Magnesium hydride(MgH_(2))is a potential material for solid-state hydrogen storage.However,the thermodynamic and kinetic properties are far from practical application in the current stage.In this work,two-dimensional ...Magnesium hydride(MgH_(2))is a potential material for solid-state hydrogen storage.However,the thermodynamic and kinetic properties are far from practical application in the current stage.In this work,two-dimensional vanadium carbide(V_(2)C)MXene with layer thickness of 50−100 nm was fist synthesized by selectively HF-etching the Al layers from V_(2)AlC MAX phase and then introduced into MgH_(2) to improve the hydrogen sorption performances of MgH_(2).The onset hydrogen desorption temperature of MgH_(2) with V_(2)C addition is significantly reduced from 318℃ for pure MgH_(2) to 190℃,with a 128℃ reduction of the onset temperature.The MgH_(2)+10 wt%V_(2)C composite can release 6.4 wt%of H_(2) within 10 min at 300℃ and does not loss any capacity for up to 10 cycles.The activation energy for the hydrogen desorption reaction of MgH_(2) with V_(2)C addition was calculated to be 112 kJ mol^(−1) H_(2) by Arrhenius’s equation and 87.6 kJ mol^(−1) H_(2) by Kissinger’s equation.The hydrogen desorption reaction enthalpy of MgH_(2)+10 wt%V_(2)C was estimated by van’t Hoff equation to be 73.6 kJ mol^(−1) H_(2),which is slightly lower than that of the pure MgH_(2)(77.9 kJ mol^(−1) H_(2)).Microstructure studies by XPS,TEM,and SEM showed that V_(2)C acts as an efficient catalyst for the hydrogen desorption reaction of MgH_(2).The first-principles density functional theory(DFT)calculations demonstrated that the bond length of Mg−H can be reduced from 1.71A for pure MgH_(2) to 2.14A for MgH_(2) with V_(2)C addition,which contributes to the destabilization of MgH_(2).This work provides a method to significantly and simultaneously tailor the hydrogen sorption thermodynamics and kinetics of MgH_(2) by two-dimensional MXene materials.展开更多
Hexagonal molybdenum carbide(Mo_(2)C)as an effective non-noble cocatalyst is intensively researched in the photocatalytic H_(2)-evolution field owing to its Pt-like H^(+)-adsorption ability and good conductivity.Howev...Hexagonal molybdenum carbide(Mo_(2)C)as an effective non-noble cocatalyst is intensively researched in the photocatalytic H_(2)-evolution field owing to its Pt-like H^(+)-adsorption ability and good conductivity.However,hexagonal Mo_(2)C-modified photocatalysts possess a limited H_(2)-evolution rate because of the weak H-desorption ability.Tofurther improve the activity,cubic MoC was introduced into Mo_(2)C toform the carbon-modified MoC-Mo_(2)C nanoparticles(MoC-Mo_(2)C@C)by a calcination method.The resultant MoC-Mo_(2)C@C(ca.5 nm)was eventually coupled with Ti0_(2)to acquire high-efficiency Ti0_(2)/MoC-Mo_(2)C@C by electrostatic self-assembly.The highest H_(2)-generation rate of Ti0_(2)/MoC-Mo_(2)C@C reached of 918μmol·h^(-1)·g^(-1)which was 91.8,2.7,and 1.5 times than that of the Ti0_(2),TiO_(2)/MoC@C,and Ti0_(2)/Mo_(2)C@C,respectively.The enhanced rate of Ti0_(2)attributes to the carbon layer as cocatalyst to transmit electrons and the hetero-phase MoC-Mo_(2)C as H_(2)-generation active sites to boost H_(2)-evolution reaction.This research offers a novel insight to design photocatalytic materials for energy applications.展开更多
FTO(Fischer-Tropsch to olefins)作为合成气制备低碳烯烃(C_(2)^(=)~C_(4)^(=))的代替路径在工业上具有重要意义。CoMnNa作为FTO反应催化剂而备受关注,但由于反应过程中CO_(2)C活性相的形成,导致CO_(2)选择性较高。引入AlO(OH)载体,制...FTO(Fischer-Tropsch to olefins)作为合成气制备低碳烯烃(C_(2)^(=)~C_(4)^(=))的代替路径在工业上具有重要意义。CoMnNa作为FTO反应催化剂而备受关注,但由于反应过程中CO_(2)C活性相的形成,导致CO_(2)选择性较高。引入AlO(OH)载体,制备了Co_(1)Mn_(1)Na/AlO(OH)催化剂,通过XRD、STEM、EDX-mapping、N_(2)吸附-脱附等温线、孔径分布曲线对催化剂进行了表征,通过H_(2)-TPR对催化剂的还原性进行了分析,并对催化剂的FTO反应性能进行了评价。结果表明,利用载体与CoMn的相互作用,降低了CoMn氧化物的还原性,有效抑制了CoMn中Co的析出及CO_(2)C的形成,减少了CoMn体系中Co和CO_(2)C活性相;在低碳烯烃选择性高达32.4%的情况下,成功将CO_(2)选择性降至10%以下。展开更多
