Theoretical analysis of the effect of boiling on the electrolysis voltage of a polymer electrolyte membrane water electrolyzer (PEMWE)

Abstract

Water boiling in a polymer electrolyte membrane water electrolyzer (PEMWE) has been experimentally demonstrated to reduce the electrolysis voltage [Ito K et al. ECS Transactions. 2017; 80(8):1117]. The boiling phenomenon and formation mechanism are studied comprehensively by introducing boiling into a PEMWE model. The gas saturation at the channel/porous transfer layer (PTL) is first determined as the boundary condition for the gas transfer in the PTL. Then, the gas transfer equation can be used to determine the oxygen and hydrogen pressures at the catalyst layer (CL). The dissolved oxygen and hydrogen activities are considered in the activation overvoltages through a variable (activation fraction). Finally, the Nernst loss, activation, and ohmic overvoltage of the PEMWE over a wide temperature range (encompassing non-boiling, boiling, and gas-phase-only conditions) are determined from the oxygen and hydrogen pressures and gas saturation at the CL. The results show that the PEMWE under boiling conditions has the lowest electrolysis voltage among the non-boiling, boiling, and gas-phase conditions. Boiling can accelerate the detachment of gas bubbles composed of gaseous oxygen and water vapor in the channel (CH). Furthermore, vigorous boiling significantly reduces the Nernst loss by reducing the oxygen and hydrogen partial pressures at the CL.