Polyoxometalate-anchored Nafion membranes with enhanced proton conductivity and suppressed hydrogen permeability for water electrolysis

Proton-exchange membrane water electrolysis (PEMWE), a key technology for green hydrogen production, is often constrained by the intrinsic trade-off between proton conductivity and hydrogen barrier properties. To ensure low H 2 crossover and safe operation, commercial PEMs such as Nafion are typically thicker than 100 μm, which increases ohmic resistance, reduces electrolysis efficiency, and raises system cost. Here we develop a bifunctional additive—polyethylene glycol-grafted polyoxometalate (PEG 500 -SiW)—that can be precisely incorporated into the ionic domains of Nafion to form hybrid membranes that concurrently enhance proton conductivity and suppress hydrogen permeation. Stabilized in the membrane via multiple noncovalent interactions, PEG 500 -SiW preserves the microphase-separated morphology of Nafion while serving two roles: it acts as a proton conductor to facilitate proton transport and provides steric hindrance to impede H 2 diffusion. As a result, the hybrid Nafion membrane achieves an electrolysis performance of 6.4 A cm −2  at 2.0 V and 80 °C, a 30.6% increase over recast Nafion (5.2 A cm −2  at 2.0 V, 80 °C). In a 500 h durability test, the voltage rise is only 4.2 μV h −1 , indicating excellent stability. At a high cathode pressure of 2 MPa, a 50 μm hybrid membrane yields a substantially reduced H 2 -in-O 2 content compared with recast Nafion and commercial Nafion 212, remaining below 2% at high current densities and meeting industrial safety standards. This work demonstrates the potential of polyoxometalates as membrane additives for PEMWE and offers a viable route to high-performance PEMs for water electrolysis.