Synthesis of Two Structurally Distinct Cu-MOFs Regulated by Imidazole and Their Proton Conducting Properties

Abstract

Developing high-performance proton conductors with robust stability remains a challenge in fuel cell technology. This study presents two copper-based metal–organic frameworks synthesized via imidazole-regulated assembly, showcasing the structural modulation effect of imidazole dosage on proton conduction properties. By adjusting the imidazole/Cu²⁺ molar ratio, we obtained two distinct frameworks: Cu-DSBPDC-1D (1D chain structure with [Cu₃(Im)₄(COO)₂] clusters) and Cu-DSBPDC-2D (2D layered structure with [Cu₉(μ₃-OH)₆(μ₂-H₂O)₄(COO)₆(Im)₈] rod-like SBUs). The 2D framework features hydrophilic channels decorated with sulfonate groups, forming continuous hydrogen-bond networks for proton transport. Both MOFs exhibit exceptional stability in boiling water and pH 3–11 solutions. Notably, Cu-DSBPDC-2D achieves a proton conductivity of 8.14 × 10^–3 S cm^–1 at 85 °C and 95% RH, retaining 90% of its initial conductivity over 72 h. Isotope-effect measurements and the moderate activation energy (0.466 eV) indicate that proton transport is mediated by sulfonate-water hydrogen bonds, operating within a regime where Grotthuss and Vehicle mechanisms coexist. This work demonstrates imidazole as a dual-functional modulator for both structural assembly and proton conduction pathways, offering a rational design strategy for stable MOF-based proton conductors.