Modelling of H2 production through low temperature electrolysis: A Multiphysics Approach

Greenhouse gas emissions can be limited through different sustainable solutions without impacting the global energy production. Nowadays the most suitable solution is represented by the insertion of Renewable Energy Sources (RES) and efficient storage systems in the energetic supply chain. In this context, hydrogen represents an interesting way to secure an economic and efficient energy supply in times of energy transition. Several routes can be experienced in the "hydrogen production paths", one of the most interesting is linked to Green Hydrogen since it comes from the coupling between electricity production from RES and electrolysis processes. Dealing with the topics above mentioned PEM water electrolysis is the most promising technique for high-pure efficient hydrogen production exploiting renewable energy sources. In this type of electrolyzer, water is split into H2 and O2 thanks to electrochemical reactions driven by electricity and to the ability of the Proton Exchange Membrane (PEM) to conduct H+ ions. The focus of this thesis work is to investigate hydrogen production through two parallel approaches, a simulation one and an experimental one. Thus, the core of this work will concern both the development of multiphysics multidimensional models of a PEM electrolyzer, but also the setting and testing of different PEM cells to extract the characteristic experimental curves. The first is necessary to simulate the different physics involved, while the second is needed to further compare the results. The experimental section of this thesis work was not only related to the extraction of the characteristic polarization curves, but also to pre-testing procedures that were carried out on the test bench to avoid the arise of additional overvoltages and to reduce the oscillations in the curves and in the assembly of the electrolyzer. Thus, the characteristic curves were extracted at different operating conditions to catch the change in slope and shape due to the variation of the main thermodynamic parameters and to validate the models. Different models were developed in COMSOL Multiphysics® environment to simulate the behaviour of the main thermodynamic parameters. In particular, a 2-D Single Phase Multiphysics Model a 2-D Multi-Phase Multiphysics Model were developed and fitted on experimental curves. A 3-D Single Phase Multiphysics Model was also developed to simulate the phenomena involved in the system even if for this case a partial implementation was carried out. The main fitting parameters used in the procedure were further compared to understand both the differences related to the different physics used to model the same phenomenon. In conclusion, the models that have been derived in this work, can be used as a tool to optimize the performances of PEM electrolyzers. Moreover, this work can also be used to further understand multi-phase transport in the splitting reaction compartment, but also to optimize the operation of PEM electrolyzers. Regarding future works linked to model development, this thesis lays the foundation for the PEM 3-D Multiphysics modelling both with a single and a multi-phase approach. On the other hand, regarding future works linked to test bench improvements, this works wants to focus the attention both towards a further automatized rig, improving the refilling system, and towards a deeper outlet gaseous mixtures analysis, for example with the permanent coupling between the rig and mass spectrometers.