The carbon dissolution in solvent plays a key role in the process of solution growth route for SiC single crystal,which could determine the growth rate and quality of the products.However,the carbon dissolving ability...The carbon dissolution in solvent plays a key role in the process of solution growth route for SiC single crystal,which could determine the growth rate and quality of the products.However,the carbon dissolving ability of binary alloy solvent still needs to be improved.Here,we demonstrate the improved carbon dissolution and enlarged carbon supersaturation in Cr-Ce-Si ternary solvent,showing great potential for SiC solution growth.The phase relations of Cr-Ce-Si-C system were determined by using CALPHAD method based on thermodynamic parameters of CeCr_(2)Si_(2)C.It is indicated that the Cr-Ce-Si ternary solvent shows much larger carbon solubility in temperature range from 1700 to 2000℃compared to Cr-Si binary one,Furthermore,the carbon supersaturation in solvent is also significantly increased in low temperature range after the addition of Ce,leading to a rapid growth rate.Our work not only demonstrates the feasibility of adding Ce in the alloy solvent for rapid growth of SiC crystal,but also provides an example for investigating the C solubility in ternary solvent.展开更多
Developing transition metal-nitrogen-carbon materials(M-N-C)as electrocatalysts for the oxygen evolution reaction(OER)is significant for low-cost energy conversion systems.Further d-orbital adjustment of M center in M...Developing transition metal-nitrogen-carbon materials(M-N-C)as electrocatalysts for the oxygen evolution reaction(OER)is significant for low-cost energy conversion systems.Further d-orbital adjustment of M center in M-N-C is beneficial to the improvement of OER performance.Herein,we synthesize a single-Mn-atom catalyst based on carbon skeleton(Mn_(1)-N_(2)S_(2)C_(x))with isolated Mn-N_(2)S_(2)sites,which exhibits high alkaline OER activity(η10=280 mV),low Tafel slope(44 mV·dec^(−1)),and excellent stability.Theoretical calculations reveal the pivotal function of isolated Mn-N_(2)S_(2)sites in promoting OER,including the adsorption kinetics of intermediates and activation mechanism of active sites.The doping of S causes the increase in both charge density and work function of active Mn center,and ortho-Mn_(1)-N_(2)S_(2)C_(x)expresses the fastest OER kinetics due to the asymmetric plane.展开更多
With the discovery of the two-dimensional(2D) MXene, it shows a great application potential in the field of electromagnetic interference(EMI) shielding, but the mechanical brittleness and easy oxidation of MXene limit...With the discovery of the two-dimensional(2D) MXene, it shows a great application potential in the field of electromagnetic interference(EMI) shielding, but the mechanical brittleness and easy oxidation of MXene limit its wide application. For this reason, a double crosslinking strategy is provided to solve the above problems in a nacre-like “brick-mortar” layered MXene/cellulose nanofiber(MXene/CNF) film.Typically, the film was firstly suffered by dopamine modification, then was further reinforced by secondary Ca^(2+)bridging, so as to obtain excellent mechanical properties and antioxidative EMI shielding performance. Comparing with the single crosslinking, the double crosslinking strategy reveals a higher efficiency in improving the mechanical property. The mechanical strength and toughness of the double crosslinking MXene/CNF film can increase to 142.2 MPa and 9.48 MJ/m^(3), respectively. More importantly, while achieving good mechanical properties, the MXene composite film still holds a very stable EMI shielding performance of more than 44.6 dB when suffering from the oxidation treatment of hightemperature annealing, showing excellent anti-oxidation ability and environment tolerance. Therefore,this work provides a universal but effective double crosslinking strategy to solve the mechanical brittleness and easy oxidation of MXene-based composites, thus showing a huge potential in flexible EMI shielding applications.展开更多
