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

氢能技术目前被认为是解决使用化石燃料所产生的问题，特别是CO2排放问题的潜在解决方案。然而，氢技术的发展遇到了许多困难，其中需要可逆地储存氢气是一个主要挑战。特别地，即使在最好的材料或器件中可实现的可逆存储容量也太低，例如LaNi 5 H6（<1.5wt%，~ 300 K）和高压或液氢罐（<4wt%），但在一些其他的高存储容量，例如NaAlH 4（> 7wt%，> 520 K）和LiBH 4（> 18.4wt%，> 553 K），不允许方便地重复使用储存的氢。在任何能量应用中，氢气仅在使用另一种形式的能量（例如来自可再生能源或核能的电力）产生氢气时起能量存储器的作用，并且在气体在内燃机中燃烧或供给到燃料电池中时起能量载体的作用。氢的这两种作用可以由其他纯元素物质，如硅和铁很好地发挥。像氢一样，储存在硅和铁中的能量可以通过与氧的化学或电化学反应释放出来。这些反应的产物，即硅和铁的氧化物，是地球的天然成分，对环境没有任何影响。氢之所以一直是研究和公众关注的焦点，原因之一是它的高比能（单位质量的能量）。不幸的是，氢在环境条件下是气体，并且通过任何已知方法储存的需要显著降低了氢的真实的比能。例如，氢气在空气中燃烧的比热为122.8kJ/g（425 ℃），但当氢气储存在25wt%时，其降低到30.7 kJ/g（理论最大储氢量），但当氢以6.5wt%储存时，达到令人失望的8.0kJ/g的低值（美国能源部的目标可逆储氢容量）。相反，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32.4 kJ/g，铁的比热为7.3 kJ/g。能量应用的另一个考虑因素是能量密度（每单位体积的能量）。使用三种元素的质量密度，可以表明，对于在空气中的燃烧，液态氢的热密度仅为8.6 kJ/cm 3，但硅为75.5 kJ/cm 3，铁为57.5 kJ/cm 3。因此，当考虑储存时，硅和铁在性能上优于氢。在技术方面，硅粉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，可以使用可再生能源，特别是太阳能轻松生产硅粉和铁粉。这项研究的目的是通过实验证明，使用硅和铁粉末作为氢的替代品作为能量储存和载体的理论预测的可行性。特别地，打算在太阳能可用条件（电和热）下使用熔盐电解从它们的氧化物生产和再生硅和铁粉末。申请人及其同事已经进行了初步测试，并使用新型FFC剑桥工艺（由申请人在英国共同发明）在相对较高的温度（800摄氏度~ 900摄氏度）下成功地生产了精细的硅和铁粉末。该项目旨在降低熔盐温度（< 500摄氏度），以便在该过程中使用太阳能。将通过TG和DSC研究产物，并测试其在空气中的燃烧。最佳粉末颗粒形态及其与电解条件的相关性将被确定

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