引用本文:
董晓放, 杨悦, 王深, 郝晓方, 王玉霞, 程鹏. 导电金属有机框架材料的研究进展[J]. 无机化学学报,
2025, 41(1): 14-34.
doi:
10.11862/CJIC.20240388
Citation: Xiaofang DONG, Yue YANG, Shen WANG, Xiaofang HAO, Yuxia WANG, Peng CHENG. Research progress of conductive metal-organic frameworks[J]. Chinese Journal of Inorganic Chemistry, 2025, 41(1): 14-34. doi: 10.11862/CJIC.20240388
Citation: Xiaofang DONG, Yue YANG, Shen WANG, Xiaofang HAO, Yuxia WANG, Peng CHENG. Research progress of conductive metal-organic frameworks[J]. Chinese Journal of Inorganic Chemistry, 2025, 41(1): 14-34. doi: 10.11862/CJIC.20240388
导电金属有机框架材料的研究进展
English
Research progress of conductive metal-organic frameworks
Abstract:
Metal-organic frameworks are porous crystalline materials with a high specific surface area. The poor electrical conductivity of the traditional metal-organic frameworks limits their applications on electrical devices. Recent studies have shown that metal-organic framework materials with high electrical conductivity can be prepared by utilizing design strategies such as ligands containing specific conjugated structures, and further to expand their applications. Herein, the design strategies, characterization methods, the latest research progress, and applications of conductive metal-organic frameworks have been summarized, and the existing problems and potential tendencies are looked ahead to in this article as well.
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0. 引言
金属有机框架(metal-organic frameworks，MOFs)材料以其较高的比表面积、优异的结晶性、良好的化学稳定性和高度的结构可调控性，在催化[1]、检测[2]、气体存储[3-4]和分离[5]等诸多领域有着广泛的应用前景[6-7]。相比于传统无机(半)导体材料(如石墨、硅、锗、砷化镓、金属氧化物等)，传统MOFs材料因受制于不良的导电性(电导率通常小于10-10 S·cm-1)而在电子器件领域的应用中面临巨大挑战[7-9]。近年来，各种新型的导电金属有机框架化合物(conductive metal-organic frameworks，cMOFs)相继问世，它们在电催化、传感、锂离子电池、超级电容器和柔性可穿戴材料等领域展示了优异的应用潜力[7-10]，为MOFs材料在电子器件中的应用带来了新的机遇。如今，电子设备成为了电气化时代的重要组成部分，cMOFs材料以其高度灵活的结构可调控性和温和的合成条件，在未来电子器件材料的开发中将展现出更大的优势[11]。
本文系统总结了cMOFs的导电原理、设计策略和常用的表征方法，展望了cMOFs的应用前景和未来发展方向。
1. cMOFs的导电原理及设计策略
与单原子体系中的线状电子能级不同，电子能级在多原子体系中会发生分裂，且相近的能级会形成连续的能带，从而形成了能带理论中的导带、价带和禁带(图 1)。具体而言，导带是电子可以自由移动的能带，价带是基态下电子充满的能带，禁带是导带与价带之间一个电子无法存在的区间，这一区间的宽度称为禁带宽度或带隙(Eg)。在禁带中存在一个费米能级(Ef)，Ef的大小表示最高能量的电子在基态(绝对零度)所占据的能级。金属的导带和价带互相重叠，连接成片(Eg=0)，其费米能级穿过这一部分充满电子的能带，其价电子均可在这一能带中自由移动。非导体材料的导带和价带相互分离，可根据带隙大小将其分为半导体(0~3 eV)和绝缘体(大于3 eV)，但半导体和绝缘体之间并没有一个清晰的界线。绝对零度时，半导体的所有价电子充满价带，导带处于全空状态，此时电荷无法在材料中传递。当温度升高，价带上的少数电子获得能量跃迁到导带，产生自由电荷，材料呈现出导电性，导电能力也随温度的上升而增强。未掺杂且无晶格缺陷的半导体称为本征半导体。本征半导体的费米能级处于导带和价带的中间，其电子和空穴数量相等。在实际应用中，通常通过掺杂的手段来改良半导体材料的性能，根据掺杂类型的不同，可分为p型半导体和n型半导体。p型半导体是在半导体材料内部掺入缺电子杂质，使得价带内部出现多余的空穴，由空穴(正电荷)的移动而产生导电性。n型半导体则是在半导体材料内部掺入富电子杂质使得导带内部出现冗余的电子，由电子(负电荷)的移动产生导电性[11-13]。cMOFs材料的电导率一般随温度的降低而升高，因而具有半导体材料的特征，从能带结构上分析，大多数cMOFs属于半导体材料范畴。根据导电性产生方式的不同，其设计策略主要可分为以下5类：化学键策略、空间策略、扩展共轭策略、客体分子策略和多级结构复合物策略[9-11]。在同一cMOF体系内，其导电性的产生可能是多方面共同作用的结果[14]。
图 1
1.1 化学键策略
通过化学键(through bond)策略电荷能够在配位原子与金属节点间依次传递，即形成 M—X—M—X……(X可以是 O、N、S等电负性较大的原子)，能够使 MOFs材料产生导电性。此类材料导电能力的强弱取决于金属离子和配位原子之间的分子轨道取向和能量的匹配度，轨道匹配度越高，轨道重叠程度越大，其导电能力越好[15]。2009 年 Kitagawa 等报道了首个具有导电性的 MOF材料 Cu[Cu(pdt)2]，该材料在室温下的电导率为 6×10-4 S·cm-1，其电导率随温度的降低而增大，符合半导体的特征(图 2a 和 2b)[16]，该材料的导电原理就属于化学键策略。使用 该策略设计导电 MOFs材料的关键是选择与金属离 子匹配的配体，根据软硬酸碱理论，配位原子较 “软” 的配体与过渡金属离子构筑的 cMOFs 往往会 具有更好的导电性，对于结构类似的 cMOFs，配位 原子为 S或 N时通常会比配位原子为 O时的导电性 更强(图 2c和表 1)[17]。
