T. H. Vu | Searcharxiv

arXiv2025

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

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.

physics.flu-dyn↗

arXiv2021

$f$-electron hybridised metallic Fermi surface in magnetic field-induced metallic YbB$_{12}$

The nature of the Fermi surface observed in the recently discovered family of unconventional insulators starting with SmB$_6$ and subsequently YbB$_{12}$ is a subject of intense inquiry. Here we shed light on this question by comparing quantum oscillations between the high magnetic field-induced metallic regime in YbB$_{12}$ and the unconventional insulating regime. In the field-induced metallic regime beyond 47 T, we find prominent quantum oscillations in the contactless resistivity characterised by multiple frequencies up to at least 3000 T and heavy effective masses up to at least 17 $m_\text{e}$, characteristic of an $f$-electron hybridised metallic Fermi surface. The growth of quantum oscillation amplitude at low temperatures in electrical transport and magnetic torque in insulating YbB$_{12}$ is closely similar to the Lifshitz-Kosevich low temperature growth of quantum oscillation amplitude in field-induced metallic YbB$_{12}$, pointing to an origin of quantum oscillations in insulating YbB$_{12}$ from in-gap neutral low energy excitations. The field-induced metallic regime of YbB$_{12}$ is characterised by more Fermi surface sheets of heavy quasiparticle effective mass that emerge in addition to the heavy Fermi surface sheets yielding multiple quantum oscillation frequencies below 1000 T observed in both insulating and metallic regimes. We thus observe a heavy multi-component Fermi surface in which $f$-electron hybridisation persists from the unconventional insulating to the field-induced metallic regime of YbB$_{12}$, which is in distinct contrast to the unhybridised conduction electron Fermi surface observed in the case of the unconventional insulator SmB$_6$. Our findings require a different theoretical model of neutral in-gap low energy excitations in which the $f$-electron hybridisation is retained in the case of the unconventional insulator YbB$_{12}$.

cond-mat.str-el↗