Serpentine flow field with changing rib width for enhancing electrolyte penetration uniformity in redox flow batteries

•Serpentine flow field leads to nonuniformity of electrolyte penetration.•Under-the-rib hydraulic resistance is adjusted along the flow passages.•Mass transfer uniformities in-plane and through-plane directions are enhanced.•Limiting current density and energy efficiency are both improved.•Impacts on the penetration uniformity are more significant in large flow cells.