图 2
图 2. (a) Cu[Cu(pdt)2]的晶体结构(绿色: Cu, 黄色: S, 灰色: C, 蓝色: N, 粉色: H); (b) Cu[Cu(pdt)2]的电导率随温度变化的趋势, 其中红线显示了对Arrhenius模型的最佳拟合[16]; (c) Fe2(DOBDC)、Fe2(DSBDC)、Mn2(DOBDC)和Mn2(DSBDC)的晶体结构[17]; (d) Fe(tri)2(BF4)x的结构及其氧化前后导电性的变化[18]Figure 2. (a) Crystal structure of Cu[Cu(pdt)2] (Color code: green, Cu; yellow, S; gray, C; blue, N; pink, H); (b) Temperature dependence of the electrical conductivity of Cu[Cu(pdt)2], where the red line shows the best fit to the Arrhenius model[16]; (c) Crystal structure and conductivity of Fe2(DOBDC), Fe2(DSBDC), Mn2(DOBDC), and Mn2(DSBDC)[17]; (d) Crystal structure of Fe(tri)2(BF4)x and its conductivity before and after oxidation[18]表 1
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cMOF Conductivity / (S·cm-1) σas-synthesized σguest free Fe2(DSBDC) 3.9×10-6 5.8×10-7 Mn2(DSBDC) 2.5×10-12 1.2×10-12 Fe2(DOBDC) 3.2×10-7 4.8×10-8 Mn2(DOBDC) 3.9×10-13 3.0×10-13 不同于上述本征半导体cMOFs，另一种常见的方法是通过对原导电性较差的MOFs进行掺杂来进一步提升其导电性能。该方法通常通过氧化还原的方式改变部分配体或金属离子的价态，在导带上引入少量自由电荷或在价带上引入少量空穴，从而增强框架的导电性。这种策略能使导电能力提升105量级以上，但需要注意的是，不同的处理方式和处理时间对导电性能提升的有着重要的影响。尽管这种导电机理有时被认为是独立的氧化还原跳跃(redox hopping)机理，但它仍然以化学键策略为基础，故也可以将此类导电机理归为化学键策略。Long等报道了一种混合价态Fe/Fe基MOF，Fe(tri)2(BF4)x(0≤x≤0.33)，可通过控制该MOF在空气中暴露的时间来控制Fe和Fe的比例，实现对该材料导电性的调控(图 2e)[18]。
1.2 空间策略
通过空间(throughspace)策略增强配体与配体之间的相互作用，也能够增强材料的导电性。当含有共轭体系配体的共轭平面互相靠近，间距达到0.35nm左右时，便会形成π-π堆积，此时电荷可沿共轭体系堆叠的方向进行传递。常见的这类配体有四硫富瓦烯(TTF)、萘、蒽的衍生物等。并非所有共轭配体均能凭借π-π堆积获得较好的导电性，例如传统芳环(如萘、蒽)间的π-π堆积，其相邻分子的π轨道重叠程度极为有限，因此电导率较低。相比之下，TTF衍生物等分子由于存在S…S相互作用，显著增强了π轨道的重叠程度，从而显著提升了材料的电导率。Dincă等报道了基于TTF衍生物的多孔cMOFs[19]。随后通过改变具有不同半径的中心离子，实现了对此类cMOFs导电性的调控(图 3a~ 3c)[20]。Cao等报道了系列Ln4(INA)3(GA)3(Ln=Gd，Tm，Lu，INA=异烟酸，GA=乙醇酸)cMOFs，其中的异烟酸配体通过层层堆叠形成π-π堆积而产生导电性，并且通过对比发现该cMOF的导电性随着金属离子半径的减小而增大，因为共轭体系间距越近，π-π相互作用越显著(图 3d和表 2)[21]。与化学键策略类似，氧化还原也能提高此类cMOFs的导电性能，通过部分配体的氧化可产生额外的自由基等载流子，从而增强其内部共轭分子的π-π相互作用[22]。
图 3
图 3. (a、b) M2(TTFTB) (M=Zn、Cd、Mn、Co)的晶体结构, 其中M、S、O、C分别为橙色、黄色、红色和灰色, a中氢原子和水分子未画出[19]; (c) M2(TTFTB)的导电性与S…S距离的关系[20]; (d)Gd4(INA)3(GA)3的结构(Gd、O、C、H、N分别为紫色、红色、浅灰、白色和蓝色)[21]Figure 3. (a, b) Crystal structure of M2(TTFTB) (M=Zn, Cd, Mn, Co), where orange, yellow, red, and grey spheres represent M, S, O, and C atoms, respectively, and H atoms and water molecules in a were omitted for clarity[19]; (c) Correlation between S…S distance and electrical conductivity in M2(TTFTB)[20]; (d) Crystal structure of Gd4(INA)3(GA)3, where Gd, O, C, H, and N are purple, red, light gray, white, and blue, respectively[21]表 2
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Compound d / nm σ / (S·cm-1) Tm4(INA)3(GA)3 0.332 2×10-6 Lu4(INA)3(GA)3 0.334 1×10-6 Gd4(INA)3(GA)3 0.335 5×10-7 1.3 扩展共轭策略
扩展共轭策略(extended conjugation)的设计思想是将芳香配体与金属离子之间的π-d共轭离域键扩展形成二维平面，在面内传递电荷。此类cMOFs的结构与导电原理类似于石墨烯，因此也被称作金属-有机石墨烯(metal-organic graphenes，MOGs)。此类材料是cMOFs的重要组成部分，目前已报道的导电性最好、种类最多的cMOFs均为MOGs。MOGs配体主要是各种多元酚、硫酚、硒酚以及芳香胺(图 4a)[23]，此类配体极易被氧化形成对应的醌或亚胺，通电时配体的氧化还原状态在邻近分子间转移，从而产生导电性。Dincă等报道的MOG材料Ni3(HITP)2被广泛地研究与应用亦得益于高比表面积(766 m2·g-1)和高导电性(40 S·cm-1)(图 4b和4c)[24]。Zhu等报道了一种具有超高导电性的cMOF材料Cu-BHT，室温条件下其薄膜电导率达到2 500 S·cm-1，与其他多数cMOFs不同，Cu-BHT的电导率随温度的下降而提高，无外加磁场时在温度低于0.25 K时转变为超导体，转变温度TC随外加磁场的增大而降低，这也是人类首次在配位化合物中观察到超导现象(图 4d和4e)[25]。
