NaCl-MgCl2-CaCl2相图计算方法研究

为满足规模化太阳能热发电中对传热蓄热的要求,针对储能材料开展探究。以熔融盐热物性及经济性作为筛选条件,选定来源广泛、价格低廉、工作温度范围宽、黏度低、相变潜热大的NaCl、MgCl₂和CaCl₂三元熔盐体系开展深入研究。应用修正的准化学溶液模型,在子二元系基础上推导计算三元混合熔盐NaCl-MgCl₂-CaCl₂相图。结果表明,该熔盐混合物共晶点温度为412.45 ℃,NaCl、MgCl₂和CaCl₂的摩尔分数分别为50.99%、22.78%和26.23%,与已有文献数据相比,误差在3%以内,验证了方法的准确性,为构建熔盐氯化物相图数据库奠定了部分基础。     

碳酸盐中CO2气化生物质制合成气

以杉木屑为原料,CO₂为气化剂,熔融碳酸盐Li2CO3-Na2CO3-K2CO3(LNK)为热介质和催化剂进行气化制合成气(H2+CO)的研究,考察气化剂CO₂流量、CO₂通入方式、复合熔盐体系中添加的金属氧化物种类和Cr2O3含量等因素对气体产物组成分布及产率的影响。结果表明:CO₂流量显著影响气化反应的平衡;以鼓泡法通入CO₂时生物质的气化效果优于吹扫法的情况,CO₂流量为99.8 L/h时气化效果较好,合成气含量和产率分别达到61.4%和350.2 mL/g生物质;添加的金属氧化物中Cr₂O₃对生物质气化过程的促进作用优于MgO和Fe₂O₃,随着Cr₂O₃含量的增大,合成气含量先增大后略微减小,在Cr₂O₃含量为10.0%时最高,为67.9%。     

Li4SiO4吸收CO2的实验研究

用固相法合成了用来循环使用的吸收CO2的Li4SiO4材料。通过热力学分析、X射线衍射(XRD)、热重分析(TG)确定了合成条件;用热重分析(TG)仪研究Li4SiO4吸附CO2的性能;用扫描电子显微镜(SEM)来观察Li4SiO4吸附CO2前后表面微观形貌的变化特征。结果发现,在900℃烧结2h可以合成Li4SiO4;材料在600～720℃段吸附CO2反应最为活跃,最高吸附量可达29.16%(质量分数)左右;材料吸附CO2后在750℃开始脱出CO2,到900℃左右可脱附完全,再生为Li4SiO4;CO2的体积百分含量(分压)对Li4SiO4吸附CO2的速度和吸附量有明显影响;气氛相同时,气体流量对吸附速度和吸附量的影响不明显。     

新型相同钠离子混合熔盐相图预测及物性测量

为了提高第三代聚光式太阳能热发电技术的效率,降低系统的运行成本,需要开发出具有更高使用温度的新型高温储热/蓄热材料.本文基于相同阳离子的原则,选取3种相同钠离子熔盐NaNO3、NaCl、Na2CO3作为基盐,借助相图原理指导混合熔盐的配制,通过FactSage软件对NaNO3-NaCl-Na2CO3三元体系进行相图热力学计算,利用差示扫描量热仪对预测最低共熔点附近多组共晶盐进行热物性分析.结果发现,当三元体系熔盐NaNO3:NaCl:Na2CO3物质的量比例为0.92:0.064:0.016时熔点最低,测得最低共熔点为279.9℃,相变潜热值为194.1 J/g,与相图预测结果(291℃)基本一致,验证了相图计算的准确性.对该体系其他热物性进行测量,得到其分解温度为595℃(质量损失率为3％),比热容为1.60 J/(g·K)(500℃),平均比热容为1.62 J/(g·K),相比于Solar Salt和Hitec平均比热容分别增加了0.12 J/(g·K)和0.28 J/(g·K).该新型三元体系熔盐具有潜热、比热容大和使用温度范围较宽的优点,在制备复合材料潜热储热方面有很大潜力,为开发新型太阳能热发电储热/蓄热材料提供了借鉴,也为借助相图理论指导混合熔盐的开发提供了参考.     

