No abstract

Hydrogen can be generated by means of PEM water electrolysis that makes use of renewably-produced electricity. To improve and maintain good performance of PEM electrolysis cells and stacks, research has been carried out mostly in the field of operation conditions, catalyst loading reduction and substitution of precious metals, two-phase flow investigation and analysing degradation effects. However, understanding mechanical interactions in the cell can additionally help to improve performance and lower investment costs [1]. In the electrolysis cell, the components are clamped against each other to ensure a good electrical contact. Excessive clamping pressure, however, leads to damage of the components. Studies on PEM fuel cells found that high clamping pressures reduces GDL porosity and leads to mass transport limitation [2]. In this work the influence of clamping pressure on the performance of different PEM electrolysis cell designs has been studied. Therefore, a test cell was designed that allows applying pressure directly on the active cell area. Polarisation curves and ohmic resistances were measured at different clamping pressures. Electrochemical impedance spectroscopy (EIS) was used to show the effect of compression on ohmic losses and mass transfer limitations. Furthermore, the pressure change within the cell over time was investigated. For all cell designs, optimal clamping pressure was found to be approximately 2.3 – 3 MPa. The impedance data show no higher mass transfer losses for higher pressures on the active area. However, the ohmic losses rise above a critical pressure. The results indicate that for PEM electrolysis, not mass transport limitations but protonic ohmic losses are crucial for a worse performance at high clamping pressures. Also it was found that stress relaxation of the membrane lead to pressure loss and thus to a worse performance over time. Borgardt, E., et al., Mechanical characterization and durability of sintered porous transport layers for polymer electrolyte membrane electrolysis. Journal of Power Sources, 2018. 374: p. 84-91. Mason, T.J., et al., A study of the effect of compression on the performance of polymer electrolyte fuel cells using electrochemical impedance spectroscopy and dimensional change analysis. International Journal of Hydrogen Energy, 2013. 38(18): p. 7414-7422.