Proton exchange membrane fuel cells (PEMF) and water electrolysers (PEMwE) are expected to play significant roles in the near future in the electrification of transport, for heat and elec tricity supply in stationary applications, and as a means of large scale storage of renewable energy by using wind or solar energy to provide power for hydrogen generation by water electrolysis [1,2] Despite their advanced development, costs must be further re duced, and the durability of the components over time must still be improved 13-5]. he membrane electrode assembly (MEA) is the core component of these electrochemical energy conversion devices. The MEA comprises a proton exchange membrane, anode and cathode, as schematically represented in Fig. 1. At the core of the MEA is the polymer membrane generally functionalised with either acid or basic groups. The membrane separates the electrodes and prevents direct reaction of reactant gases and transport ions between the electrodes. It also provides mechanical integrity to the assembly Proton conductivity in elec trolyte membranes strongly depends on water content as water molecules act as proton carriers. Materials providing the best association of the above properties of conductivity, chemical sta bility and mechanical strength are perfluorosulfonic acid (PFSA) ionomers such as Nafion ru, Aquivion?, 3M Corporation ionomers The high proton conductivity of membranes is correlated with their morphology in which ionic domains are well-percolated and phase separated from hydrophobic domains that provide mechanical strength [17k The importance of the spatial organisa tion of hydrophilic and hydrophobic domains in determining the conductivity and mechanical properties of ionomer membranes well-established. This is influenced by the nature of the te polymer backbone and side chain compositions, and the spatial el organisation of functional and non-functional groups in random polymers and block copolymers In an operating fuel cell or electrolyser particular constraints or stresses arise that lead to accelerated materials ageing. For ex ample, membrane mechanical failure is accelerated by the swel ling and shrinkage that occurs during membrane hydration and dehydration that accompany operation under variable load