Parasitic hydrogen bubble evolution in vanadium redox flow batteries: A lattice Boltzmann study

TL;DR

The parasitic hydrogen evolution reaction in vanadium redox flow batteries creates bubbles that obstruct electrolyte transport and reduce active area. The authors employ a three-dimensional color-gradient lattice Boltzmann method, driven by μ-CT–derived carbon felt geometries, to resolve HER-driven bubble nucleation, growth, and detachment across varying reaction rates, flow rates, and compression ratios in a capillary-dominated regime. They demonstrate that increased gas production leads to uneven bubble removal, that an optimal flow rate minimizes bubbles while saving pumping energy, and that higher compression enhances conductivity but traps larger bubbles, outlining practical design trade-offs. The findings offer mechanistic insights and design guidance for VRFB electrodes and related carbon-fiber-based porous electrodes, with a framework extensible to broader electrochemical systems.

Abstract

Vanadium redox flow batteries (VRFBs) are a promising technology to capture and store energy from renewable sources, reducing the reliance on fossil fuels for energy generation. However, during the charging process, the parasitic hydrogen evolution reaction at the negative electrode affects the performance and durability of VFRBs. The evolution of hydrogen bubbles causes the loss of effective reaction area and blocks the transport of reactants. We employ the lattice Boltzmann method to investigate the two-phase flow transport in the negative electrode of VRFBs. Systematic parametric analyses reveal that increased gas production leads to uneven gas removal from the electrode, while an optimal flow rate can effectively remove bubbles and reduce external pumping energy. Additionally, increasing the compression ratio hinders gas removal but enhances electrode electrical conductivity. Overall, the present study provides valuable mechanistic insights into bubble generation at the negative electrode of VRFBs and offers a theoretical reference for designing and optimizing VRFBs.

Figures (14)

• Figure 1: An illustration of the working principle for a vanadium redox flow battery.
• Figure 2: (a) A synchrotron tomography image (the yellow box marks the selected region); (b) pore size distribution with different compression ratios; (c) 3D visualizations of different microstructures corresponding to different compression ratios.
• Figure 3: Schematic diagram of the simulation geometry.
• Figure 4: a) 3D visualization of bubble distribution in the electrolyte domain during the simulation. The color map represents the relative gas density; b) Electrolyte saturation curve plotted as a function of iteration steps for different reaction rates; c) Bubble coverage curve over time, also plotted for the same reaction rates.
• Figure 5: 3-D visualization of the spatial bubble distribution at $t = 1.57\times 10^{5} \delta t$: (a) $k_r = 1\times 10^{-6}\;\mathrm{l.u.}$; (b) $k_r = 1\times 10^{-5}\;\mathrm{l.u.}$; (c) $k_r = 1\times 10^{-4}\;\mathrm{l.u.}$.