Optimization of membrane-electrode assemblies for SPE water electrolysis by means of design of experiments

The key component of a solid polymer electrolyte water electrolyser is the membrane electrode assembly (MEA). The MEA basically consists of a solid polymer electrolyte (usually Nafion. or similar proton conducting membranes) coated with thin layers of catalytically active metals, generally of the platinum metal group. In this thesis, the technique design of experiments (DoE) has been applied to identify and optimize the variables that have significant influence on the performance of MEAs prepared by the hot-pressing and chemical deposition methods. An energy efficiency of about 83 % (at 0.6 A/cm², 80 °C and 1 atm.), which is localized within the range of the energy efficiencies encountered in the industrial use of water electrolysis (75 % to 90 %) was achieved using a loading of platinum (cathode) and iridium (anode) of about 2 mg/cm². The use of a mixed oxide anode catalyst for the MEAs made with the optimized manufacturing conditions resulted in an improvement of the energy efficiency of about 94 % (at 0.6 A/cm², 80 °C and 1 atm.). One MEA coated with platinum as the cathode catalyst and a mixed oxide as the anode catalyst was submitted to a long-term stability test at a current density of 1 A/cm², 80 °C and atmospheric pressure for 450 hours. After 350 hours a loss of 7 % of the initial energy efficiency was observed. No further changes were detected during the final 100 hours.