Synthesis of inorganic-organic hybrid membranes consisting of organotrisiloxane linkages and their fuel cell properties at intermediate temperatures

Inorganic-organic hybrid membranes consisting of an aliphatic main-chain polymer and trisiloxane bond were synthesized using a simple, one-pot process from a trisiloxane derivative, phosphonic acid acrylate, and vinylbenzotriazole. 1,5-Divinyl-3-phenylpentamethyltrisiloxane (DPPMTS) was copolymerized with 2-hydroxyethyl methacrylate acid phosphate (HEMAP), and N-vinylbenzotriazole (VBT), yielding inorganic-organic hybrid composites. The formation of the inorganic-organic hybrid structure was confirmed by IR, ¹³C, and ²⁹Si NMR spectroscopy. The membranes exhibited good thermal stabilities up to 200 °C. The aliphatic chains of the methacrylate derivative copolymerized with trisiloxane in the hybrid membranes improved the mechanical properties of the membranes. The tensile modulus of the VBT/HEMAP/DPPMTS membrane with a composition of 1:9:5 was 1.19 GPa. The conductivities of the 1:9:5 membranes were 5.3 × 10⁻² S cm⁻¹ and 4.1 × 10⁻⁴ S cm⁻¹ at 100 and 19.3% relative humidity (RH), respectively, and 130 °C. The membrane electrode assembly (MEA) using the hybrid membrane exhibited a peak power of 7.8 mW cm⁻² at 140 °C and 30% RH.