图 4
图 4. (a) 已报道的扩展共轭型cMOFs中配体和金属离子的选择[23]; (b) Ni3(HITP)2的合成步骤; (c) 范德堡法测得的Ni3(HITP)2的变温电导率[24]; (d) 从50 mK到300 K时归一化电阻率R(T)/R(300 K)的温度依赖性; (e) 引入不同外加磁场条件下R(T)/R(300 K)在TC附近的温度依赖性[25]Figure 4. (a) Representative organic monomers and metal centers reported in conductive MOFs based on extended conjugation[23]; (b) Synthesis of Ni3(HITP)2; (c) Variable-temperature van der Pauw conductivity measurement[24]; (d) Temperature dependence of the normalized resistance R(T)/R(300 K) of Cu-BHT from 50 mK to 300 K; (e) Temperature dependence of R(T)/R(300 K) of Cu-BHT near TC in constant applied magnetic fields up to 2 500 Oe[25]1.4 客体分子策略
由于MOFs具有丰富的孔道，若在其孔道中插入某些适宜的客体也可增强其导电性，常见的客体有I2、四氰基乙烯(TCNE)、7，7，8，8-四氰基对苯二醌二甲烷(TCNQ)等。但这一策略有一个弊端，客体的插入会降低MOFs的比表面积。因此，设计此类cMOFs时要充分考虑插入客体分子与MOFs主体孔道尺寸间的关系。另外，TCNE和TCNQ增强导电性的原理是直接与金属离子配位，使用TCNE或TCNQ时就要考虑金属离子间距与客体分子尺寸的匹配程度。Allendorf等首次报道了在HKUST-1(Cu3(BTC)2)中插入TCNQ及其衍生物以增强导电性的研究。其中插入TCNQ的HKUST-1样品电导率达到0.07S·cm-1，比未经处理的样品增大了107倍，而且该复合物稳定性很好，材料在室温暴露于空气中40d后性能仍无明显变化(图 5)[26]。
图 5
图 5. (a) ab initio算法计算的HKUST-1-TCNQ复合物最低能量构型; (b) 未经处理(红色)、插入TCNQ(绿色)、插入F4-TCNQ(金色)以及插入H4-TCNQ(紫色)的HKUST-1的I-V曲线[26]Figure 5. (a) Minimum-energy configuration for TCNQ@Cu3(BTC)2 obtained from ab initio calculations; (b) I-V curves before (red) and after infiltration with TCNQ (green), F4-TCNQ (gold), or H4-TCNQ (purple)[26]1.5 多级结构复合物策略
除了将能促进导电的客体分子插入MOFs孔道外，将MOFs材料负载到导电基质上形成多级结构是使MOFs材料增强导电性的另一重要思路，常用的导电基质有聚吡咯(PPy)、聚噻吩(PT)、碳纳米管、金纳米线等。Li等在聚吡咯纳米管外层负载了一层Cu3(HHTP)2，制成了一种可吸收电磁波的吸波材料，复合之后cMOF的导电性得到显著提升，对电磁波的吸收达到-49.56 dB(图 6)[27]。
图 6
图 6. (a) Cu3(HHTP)2-聚吡咯复合物合成过程示意图; (b) Cu3(HHTP)2-聚吡咯复合物吸收电磁波原理; (c) 质量分数均为30%的Cu3(HHTP)2、PPy和Cu3(HHTP)2@PPy的电导率; (d~f) 质量分数均为30%的Cu3(HHTP)2、PPy和Cu3(HHTP)2@PPy在不同厚度下反射损耗的频率依赖性[27]Figure 6. (a) Synthetic route of Cu3(HHTP)2@PPy; (b) Schematic mechanism of electromagnetic wave absorption for Cu3(HHTP)2@PPy; (c) Electrical conductivity of Cu3(HHTP)2, PPy, Cu3(HHTP)2@PPy in the same mass ratio of 30%; (d-f) Frequency-dependence of 2D reflection loss of Cu3(HHTP)2, PPy, Cu3(HHTP)2@PPy in 30% mass ratio with different thickness[27]2. cMOFs导电性的常用表征方法
测量cMOFs材料电导率的常用方法是将材料研磨并压成薄片或直接生长cMOFs薄膜，测量薄片或薄膜的电导率，对于能够长出较大尺寸单晶的样品，也可以在特定的晶面上制作电极，测量沿特定方向的电导率。
2.1 两点法和四点法
对于电阻较大、形状规则的材料可采用两点法(two-point probe)测量其电阻率。如图 7a所示，对于一横截面积为S、长度为L的材料，在被测样品的两端通电，若电流为I，电压为U，则该材料电阻率：
$ \rho =\frac{US}{IL} $ (1) 图 7
如图 7b~ 7c所示，Cao等利用两点法测试了Gd4(INA)3(GA)3单晶沿a和c轴方向的导电性[21]。
两点法的测试优点在于测量方便且电路连接简便，但两点法将导线电阻、电极与材料间的接触电阻等外界影响因素计入了测量结果，这些因素在测量电阻较小的材料时，将引入不能忽略的误差。因此，低电阻材料的测量一般采用四点法(four-point probe)，该方法将供电电路和测量电路互相分开，由于电压表的内阻很大，导线电阻以及接触电阻等因素对测量电压的影响不大。四点法测量主要分为以下2种情况：
对于形状规则的材料，其测试及计算方法与两点法类似。例如对于一横截面积为S、长度为L的材料，按照图 8a所示方式连接电路，若电流为I，电压为U，则该材料电阻率仍可通过式1算出。
图 8
若材料为均匀薄膜或薄片，可将电极按如图 8b所示的方式以等间距(s)连接，该方法要求材料的尺寸远大于电极之间的距离，可将材料看作无穷大平面。若材料厚度为w，电流为I，电压为U，则电阻率可表示为下式[28]：
$ \rho =\frac{\mathrm{\pi }w}{\mathrm{l}\mathrm{n}2}·\frac{U}{I}=4.532\mathrm{ }4w\frac{U}{I} $ (2) 若不考虑材料厚度，只计算面电阻率，可以得出[28]：
$ {\rho }_{s}=2\mathrm{\pi }s\frac{U}{I} $ (3) Saha等将cMOFs薄膜制成如图 8c中插图所示的装置，等间距地平行连接4个金电极，测量了插入客体前后cMOFs薄膜导电性的变化[29]。
