Electrolytic Silicon and Iron Powders as Alternatives to Hydrogen as Energy Carrier and Store

氢气技术目前被认为是解决使用化石燃料造成的问题的潜在解决方案，特别是二氧化碳排放。然而，氢气技术的发展遇到了一些困难，其中需要可逆地储存氢气是一大挑战。特别是，即使在最好的材料或器件中也能实现的可逆存储容量太低，例如LaNi5H6(1.5wt%，~300K)和高压或液氢罐(&lt；4wt%)，但在一些其他材料或器件中的高存储容量，例如NaAlH4(&gt；7wt%，&gt；520K)和LiBH4(&gt；18.4wt%，&gt；553K)，不允许方便地重复使用存储的氢。事实上，氢气不是一种能源，因为它在自然界中不存在。在任何能源应用中，氢气只有在使用另一种形式的能源(如来自可再生能源或核能的电力)生产时才起到储能的作用，而当气体在内燃机中燃烧或送入燃料电池时才起到能量载体的作用。氢的这两个作用可以被其他纯元素物质很好地发挥作用，如硅和铁。与氢一样，储存在硅和铁中的能量可以通过与氧的化学反应或电化学反应释放出来。这些反应的产物，即硅和铁氧化物，是地球的天然成分，对环境没有任何影响。到目前为止，氢一直是研究和公众关注的焦点之一，原因之一是它的高比能量(单位质量能量)。不幸的是，氢在环境条件下是一种气体，需要用任何已知的方法来储存，这大大降低了氢的实际比能量。例如，氢气在空气中燃烧的比热是122.8 kJ/g(425℃)，但当氢气储存在25wt%(理论最大储氢容量)时，它会减少到30.7kJ/g，但当氢气储存在6.5wt%(美国能源部的目标可逆储氢容量)时，它会下降到令人失望的低值8.0kJ/g。相比之下，铁和硅在环境条件下是稳定的固体，不存在储存问题。在空气中燃烧时，硅的比热为32.4kJ/g，铁的比热为7.3kJ/g。能量利用的另一个考虑因素是能量密度(单位体积的能量)。利用这三种元素的质量密度，同样可以表明，在空气中燃烧时，液氢的热密度仅为8.6kJ/cm~3，而硅和铁的热密度分别为75.5kJ/cm~3和57.5kJ/cm~3。因此，当考虑到储存时，硅和铁在热力学上比氢更好。在技术方面，硅和铁粉的燃烧早已在研究中得到证实，现在是时候开发一种技术，利用可再生能源，特别是太阳能，轻松地生产硅和铁粉。这项拟议的研究旨在从实验上证明用硅粉和铁粉替代氢气作为储能和载体的热力学预测的可行性。特别是，它的目的是在太阳能可行的条件下(电力和热能)使用熔盐电解法从它们的氧化物中生产和再生硅和铁粉。申请人和同事已经进行了初步测试，并成功地在相对较高的温度(800摄氏度~900摄氏度)下使用新型FFC剑桥工艺(由申请人在英国共同发明)生产了微细硅和铁粉。该项目旨在降低熔盐温度(&lt；500摄氏度)，以便在该过程中利用太阳能。产品将进行热重和差示扫描量热分析，并在空气中进行燃烧测试。确定最佳的粉末颗粒形态及其与电解条件的相关性

The hydrogen technology is at present regarded as a potential solution to the problems resulting from using fossil fuels, particularly CO2 emission. However, the development of the hydrogen technology has encountered a number of difficulties, of which the need to reversibly store the hydrogen gas is a major challenge. Particularly, the reversible storage capacities achievable even in the best materials or devices are too low, for example, LaNi5H6 (< 1.5 wt%, ~300K) and high pressure or liquid hydrogen tank (< 4 wt%), but the high storage capacity in some others, e.g. NaAlH4 (> 7 wt%, >520K) and LiBH4 (>18.4 wt%, >553K), does not allow convenient reuse of the stored hydrogen.In fact, hydrogen gas is not an energy source because it does not exist in nature. In any energy application, the hydrogen gas only plays the roles of the energy store when the hydrogen gas is produced using another form of energy, such as electricity from the renewable or nuclear energy, and of the energy carrier when the gas is combusted in an internal combustion engine or fed into a fuel cell. These two roles of hydrogen can be well played by other pure elemental substances, such as silicon and iron. Like hydrogen, the energy stored in silicon and iron can be released through a chemical or an electrochemical reaction with oxygen. The products from these reactions, i.e. silicon and iron oxides, are the natural components of the Earth and will have zero environmental impact. One of the reasons why hydrogen has been so far the research and public focus is its high specific energy (energy per unit mass). Unfortunately, hydrogen is a gas under ambient conditions and the need for storage by any known method significantly reduces hydrogen's real specific energy. For example, the specific heat from the combustion of hydrogen gas in air is 122.8 kJ/g (425 degC), but it reduces to 30.7 kJ/g when hydrogen is stored at 25wt% (the theoretical maximum hydrogen storage capacity), but to a disappointing low value of 8.0 kJ/g when hydrogen is stored at 6.5 wt% (the targeted reversible hydrogen storage capacity of the US Department of Energy). On the contrast, iron and silicon are stable solids under ambient conditions and there is no storage problem. For combustion in air, the specific heat of silicon is 32.4 kJ/g and that of iron is 7.3 kJ/g. The other consideration for energy application is the energy density (energy per unit volume). Using the mass density of the three elements, it can be shown that, again for combustion in air, the heat density is only 8.6 kJ/cm3 for liquid hydrogen, but 75.5 kJ/cm3 for silicon and 57.5 kJ/cm3 for iron. Therefore, silicon and iron are thermodynamically better than hydrogen when storage is considered. On the technical side, the combustion of silicon and iron powders has long been proven in research, and it is now the time to develop a technique in which silicon and iron powders can be produced easily using renewable energy, particularly solar energy. This proposed research aims to experimentally demonstrate the thermodynamically predicted feasibility of using silicon and iron powders as the alternatives to hydrogen as the energy store and carrier. Particularly, it is intended to produce and regenerate the silicon and iron powders from their oxides using molten salt electrolysis under solar energy workable conditions (electricity and heat). The applicant and co-workers have already performed preliminary tests and produced successfully fine silicon and iron powders using the novel FFC Cambridge Process (co-invented by the applicant in the UK) at relatively high temperatures (800 degC ~ 900 degC). It is intended to lower the molten salt temperatures in this project (< 500 degC) so that solar heat can be used in the process. The products will be investigated by TG and DSC and tested for combustion in air. The optimal powder particle morphology and its correlation with the electrolysis conditions will be identified