Multiphase Fluid Dynamics and Mass Transport Modeling in a Porous Electrode toward Hydrogen Evolution Reaction

Abstract

The intrinsic activity of hydrogen evolution reaction (HER) catalysts has been significantly improved in the past decades, and current efforts are devoted to implement these catalysts for HER applications through electrode design and fabrication. However, HER in an electrode usually involves complex processes including electrochemical reaction, ion transport, bubble behavior, and gas–liquid flow near the electrode surface. The coupling of different processes makes it difficult to accurately analyze the effect of each process on the HER performance of the electrode. In this paper, a multiphase fluid dynamics and mass transport model is proposed to decouple the HER processes and provide a deep understanding on the interactions among those processes. The results reveal a strong interaction between ion transport inside the electrode and bubble detachment/ascending outside the electrode. The surface design can effectively improve the velocity profile of the liquid and hence dominate the ion transport near the electrode, whereas the design of pore structure can remarkably enhance the ions diffusion inside the electrode. In addition, external forced electrolyte flow can further enhance the fluid convection and ion transport when the speed of forced flow is higher than that induced by bubble ascending. These results conclude that the proposed model contributes to the understanding of interactions among electrochemical reaction, ion transport, bubble behavior, and gas–liquid flow near the electrode surface, providing a guideline for HER electrode design.

Mathematical Model of Multiphysics in the Hydrogen Evolution Reaction under Near-Neutral pH Conditions

“…(4) Hydrogen was regarded as an ideal gas and incompressible. (5) Due to the distance between the bubble and the electrode, bubble ascent was not affected by the walls. 2.1.…”

“…The rapid development of the economy and society has led to extensive consumption of fossil fuels and emission of CO 2 , resulting in energy shortage and global climate change. , Developing sustainable energy conversion and storage technologies is a promising pathway to mitigate the above issues. Hydrogen as an energy carrier with a high energy density (120–140 MJ/kg) has been widely used as a fuel or indispensable raw material in industries. , At present, there are three main technologies to produce hydrogen, including steam methane reforming, coal gasification, and water electrolysis . Among them, water electrolysis is a sustainable pathway without the consumption of fossil fuels, benefiting the green vision of the hydrogen economy and powering the world via a zero-carbon approach. , With the rapid development of electricity generation from renewable energy resources (such as solar and wind power), the coupling of water electrolysis with renewable electricity has attracted broad interests from both academic and industrial communities …”

“…3,4 At present, there are three main technologies to produce hydrogen, including steam methane reforming, coal gasification, and water electrolysis. 5 Among them, water electrolysis is a sustainable pathway without the consumption of fossil fuels, benefiting the green vision of the hydrogen economy and powering the world via a zero-carbon approach. 6,7 With the rapid development of electricity generation from renewable energy resources (such as solar and wind power), the coupling of water electrolysis with renewable electricity has attracted broad interests from both academic and industrial communities.…”

Rational Design of Hydrogen Evolution Reaction Electrocatalysts for Commercial Alkaline Water Electrolysis

“…[ 57 ] Meanwhile, Bao et al demonstrated that the external bubble detachment could have a great influence on the ion transport inside the electrode by building a two‐phase mathematical model. [ 58 ] In addition, at high current densities, bubbles are generated on the electrode surface in the form of thermal evolution. This phenomenon of heat loss is called the “water anode effect”.…”

Two-Phase Flow Model to Define the Mass Transport in a Bicarbonate Electrolyzer for a CO2 Reduction Reaction

“…Momentum conservation can be described by the Navier–Stokes equations, which are expressed as α g ρ g ( ∂ u normalg ∂ t + u normalg · ∇ u normalg ) = α g ∇ [ − p + τ normalg ] + α g ρ g normalg + F normalm , normalg + F g + m dc ( u int − u normalg ) α l ρ l ( ∂ u normall ∂ t + u normall · ∇ u normall ) = α l ∇ [ − p + τ normall ] + α l ρ l normalg + F normalm , normall + F l − m dc ( u int − u normall ) where τ g (τ l ), F m,g ( F m,l ), and F g ( F l ) are the stress tensor, the interphase momentum transfer, and other volume force te...…”