Preparation of homogeneous Ca_ 3-xLa_xCo_4O_9 (x=0～0.4) single-phase ceramic powders was described using a tartrate complex method. The results show Ca3Co_4O_9 phase can be obtained by calcining the dry gel at 750 ℃...Preparation of homogeneous Ca_ 3-xLa_xCo_4O_9 (x=0～0.4) single-phase ceramic powders was described using a tartrate complex method. The results show Ca3Co_4O_9 phase can be obtained by calcining the dry gel at 750 ℃ for 5 h. The Ca_ 3-xLa_xCo_4O_9 ceramics have been prepared by spark plasma sintering at 800 ℃ for 5 min. Spark plasma sintering process is effective in synthesis of Ca_ 3-xLa_xCo_4O_9 compact ceramics. The thermal conductivity of Ca_ 3-xLa_xCo_4O_9 bulks was investigated from room temperature to 700 ℃. The results show that Ca_ 2.7La_ 0.3Co_4O_9 has lowest thermal conductivity due to the increasing of phonon scattering by La substitution.展开更多
The tuning of electron and phonon by ion doping is an effective method of improving the performances of thermoelectric materials.A series of lower concentration K-doped Ca_(3-x)K_(x)Co_(4)O_(9)(x=0,0.05,0.10,0.15)poly...The tuning of electron and phonon by ion doping is an effective method of improving the performances of thermoelectric materials.A series of lower concentration K-doped Ca_(3-x)K_(x)Co_(4)O_(9)(x=0,0.05,0.10,0.15)polycrystalline ceramic samples are prepared by combining citrate acid sol-gel method with cold-pressing sintering method.The single-phase compositions and plate-like grain morphologies of all samples are confirmed by x-ray diffraction and field emission scanning electron microscope.The effects of lower concentration K doping on the thermoelectric properties of the material are evaluated systematically at high temperatures(300–1026 K).Low concentration K doping causes electrical conductivity to increase up to 23%with little effect on the Seebeck coefficient.Simultaneously,the thermal conductivity of K-doped sample is lower than that of the undoped sample,and the total thermal conductivity reaches a minimum value of approximately1.30 W·m^(-1)·K^(-1),which may be suppressed mainly by the phonon thermal conduction confinement.The dimensionless figure-of-merit ZT of Ca_(2.95)K_(0.05)Co_(4)O_(9)is close to 0.22 at 1026 K,representing an improvement of about 36%compared with that of Ca_(3)Co_(4)O_(9),suggesting that lower concentration K-doped Ca_(3)Co_(4)O_(9)series materials are promising thermoelectric oxides for high-temperature applications.展开更多
Defect and charge transfer efficiency of nano-photocatalysts are important factors which influence their photocatalytic performance.In this work,oxygen vacancies are successfully introduced in the synthesis process of...Defect and charge transfer efficiency of nano-photocatalysts are important factors which influence their photocatalytic performance.In this work,oxygen vacancies are successfully introduced in the synthesis process of Bi_(2)Al_(4)O_(9)/β-Bi_(2)O_(3)heterojunctions through one-step in situ selfcombustion method.High-resolution transmission electron microscopy (HRTEM),UV-Vis diffuse reflectance spectra (UV-Vis DRS),and electron spin resonance (ESR) measurements confirm the existence of oxygen vacancies.In addition,by controlling the ratio of reactants of Bi(NO_(3))_(3)to Al(NO_(3))_(3),the ratio of Bi_(2)Al_(4)O_(9)and β-Bi_(2)O_(3)in the heterojunction can be easily adjusted.Photocurrent responses and surface photovoltage spectroscopy (SPV) indicate that the construction of the Bi_(2)Al_(4)O_(9)/β-Bi_(2)O_(3)heterostructure improves the separation efficiency of the photo-generated electrons and holes.CO_(2)-TPD results imply that the amounts and stability of heterojunctions are enhanced compared with their counterparts.The Bi_(2)Al_(4)O_(9)/β-Bi_(2)O_(3)heterojunction with 14 mol%Bi_(2)Al_(4)O_(9)shows the highest photocatalytic ability for reduction of CO_(2)into CO.The enhanced photoreduction of CO_(2)performance can be ascribed to the synergistic effects of the heterojunction for electron separation and oxygen vacancies for CO_(2)activation.展开更多