2.2 范德堡法[30-31]
范德堡(van der Pauw)法是一种常见的精确测量二维材料导电性的测试方法。与两线法和四线法测量材料在特定方向上的导电性不同，范德堡法消除了各向异性的影响，测量的是二维平面内各个方向的平均电阻。
范德堡法要求被测样品内部无裂缝、孔洞，一般为质地、厚度均匀的二维薄膜或薄片(要求材料的厚度远小于其长、宽)，4个触点位于样品边缘且面积远小于样品面积。测试时按照如图 9a所示的方式连接电路，测出如下电阻：
$ {R}_{\mathrm{a}\mathrm{b}, \mathrm{c}\mathrm{d}}=\frac{{U}_{\mathrm{c}\mathrm{d}}}{{I}_{\mathrm{a}\mathrm{b}}} $ (4) 图 9
再按照同样的方法测出如下电阻：
$ {R}_{\mathrm{b}\mathrm{c}, \mathrm{d}\mathrm{a}}=\frac{{U}_{\mathrm{d}\mathrm{a}}}{{I}_{\mathrm{b}\mathrm{c}}} $ (5) 两种电阻满足下式：
$ \mathrm{e}\mathrm{x}\mathrm{p}\left(-\frac{\mathrm{\pi }d}{\rho }{R}_{\mathrm{a}\mathrm{b}, \mathrm{c}\mathrm{d}}\right)+\mathrm{e}\mathrm{x}\mathrm{p}\left(-\frac{\mathrm{\pi }d}{\rho }{R}_{\mathrm{b}\mathrm{c}, \mathrm{d}\mathrm{a}}\right)=1 $ (6) 其中ρ为材料电阻率，d为样品厚度，由此可以得出
$ \rho =\frac{\mathrm{\pi }d}{\mathrm{l}\mathrm{n}2}·\frac{{R}_{\mathrm{a}\mathrm{b}, \mathrm{c}\mathrm{d}}+{R}_{\mathrm{b}\mathrm{c}, \mathrm{d}\mathrm{a}}}{2}·f $ (7) 其中f为校正因子，当Rab, cd和Rbc, da相差不大时，f接近于1，算式可简化为
$ \rho =\frac{\mathrm{\pi }d}{\mathrm{l}\mathrm{n}2}·\frac{{R}_{\mathrm{a}\mathrm{b}, \mathrm{c}\mathrm{d}}+{R}_{\mathrm{b}\mathrm{c}, \mathrm{d}\mathrm{a}}}{2} $ (8) 范德堡法对二维材料的形状以及电极的连接位点没有严格要求，因此十分适合生长在基底上的cMOFs薄膜的导电性测量。Dincă等利用范德堡法测量了一种cMOF压片样品的电导率(图 9b)[32]。
3. cMOFs的应用
随着科技的发展，人类的生产生活对能源的依赖越来越重，但化石能源的不断消耗以及环境污染的加剧，迫使人类寻找新的可再生能源。近几十年来，风能、水能、太阳能、潮汐能等新型绿色能源被不断开发出来，但这些能源都有一个共同的劣势，难以恒定地输出能量，因此能量的存储就变得尤其重要。cMOFs作为一种新型的半导体材料，在锂离子电池及超级电容器的电极材料方面有着巨大的应用前景。除此之外，cMOFs在传感器、电催化以及柔性可穿戴材料方面也具有潜在的应用价值。
3.1 超级电容器
超级电容器是一种具有高能量密度、快速充放电、长循环寿命的电子元器件，主要分为2类：双电层型和赝电容型。双电层型电容器的充放电过程完全是物理过程，依靠大表面积产生的大电容，没有电极与电介质间的电子转移；赝电容器依靠的是电极表面与电解液间发生的快速可逆的氧化还原反应。理想的电极材料需要良好的导电性、高比表面积以及大量活性反应位点等性质。cMOFs作为一类具有高比表面积的多孔导电材料有望应用于超级电容器的电极材料[10, 33-34]。Dincă等报道了一例二维cMOF材料Ni3(HITP)2制成的双电层型超级电容器，该电容器的比电容达到111 F·g-1，电阻只有0.47 Ω，其优越的性能能够达到甚至超越很多碳基材料[35]。Chen等报道了一种DDA-Cu一维cMOF制成的电容器，其比电容达到118 F·g-1，机理研究表明其链内和链间分别通过扩展共轭和π-π堆积形成导电性(图10a~ 10d)[14]。Pang等报道了一系列Co化合物与M-HHTP(M=Ni、Co、NiCo)形成的复合物，将其制成超级电容器，具有良好的能量存储性能，其中Ni-HHTP@ Co(OH)2性能最佳，在电流密度从0.5 A·g-1增加到5 A·g-1时，倍率性能达到88.64%(图10e~ 10g)[36]。
图 10
图 10. (a) DDA-Cu的晶体结构; (b) DDA-Cu电容器在不同电压扫描速率下的循环伏安(CV)图; (c) DDA-Cu电容器在不同电流密度下的比电容; (d) DDA-Cu电容器的循环稳定性[14]; (e) Ni-HHTP@Co(OH)2、Ni-HHTP@CoP和N-HHTP@Co3O4在不同电流密度下的倍率性能; (f) Ni-HHTP@Co(OH)2和Ni-HHTP@CoP在电流密度为3 A·g-1时, 循环5 000次的稳定性; (g) 拉贡图表示的一系列基于Co(OH)2/MOF的电容器的能量和功率密度[36]Figure 10. (a) Crystal structure of DDA-Cu; (b) Cyclic voltammetry (CV) curves of the symmetrical supercapacitor at different scan rates; (c) Calculated specific gravimetric capacitance at different current densities; (d) Cycling stability of the device[14]; (e) Rate performance of Ni-HHTP@Co(OH)2, Ni-HHTP@CoP, and Ni-HHTP@Co3O4 at different current densities; (f) Cycling stability of Ni-HHTP@Co(OH)2 and Ni-HHTP@CoP at 3 A·g-1 after 5 000 cycles; (g) Ragone plots illustrated energy and power density of some Co(OH)2/MOF-based devices[36]3.2 锂离子电池
