Alkaline water electrolysis is a key technology for large-scale hydrogen production powered by renewable energy. As conventional electrolyzers are designed for operation at fixed process conditions, the implementation of fluctuating and highly intermittent renewable energy is challenging. This contribution shows the recent state of system descriptions for alkaline water electrolysis and renewable energies, such as solar and wind power. Each component of a hydrogen energy system needs to be optimized to increase the operation time and system efficiency. Only in this way can hydrogen produced by electrolysis processes be competitive with the conventional path based on fossil energy sources. Conventional alkaline water electrolyzers show a limited part-load range due to an increased gas impurity at low power availability. As explosive mixtures of hydrogen and oxygen must be prevented, a safety shutdown is performed when reaching specific gas contamination. Furthermore, the cell voltage should be optimized to maintain a high efficiency. While photovoltaic panels can be directly coupled to alkaline water electrolyzers, wind turbines require suitable converters with additional losses. By combining alkaline water electrolysis with hydrogen storage tanks and fuel cells, power grid stabilization can be performed. As a consequence, the conventional spinning reserve can be reduced, which additionally lowers the carbon dioxide emissions.

The separator is a critical component for the performance of alkaline water electrolysis as it ensures the ionic contact between the electrodes and prevents the product gases from mixing. While the ionic conductivity of the separator affects the cell voltage, the permeability of the dissolved product gases influences the product gas impurity. Currently, diaphragms are used as separators, the pore system of which is filled with the electrolyte solution to enable the exchange of ions. The breakthrough of the gas phase can be prevented up to a specific differential pressure. A drawback of diaphragms is the requirement of a highly concentrated electrolyte solution to maintain a high ionic conductivity. The usage of anion-exchange membranes could solve this problem. However, the long-term stability of such materials remains unproven. This study compares two pre-commercial diaphragms, an anion-exchange membrane, and an ion-solvating membrane with the state-of-the-art diaphragm Zirfon^TM Perl UTP 500. Besides physical characterization, the material samples were evaluated electrochemically to determine the ohmic resistance and the product gas impurities. The results show that the thinner diaphragm outperforms the reference material and that polymer membranes can compete with the performance of the reference material.

Alkaline water electrolysis is a key technology for large-scale hydrogen production. In this process, safety and efficiency are among the most essential requirements. Hence, optimization strategies must consider both aspects. While experimental optimization studies are the most accurate solution, model-based approaches are more cost and time-efficient. However, validated process models are needed, which consider all important influences and effects of complete alkaline water electrolysis systems. This study presents a dynamic process model for a pressurized alkaline water electrolyzer, consisting of four submodels to describe the system behavior regarding gas contamination, electrolyte concentration, cell potential, and temperature. Experimental data from a lab-scale alkaline water electrolysis system was used to validate the model, which could then be used to analyze and optimize pressurized alkaline water electrolysis. While steady-state and dynamic solutions were analyzed for typical operating conditions to determine the influence of the process variables, a dynamic optimization study was carried out to optimize an electrolyte flow mode switching pattern. Moreover, the simulation results could help to understand the impact of each process variable and to develop intelligent concepts for process optimization.

Alkaline water electrolysis is a well-known technology for sustainable hydrogen production powered by renewable energy. The use of gas diffusion electrodes (GDEs) based on nonprecious materials eliminates the need for an anolyte cycle, leading to a cost reduction of the electrolysis process. In this work, the production of GDEs made of nickel particles and different iron precursors is investigated for the improvement of the oxygen evolution reaction. The GDE production followed an established four-step process: dispersing, spraying, hot pressing, and sintering. Physical characterization comprised the determination of the pore size distribution by capillary flow porometry and mercury porosimetry, as well as BET surface area measurements. Electrochemical characterization through linear sweep voltammetry and EIS measurements was performed in a custom half cell. The results show that the overall performance of the GDE based on low-cost iron compounds was comparable to existing GDE formulations, while improvements could be achieved regarding the overpotential in the kinetic region. Nevertheless, future investigations concerning the gas purity and long-term stability of the GDEs will be the next steps of the electrode development.