Multi-scale modelling on PEM-based electrolyte dehumidifier: Transient heat and mass transfer in anode catalyst layer with microstructures

Abstract

As an independent and ultra-compact method, PEM-based dehumidifiers are promising, while accurate modelling of anode-side transport is still challenging. The theoretical model developed in this study is transient, two-dimensional and non-isothermal based on the lattice Boltzmann method, emphasizing the anode-side catalyst layer (CL) with reconstructed microstructures. Then the pore-scale CL modelling was coupled with the macro-scale simulation of air channel and diffusion layer (DL), and experimentally validated by a 3.5 cm2 dehumidifier. Results showed that the CL microstructure significantly affects the air outlet parameters of PEM dehumidifiers, especially in the beginning state. Although the uniform distribution of vapor concentration can be achieved immediately in CL, the time required for the air outlet to reach transient equilibrium is much longer, which is around 1000s for the moisture content and 7000s for the temperature. The moisture transfer resistance at the beginning state mainly exists in CL, then it moves to both CL and DL (close to the interface) when it reaches equilibrium. Due to the continuous heat generation, the temperature flux in CL dominates in the anode side, and increases by 5-6 times during dehumidification. The calculated values of effective mass diffusivity and thermal conductivity of CL are 7.71×10−6 m2/s and 0.063 W/m•K. The randomly arranged catalyst particles makes CL the hottest (2~3°C higher) and driest (half the DL concentration) part of PEM element, which severely limits the whole performance. This modelling reveals the interaction between anode-side CL with microstructures and the performance, considering the transient heat and mass transfer.