锂离子电池是一类通过锂离子在电池正负极之间的定向移动而充放电的电池，锂离子电池具有高能量密度、长循环寿命、无记忆效应等优点[37-38]。常见的锂离子电池可以分为3类：插入型、转化型和合金型。插入型锂离子电池是锂离子在阴极上嵌入和脱嵌的锂离子电池，充放电过程中电极体积的变化不大，电池循环寿命长但容量较小，最广泛使用的石墨电极锂离子电池就属于插入型；转化型锂离子电池是阴极材料能够与锂离子反应转化成其他物质的锂离子电池；合金型锂离子电池则是指锂离子在阴极还原时能与阴极材料形成合金的锂离子电池，常见的有硅电极锂离子电池，这种电池容量较大，但由于充放电过程中电极体积变化较大导致电极会在应力作用下破碎和崩落，电池循环寿命差。cMOFs阴极的锂离子电池主要是嵌入型，锂离子在孔道中的嵌入和脱嵌形成了充放电过程，但框架本身不发生反应；少数属于转化型，充放电过程中其锂离子与框架中的金属节点发生交换[10]。除了锂离子电池外，cMOFs也可用于钠离子[39]和钾离子电池[40]，相比于锂离子电池，钠离子和价离子电池的原料更易获得，成本更低，但由于离子质量更大、尺寸更大，钠离子和钾离子电池的能量密度较低，且充放电过程中，大尺寸阳离子的嵌入和脱嵌更容易对电极材料的结构造成破坏，其循环稳定性通常低于锂离子电池[41]。Nishihara等报道了一种二维cMOF材料Ni-HAB在锂离子电池上的应用，将其用于阴极材料，在电流密度为10 mA·g-1时，容量为155 mAh·g-1，在电压范围为2.0~4.5 V时，可稳定循环充放电300次以上(图11a~11c)[42]。Bu等合成了一种二维cMOF材料Cu-TAC，用于锂离子电池的阴极材料，在电流密度为300 mA·g-1时，容量达到772.4 mAh·g-1，循环600次后容量仍可保持83%(图11d~11f)[43]。
图 11
图 11. (a) Ni-HAB的结构; (b) Ni-HAB和对应离子的氧化还原反应示意图; (c) 扫描速率为0.1 mV·s-1时, 不同电势窗口下Ni-HAB的CV图[42]; (d) Cu-TAC的合成与结构示意图; (e) 电导率随温度的变化曲线; (f) 几种cMOFs制成锂离子电池的容量对比[43]Figure 11. (a) Chemical structure of Ni-HAB; (b) Illustration of the redox reactions of Ni-HAB with respective counter ions; (c) Cyclic voltammograms of Ni-HAB at 0.1 mV·s-1 in various potential windows[42]; (d) Synthetic and structure scheme of Cu-TAC; (e) Temperature-dependent conductivity of Cu-TAC; (f) Comparison of capacity of Cu-TAC to other 2D cMOF anodes for LIBs[43]3.3 化学传感器
化学传感器是一类能够将待检测物质的浓度信号转化为电信号的元件。cMOFs由于其高比表面积、良好的导电性以及易加工成膜等性质，被用作新型化学传感器的材料。其中使用最为广泛的是MOGs，待检测物质的吸附和脱附能够改变框架的导电性，从而使待检测物质浓度转化为电信号。
首个用于化学传感器的MOG是Cu3(HITP)2，Dincă等通过将Cu3(HITP)2附在金电极上实现了对NH3气体浓度的检测(图12a~ 12c)[44]。Liu等用Cu-BHT薄膜制成了一种生物传感微芯片，可对H2O2浓度进行特异性检测(图12d~ 12f)[45]。
图 12
Fig.12 (a) Schematic of the NH3 sensor (MFC=mass flow controller); (b) Relative responses of a Cu3(HITP)2 device to 0.5, 2, 5, and 10 mg·kg-1 ammonia; (c) Device response as a function of ammonia concentration (R2 for linear fit: 0.99)[44]; (d) Proposed sensing process on the surface of the Cu-BHT film; (e) Plots of current vs H2O2 concentration of the BS-Cu-BHT and US-Cu-BHT toward H2O2 (US stands for up-side surface upward, and BS stands for bottom-side surface upward)[45]
3.4 电催化
电化学反应中，过电势以及离子输运速率是限制能量转化效率和反应速率的主要因素，cMOFs作为一类结构灵活可调、导电性良好的多孔材料，近些年来在电催化领域备受关注。主要包括催化电解水制氢(HER)[46]以及催化二氧化碳转化(CO2RR)[47]等应用[9]。
电解水制氢的反应通常需要克服巨大的过电势才能顺利进行，这就产生了大量热损耗, 导致能量转化率低下。传统的解决方法是使用贵金属(如Pt)电极降低过电势，但其价格高昂，而且随着使用时间的增长，金属微颗粒会发生聚集，导致反应活性降低。而cMOFs作为一类拥有大量活性位点且具有高稳定性的导电材料，在电解水制氢领域有很好的应用前景，可有效降低过电势，降低氢气的成本，促进氢能这种清洁高效能源的发展[9]。Chen等报道了Ni3(Ni3HAHATN)2在催化电解水制氢上的应用，在电流密度为10 mA·cm-2时，过电势仅有115 mV (图13)[48]。
图 13
图 13. (a) Ni3(HITP)2和Ni3(Ni3HAHATN)2的电催化析氢反应极化曲线; (b) 几种不同(M2)3((M1)3HAHATN)2样品的电催化析氢反应极化曲线以及(c) 对应的Tafel图; (d) Ni3(Ni3HAHATN)2纳米薄层电催化水分解示意图[48]Figure 13. (a) HER polarization curves of Ni3(HITP)2 and Ni3(Ni3HAHATN)2; (b) Polarization curves of the various (M2)3((M1)3HAHATN)2 samples and (c) the corresponding Tafel plots; (d) Electrocatalytic diagram of Ni3(Ni3HAHATN)2 nanosheets toward HER[48]随着工业的不断发展，化石燃料的消耗带来了大量的二氧化碳排放，导致全球气候变暖。为应对气候问题，节能减排、碳捕获与碳中和逐渐成为当今热议的话题，而二氧化碳的催化转化是重要方案之一。Cao等报道了一例NiPc-NiO4，用于将二氧化碳电催化还原成一氧化碳，对于产物一氧化碳的选择性达到98.4%(图 14a~ 14c)[49]。Salehi-Khojin等合成了一种平均尺寸140 nm的Cu-THQ纳米片，用于将二氧化碳转化为一氧化碳的过电势仅16 mV，在电势为-0.45 V时，电流密度达到173 mA·cm-2，对一氧化碳的法拉第效率(FE)为92%[50]。Wang等合成了一种新型MOG：2D-vc-MOF(Cu)，其共轭平面与传统MOGs的共轭平面垂直，能够催化二氧化碳还原成甲烷，在电势为1.4 V时，FE为65%(图 14d~ 14g)[51]。
图 14
