Performance and Design Limits of Membraneless Flow Electrochemical Cells: A Combined Secondary Current and Multiphase Flow Analysis

The membraneless electrolyzer concept has recently gained significant attention as an alternative electrolyzer design which is potentially more durable, flexible, and inexpensive due to the absence of any fragile membrane or diaphragm. While different conceptual designs have been put forward so far, the literature lacks clear quantitative insights on key design and performance parameters. This work presents a comprehensive analysis of the membraneless design encompassing all the primary design concepts i.e. flow-by and flow-through. The study combines experimentally validated Euler-Euler coupled secondary current distribution model, Euler-Lagrange models, and an analytical mass balance model. First, the self-similarity in the parametric Euler-Euler analysis is exploited to formulate a dimensionless correlation by Buckingham Pi analysis for the average gas fraction in H2 and O2 gas plumes (99%). This correlation is complimentary to the analytical bubble mass balance equation presented here that enables simplified estimation of gas plume contours as well as maximum flow-by electrode height, inline with experimental observations. The same dimensional analysis also yields a correlation for plume contours across different operating conditions. For an operating current density of 0.2 A cm-2, Reynolds number of 1600 and 1000, and interelectrode spacing from 1 mm to 6 mm, the maximum flow-by electrode length has been estimated. It is shown with a strong enough flow i.e. Re>1000, the bulk bubble ohmic resistance can be neglected. The self-similarity of the polarization curves for the flow-through membraneless electrolyzer was also established via a Buckingham Pi dimensional analysis. Finally, the analysis draws an unbiased global comparison to assess the performance limits of membraneless electrolyzer designs quantitatively alongside the conventional alkaline electrolyzer.