Experimental and theoretical investigation of gas purity in pressurized alkaline water electrolysis

水电解是将可再生电能转化为化学能的关键技术，化学能可以以不同的形式使用或储存后再转化。碱性电解是现有技术中最成熟和工业上最广泛的选择。迄今为止尚未解决和很少理解的问题是所产生的气体氢气和氧气被各自的外来气体污染。特别是在部分负荷运行时，外来气体的浓度可能会升高到如此高的值，以至于出于安全原因（爆炸极限）而关闭电解槽变得不可避免。除了安全方面之外，这种污染还降低了电解过程的效率。在大气压下的初步工作中，可以表明污染物的主要来源是气体在电解质中的溶解和由电解质混合引起的向电池的另一侧的输送，而不是通常假设的通过隔板的输送。本项目拟对加压碱性电解过程中产品气质量的影响因素进行系统的实验和理论研究。为此，应考虑所有相关参数，如电流密度、压力、温度、电解质浓度和体积流速以及电解质管理策略。将定量确定各个污染过程（气体饱和电解液流的混合、通过分离器的扩散和对流）的作用。首先，所有测量应在稳态条件下进行，随后用适当的数学模型进行描述。为此，还需要测量当前未知的数据，例如气体溶解度。基于实验结果和建模，应开发用于效率改进和部分负载范围扩展的动态策略。这些措施的有效性将首先在恒定电流密度下进行测试。最后，电解池将经受典型的动态电力曲线，并且将用合适的动态电解器模型描述测量的性能。

Water electrolysis is a key technology for the transformation of renewable electrical energy into chemical energy, which can be used in different forms or reconverted after storage. Alkaline electrolysis is the most mature and industrially most widespread option among the available technologies. A hitherto unresolved and little understood problem is the contamination of the produces gases hydrogen and oxygen with the respective foreign gas. Especially in part-load operation, the concentrations of the foreign gases can rise to such high values that shutdown of the electrolyzer for safety reasons (explosion limits) becomes inevitable. Besides the safety aspect, this contamination also decreases the efficiency of the electrolysis process. I preliminary work at atmospheric pressure, it could be shown that the main source of the contaminations is the dissolution of the gases in the electrolyte and the transport to the other side of the cell caused by electrolyte mixing, and not the transport through the separator as usually assumed. In the proposed project, a systematic experimental and theoretical study regarding the influencing factors on the quality of the product gases during pressurized alkaline electrolysis shall be conducted. For this purpose all relevant parameters such as current density, pressure, temperature, electrolyte concentration and volume flow rate, as well as electrolyte management strategies shall be taken into account. The role of the individual contamination processes (mixing of gas-saturated electrolyte streams, diffusion and convection through separator) will be quantitatively determined. Firstly, all measurements shall be carried out under steady-state conditions and subsequently described with an adequate mathematical model. For this purpose, it is also necessary to measure currently unknown data such as gas solubilities. Based on the experimental findings and modeling, dynamic strategies for efficiency improvement and extension of the part load range shall be developed. The effectiveness of these measures will be firstly tested under constant current density. Finally, the electrolysis cell will be subjected to typical dynamic electricity profiles and the measured performance will be described with a suitable dynamic electrolyzer model.