Single-Anion Conductor Enabled by Quaterization and Ion Exchange in an Imidazole-Modified Metal-Organic Framework

Metal-organic frameworks (MOFs) have emerged as hydroxide conductors for alkaline membrane fuel cells due to their porosity, designability, and ease of functionalization. However, related frameworks, especially single OH^- conductive MOFs, are rarely reported because it is difficult to simultaneously balance efficient hydroxide conductivity and high base stability. We synthesized a stable hydroxide ion conductor, [Zr₆(μ₃-O)₄(μ₃-OH)₄(Meim-BDC)₆](OH^-)₆ [Meim(OH^-)-UiO-66 or SXE-6, where SXE = Shanxi electrolyte and Meim-H₂BDC = 2-(methylimidazol-1-yl)terephthalic acid], through quaterization of N atoms and subsequent ion exchange of [Zr₆(μ₃-O)₄(μ₃-OH)₄(Im-BDC)₆] [Im-UiO-66, where Im-H₂BDC = 2-(imidazol-1-yl)terephthalic acid]. Compared to the original neutral network material, the conductivity of the modified material is increased by 10 times, up to 3.44 mS cm^-1 at 80 °C and 99% relative humidity. It should be pointed out that Meim(OH^-)-UiO-66 represents the single OH^- conductor with the highest conductivity in pure MOFs. What is more, a conductive mechanism is visually exhibited by molecular dynamics simulation, suggesting Grotthuss-like migration in void spaces.