Investigation of the Influence of Selected Factors of the Electrode Structure on the Requirements to the Quality of the Water Feed of Anion Exchange Membrane Water Electrolysis Cells

Over the past decades climate change has risen to prominence as one of the main challenges facing humanity. The increasing warming of the earth, caused by man-made emission of greenhouse gases (GHG), mostly carbon dioxide and methane, is already starting to show its drastic impacts on earth’s ecosphere. A recent investigation by renowned climate analysis website CarbonBrief where data sets from multiple sources such as the IPCC, NASA and many more were analyzed found that 2024 will be the first year where 1.5 ◦C of warming compared to pre-industrial times are overstepped The most important mitigation measure is the transformation of the global energy system from GHG-emitting fossil fuels to carbon-neutral renewable energy resources, such as wind, solar, hydropower and geothermal [2, 3]. This transformation comes with numerous challenges. Overall, renewable resources need to be deployed at a much faster rate. Sectors which traditionally relied on the combustion of fossil fuels, such as transportation, industrial process heat and space heating of buildings, have to be electrified [3]. It follows that conventional, rankine cycle based power plants running on fossil fuels also need to be replaced by renewables to make the electrification effort worthwhile. This will increase the stress on the electrical system twofold. First, the capacity of transmission systems will have to be increased by a large margin to tackle the rising electricity consumption. Second, the inherent intermittency of wind and solar comes with a whole new set of challenges in regards to load balancing and grid stability [4]. A possible solution to this is the deployment of energy storage systems [5]. With their help, electricity surplus from time periods with high productivity of renewable resources can be stored for later use. While batteries seem promising for short- and medium term storage, green hydrogen produced by water electrolysis is seen as a strong candidate for long-term and seasonal storage [6]. The stored hydrogen can be used to shave demand peaks by turning it back into electricity via fuel cells or combustion in turbine chambers. Furthermore, hydrogen could be used for transportation in fuel cell vehicles [7] or to decarbonize space heating [8], which both would reduce the stress on the electrical grid. Another interesting use case is the decarbonization of hard-to-decarbonize sectors. An example would be the steel industry, where hydrogen can be used for direct reduction of iron ore. The burning of coke could be omitted as carbon monoxide is no longer used as a reducing agent. This would have a great impact as the steel industry alone is responsible for roughly 7 % of global GHG emissions [9]. Fossil hydrogen produced via steam reforming is frequently used as a feedstock in the chemical industry, for example in fertilizer or methanol production [10, 11]. The production of this so-called gray hydrogen emits GHGs. Thus, replacing the fossil hydrogen with green hydrogen is key to reduce the emissions of the chemical sector. Methanol made from green hydrogen is also a promising marine fuel [12]. As can be seen, hydrogen is a major component for the decarbonization of the energy system, transportation and the heavy industries. Largely as a result of this multiple technologies for water electrolysis are currently being deployed or developed. Recently, anion exchange membrane water electrolysis (AEMEL) has risen in interest, as it is a promising technology which combines some of the advantages of other methods [13, 14, 15]. The electrochemical reactions take place in an alkaline environment, which enables the use of cheaper catalysts that are not made from platinum-group metals (PGMs), for example Ni-based materials [16]. This results in a significant reduction of CAPEX for AEMEL in comparison to proton exchange membrane water electrolysis (PEMEL). Compared to conventional alkaline electrolysis (AEL) a supporting electrolyte of much lower alkalinity is required [15], which greatly reduces safety concerns. Also they might be more resilient towards lower feed water quality [17], which in turn would greatly reduce OPEX from water purification and make the technology more accessible in remote regions.The goal of this thesis is to carry out investigations into multiple properties of AEM electrolysis cells. First, the influence of the ionomer content and the solvent properties on the performance of the cells is examined. For this, multiple samples with varying ionomer contents and with varying ink solvents are fabricated. This is first done for cells consisting of Pt/C cathodes and IrO2 anodes. This PGM system is used as a benchmark against which Ni-based electrodes are then compared. The Ni-based electrodes will also be examined regarding the influence of the ionomer content and the solvent. The best combinations of ionomer content and solvent will then be used to test the effects of varying feed water qualities on the electrolyzer performance and the reversibility of said effects. Hopefully, this will serve as a good starting point for further research on this promising technology.