ru)^(–1)), RuO_(2) SNSs(0.03 A mg_(Ru)^(–1)), and commercial Pt/C(0.43 A mg_(Ru)^(–1)), respectively.Moreover, Ru/RuO_(2) SNSs display improved HER activity with a low overpotential of 20.2 m V for achieving10 m A cm^(-2)in 1 mol L^(–1)KOH. This work not only provides an efficient catalyst for HOR and HER, but also promotes fundamental research on the fabrication and modification of catalysts in heterogeneous catalysis.展开更多
文摘Different silicidation processes are employed to form NiSi,and the NiSi/Si interface corresponding to each process is studied by cross-section transmission electron microscopy （XTEM）. With the sputter deposition of a nickel thin film,nickel silicidation is realized on undoped and doped （As and B） Si（001） substrates by rapid ther mal processing （RTP）. The formation of NiSi is demonstrated by X-ray diffraction and Raman scattering spectros- copy. The influence of the substrate doping and annealing process （one-step RTP and two-step RTP） on the NiSi! Si interface is investigated. The results show that for one-step RTP the silicidation on As-doped and undoped Si substrates causes a rougher NiSi/Si interface,while the two-step RTP results in a much smoother NiSi/Si interface. High resolution XTEM study shows that axiotaxy along the Si（111） direction forms in all samples, in which specific NiSi planes align with Si（111） planes in the substrate. Axiotaxy with spacing mismatch is also discussed.
文摘This study of the thermal decomposition kinetics of various average diameter nano-particles of cal-cium carbonate by means of TG-DTA(thermogravimetry and differential thermal analysis) showed that the thermal decomposition kinetic mechanisms of the same crystal type of calcium carbonate samples do not vary with decreasing of their average diameters ; their pseudo-active energy Ea; and that the top-temperature of decom-position Tp decreases gently in the scope of micron-sized diameter, but decreases sharply when the average di-ameter decreases from micron region to nanometer region. The extraordinary properties of nano-particles were explored by comparing the varying regularity of the mechanisms and kinetic parameters of the solid-phase reac-tions as well as their structural characterization with the variation of average diameters of particles. These show that the aggregation, surface effect as well as internal aberrance and stress of the nano-particles are the main reason causing both Ea and Tp to decline sharply with the decrease of the average diameter of nano-particles.
基金This work was supported by the National Key R&D Program of China(2017YFA0700102)the National Natural Science Foundation of China(21703237,21573222,91545202)+1 种基金Dalian Institute of Chemical Physics(DICP DMTO201702)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB17020200)and CAS Youth Innovation Promotion(2015145)~~
文摘La（0.6）Sr（0.4）Co（0.2）Fe（0.8）O（3-δ）（LSCF） anodes were infiltrated by Gd（0.2）Ce（0.8）O（1.9）GDC） nanoparticles to improve the oxygen evolution reaction（OER） performance of solid oxide electrolysis cells（SOECs） in CO2 electroreduction. The effect of GDC loading was investigated, and 10 wt% GDC nanoparticle infiltration of the LSCF（10 GDC/LSCF） anode results in the highest OER performance. Electrochemical impedance spectra measurements indicate that the infiltration by GDC nanoparticles greatly decreases the polarization resistance of the SOECs with the 10 GDC/LSCF anodes. The following distribution of relaxation time analysis suggests that four individual electrode processes are involved in the OER and that all of them are accelerated on the 10 GDC/LSCF anode. Three phase boundaries, surface oxygen vacancies, and bulk oxygen mobility increased, based on scanning electron microscopy and temperature-programmed desorption of O2 characterizations, and contributed to the enhancement of the four electrode processes of the OER and electrochemical performance of SOECs.
基金The financial supports from the National Natural Science Foundation of China (Nos. 52004101 and 52071269)the Chinese Postdoctoral Science Foundation (No. 2020T130246)+2 种基金the Fund of the State Key Laboratory of Solidification Processing in NWPU, China (No. SKLSP202121)the Guangdong Basic and Applied Basic Research Foundation, China (No. 2020A1515110621)the Fundamental Research Funds for the Central Universities, China (No. 11620345)。
文摘The carbon nanotubes(CNTs) reinforced Al-Cu matrix composites were prepared by hot pressing sintering and hot rolling, and the effects of Cu content on the interfacial reaction between Al and CNTs, the precipitation behavior of Cu-containing precipitates, and the resultant mechanical properties of the composites were systematically investigated. The results showed that the increase of Cu content can not only increase the number and size of Cu-containing precipitate generated during the composite fabrication processes, but also promote the interfacial reaction between CNTs and Al matrix, leading to the intensified conversion of CNTs into Al_(4)C_(3). As a result, the composite containing 1 wt.% Cu possesses the highest strength, elastic modulus and hardness among all composites, due to the maintenance of the original structure of CNTs. Moreover, the increase of Cu content can change the dominant strengthening mechanisms for the enhanced strength of the fabricated composites.