图 14. (a) NiPc-NiO4催化CO2RR机理示意图; (b) 几种MOFs材料的转换频率(TOF)和最大CO偏电流密度对比; (c) NiPc-NiO4和NiPc-OH对CO的FE[49]; (d) 平面和垂直扩展结构的二维MOFs示意图; (e) 2D-vc-MOF(Cu)的合成和结构模型(C、O、Cu分别为灰色、红色和蓝色, H原子省略); (f) 2D-vc-MOF(Cu)的线性扫描伏安图; (g) 2D-vc-MOF(Cu)与Cu3(HHTP)2对甲烷的FE对比[51]Figure 14. (a) Illustration of the mechanism of CO2RR reaction catalyzed by NiPc-NiO4; (b) Comparison of the turnover frequencies (TOFs) and maximum CO partial current densities of reported MOF catalysts; (c) FEs of CO for NiPc-NiO4 and NiPc-OH[49]; (d) Schematic illustration of planarly/vertically extended structures in 2D MOFs; (e) Synthesis and structural model of 2D-vc-MOF(Cu) (Grey, red, and blue spheres represent C, O, and Cu, respectively, and H atoms are omitted); (f) Linear sweep voltammetry (LSV) curves of 2D-vc-MOF(Cu); (g) Comparison of FEs of CH4 for 2D-vc-MOF and Cu3(HHTP)2[51]3.5 可穿戴设备
可穿戴设备指的是一类可直接佩戴在人身体上或附在衣服上的便携式智能电子设备(如手环、眼镜、耳机、运动鞋、运动衣等)，可穿戴设备可直接与人体接触采集人体健康数据。目前，可穿戴设备的发展仍处于初步研究阶段，而cMOFs因其结构多样性和良好的导电性，在这一领域的应用研究不断涌现。
Xia等报道了一种能够给可穿戴设备供电的柔性超级电容器，这种超级电容器是基于Ni-CAT构筑的MOF材料作为电极材料，具有高弯折寿命和较平稳的电容-温度曲线，弯折1000次后性能仍可保持80%，在-20℃的低温环境中也能保持较好的性能(图 15a~ 15d)[[53]。Chen等报道了一种基于Ni3HHTP2的柔性汗液传感器，能够选择性地检测汗液中的尿素和维生素C浓度，且其检测精度能够媲美高效液相色谱(图 15e~ 15g)[54]。Yuan等报道了一种由Ni3(HITP)2和NUS-8两种MOFs层叠复合而成的材料，并制成了柔性传感器，实现了H2S的高精度检测(图 15h~ 15i)[55]。
图 15
图 15. PPy HF/Ni-CAT-NWs柔性超级电容器的(a) 结构示意图和(b) CV曲线; (c) Ni-CAT/Ni-CAT-NWs柔性超级电容器在不同弯折程度下的CV曲线; (d) Ni-CAT/Ni-CAT-NWs柔性超级电容器在不同弯折次数的容量保持率和CV曲线[53]; (e) Ni3HHTP2汗液传感器结构示意图; (f) Ni3HHTP2汗液传感器对维生素C的检测结果与高效液相色谱对比; (g) 检测数据由传感器无线传输到手机的过程示意图[54]; (h) Ni3(HITP)2-NUS-8复合材料的合成策略及其在传感器上的应用; (i) Ni3(HITP)2/NUS-8传感器对H2S响应的信号强度与H2S浓度的关系曲线[55]Figure 15. (a) Schematic illustration and (b) CV curves of the symmetric flexible supercapacitor based on PPy HF/Ni⁃CAT⁃NWs; (c) CV curves of the supercapacitor at different bending angles; (d) Capacitance retention and CV curves of the supercapacitor at different cycles of continuous bending[53]; (e) Configuration of the layered film sensor; (f) Comparison of the vitamin C concentrations of five sweat samples detected using the cMOF⁃based sweat sensor and HPLC; (g) Illustration of the wireless transmission from the sensors to a mobile phone[54]; (h) Schematic diagram on the synthesis strategy of Ni3(HITP)2/NUS⁃8 and its application for multiple detection; (i) Linear plots of response vs concentration of H2S for the Ni3(HITP)2/NUS⁃8 coated sensors[55]4. 总结与展望
近年来cMOFs作为一种兼具导电性和多孔性的晶态材料已成为重要的研究热点之一，并在电催化、能量存储、传感器和可穿戴设备等领域取得了重要突破。本文对现有cMOFs的设计思路、性能提升策略、主要的表征方法和应用领域进行了系统总结，表 3列出了近年来报道的一些cMOFs及其基本性能参数。迄今为止，该领域依然面临诸多挑战亟待解决，例如，大尺寸单晶的合成困难使得大多数cMOFs材料的测试仅能依赖于粉末样品，因而无法有效地获取这些材料的各向异性参数。此外，高导电性cMOFs材料的定向合成也是另一难题，加之MOFs晶体生长过程中的不确定性，易导致产物的结构与预期结构之间存在一定的偏离，进而导致其导电性能受到影响。同时，现有cMOFs的导电性和比表面积受到其二维结构的限制，尽管三维cMOFs展现出更大的潜力，但要设计并合成高导电性的三维cMOFs仍然存在较大难度。另外，cMOFs的配体合成困难和成本高昂是限制其应用的关键因素，因此通过降低合成材料的成本有望推进cMOFs的实际应用。尽管如此，基于分子晶态材料的合成经验及其自身优势，cMOFs在导电、多孔和催化等研究领域的应用基础上，也有望在发光材料、热电材料、磁性材料、自旋电子器件等领域大放异彩。
表 3
表 3 cMOFs的组成及性能参数Table 3. Compositions and characteristics of cMOFs下载:
导出CSV
Material Ligand σ / (S·cm-1) Measurement method Strategy SBET* / (m2·g-1) Reference Cu[Cu(pdt)2] 
6×10-4 Through bond [16] Mn2[Ni(dbg)2] 
8×10-8 Single crystal, two-point