Increasing the phonon scattering center by adding nanoparticles to thermoelectric materials is an effective method of regulating the thermal conductivity.In this study,a series of Ca3 Co_(4)O_(9)/x wt.%CNTs(x=0,3,5,7,...Increasing the phonon scattering center by adding nanoparticles to thermoelectric materials is an effective method of regulating the thermal conductivity.In this study,a series of Ca3 Co_(4)O_(9)/x wt.%CNTs(x=0,3,5,7,10)polycrystalline ceramic thermoelectric materials by adding carbon nanotubes(CNTs)were prepared with sol-gel method and cold-pressing sintering technology.The results of x-ray diffraction and field emission scanning electron microscopy show that the materials have a single-phase structure with high orientation and sheet like microstructure.The effect of adding carbon nanotubes to the thermoelectric properties of Ca_(3)Co_(4)O_(9)was systematically measured.The test results of thermoelectric properties show that the addition of carbon nanotubes reduces the electrical conductivity and Seebeck coefficient of the material.Nevertheless,the thermal conductivity of the samples with carbon nanotubes addition is lower than that of the samples without carbon nanotubes.At 625 K,the thermal conductivity of Ca3 Co_(4)O_(9)/10 wt.%CNTs sample is reduced to0.408 W·m^(-1)·K^(-1),which is about 73%lower than that of the original sample.When the three parameters are coupled,the figure of merit of Ca_(3)Co_(4)O_(9)/3 wt.%CNTs sample reaches 0.052,which is 29%higher than that of the original sample.This shows that an appropriate amount of carbon nanotubes addition can reduce the thermal conductivity of Ca_(3)Co_(4)O_(9)ceramic samples and improve their thermoelectric properties.展开更多
Perovskite oxide La_(0.6)Ca_(0.4)Fe_(0.8)Ni_(0.2)O_(3-δ)(LCFN)has been used in symmetric solid oxide cells(SSOCs)to obtain good electrochemical performance in both fuel cells(SOFCs)and electrolysis cells(SOECs)modes....Perovskite oxide La_(0.6)Ca_(0.4)Fe_(0.8)Ni_(0.2)O_(3-δ)(LCFN)has been used in symmetric solid oxide cells(SSOCs)to obtain good electrochemical performance in both fuel cells(SOFCs)and electrolysis cells(SOECs)modes.However,its structural stability still faces challenges and the electrocatalytic activity also needs to be further improved.Herein,tungsten-doped La_(0.6)Ca_(0.4)Fe_(0.7)Ni_(0.2)W_(0.1)0_(3-δ)(LCFNW)perovskite oxide material was synthesized which exhibits good structural stability under H_(2)and superior electrochemical performance as an electrode for SSOCs.In SOFCs mode,the cell achieved the maximum power density of 0.58 W·cm^(-2)with wet H_(2)as fuel at 850℃.In SOECs mode,the current density can reach 1.81 A·cm^(-2)for pure CO_(2)electrolysis at 2 V.Moreover,the SSOCs exhibits outstanding long-term stability in both SOFCs and SOECs modes,proving that doping W in perovskite oxide is an effective strategy to enhance the catalytic activity and stability of the electrode.The LCFNW material developed in this work shows promising prospect as an electrode candidate for SSOCs.展开更多
文摘Preparation of homogeneous Ca_ 3-xLa_xCo_4O_9 (x=0～0.4) single-phase ceramic powders was described using a tartrate complex method. The results show Ca3Co_4O_9 phase can be obtained by calcining the dry gel at 750 ℃ for 5 h. The Ca_ 3-xLa_xCo_4O_9 ceramics have been prepared by spark plasma sintering at 800 ℃ for 5 min. Spark plasma sintering process is effective in synthesis of Ca_ 3-xLa_xCo_4O_9 compact ceramics. The thermal conductivity of Ca_ 3-xLa_xCo_4O_9 bulks was investigated from room temperature to 700 ℃. The results show that Ca_ 2.7La_ 0.3Co_4O_9 has lowest thermal conductivity due to the increasing of phonon scattering by La substitution.
基金Project supported by the National Key R&D Program of China(Grant No.2016YFB0601101)the National Natural Science Foundation of China(Grant No.51476173)
文摘The tuning of electron and phonon by ion doping is an effective method of improving the performances of thermoelectric materials.A series of lower concentration K-doped Ca_(3-x)K_(x)Co_(4)O_(9)(x=0,0.05,0.10,0.15)polycrystalline ceramic samples are prepared by combining citrate acid sol-gel method with cold-pressing sintering method.The single-phase compositions and plate-like grain morphologies of all samples are confirmed by x-ray diffraction and field emission scanning electron microscope.The effects of lower concentration K doping on the thermoelectric properties of the material are evaluated systematically at high temperatures(300–1026 K).Low concentration K doping causes electrical conductivity to increase up to 23%with little effect on the Seebeck coefficient.Simultaneously,the thermal conductivity of K-doped sample is lower than that of the undoped sample,and the total thermal conductivity reaches a minimum value of approximately1.30 W·m^(-1)·K^(-1),which may be suppressed mainly by the phonon thermal conduction confinement.The dimensionless figure-of-merit ZT of Ca_(2.95)K_(0.05)Co_(4)O_(9)is close to 0.22 at 1026 K,representing an improvement of about 36%compared with that of Ca_(3)Co_(4)O_(9),suggesting that lower concentration K-doped Ca_(3)Co_(4)O_(9)series materials are promising thermoelectric oxides for high-temperature applications.
