Shen Cheng-Hui, Chen Yu-Hsiu, Wang Yi-Ching, Chang Tzu-En, Chen You-Liang, Kung Chung-Wei
Department of Chemical Engineering, National Cheng Kung University, Tainan City, 70101, Taiwan.
Phys Chem Chem Phys. 2022 May 4;24(17):9855-9865. doi: 10.1039/d2cp00117a.
Three topologically distinct zirconium-based metal-organic frameworks (Zr-MOFs) constructed from redox-innocent linkers, MOF-808, defective UiO-66, and CAU-24, are synthesized, and the spatially dispersed redox-active manganese sites are post-synthetically immobilized on the hexa-zirconium nodes of these Zr-MOFs. The crystallinity, morphology, porosity, manganese loading, and bulk electrical conductivity of each material are studied. The redox-hopping-based electrochemical reaction between the installed Mn(III) and Mn(IV) occurring within the thin films of these MOFs in aqueous electrolytes is investigated, in the presence of various concentrations of NaSO in the electrolytes. Cyclic voltammetry is used to qualitatively study the redox-hopping process, and chronoamperometry is used to quantify the electrochemically active fractions of manganese sites within the MOF thin film as well as the values of apparent diffusivity for the redox-hopping process. By adjusting the concentration of NaSO in the electrolyte, the rate-determining step for the redox-hopping process can be tuned from ionic transport to electronic transport, and the Mn-decorated MOF-808, which possesses the largest pore size, can achieve the highest value of apparent diffusivity. Findings here shed light on the selection of Zr-MOF as well as the choice of electrolyte concentration for the applications of MOFs in supercapacitors and electrocatalysis relying on such redox-hopping processes in aqueous electrolytes.
合成了三种由无氧化还原活性连接体构建的拓扑结构不同的锆基金属有机框架（Zr-MOFs），即MOF-808、缺陷UiO-66和CAU-24，并通过后合成方法将空间分散的氧化还原活性锰位点固定在这些Zr-MOFs的六锆节点上。研究了每种材料的结晶度、形态、孔隙率、锰负载量和体电导率。研究了在水性电解质中，这些MOFs薄膜内安装的Mn(III)和Mn(IV)之间基于氧化还原跳跃的电化学反应，电解质中存在不同浓度的NaSO。循环伏安法用于定性研究氧化还原跳跃过程，计时电流法用于量化MOF薄膜内锰位点的电化学活性分数以及氧化还原跳跃过程的表观扩散率值。通过调节电解质中NaSO的浓度，氧化还原跳跃过程的速率决定步骤可以从离子传输调整为电子传输，并且具有最大孔径的Mn修饰的MOF-808可以实现最高的表观扩散率值。这里的研究结果为在超级电容器和依赖于水性电解质中这种氧化还原跳跃过程的电催化应用中选择Zr-MOF以及选择电解质浓度提供了启示。