probeThrough space 543.2 [56] 1×10-9 Pellet, two-point probe Zn2[Ni(dbg)2] 8×10-11 Pellet, two-point probe Through space 539.8 [56] Cd2[Ni(dbg)2] 6×10-7 Single crystal, two-point
probeThrough space 486.7 [56] 1×10-11 Pellet, two-point probe Ni-PTC 
9 Pellet, four-point probe Extended conjugation [57] Co-PTC 455 Pellet, four-point probe Extended conjugation [58] 2D-vc-MOF(Cu) 
2.25×10-5 Pellet, four-point probe Extended conjugation 556 [51] Ni3(HAB)2 (Ni3(HIB)2) 
0.7 Pellet, four-point probe Extended conjugation 180-350 [59] Cu3(HAB)2 (Cu3(HIB)2) 0.11 Pellet, four-point probe Extended conjugation 180-350 [59] Co3(HAB)2 (Co3(HIB)2) 15.23 Pellet, four-point probe Extended conjugation [60] Zn3(HAB)2 (Zn3(HIB)2) 8.6×10-4 Pellet, van der Pauw Extended conjugation 145 [61] Ni3(HITP)2 
2 Pellet, two-point probe Extended conjugation 766 [24, 62] 40/58.8 Film, van der Pauw Cu3(HITP)2 0.2 Pellet, two-point probe Extended conjugation [44] Co3(HITP)2 67.796 6 Pellet, four-point probe Extended conjugation 856, 2 338 [63] Mn3(HITP)2 44.923 6 Pellet, four-point probe Extended conjugation 843, 2 302 [63] Cu-BHT 
2 500 Film, four-point probe Extended conjugation [25, 64] Ag3BHT2 363 Pellet, four-point probe Extended conjugation [65] Au3BHT2 9.15×10-5 Pellet, four-point probe Extended conjugation [65] Tm4(INA)3(GA)3 
2×10-6 Single crystal, two-point
probeThrough space [21] Lu4(INA)3(GA)3 1×10-6 Single crystal, two-point
probeThrough space [21] Gd4(INA)3(GA)3 5×10-7 Single crystal, two-point
probeThrough space 312 [21] Cu3(HHB)2 
7.3×10-8 Pellet, van der Pauw Through space 158 [66] (Cu3(HOB)2) Cu-TAC 
3.2×10-5 Pellet, two-point probe Extended conjugation 114 [43] DDA-Cu 
9.4×10-2 Film, two-point probe Extended conjugation,
Through space127.3 [14] Cu3(HHTP)2 
1×10-4 Extended conjugation 334 [67-68] 0.02 Film, two-point probe LaHHTP 9×10-4 Pellet, two-point probe Through space 325 [69] NdHHTP 8×10-4 Pellet, two-point probe Through space 513 [69] HoHHTP 0.05 Pellet, two-point probe Through space 208 [69] YbHHTP 0.01 Pellet, two-point probe Through space 452 [69] M6(μ6-NO3)(HOTP)2
(M=Y, La, Eu)10-5-10-6 Pellet, two-point probe Extended conjugation 780 [70] Cu3(HHTQ)2 
1×10-3 Pellet, four-point probe Extended conjugation 516.99, 1 360 [71-73] (Cu3(HHTT)2) 2.74×10-5 Pellet, two-point probe Ni3(HHTQ)2 2.27×10-5 Pellet, two-point probe Extended conjugation 1 114 [72-73] (Ni3(HHTT)2) Cu3(HHTN)2 
9.55×10-10 Pellet, two-point probe Extended conjugation 486 [74] (M2)3((M1)3HAHATN)2
(M=Ni, Cu, Co)
2 M1=M2=Ni, pellet,
four-point probeExtended conjugation [48] Cd2(TTFTB) 
4.39×10-8 Pellet, four-point probe Through space 559 [32] 2.7×10-8 Pellet, van der Pauw 1.91×10-6 Single crystal,
four-point probeLa4(HTTFTB)4 2.57×10-6 Pellet, two-point probe Through space 596 [22] La(HTTFTB) 9.4×10-7 Pellet, two-point probe Through space 454 [22] La4(TTFTB)3 1.05×10-9 Pellet, two-point probe Through space 362 [22] Yb6(TTFTB)5 9×10-7 Pellet, two-point probe Through space 400 [75] Lu6(TTFTB)5 3×10-7 Pellet, two-point probe Through space 70 [75] Co-TPHS 
1×10-6 Pellet, two-point probe Extended conjugation 246 [76] Ni2[CuPc(NH)8] 
