Proton-conducting organic-inorganic nanocomposites with fast proton-transfer pathways through acid-base pairs

The drive for global environmental sustainability is accelerating the transition to renewable energy technologies, with polymer electrolyte membrane fuel cells (PEMFCs) emerging as a key contender due to their superior energy efficiency and compact design, although traditional Nafion®-based PEMFCs face critical challenges, such as elevated costs and diminished performance under high-temperature and low-humidity environments, which limit their broader implementation. To overcome these challenges and meet stringent environmental standards, the development of non-fluorinated electrolyte membranes is essential to ensure stable conductivity across diverse operating conditions. In this study, a hybrid inorganic-organic matrix was synthesized via a sol-gel process by combining (3-glycidoxypropyl)trimethoxysilane (GPTS) and (3-mercaptopropyl)trimethoxysilane (MPTS) (referred as G-M) and subsequently functionalized with three distinct basic additives-(aminopropyl)triethoxysilane (APTES), polydopamine (PDA), and chitosan (CS). These additives were incorporated through electrostatic interactions between acidic and basic components within the composite polymer matrix to enhance proton conductivity. The resulting G-M/APTES, G-M/PDA, and G-M/CS composite membranes exhibited enhanced proton transport through acid-base pairing interactions between the matrix’s –sulfonic acid (-SO₃H) groups and additives’ amino (–NH₂) groups. The G-M/CS membrane, incorporating 20 wt% CS, exhibited the highest through-plane proton conductivity (σ_th) of 1.59 mS/cm, corresponding to a 4.68-fold improvement over the pristine G-M matrix. Conversely, the G-M/PDA membrane, functionalized with 40 wt% PDA, achieved a remarkable in-plane proton conductivity (σ_in) of 37.10 mS/cm under conditions of 80 °C and 100 % relative humidity (RH), reflecting an over thousand-fold enhancement relative to the σ_in of pristine G-M membranes. These results underscore the efficacy of acid-base interactions in advancing polymer electrolyte membranes for electrochemical applications.