Experimental study on degradation of low temperature PEM electrolyzers and iR compensation

The dramatic events related to climate change continue to highlight the importance of achieving the decarbonization targets set at the COP21 conference in Paris, supported by various policies, such as the European Green Deal. In the years of recovery from the COVID-19 pandemic, the huge energy crisis triggered by Russia's invasion of Ukraine has put all previously assumed energy scenarios to the test. Technologies based on renewable energy sources are key to achieving the goals of decarbonization scenarios, and among these, green hydrogen is considered one of the most promising energy carriers. However, its production by electrolysis of water needs to be studied in more detail. In addition, analyses and experiments with electrolyzers are needed to bring the performance and competitiveness of this technology to the level of other processes for producing hydrogen from fossil fuels. One of the main challenges to overcome in electrolysis processes is cost efficiency compared to conventional hydrogen production processes based on environmentally harmful raw materials such as methane or coal. The present work aims to investigate the degradation effects on a single-cell proton exchange membrane water electrolyzer caused by the dynamic behavior of the operating parameters with a specific focus on the iR compensation. iR compensation is studied to examine the various methods that have been used to identify and separate the contributions of components of the cell to resistance. After analyzing the literature, which made it possible to determine the causes and effects of the degradation of the electrolytic cell and the different test conditions, an experimental campaign was carried out with two different cells, an already aged and degraded cell and a new cell, where new membrane, gas diffusion layers and sealings were assembled in-situ. Electrochemical characterization was performed for both cells by recording polarization curves. The new MEA was subsequently subjected to a degradation test, the protocol of which was specifically designed. All the instruments used in the test bench were catalogued in detail with their specifications such as measuring range and level of accuracy. The polarization data for both MEAs were then corrected with numerical methods to perform iR compensation accounting for the resistance of the hardware of the cell. Data fitting, empirical formulae and comparing the polarization curves of the new and old cell were the tools used to estimate all the resistances required to perform the iR compensation correctly. This can be a useful method, also for future work, to correct polarization data by taking into account the resistance contribution of the cell hardware without the need for a dedicated measurement procedure.