高温下Ti掺杂对Li4SiO4吸收CO2性能的影响

采用固相合成法和溶胶凝胶法分别制备了可直接在高温下吸收CO2的硅酸锂(Li4SiO4),并进行了Ti的掺杂改性.采用X射线衍射仪、比表面积测定仪和热重分析仪对Li4SiO4进行了表征及CO2吸收性能的测试,并在固定床台架上进行了CO2循环吸收/解吸的试验研究.结果表明:溶胶凝胶法制备的纯Li4SiO4更有利于在高温下对CO2的吸收;CO2的分压对高温下Li4SiO4吸收CO2有很大影响,分压越大,吸收的CO2量越大;当TiO2的掺杂比例x=0.02时,改性的Li4SiO4对CO2的最大吸收量可达31.59%;经过20次循环后,固溶体Li4Si0.98Ti0.02 O4对CO2的吸收量仅下降了20%,从第4次循环后此样品基本达到完全再生,说明其具有较大的CO2吸收量和优良的再生性能.     

低温固体氧化物燃料电池SDC-(Li/Na)2CO3复合电解质材料优化

采用两种工艺(干法和湿法)制备了钐掺杂的氧化铈(SDC)-(Li/Na)2CO3复合电解质,其中碳酸盐的质量分数分别为20%、25%和30%.通过XRO和SEM观察了不同制备工艺和碳酸盐含量的复合电解质材料的物相结构和表面形貌.采用交流阻抗法测量了复合电解质在空气中400～600℃温度范围的电导率.采用于压法制作了基于(SDC)-(Li/Na)2CO3电解质的单电池,并在氢气/燃料中评价了该电池的输出性能.     

高浓度CO2下CaCO3循环煅烧试验与模拟

建立了高浓度CO2气氛下CaCO3循环煅烧过程数学模型,利用钙基吸收剂多次循环煅烧试验对模型进行了验证,在此基础上分析了CO2浓度、吸收剂种类、粒径和循环次数等参数对CaCO3煅烧的影响。结果表明:CaCO3分解温度随气相中CO2含量的增加而增大;在高浓度CO2下,随循环反应次数的增加,吸收剂循环反应活性下降,使得所生成的CaCO3质量也随循环次数的增加而减少,致使CaCO3煅烧完全所需时间会随循环反应次数的增加而减少。     

添加剂对连铸保护渣粘度及流动性的影响

研究了不同添加剂Li2CO3,NaF,Na2CO3,冰晶石及硼砂对连铸保护渣粘度及流动性的影响。实验表明,Li2CO3,NaF,Na2CO3,冰晶石及硼砂均可以降低连铸保护渣粘度,增加流动长度,其中Li2CO3和NaF的作用效果更加明显。     

Li_4SiO_4回收CO_2的实验研究

CO2资源化利用对实现节能减排意义重大,在利用HSC5.1热力学数据库对Li4SiO4吸附CO2的热力学进行分析的基础上,采用自行研制的热天平分析研究Li4SiO4吸收CO2的性能,用X射线衍射仪和扫描电子显微镜(SEM)分别观察和评价在不同温度下Li4SiO4吸收CO2后的物相组成与Li4SiO4吸收CO2前后表面微观形貌的变化特征.分析与实验结果发现,材料在600～720 ℃段吸收CO2反应最为活跃,最高吸收量可达29.16%(wt)左右;材料吸收CO2后在750 ℃开始脱出CO2,再生为Li4SiO4;CO2的体积百分含量对Li4SiO4吸收CO2的速度和吸收量有明显影响;气氛相同时,气体流量对吸收速度和吸收量的影响不明显.     

低熔点多元混合熔盐的制备及其性能研究

为了获得聚光型太阳能热发电用的更低熔点熔融盐储热传热材料,采用材料掺杂改性方法,在Li NO3-KNO3-Ca(NO3)2三元低熔点共晶混合盐中加入Na Cl,制备了Li NO3-KNO3-Ca(NO3)2-Na Cl新混合熔盐。对新混合熔盐分别进行了DSC熔点测定、TG动态热稳定测定、48 h静态热稳定测试和熔盐液态密度测定。DSC实验结果表明,新混合熔盐的熔点为109.3℃,比原三元混合熔盐的熔点(117.2℃)降低了7.9℃,对应的相变潜热为48.6 J/g;TG动态热稳定和静态热稳定实验表明,新混合熔盐的热稳定温度为500℃,比原三元混合熔盐的热稳定温度(450℃)高50℃;液态密度实验发现,该混合熔盐在180~500℃时的液态密度为1.7~1.9g/cm3。     

Thermal stability of Li2CO3-Na2CO3 based high-temperature phase change materials

利用静态熔融法制备了Li₂CO₃-Na₂CO₃(4∶6,质量比)二元熔盐.采用自制"自动热循环测试系统"测试了400~600 ℃内此二元熔盐1010次热循环,分析了其相变参数动态变化特性,利用DSC测试了其热稳定性,利用XRD分析了其化学组分.结果表明:"自动热循环测试系统"可以替代DSC定性测试相变材料的热循环稳定性;Li₂CO₃-Na₂CO₃二元熔盐熔化/凝固过程中主要以LiNaCO₃形式存在,其峰值温度为499.1 ℃,其相变潜热为365.5J/g;热循环过程中,此二元熔盐的熔化和凝固温度变化不大,相变潜热最大降低了45.3J/g;通过XRD物相分析,可知整个循环过程中此二元熔盐的物相没有明显的变化.总之,Li₂CO₃-Na₂CO₃二元熔盐能够满足太阳能高温热发电和其它高温储热需求.     

