Monolayer Hexagonal Boron Nitride Nanosheets as Proton-Conductive Gas Barriers for Polymer Electrolyte Membrane Water Electrolysis

In a proton exchange membrane (PEM) water electrolyzer, the poor gas barrier property of conventional perfluorosulfonic acid (PFSA) membranes results in membrane degradation and safety-related explosion issues. In this report, we investigate the potential of monolayer hexagonal boron nitride (hBN) as an effective hydrogen gas barrier for PEMs in a water electrolyzer. An hBN/Nafion composite membrane is prepared by transferring large-area monolayer hBN (∼25 cm2), which is prepared using chemical vapor deposition, onto Nafion 117. This one-atom-thick monolayer hBN, which is known as an impermeable material to most molecules except protons, significantly enhances the hydrogen barrier property of Nafion 117, even at high temperatures, and increases the mechanical stability of the membrane. Although a trade-off between proton conductivity and hydrogen barrier properties is observed, the water electrolysis efficiency of the cell containing the composite membrane is improved by increasing the operating temperature while minimizing the decrease in proton conductivity. By employing monolayer hBN, hydrogen permeability is significantly reduced by approximately 40%, and the corresponding electrolysis efficiency decreases by 19% compared to that of pristine Nafion. Furthermore, the enhanced gas barrier property of the composite shows slightly higher long-term (100 h) stability than that of Nafion 117.