Polymeric membranes offer economic separation processes but are less explored for H2 separation application. This work aims to unveil the H2 separation potential of polymeric membrane by developing PVA-based reverse selective composite membrane. CO2-selective PEBAX was blended at different PVA:PEBAX ratio. The effect of PEBAX blending on membrane morphology, crystallinity and gas separation behavior was studied. Incorporation of PEBAX at <50 wt% resulted in composite with improved CO2 permeability but selectivity loss. Blending of >60 wt% PEBAX enhanced both permeance and selectivity of the resulted composite as the host matrix was dominated by this PEO containing material thus greatly enhancing polymer chain mobility and promoting CO2-solubility. The best composite which contains 60 wt% PEBAX exhibited CO2 permeability of 20.0 Barrer and CO2/H2 selectivity of 7.6. This performance surpasses the Robeson's boundary and unleashes the potential of tailoring the properties of polymeric nanocomposite membrane for H2 separation application through facile PVA/PEBAX blending.