基金supported by National Natural Science Foundation of China(No.52001079)Education Department of Guangxi Zhuang Autonomous Region(No.2019KY0021)the Natural Science Foundation of Guangxi Province(2019GXNSFBA185004,2018GXNSFAA281308,2019GXNSFAA245050)。
文摘Magnesium hydride(MgH_(2))is a potential material for solid-state hydrogen storage.However,the thermodynamic and kinetic properties are far from practical application in the current stage.In this work,two-dimensional vanadium carbide(V_(2)C)MXene with layer thickness of 50−100 nm was fist synthesized by selectively HF-etching the Al layers from V_(2)AlC MAX phase and then introduced into MgH_(2) to improve the hydrogen sorption performances of MgH_(2).The onset hydrogen desorption temperature of MgH_(2) with V_(2)C addition is significantly reduced from 318℃ for pure MgH_(2) to 190℃,with a 128℃ reduction of the onset temperature.The MgH_(2)+10 wt%V_(2)C composite can release 6.4 wt%of H_(2) within 10 min at 300℃ and does not loss any capacity for up to 10 cycles.The activation energy for the hydrogen desorption reaction of MgH_(2) with V_(2)C addition was calculated to be 112 kJ mol^(−1) H_(2) by Arrhenius’s equation and 87.6 kJ mol^(−1) H_(2) by Kissinger’s equation.The hydrogen desorption reaction enthalpy of MgH_(2)+10 wt%V_(2)C was estimated by van’t Hoff equation to be 73.6 kJ mol^(−1) H_(2),which is slightly lower than that of the pure MgH_(2)(77.9 kJ mol^(−1) H_(2)).Microstructure studies by XPS,TEM,and SEM showed that V_(2)C acts as an efficient catalyst for the hydrogen desorption reaction of MgH_(2).The first-principles density functional theory(DFT)calculations demonstrated that the bond length of Mg−H can be reduced from 1.71A for pure MgH_(2) to 2.14A for MgH_(2) with V_(2)C addition,which contributes to the destabilization of MgH_(2).This work provides a method to significantly and simultaneously tailor the hydrogen sorption thermodynamics and kinetics of MgH_(2) by two-dimensional MXene materials.
基金the National Natural Science Foundation of China(Nos.51872221,21771142)the Fundamental Research Funds for the Central Universities(No.WUT2019IB002).
文摘Hexagonal molybdenum carbide(Mo_(2)C)as an effective non-noble cocatalyst is intensively researched in the photocatalytic H_(2)-evolution field owing to its Pt-like H^(+)-adsorption ability and good conductivity.However,hexagonal Mo_(2)C-modified photocatalysts possess a limited H_(2)-evolution rate because of the weak H-desorption ability.Tofurther improve the activity,cubic MoC was introduced into Mo_(2)C toform the carbon-modified MoC-Mo_(2)C nanoparticles(MoC-Mo_(2)C@C)by a calcination method.The resultant MoC-Mo_(2)C@C(ca.5 nm)was eventually coupled with Ti0_(2)to acquire high-efficiency Ti0_(2)/MoC-Mo_(2)C@C by electrostatic self-assembly.The highest H_(2)-generation rate of Ti0_(2)/MoC-Mo_(2)C@C reached of 918μmol·h^(-1)·g^(-1)which was 91.8,2.7,and 1.5 times than that of the Ti0_(2),TiO_(2)/MoC@C,and Ti0_(2)/Mo_(2)C@C,respectively.The enhanced rate of Ti0_(2)attributes to the carbon layer as cocatalyst to transmit electrons and the hetero-phase MoC-Mo_(2)C as H_(2)-generation active sites to boost H_(2)-evolution reaction.This research offers a novel insight to design photocatalytic materials for energy applications.
