A concept for high efficiency operation of a proton exchange membrane electrolyzer

We present fundamental calculations to identify operating conditions of a proton exchange membrane electrolyzer such that the product gases are exactly saturated with water vapor. The required stoichiometric flow ratios depend strongly on the electrolyzer temperature and reactant pressures, and they are below ξ = 3 which necessitates a symmetric electrolyzer design and uniform water feeding. Preheating the incoming water leads to a voltage gain in the order of 50 mV, and it is shown, how the electrolyzer temperature can conceivably be controlled via the water flow rate. The analysis results in diagrams to determine suitable operating conditions for three different electrolyzer operation modes: standby operation to reduce the startup time, normal operation and high-power operation with efficiencies of 96%, 91%, and 86%, respectively. A comparison with literature data gives indications about the expected current densities at the respective voltages. Finally, it is suggested that electrolyzer operation where the anode side pressure is at a partial vacuum can facilitate the proposed operation mode as well as reduce the iridium loading. • PEM Electrolyzer thermodynamic analysis. • High efficiency operation points have been identified. • Electrolyzer includes integrated heat exchanger for phase change. • Novel thermodynamic diagrams have been constructed.