Physical modeling of two-phase flow in porous gas-evolving electrodes

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ZincNyx Energy Solutions (ZES) is developing a range of industrial-scale regenerative alkaline zinc-air fuel cells for stationary power applications. Demonstrated positive attributes of this electrochemical energy storage technology include high thermodynamic efficiency, scalability, high level of security during operation, ease-of-manufacture, and low cost. During the regeneration cycle (charging), zinc is electroplated at one electrode while oxygen gas is generated at the counter-electrode. In order to ensure efficient zinc growth, the expulsion of oxygen from the regeneration unit requires a highly efficient oxygen flow through a three-phase system. Insufficient oxygen expulsion would lead to deactivation of the electrode-solution interface by oxygen bubbles. Major efforts in materials development and system-level engineering of regenerative alkaline zinc-air fuel cells thus focus on the fabrication and integration of porous electrodes for the oxygen evolution anode. Current approaches in electrode design rest upon a trial-and-error approach, i.e., building physical prototypes and observing performance at the device level. This development approach is expensive and time consuming and it is unlikely to lead to optimal outcomes. Through this project, ZES is pursuing a systematic design strategy based on physical modeling. The aim of the proposed Engage Plus project is to develop a detailed understanding of gas formation and transport in porous electrodes. For this purpose, we will incorporate a model of bubble formation into the existing porous electrode model. The integrated model will be used to predict the set of structural parameters that optimizes bubble transport and maximizes the electrochemical performance of the regenerator system. Design recommendations will be developed, which will be tested against experimental data provided by ZyncNyx. An additional benefit is expected to be the transfer of modelling expertise from SFU to ZES in the field of gas-liquid transport phenomena.