UC Irvine

Nowadays, Proton Exchange Membrane Electrolysis Cells (PEMEC) have gained interest for being one of the most promising technologies for high-purity hydrogen production with zero emissions when coupled with renewable energy. Therefore, studying the factors affecting PEMEC performance is one of the most important areas of study for this technology. This work presents a component-level PEMEC model describing water exchange between electrodes, proton conductance, electrochemical reaction kinetics, two-phase oxygen-liquid water mixture in the flow channel, and two-phase transport in the porous transport layer (PTL). At the channel/PTL interface, an interfacial resistance sub-model is proposed for oxygen removal. The model investigates the cell performance under high current density considering 1.) homogeneous properties in each component, 2.) isothermal conditions, and 3.) Tafel equation to approximate electrochemical reaction kinetics. The model is implemented in MATLAB/Simulink for predicting the contribution of the different voltage losses to the polarization curve under different temperature (40℃ to 80℃), pressure (1 to 10 bar), current density (0 to 5A/cm2), and liquid saturation percentages (100% to 45%). The present model is validated against various sets of experimental data available in the literature. The obtained results show that ohmic and activation overpotential contribute to a major voltage loss representing about 27% and 19% when working at 5A/cm2, 1 atm, and 80℃. Additionally, when working at high current density, oxygen bubbles are found to occupy an areal portion as large as 55% at the PTL/Ch interface, blocking the available region for water transport to the catalyst layer and reducing the cell performance. Furthermore, high-temperature operation helps the overall voltage by decreasing it around 4% from 40℃ to 60℃ and about 8% from 60℃ to 80℃. Increase in operating pressure raises the overall voltage of the cell. However, the voltage rise is considered small compared to the effects of temperature. PEMEC modeling is a powerful tool for predicting hydrogen generation. This is especially true when considering a two-phase oxygen-liquid water mixture flow and two-phase transport while working under high current densities, which is considered the most important contribution of this work.