Achieving High-Performance Proton Conduction by Constructing Sulfate-Doped Titanium-Oxo Clusters

Developing new strategies to fabricate highly efficient proton-conductive materials with defined structures and high proton conductivities is of great significance. We synthesized two novel heteropolytitanium oxo clusters doped with sulfate ions (SO₄²⁻) through a simple one-step solvothermal reaction: [Ti₆O₂(OH)₂(SO₄)₄(OiPr)₁₀]·2C₃H₈O (Ti₆S₄) and [Ti₁₆O₁₅(SO₄)₄(OCH₃)₂₆] (Ti₁₆S₄). The crystalline materials exhibit superior proton conduction performance. The hydrophilic sulfate ions in the titanium-oxo clusters, along with surrounding water molecules, form continuous proton transport pathways, achieving high proton conductivities for Ti₆S₄ and Ti₁₆S₄. Notably, Ti₆S₄ and Ti₁₆S₄ display ultrahigh proton conductivities of 4.90 × 10⁻¹ and 1.39 × 10⁻¹ S cm⁻¹ at 60 °C and 95% relative humidity (RH), respectively, which are comparable to that of Nafion117 (60 °C, 95% RH). This study offers significant insights for the systematic design of proton conductors and expands the synthesis methodologies of advanced materials.