In a vanadium redox flow battery (VRFB), a membrane is a key part affecting the cost and the performance of a VRFB. Here, we have shown geometry-induced asymmetric vanadium permeation through hydrophobic asymmetric ultrafiltration polyvinylidene fluoride (PVDF) membranes. The asymmetric PVDF membranes were prepared via non-solvent induced phase separation (NIPS) protocol at various coagulation bath temperature from 30 - 70 °C. In all temperatures, under a thin skin layer, a finger-like, and a sponge-like morphologies were formed at near the top, and the bottom, respectively. Vanadium permeability was significantly affected by the direction, where a membrane faces the vanadium solution, while proton conductivity was identical regardless the direction. when the bottom surface was exposed to the vanadium solution, the membranes showed higher selectivity of proton to VO²⁺. In a single cell test, VRFBs were also performed better, when the bottom surface was on the catholyte side.