High-Pressure Polymer Electrolyte Membrane Water Electrolyzers: Is It Worth It?

Abstract

As a future fuel hydrogen should be stored at elevated pressure because of its low volumetric energy density. For transport in pipelines, a suitable pressure is about 200 bar. There are different paths conceivable to achieve this storage pressure. As an alternative to the conventional way of compressing the gas in external compressors subsequently, it is frequently discussed to operate electrolyzers at elevated pressure, which can save costly compressor stages. High Faraday efficiencies will be achieved by using improved materials with low permeation rates or thick membranes. However, thick membranes worsen the system performance since the decreased protonic conductivity of the cells ultimately reduces the amount of hydrogen produced. Therefore, it is recommendable to take a closer look at this context and to evaluate an optimized pressure operation depending on the application and cell parameters. In a comprehensive analytical model approach we discuss how voltage efficiency, Faraday efficiency and energy required for external gas compression are affected by a various number of system parameters. We demonstrate that the optimum gas pressure in electrolyzers is not only a function of the membrane thickness but strongly depends on the entire system configuration. To answer the question of whether high-pressure polymer electrolyte membrane electrolyzers are worthwhile both energetically and economically, our model was fed with a typical parameter set for systems based on Nafion 212 and Nafion 117. Our results demonstrate impressively why the use of thin membranes and their future development are a must for the meaningful use of PEM water electrolysis in a future energy grid.