Alkaline water electrolysis with gas-diffusion electrodes

在本项目中，将对气体扩散电极（GDE）在新型“混合”电池结构中与经典气体演化电极结合进行碱性水电解的实验和理论研究。主要重点放在GDE用于析氧上，因为这种配置已经在以前的工作中成功地演示过。此外，GDE还应用于析氢。首先，将制备一系列以镍和铁为电催化剂的GDE，并采用物理化学方法对其进行表征，以实现GDE的组成和孔隙系统性质的广泛变化。随后，在一个特殊的电池中测试GDE，该电池可以确定GDE的过电压作为不同工艺条件下电流密度的函数（温度、电解质浓度、电解质和气体之间的压差以及分离电极组件的接触压力）。通过这种方式，可以确定结构-性能关系，并可以选择最有希望用于后续研究的电极。这些进一步测量的一个重要目标是确定新开发的电池配置的性能极限作为工艺条件和GDE特性的函数。此外，还需要收集演化氧气纯度的定量信息，以验证气体纯度主要由分离器的渗透性决定的假设，该假设明显高于传统电池中混合电解质循环的情况。此外，持续时间较长的测量将提供有关电解质和冷凝液通过GDE的交叉以及GDE稳定性的信息。在一个探索性工作包中，GDE也将用作阴极，以研究由更强的氢气演化引起的差异。与实验工作包并行，将开发一个数学模型，利用该模型可以描述电化学反应与GDE中不同传输过程之间的相互作用，并可以计算过电压作为过程条件的函数。通过这种方式，可以明确主要的损失机制，并可以开发改进GDE的基于模型的方法。

In the proposed project, an experimental and theoretical study on the use of gas-diffusion electrodes (GDE) for alkaline water electrolysis in a novel „hybrid“ cell configuration in combination with a classical gas evolving electrode shall be conducted. Main emphasis is placed on the use of the GDE for oxygen evolution, since this configuration was already successfully demonstrated in previous work. Additionally, GDE shall be also employed for hydrogen evolution. First, a series of GDE with nickel and iron as electro-catalysts will be prepared and characterized with physico-chemical methods in order to achieve a broad variation of composition and pore system properties of the GDE. Subsequently, the GDE are tested in a special cell, that allows to determine the overvoltage at the GDE as a function of current density at different process conditions (temperature, electrolyte concentration, differential pressure between electrolyte and gas as well as contact pressure of the separator electrode assembly. In this way, structure-property relationships shall be determined and the most promising electrodes for the following investigations can be selected. On important goal of these further measurements is the determination of the performance limit of the newly developed cell configuration as a function of process conditions and GDE properties. Furthermore, quantitative information on the purity of the evolving oxygen shall gathered in order to test the hypothesis that the gas purity is mainly determined by the permeability of the separator and significantly higher than in the case of mixed electrolyte cycles in a classical cell. Moreover, measurements with a longer duration will deliver information about the crossover of electrolyte and condensate through the GDE as well as about the GDE stability. In an exploratory work package, the GDE will be also used as cathode in order to investigate the differences resulting from the stronger hydrogen gas evolution. Parallel to the experimental work packages, a mathematical modell will be developed with which the interaction between electrochemical reaction and the different transport processe in the GDE can be described and the overvoltage as a function of the process conditions can be calculated. In this way can the main loss mechanisms be clarified and model-based approaches for improved GDE can be developed.