Predictions of the optimum ternary alkali-carbonate electrolyte composition for MCFC by computational calculation

Various kinds of phase diagrams for Li–Na–K ternary carbonate systems were plotted and the vapor pressures of chemical species such as alkali cations and oxygen molecule at various compositions and various temperatures were calculated by computational manipulation of thermodynamic databases. The liquidus temperature of (Li_0.52Na_0.48)₂CO₃–(Li_0.62K_0.32)₂CO₃, (Li_0.62K_0.32)₂CO₃–(Li_0.44Na_0.30K_0.26)₂CO₃, and (Li_0.44Na_0.30K_0.26)₂CO₃–(Li_0.52Na_0.48)₂CO₃ binary systems decrease with the increase of Li₂CO₃ content without any ternary intermediate compound. Total vapor pressure of alkali metal species governed by the summation of the vapor pressure of free Na and K and the vapor pressure of alkali metal species starts to decrease abruptly when the content of (Li_0.52Na_0.48)₂CO₃ is over 70 mol% in (Li_0.52Na_0.48)₂CO₃–(Li_0.62K_0.32)₂CO₃ system while over 50 mol% in (Li_0.44Na_0.30K_0.26)₂CO₃–(Li_0.52Na_0.48)₂CO₃ system. On the contrary, the equilibrium vapor pressure of oxygen molecule abruptly increases at the same composition range.     

Solubility and electrochemical studies of LiFeO2–LiCoO2–NiO materials for the MCFC cathode application

The dissolution of the state-of-the-art lithiated NiO is still considered as one of the main obstacles to the commercialisation of the molten carbonate fuel cell (MCFC). Development of alternative cathode materials has been considered as a main strategy for solving this problem. Ternary compositions of LiFeO₂, LiCoO₂ and NiO are expected to decrease the cathode solubility while ensuring a good electrical conductivity and electrochemical activity towards the oxygen reduction.

In this work, new material compositions in the LiFeO₂–LiCoO₂–NiO ternary system were synthesised using Pechini method and investigating their electrical conductivity by the DC four probe method. Then the influence of the cobalt content in the composition was determined in terms of AC impedance analysis and solubility measurements after 200 h of immersion in Li₂CO₃–Na₂CO₃ at 650 °C. The DC electrical conductivity study reveals the ability of improving the electrical conductivity, adequate for MCFC cathode application, by controlling the Co content of the composition. A special attention was given to the evolution of the open circuit potential as a function of time and to the impedance spectroscopy characterization related to microstructure modifications. Taking into account solubility, electrical conductivity, as well as electrochemical performance in the fuel cell, this study reveals the possibility of using LiFeO₂–LiCoO₂–NiO ternary materials for MCFC cathode.     

Ag/Al2O3(Li2O)/g-C3N4光催化乙醇制取环氧乙烷

本文制备了一系列Ag/Al₂O₃(Li₂O)/g-C₃N₄复合催化剂,考察了其可见光催化乙醇制取环氧乙烷的性能。Li₂O可调变Al₂O₃表面的酸性,从而降低了主要副产物乙醛的选择性。Ag/Al₂O₃(Li₂O) 在g-C₃N₄上的负载量对产物环氧乙烷的选择性有较大影响,当Ag/Al₂O₃(Li₂O) 负载量为5wt%时,乙醇具有较高的转换率,且环氧乙烷的选择性高达100%。     

Preparation and thermal stability of ternary sulfate molten salt

以硫酸钠、硫酸钾和硫酸镁为原料,采用在硫酸钠-硫酸钾二元共晶盐中加入硫酸镁的方法制备三元硫酸熔盐。应用TG-DSC联用分析仪、热常数分析仪、X射线衍射仪以及热循环法对复合熔盐的熔点、相变潜热、热导率、比热容、分解点以及热稳定性进行表征。结果表明：所制备的三元硫酸熔盐熔点分布在667.5～669.7 ℃之间,较二元熔盐熔点降低了160 ℃左右,硫酸镁含量为30%（质量分数）的三元硫酸熔盐相变潜热值最大为94.3 J/g,比热容最大为1.13 J/(g·K)（720℃≤T≤800℃）,导热系数为0.41 W/(m·K),分解温度为1070 ℃,经50次热循环后,相变潜热值降低约4.34%,熔点和物相保持基本恒定,具有良好的热稳定性。该研究为硫酸盐作为高温传热蓄热介质提供了依据。     