文摘FTO(Fischer-Tropsch to olefins)作为合成气制备低碳烯烃(C_(2)^(=)~C_(4)^(=))的代替路径在工业上具有重要意义。CoMnNa作为FTO反应催化剂而备受关注,但由于反应过程中CO_(2)C活性相的形成,导致CO_(2)选择性较高。引入AlO(OH)载体,制备了Co_(1)Mn_(1)Na/AlO(OH)催化剂,通过XRD、STEM、EDX-mapping、N_(2)吸附-脱附等温线、孔径分布曲线对催化剂进行了表征,通过H_(2)-TPR对催化剂的还原性进行了分析,并对催化剂的FTO反应性能进行了评价。结果表明,利用载体与CoMn的相互作用,降低了CoMn氧化物的还原性,有效抑制了CoMn中Co的析出及CO_(2)C的形成,减少了CoMn体系中Co和CO_(2)C活性相;在低碳烯烃选择性高达32.4%的情况下,成功将CO_(2)选择性降至10%以下。
基金supported by the Beijing Municipal Science and Technology Commission Project(Z211100004821004)the National Natural Science Foundation of China(51872028)。
文摘The carbon dissolution in solvent plays a key role in the process of solution growth route for SiC single crystal,which could determine the growth rate and quality of the products.However,the carbon dissolving ability of binary alloy solvent still needs to be improved.Here,we demonstrate the improved carbon dissolution and enlarged carbon supersaturation in Cr-Ce-Si ternary solvent,showing great potential for SiC solution growth.The phase relations of Cr-Ce-Si-C system were determined by using CALPHAD method based on thermodynamic parameters of CeCr_(2)Si_(2)C.It is indicated that the Cr-Ce-Si ternary solvent shows much larger carbon solubility in temperature range from 1700 to 2000℃compared to Cr-Si binary one,Furthermore,the carbon supersaturation in solvent is also significantly increased in low temperature range after the addition of Ce,leading to a rapid growth rate.Our work not only demonstrates the feasibility of adding Ce in the alloy solvent for rapid growth of SiC crystal,but also provides an example for investigating the C solubility in ternary solvent.
基金supported by the National Natural Science Foundation of China(No.22075099)the Natural Science Foundation of Jilin Province(No.20220101051JC)the Education Department of Jilin Province(No.JJKH20220967KJ)。
文摘Developing transition metal-nitrogen-carbon materials(M-N-C)as electrocatalysts for the oxygen evolution reaction(OER)is significant for low-cost energy conversion systems.Further d-orbital adjustment of M center in M-N-C is beneficial to the improvement of OER performance.Herein,we synthesize a single-Mn-atom catalyst based on carbon skeleton(Mn_(1)-N_(2)S_(2)C_(x))with isolated Mn-N_(2)S_(2)sites,which exhibits high alkaline OER activity(η10=280 mV),low Tafel slope(44 mV·dec^(−1)),and excellent stability.Theoretical calculations reveal the pivotal function of isolated Mn-N_(2)S_(2)sites in promoting OER,including the adsorption kinetics of intermediates and activation mechanism of active sites.The doping of S causes the increase in both charge density and work function of active Mn center,and ortho-Mn_(1)-N_(2)S_(2)C_(x)expresses the fastest OER kinetics due to the asymmetric plane.
基金financially supported by the National Key R&D Program of China(No.2019YFA0706802)the National Natural Science Foundation of China(Nos.51903223 and 12072325)the Key Technologies R&D Program of Henan Province(No.212102210302)。
文摘With the discovery of the two-dimensional(2D) MXene, it shows a great application potential in the field of electromagnetic interference(EMI) shielding, but the mechanical brittleness and easy oxidation of MXene limit its wide application. For this reason, a double crosslinking strategy is provided to solve the above problems in a nacre-like “brick-mortar” layered MXene/cellulose nanofiber(MXene/CNF) film.Typically, the film was firstly suffered by dopamine modification, then was further reinforced by secondary Ca^(2+)bridging, so as to obtain excellent mechanical properties and antioxidative EMI shielding performance. Comparing with the single crosslinking, the double crosslinking strategy reveals a higher efficiency in improving the mechanical property. The mechanical strength and toughness of the double crosslinking MXene/CNF film can increase to 142.2 MPa and 9.48 MJ/m^(3), respectively. More importantly, while achieving good mechanical properties, the MXene composite film still holds a very stable EMI shielding performance of more than 44.6 dB when suffering from the oxidation treatment of hightemperature annealing, showing excellent anti-oxidation ability and environment tolerance. Therefore,this work provides a universal but effective double crosslinking strategy to solve the mechanical brittleness and easy oxidation of MXene-based composites, thus showing a huge potential in flexible EMI shielding applications.