基金financial support from the National Natural Science Foundation of China(21776059,21376061)the Natural Science Foundation for Distinguished Young Scholars of Hebei Province(B2015208010)the Research Foundation of Hebei Province Education Department(No.ZC2016007)。
文摘Defect and charge transfer efficiency of nano-photocatalysts are important factors which influence their photocatalytic performance.In this work,oxygen vacancies are successfully introduced in the synthesis process of Bi_(2)Al_(4)O_(9)/β-Bi_(2)O_(3)heterojunctions through one-step in situ selfcombustion method.High-resolution transmission electron microscopy (HRTEM),UV-Vis diffuse reflectance spectra (UV-Vis DRS),and electron spin resonance (ESR) measurements confirm the existence of oxygen vacancies.In addition,by controlling the ratio of reactants of Bi(NO_(3))_(3)to Al(NO_(3))_(3),the ratio of Bi_(2)Al_(4)O_(9)and β-Bi_(2)O_(3)in the heterojunction can be easily adjusted.Photocurrent responses and surface photovoltage spectroscopy (SPV) indicate that the construction of the Bi_(2)Al_(4)O_(9)/β-Bi_(2)O_(3)heterostructure improves the separation efficiency of the photo-generated electrons and holes.CO_(2)-TPD results imply that the amounts and stability of heterojunctions are enhanced compared with their counterparts.The Bi_(2)Al_(4)O_(9)/β-Bi_(2)O_(3)heterojunction with 14 mol%Bi_(2)Al_(4)O_(9)shows the highest photocatalytic ability for reduction of CO_(2)into CO.The enhanced photoreduction of CO_(2)performance can be ascribed to the synergistic effects of the heterojunction for electron separation and oxygen vacancies for CO_(2)activation.
基金supported by the National Natural Science Foundation of China(Grant No.51836009)。
文摘Increasing the phonon scattering center by adding nanoparticles to thermoelectric materials is an effective method of regulating the thermal conductivity.In this study,a series of Ca3 Co_(4)O_(9)/x wt.%CNTs(x=0,3,5,7,10)polycrystalline ceramic thermoelectric materials by adding carbon nanotubes(CNTs)were prepared with sol-gel method and cold-pressing sintering technology.The results of x-ray diffraction and field emission scanning electron microscopy show that the materials have a single-phase structure with high orientation and sheet like microstructure.The effect of adding carbon nanotubes to the thermoelectric properties of Ca_(3)Co_(4)O_(9)was systematically measured.The test results of thermoelectric properties show that the addition of carbon nanotubes reduces the electrical conductivity and Seebeck coefficient of the material.Nevertheless,the thermal conductivity of the samples with carbon nanotubes addition is lower than that of the samples without carbon nanotubes.At 625 K,the thermal conductivity of Ca3 Co_(4)O_(9)/10 wt.%CNTs sample is reduced to0.408 W·m^(-1)·K^(-1),which is about 73%lower than that of the original sample.When the three parameters are coupled,the figure of merit of Ca_(3)Co_(4)O_(9)/3 wt.%CNTs sample reaches 0.052,which is 29%higher than that of the original sample.This shows that an appropriate amount of carbon nanotubes addition can reduce the thermal conductivity of Ca_(3)Co_(4)O_(9)ceramic samples and improve their thermoelectric properties.
基金financial support from National Key R&D Program for Young Scientists(2021YFA1501900)National Natural Science Foundation of China(52272257)+4 种基金Material Science and Engineering Discipline Guidance Fund of China University of Mining and Technology(CUMTMS202203)Foundation of State Key Laboratory of Clean and Efficient Coal Utilization,Taiyuan University of Technology(Grant No.SKL2022008)the Jiangsu Provincial Shuangchuang Doctor Program(JSSCBS20211224)Young Elite Scientists Sponsorship Program by(CAST2022QNRC001)the Open Sharing Fund for the Large-scale Instruments(DYGX-2021026)and Equipments of China University of Mining and Technology(CUMT)Analytical for sample characterizations assistance。
文摘Perovskite oxide La_(0.6)Ca_(0.4)Fe_(0.8)Ni_(0.2)O_(3-δ)(LCFN)has been used in symmetric solid oxide cells(SSOCs)to obtain good electrochemical performance in both fuel cells(SOFCs)and electrolysis cells(SOECs)modes.However,its structural stability still faces challenges and the electrocatalytic activity also needs to be further improved.Herein,tungsten-doped La_(0.6)Ca_(0.4)Fe_(0.7)Ni_(0.2)W_(0.1)0_(3-δ)(LCFNW)perovskite oxide material was synthesized which exhibits good structural stability under H_(2)and superior electrochemical performance as an electrode for SSOCs.In SOFCs mode,the cell achieved the maximum power density of 0.58 W·cm^(-2)with wet H_(2)as fuel at 850℃.In SOECs mode,the current density can reach 1.81 A·cm^(-2)for pure CO_(2)electrolysis at 2 V.Moreover,the SSOCs exhibits outstanding long-term stability in both SOFCs and SOECs modes,proving that doping W in perovskite oxide is an effective strategy to enhance the catalytic activity and stability of the electrode.The LCFNW material developed in this work shows promising prospect as an electrode candidate for SSOCs.