Lithium insertion into manganese dioxide electrode in MnO2/Zn aqueous battery: Part I. A preliminary study

The discharge characteristics of manganese dioxide (γ-MnO₂ of electrolytic manganese dioxide (EMD) type) as a cathode material in a Zn–MnO₂ battery containing saturated aqueous LiOH electrolyte have been investigated. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) data on the discharged material indicate that lithium is intercalated into the host structure of EMD without the destruction of its core structure. The XPS data show that a layer of insoluble material, possibly Li₂CO₃, is deposited on the cathode, creating a barrier to H₂O, thus preventing the formation of Mn hydroxides, but allowing the migration of Li ions into the MnO₂ structure. The cell could be reversibly charged with 83% of voltaic efficiency at 0.5 mA/cm² current density to a 1.9 V cutoff voltage. The percentage utilization of the cathode material during discharge was 56%.     

Lithium metal rechargeable cells using Li2MnO3 as the positive electrode

Rechargeable lithium cells have been fabricated using Li₂MnO₃ as the positive electrode, lithium metal as the negative electrode and 1 M LiAsF₆ in DMC/EC (1:1 v/v) as the electrolyte. Charge/discharge behaviour was evaluated and the cells showed improved performance after the first five cycles. The cells could be cycled at least 15 times without loss in capacity. Similar electrochemical trends were observed with LiPF₆ in a EC/DEC mixture.     

Synthesis and electrochemical studies of the 4 V cathode, Li(Ni2/3Mn1/3)O2

Layered Li(Ni_2/3Mn_1/3)O₂ compounds are prepared by freeze-drying, mixed carbonate and molten salt methods at high temperature. The phases are characterized by X-ray diffraction, Rietveld refinement, and other methods. Electrochemical properties are studied versus Li-metal by charge–discharge cycling and cyclic voltammetry (CV). The compound prepared by the carbonate route shows a stable capacity of 145 (±3) mAh g⁻¹ up to 100 cycles in the range 2.5–4.3 V at 22 mA g⁻¹. In the range 2.5–4.4 V at 22 mA g⁻¹, the compound prepared by molten salt method has a stable capacity of 135 (±3) mAh g⁻¹ up to 50 cycles and retains 96% of this value after 100 cycles. Capacity-fading is observed in all the compounds when cycled in the range 2.5–4.5 V. All the compounds display a clear redox process at 3.65–4.0 V that corresponds to the Ni^2+/3+–Ni^3+/4+ couple.     

Electrochromic properties of lithiated Co-oxide (LixCoO2) and Ni-oxide (LixNiO2) thin films prepared by the sol–gel route

Layered Li_xCoO₂ and Li_xNiO₂ thin films (x1) were prepared by a peroxo wet chemistry route from Li(I), Co(II) and Ni(II) acetate precursors and the addition of H₂O₂. Structural changes during the processing of xerogel to final oxide were followed by X-ray diffraction and infrared spectroscopy. Electrochromic properties were determined with in-situ potentiodynamic, potentiostatic and galvanostatic spectroelectrochemical measurements. Single dipped films with composition Li_0.99Co_1.01O₂ or Li_0.94Ni_1.06O₂ exhibited stable voltammetric response in 1 M LiClO₄/propylene carbonate electrolyte after about 60 cycles. The total charge exchanged in a reversible charging/discharging cycle was about ±30 mC cm⁻² for Li_0.99Co_1.01O₂ and ±20 mC cm⁻² for Li_0.94Ni_1.06O₂ oxide films. Galvanostatic measurements showed that about 1/2 (x0.5) and 2/3 (x0.3) of Li⁺ ions could be reversibly removed from the structure of Li_0.99Co_1.01O₂ and Li_0.94Ni_1.06O₂ films, respectively. Practical applicability of Li_0.99Co_1.01O₂ and Li_0.94Ni_1.06O₂ oxide films was studied in electrochromic devices with WO₃(H⁺)Li⁺ormolyteLi_0.99Co_1.01O₂ and WO₃(H⁺)Li⁺ormolyteLi_0.94Ni_1.06O₂ configuration. The monochromatic transmittance T_s (λ=633 nm) of dark blue coloured devices was extremely low (T_s3%), whereas in bleached state the value reached around T_s70%.