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

Zhao, Peng; Chen, Lian-Hong; Shen, Jian-Qiang; Gao, Hui; Yu, Ling; Zhao, Tian-Tian; Zhang, Xian-Ming · Nano Lett · 2025

basic_science · Level V

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Abstract

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<sup>-</sup> 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, [Zr<sub>6</sub>(μ<sub>3</sub>-O)<sub>4</sub>(μ<sub>3</sub>-OH)<sub>4</sub>(Meim-BDC)<sub>6</sub>](OH<sup>-</sup>)<sub>6</sub> [<b>Meim(OH</b><sup><b>-</b></sup><b>)-UiO-66</b> or <b>SXE-6</b>, where <b>SXE</b> = Shanxi electrolyte and Meim-H<sub>2</sub>BDC = 2-(methylimidazol-1-yl)terephthalic acid], through quaterization of N atoms and subsequent ion exchange of [Zr<sub>6</sub>(μ<sub>3</sub>-O)<sub>4</sub>(μ<sub>3</sub>-OH)<sub>4</sub>(Im-BDC)<sub>6</sub>] [<b>Im-UiO-66</b>, where Im-H<sub>2</sub>BDC = 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<sup>-1</sup> at 80 °C and 99% relative humidity. It should be pointed out that <b>Meim(OH</b><sup><b>-</b></sup><b>)-UiO-66</b> represents the single OH<sup>-</sup> 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.