Increased Efficiency of PEM Water Electrolyzers through Operating Temperature and Pressure Optimization

Abstract

Green hydrogen enables the reduction of greenhouse gas emissions as it can replace fossil fuels in various areas of application. Given today's high demand for fossil fuels, there are challenges in producing cost-competitive green hydrogen. A vast amount of renewable electricity must be generated and converted into hydrogen, which requires much space and rare materials. Therefore, it is reasonable to improve the efficiency of the energy converters involved. Although the efficiency levels can be increased through components development, the optimization of the operating conditions is another innovative way to improve (commercially) available electrolyzer systems. In this talk, a model is introduced that comprises the description of electrolyzers from electrodes to the product-gas processing. Overpotential at stack level, the heat balance of the whole system, and the compression of the product gases are taken into account with regard to their impact on the overall system efficiency. Our analysis results are crucial in terms of defining the optimal operating temperature and pressure, as both parameters are no constants but highly depend on the operating conditions and the system configuration.By comparing systems that use different membrane thicknesses for instance, it can be seen that the efficiency and optimal pressure decrease with increasing thickness, while interestingly no safety problems due to hydrogen permeation across thin membranes.1 On the other hand, the results indicate that the notion of ‘the higher the temperature the higher the efficiency’ has no general validity. Fortunately, the model reveals that an analytical solution exists to calculate the optimal operating temperature in special cases.2 Moreover, this solution is independent of the system configuration and only depends on the operating point and pressure. In summary, novel ideas for the configuration and operation of electrolyzers are presented in this talk in order to obtain the highest possible efficiency from existing materials and components. Heavily depending on the operating conditions and cell voltage, the advantage can be up to 10% compared to the current operating strategy. Scheepers, F.; Stähler, M.; Stähler, A.; Rauls, E.; Muller, M.; Carmo, M.; Lehnert, W., Improving the Efficiency of PEM Electrolyzers through Membrane-Specific Pressure Optimization. Energies 2020, 13 (3).Scheepers, F.; Stähler, M.; Stähler, A.; Rauls, E.; Müller, M.; Carmo, M.; Lehnert, W., Temperature optimization for improving polymer electrolyte membrane-water electrolysis system efficiency. Applied Energy 2020, 116270.