文摘Solid-aqueous interfaces and phenomena occurring at those interfaces are ubiquitously found in a plethora of chemical systems.When it comes to heterogeneous catalysis,however,our understanding of chemical transformations at solid-aqueous interfaces is relatively limited and primitive.This review phenomenologically describes a selection of water-engendered effects on the catalytic behavior for several prototypical acid-base-catalyzed reactions over solid catalysts,and critically assesses the general and special roles of water molecules,structural moieties derived from water,and ionic species that are dissolved in it,with an aim to extract novel concepts and principles that underpin heterogeneous acid-base catalysis in the aqueous phase.For alcohol dehydration catalyzed by solid Bronsted acids,rate inhibition by water is most typically related to the decrease in the acid strength and/or the preferential solvation of adsorbed species over the transition state as water molecules progressively solvate the acid site and form extended networks wherein protons are mobilized.Water also inhibits dehydration kinetics over most Lewis acid-base catalysts by competitive adsorption,but a few scattered reports reveal substantial rate enhancements due to the conversion of Lewis acid sites to Brønsted acid sites with higher catalytic activities upon the introduction of water.For aldol condensation on catalysts exposing Lewis acid-base pairs,the addition of water is generally observed to enhance the rate when C–C coupling is rate-limiting,but may result in rate inhibition by site-blocking when the initial unimolecular deprotonation is rate-limiting.Water can also promote aldol condensation on Brønsted acidic catalysts by facilitating inter-site communication between acid sites through hydrogen-bonding interactions.For metallozeolite-catalyzed sugar isomerization in aqueous media,the nucleation and networking of intrapore waters regulated by hydrophilic entities causes characteristic enthalpy-entropy tradeoffs as these water moieties interact with kinetically relevant hydride transfer transition states.The discussed examples collectively highlight the utmost importance of hydrogen-bonding interactions and ionization of covalently bonded surface moieties as the main factors underlying the uniqueness of water-mediated interfacial acid-base chemistries and the associated solvation effects in the aqueous phase or in the presence of water.A perspective is also provided for future research in this vibrant field.
基金supported by the National Natural Science Foundation of China(21773128,21534005,and 21421001)。
文摘Nonprecious metal-based oxygen reduction reaction(ORR)electrocatalysts with high efficiency in both alkaline and acidic media are being intensively studied for the purpose of replacing expensive Pt-based catalysts;however,it is still a challenge to achieve superior ORR performances,especially in acidic media.Herein,by pyrolysis of mixed precursors of diammonium phosphate,melamine and hemin,we prepared a nanocomposite catalyst(denoted as FeP@PGL)composed of nitrogen-doped carbon nanosheets with embedded FeP nanoparticles(NPs),which were encapsulated by in-situ formed phosphorus-doped graphene layers.It is found that phosphorous was preferentially doped in the coating layers on FeP NPs,instead of in the carbon nanosheets.The FeP@PGL catalyst exhibited excellent ORR performance,with the onset and half-wave potential up to 1.01 and 0.90 V vs.the reversible hydrogen electrode(RHE)in alkaline media,and0.95 and 0.81 V vs.RHE in acidic media,respectively.By thorough microscopy and spectroscopy characterizations,the interfacial charge transfer between the encapsulated FeP NPs and P-doped graphene layers was identified,and the local work function of the catalyst surface was also reduced by the interfacial interaction.The interfacial synergy between the encapsulated FeP and phosphorus-doped graphene layers was essential to enhance the ORR performance.This study not only demonstrates the promising ORR properties of the encapsulated-FeP-based nanocomposite catalyst,but also provides direct evidence of the interfacial charge transfer effect and its role in ORR process.
基金supported by the National Key R&D Program of China(2020YFB1505802)the Ministry of Science and Technology of China(2017YFA0208200,2016YFA0204100)+4 种基金the National Natural Science Foundation of China(22025108,U21A20327,and22121001)China Postdoctoral Science Foundation(2020M682083)Guangdong Provincial Natural Science Fund for Distinguished Young Scholars(2021B1515020081)Start-up Support from Xiamen University and the Guangzhou Key Laboratory of Low Dimensional Materials and Energy Storage Devices(20195010002)。
文摘Ru has recently been regarded as a promising catalyst for hydrogen oxidation reaction(HOR) and hydrogen evolution reaction(HER) due to its similar binding energy towards *H but lower price compared to Pt.Nevertheless, the quest of high-efficiency Ru-based catalysts for HOR and HER is driven by the current disadvantages including low activity and unsatisfactory stability. Herein, we have fabricated and engineered two-dimensional(2D) Ru-based snow-like nanosheets with Ru/Ru O2interface(Ru/Ru O2SNSs)via a post-annealing treatment. Detailed characterizations and theoretical calculations indicate that the interfacial synergy, which is dependent on the temperature for annealing, can alter the hydrogen binding energy(HBE) and hydroxide binding energy(OHBE), as a result of the enhanced HOR and HER performance. Impressively, the optimal Ru/RuO_(2) SNSs display a mass activity of 9.13 A mgRu^(–1) at an overpotential of 50 m V in 0.1 mol L^(–1) KOH for HOR, which is 65, 304, and 21 times higher than those of Ru SNSs(0.14 A mg_(Ru)^(–1)), RuO_(2) SNSs(0.03 A mg_(Ru)^(–1)), and commercial Pt/C(0.43 A mg_(Ru)^(–1)), respectively.Moreover, Ru/RuO_(2) SNSs display improved HER activity with a low overpotential of 20.2 m V for achieving10 m A cm^(-2)in 1 mol L^(–1)KOH. This work not only provides an efficient catalyst for HOR and HER, but also promotes fundamental research on the fabrication and modification of catalysts in heterogeneous catalysis.
