Coupled mechanical and electrochemical modeling and simulations for electrochemical hydrogen compressors (EHC)

A three-dimensional (3-D) model of an electrochemical hydrogen compressor (EHC) cell was developed by rigorously accounting for the hydrogen oxidation and evolution reactions and resulting species and charge transport through various EHC components. Particular emphasis was placed on coupling computational fluid dynamics (CFD) and finite element method (FEM) methodology to predict EHC performance numerically under the deformed cell geometries, i.e., induced by the cell assembly and the hydrogen pressure difference between the anode and cathode sides. First, the EHC model was validated experimentally against polarization curves and impedance spectra measured under different hydrogen compression ratios and operating temperatures. In general, the simulation results compared well with the measured data and further revealed the operating characteristics of the EHC cells. In particular, the most irreversible voltage rise comes from the ohmic overpotential because of the proton transport through the membrane, clearly indicating dehydration of the electrolyte due mainly to the electro-osmotic drag effect is one of the most critical issues for efficient EHC operations. While the dehydration issue tends to be mitigated under higher hydrogen discharge pressure or higher operating temperatures, the cell deformation toward the low-pressure side (anode) is visible even with the low hydrogen compression ratio of 10, clearly requiring improvement in the mechanical properties of EHC components and cell structure for a higher compression of hydrogen gas.