Computational Modeling of Proton Exchange Membrane Electrolyzer

Abstract

Listen

Translate article

Hydrogen holds great promise to help decarbonize our energy sector. Proton exchange membrane electrolyzers (PEMELs) are undergoing rapid development and deployment for the generation of green hydrogen based on renewable sources of electricity. The inherent capacity of PEMELs to readily respond to fluctuations in electricity input is an added advantage for the generation of hydrogen. PEMEL optimization with regard to materials, component design, and operating conditions is critical for high performance and efficiency. The development of a robust computational model for PEMELs can facilitate not only an improved understanding of the relevant physical and electrochemical phenomena but also help to develop and test effective strategies for performance optimization. The current research is aimed at developing a 3D parallel flowfield channel PEMEL model in COMSOL Multiphysics. To date, results have been obtained for a single-phase model with the baseline operating temperature and relative humidity (RH) of 60°C and 90%, respectively, under the following assumptions: (1) the feed gas (water vapor) is treated as an ideal gas, (2) the flow in the channel is laminar and incompressible, (3) membrane, catalyst layer (CL), and porous transport layer (PTL) microstructures are assumed to be homogeneous and isotropic, and (4) all physical and electrochemical processes are considered to be at steady state. The simulated polarization curve was validated against in-house experimental data for Nafion 115 at 60°C. We then investigated the effect of operating temperature and membrane thickness on current density, overpotentials due to cell resistance, and polarization curves. It was observed that the PEMEL performance improved significantly with temperature, owing primarily to the higher protonic conductivity of the membrane and improved catalyst kinetics. Polarization curves were also obtained for Nafion 212 (50.4 µm) and 117 (178 µm) at 80°C and the thinnest membrane, i.e. Nafion 212, performed better than its thicker counterparts due to reduced ohmic losses. We are currently developing a two-phase flow PEMEL model wherein liquid water is supplied to the anode inlet, and oxygen gas mixed with liquid water emerges from the anode exit. At high current density, oxygen bubbles can obstruct the reactant flow to the anode catalyst layer resulting in suboptimal PEMEL performance. Results will be presented for the dynamics of two-phase flow in a PEMEL system under various operating conditions from which we may draw insights to optimize PEMEL performance.