全钒氧化还原液流电池电解液的热力学性质研究

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	全钒氧化还原液流电池电解液的热力学性质研究
	秦野
学位类型	博士
导师	曾潮流 ; 严川伟
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	腐蚀科学与防护
关键词	钒氧化还原液流电池电解液热容溶解焓体积性质 Vanadium Redox Flow Battery Electrolyte Heat Capacity Enthalpies Of Solution Volumetric Property
摘要	"全钒氧化还原液流电池是一种新型的电化学储能系统，具有可快速、大电流充放电、自放电率低和电池结构简单等特点，它是满足风能、太阳能等新型能源大规模储能的理想电源形式。钒电池正负极电解液为含VO2+/VO2+与V2+/V3+氧化还原电对的硫酸水溶液，它不仅是导电介质，更是实现能量存储的电活性物质，是钒电池储能及能量转化的核心，所以研究电解液的热力学性质对认识电解液中离子的存在形式、提高电解液的热稳定性及浓度，进而优化钒电池的性能至关重要。然而，国内外少有关这方面的系统研究工作，致使实验数据十分匮乏，成为进一步提高钒电池的运行性能和扩大应用的障碍之一。本文使用三种经典热力学研究方法研究了钒电解液的热力学性质，通过绝热量热法研究了不同温度下VOSO4·nH2O的热容，确定了VOSO4·nH2O可稳定存在的温区。用溶解热法研究了VOSO4在水和硫酸水溶液中的溶解焓，证明了氧钒离子在溶液中主要以[VOSO4]0离子对的形式存在，并获得了该离子对和自由氧钒离子的真实浓度。用密度法研究了不同温度和浓度硫酸氧钒水溶液的体积性质。通过绝热量热计测量了VOSO4·nH2O在78-388 K温区内的低温热容，确定了VOSO4·nH2O可稳定存在的温区，并计算了80-370 K温区内的(HT - H298.15)、(ST - S298.15) 和(GT -G298.15)热力学函数值。此外，在372-382K温区内观察到了VOSO4·nH2O的脱水峰，根据脱水峰的热容曲线确定了脱水峰的峰温并计算了脱水过程的摩尔焓和摩尔熵。利用恒温环境溶解反应量热计测量了不同质量摩尔浓度的 VOSO4·nH2O (n = 4.21、3.90、3.00和2.63)水溶液在(298.15±0.01) K的摩尔溶解焓，根据Archer的方法计算了VOSO4·nH2O的标准摩尔溶解焓。用外推的方法，获得了无水VOSO4的标准摩尔溶解焓，并计算了相对表观摩尔焓φL。根据Bjerrum离子结合理论和的φL值，结合半经验的方法，估算了[VOSO4]0离子对的形成反应焓。利用恒温环境溶解反应量热计测定了VOSO4在水和硫酸水溶液中的摩尔溶解焓。在硫酸水溶液中VOSO4 摩尔溶解焓的负值比在纯水中要小很多，并证明了氧钒离子在溶液中主要以[VOSO4]0离子对的形式存在。借助VOSO4水溶液的离子缔合平衡和硫酸的二级解离平衡，改进了Archer方法，并用这种改进的方法分别估算了VOSO4在水中以及在硫酸水溶液中的标准摩尔溶解焓。根据离子缔合平衡和硫酸二级解离平衡的计算结果，计算了溶液中离子对和自由氧钒离子的浓度。用Westphal天平测定了不同浓度和温度下VOSO4水溶液的密度，计算了硫酸氧钒水溶液的表观摩尔体积φVB、偏摩尔体积和热膨胀系数a，研究了三者随温度和浓度的变化规律。通过热膨胀系数a可计算在冷热交替的环境下温度对电解质溶液体积胀缩值的影响。用Pitzer的表观摩尔体积方程对硫酸氧钒水溶液的表观摩尔体积进行了多元线性拟合，得到了标准偏摩尔体积和Pitzer参数。"
其他摘要	"Vanadium redox flow battery (VRFB) is a new electrochemical energy storage system, with the fast and large current charge and discharge, low self-discharge rate and simple structure . VRFB is the ideal power form for the mass storage of mind energy, solar energy and other new energy. In this cell employs the VO2+/VO2+ and V2+/V3+ redox couples are used as the positive and negative half-cell electrolytes, respectively, with sulfuric acid as the supporting electrolyte. Vanadium electrolyte acts as not only an ionic conductor, but also a energy-storage medium and thus it is the core of energy storage and energy conversion of vanadium redox battery. Reliable thermodynamic data are helpful to good description of interactions of various species in the VRFB electrolyte and to optimizing the overall performances of the VRFB. So, the study fo the thermodynamic properties of electrolyte is of great importance to understanding the ionic forms in the electrolyte, improving the thermal stability and the concentration of electrolyte, and optimizing performance of battery. However, there are limited reports on the thermodynamic properties of VRFB electrolyte, which has become an obstacle to enhancing the vanadium battery performance, and expanding the application of VRFB. In this paper, thermodynamic properties of vanadium electrolyte has been investigated by three classical methods. The heat capacity of VOSO4·nH2O at different temperatures was studied by adiabatic calorimetry, and the stable temperature region of VOSO4·nH2O was determined. The molal enthalpies of solution of vanadyl sulfate in water and in aqueous sulfuric acid were measured by a solution-reaction isoperibol calorimeter, the volumetric properties of aqueous vanadyl sulfate with various molalities are determined by Westphal balance at different temperatures. The low-temperature heat capacities of VOSO4·2.63H2O(s) were measured by adiabatic calorimetry in the temperature range of 78-388 K. The fundamental thermodynamic functions of the compound relative to the standard reference temperature 298.15 K, (HT - H298.15), (ST - S298.15) and (GT -G298.15), were calculated. Additionally, a dehydration process occurred in the temperature range of 372-382 K and the peak temperature, molar enthalpy of dehydration, and molar entropy of dehydration were determined in terms of the heat capacity curve. The molal enthalpies of solution of VOSO4·nH2O (n = 4.21, 3.90, 3.00 and 2.63) at various molalities in water, ΔsolHm, were measured by a solution-reaction isoperibol calorimeter at (298.15±0.01) K. The standard molal enthalpies of solution of VOSO4·n H2O(s), DsolH0m(n), were determined according to Archer’s method. The standard molal enthalpies of solution for anhydrous VOSO4(s) were obtained using extrapolation, the relative apparent molal enthalpies, φL, of aqueous VOSO4 were calculated. In terms of the Bjerrum theory for ion association and the values of φL, the enthalpy of reaction for the formation of the ion pair [VOSO4]0 was estimated using a semi-empirical method. The molal enthalpies of solution of VOSO4 with various molarities in water and aqueous sulfuric acid were measured by a solution-reaction isoperibol calorimeter. An improved Archer’s method was put forward to estimate standard molal enthalpy of solution. In terms of the improved method, the values of standard molal enthalpy of solution in water and aqueous sulfuric acid were obtained. In terms of the ion association equilibrium and the second dissociation equilibrium of H2SO4, the values of free VO2+ in solution were caculated. The densities of aqueous VOSO4 with various molalities were measured by Westphal balance at different temperatures. The apparent molar volume, the partial molar volume of VOSO4 and coefficient of thermal expansion of the solution were calculated. The values of the apparent molar volume were fitted as Pitzer’s model, the partial molar volume of the VOSO4 at infinite dilution and the Pitzer’s were obtained."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64422
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	秦野. 全钒氧化还原液流电池电解液的热力学性质研究[D]. 北京. 中国科学院金属研究所,2012.