Abstract
Electrochemically gas-evolving systems are utilized in alkaline water electrolysis, hydrogen production, and many other applications. To design and optimize these systems, high-fidelity models must account for electron-transfer, chemical reactions, thermodynamics, electrode porosity, and hydrodynamics as well as the interconnectedness of these phenomena. Further complicating these models is the production and presence of bubbles. Bubble nucleation naturally occurs due to the chemical reactions and impacts the reaction rate. Modeling bubble growth requires an accurate accounting of interfacial mass transfer. When the bubble becomes large, detachment occurs and the system is modeled as a two-phase flow where the bubbles can then impact material transport in the bulk. In this paper, we review the governing mathematical models of the physicochemical life cycle of a bubble in an electrolytic medium from a multiscale, multiphysics viewpoint. For each phase of the bubble life cycle, the prevailing mathematical formulations are reviewed and compared with particular attention paid to physicochemical processes and the impact the bubble. Through the review of a broad range of models, we provide a compilation of the current state of bubble modeling in electrochemically gas-evolving systems.
Highlights
Gas-evolving systems are utilized in alkaline water electrolysis, hydrogen production, and many other applications
Due to the continuous production of these gases by the chemical reactions, the electrolytic medium becomes supersaturated and gas bubbles start forming at the electrode surface.[5]
Despite the importance of electrochemical gas-evolving systems and their frequent applications, further development and incorporation of several underlying physicochemical phenomena, such as bubble nucleation, electrical field and Marangoni stress effects on the bubble, and liquidbubble momentum and mass exchanges, are required to accurately model the bubbles in the electrolyte.[6,7,8,9]. While all of these effects have been studied in isolation, their interactions and importance to other scales demands a multiscale, multi-physics framework to enable a comprehensive description of electrochemically gas-evolving system
Summary
Multiscale modeling aims to analytically or numerically link different physical models that span different degrees of simplifying assumptions and resolution to investigate a system. Passing the unknown parameters between the single physical models requires a reliable strategy to fit and transfer these parameters.[38] Parameter passing requires the implementation of phenomenological theories to derive the key parameters of the large-scale models from the smaller models These derivations are based on simplifications and local approximations that limits this technique to only a few key parameters.[36] the computational cost of fitting the full constitutive relations (parameters) is too expensive to gather highly accurate information from the smaller scales to the larger scale models, so power law relationships are often used where coefficients are determined from the smaller scale models. The bubble models we present are applicable to both the sequential and concurrent approaches
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