Overview of diaphragm compressors for hydrogen service: capacity, discharge pressure and operational challenges

Hydrogen is considered an important part of the solutions to reduce carbon dioxide emissions over the coming decades. As a matter of fact, it can be obtained from renewable energy and stored on large scale for long period of time, for later direct reconversion into electric energy and heat with no greenhouse gas emissions or used as energy carrier in industrial or vehicle applications. However, compared to nowadays commonly used fuels, hydrogen has the lowest volumetric energy density at atmospheric pressure, which hinders the storage phase. Thus, reliable compression techniques that are able to provide pure hydrogen at very high pressure are necessary. Among the hydrogen compression systems, especially those for operation in hydrogen refueling stations, the diaphragm compressor is a very interesting option, capable of delivering up to around 2000 Nm3/h of hydrogen in a single unit at a pressure of 100 MPa or even more. The current work aims at providing a systematic overview and discussing some operational limits that are typical of diaphragm compressors for hydrogen service. Both technical literature results and, in some cases, original considerations are reported to better understand the specific features and the operational challenges, as well as the main issues that engineers and scholars are facing to improve efficiency and reliability. Ultimately, thermodynamic calculations are reported to assess an energy performance figure based on technical data of a few commercial diaphragm compressors.