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，可以不同的形式利用，也可以储存后再转化。碱电解法是现有技术中最成熟、工业应用最广泛的选择。到目前为止，一个尚未解决且鲜为人知的问题是产生的气体氢气和氧气与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上升到如此高的值，因此出于安全原因(爆炸极限)关闭电解槽是不可避免的。除了安全方面，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表明，污染物的主要来源是电解液中气体的溶解和电解液混合引起的向电池另一侧的输送，而不是通常假设的通过分离器的输送。在拟建项目中，应对加压碱电解过程中影响产品气质量的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、电解液浓度和体积流量，以及电解液管理策略。个别污染过程(气体饱和电解液的混合、通过分离器的扩散和对流)的作用将被定量确定。首先，所有测量应在稳态条件下进行，并随后用适当的数学模型进行描述。为此，还有必要测量目前未知的数据，如气体的溶解度。基于实验结果和模型，应制定提高效率和扩大部件载荷范围的动态策略。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，电解槽将受到典型的动态电场分布的影响，测量的性能将用合适的动态电解槽模型来描述。

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.