For the future defossilization of the energy and transport sector, hydrogen as an energy storage and carrier will play a key role. Important energy conversion paths will be the formation of green hydrogen with electrolyzers (EL) and its conversion to electric energy in power plants and automotive applications with the help of fuel cells (FC). The most widespread current technologies are based on polymer electrolyte membranes exchanging membranes and operate below 100 °C. It is well known that there is a risk of thermal, chemical and mechanical material degradation if non-ideal operating conditions prevail, which has a harmful impact on the FCs or ELs performance and lifetime. Membranes, electrodes, and gas diffusion layers may undergo mechanical damages like cracks and ruptures, delamination of the active layers from the membrane and gas diffusion layer, rarefaction, agglomeration, and deactivation of active sites. Sources of these degradations are manifold. Temperatures, material humidification and electric potentials that are out of the recommended range contribute to material downgrading. Switching on and off processes and transient operation, as is common for fuel cells in the automotive sector, for example, lead to an uneven distribution of reactive species and humidification, which also has an influence on the durability and performance of the materials. Considering the manifold challenges and degradation scenarios, a wide range of numerical approaches has been applied to FCs and ELs to model the performance and material degradation, ranging from detailed 3D CFD simulation to represent to flow field accurately to 0D mathematical modelling of the different layers to allow numerical studies in real-time or faster in order to cover long physical time durations, which are usually involved if material degradation is to be analyzed. With this minisymposium, we invite researchers to present their results in the field of numerical material modelling in fuel cells and electrolyzers and to evaluate material ageing. Beside the numerical simulations, experimental results that allow model validation are welcome. Though polymer exchange membranes are currently the most widely spread technology, investigations of other chemistries like solid oxide or alkaline may be submitted and will allow a holistic discussion of this very relevant issue of the energy and mobility transformation.