8×10-3 Pellet, van der Pauw Extended conjugation 556 [60] Cu2[CuPc(NH)8] 6×10-5 Pellet, van der Pauw Extended conjugation 659 [77] Cu3(TATHB)2 
1.54×10-7 Pellet, four-point probe Extended conjugation [77] (Me2NH2)2[Fe2L3]·
2H2O·6DMF
1.4×10-2 Pellet, two-point probe Through bond 1 175 [78] Fe2(DOBDC) 
3.2×10-7 As synthesized, pellet,
two-point probeThrough bond 241 [17] 4.8×10-2 Guest free, pellet,
two-point probeMn2(DOBDC) 3.9×10-13 As synthesized, pellet,
two-point probeThrough bond 287 [17] 3.0×10-13 Guest free, pellet,
two-point probeFe2(DSBDC) 
3.9×10-6 As synthesized, pellet,
two-point probeThrough bond 54 [17] 5.8×10-7 Guest free, pellet,
two-point probeMn2(DSBDC) 2.5×10-12 As synthesized, pellet,
two-point probeThrough bond 232 [17] 1.2×10-12 Guest free, pellet,
two-point probe(NBu4)2Fe2(DHBQ)3 
1.07×10-3 Pellet, four-point probe Extended conjugation 5.42 [79] {[Cu2(6-Hmna)(6-mn)]·
NH4}n
10.96 Single crystal,
four-point probeThrough bond [80] NiPc-Ni 
4.8×10-5 Pellet, two-point probe Extended conjugation 101 [49, 81] 7.22×10-4 Pellet, four-point probe NiPc-Cu 1.43×10-2 Pellet, four-point probe Extended conjugation 284 [81] NiNPc-Ni 
1.78×10-2 Pellet, four-point probe Extended conjugation 174 [81] NiNPc-Cu 3.13×10-2 Pellet, four-point probe Extended conjugation 267 [81] * The specific surface area was determined using the Brunauer-Emmett-Teller (BET) method.
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图 2 (a) Cu[Cu(pdt)2]的晶体结构(绿色: Cu, 黄色: S, 灰色: C, 蓝色: N, 粉色: H); (b) Cu[Cu(pdt)2]的电导率随温度变化的趋势, 其中红线显示了对Arrhenius模型的最佳拟合[16]; (c) Fe2(DOBDC)、Fe2(DSBDC)、Mn2(DOBDC)和Mn2(DSBDC)的晶体结构[17]; (d) Fe(tri)2(BF4)x的结构及其氧化前后导电性的变化[18]
Figure 2 (a) Crystal structure of Cu[Cu(pdt)2] (Color code: green, Cu; yellow, S; gray, C; blue, N; pink, H); (b) Temperature dependence of the electrical conductivity of Cu[Cu(pdt)2], where the red line shows the best fit to the Arrhenius model[16]; (c) Crystal structure and conductivity of Fe2(DOBDC), Fe2(DSBDC), Mn2(DOBDC), and Mn2(DSBDC)[17]; (d) Crystal structure of Fe(tri)2(BF4)x and its conductivity before and after oxidation[18]
图 3 (a、b) M2(TTFTB) (M=Zn、Cd、Mn、Co)的晶体结构, 其中M、S、O、C分别为橙色、黄色、红色和灰色, a中氢原子和水分子未画出[19]; (c) M2(TTFTB)的导电性与S…S距离的关系[20]; (d)Gd4(INA)3(GA)3的结构(Gd、O、C、H、N分别为紫色、红色、浅灰、白色和蓝色)[21]
Figure 3 (a, b) Crystal structure of M2(TTFTB) (M=Zn, Cd, Mn, Co), where orange, yellow, red, and grey spheres represent M, S, O, and C atoms, respectively, and H atoms and water molecules in a were omitted for clarity[19]; (c) Correlation between S…S distance and electrical conductivity in M2(TTFTB)[20]; (d) Crystal structure of Gd4(INA)3(GA)3, where Gd, O, C, H, and N are purple, red, light gray, white, and blue, respectively[21]
图 4 (a) 已报道的扩展共轭型cMOFs中配体和金属离子的选择[23]; (b) Ni3(HITP)2的合成步骤; (c) 范德堡法测得的Ni3(HITP)2的变温电导率[24]; (d) 从50 mK到300 K时归一化电阻率R(T)/R(300 K)的温度依赖性; (e) 引入不同外加磁场条件下R(T)/R(300 K)在TC附近的温度依赖性[25]
Figure 4 (a) Representative organic monomers and metal centers reported in conductive MOFs based on extended conjugation[23]; (b) Synthesis of Ni3(HITP)2; (c) Variable-temperature van der Pauw conductivity measurement[24]; (d) Temperature dependence of the normalized resistance R(T)/R(300 K) of Cu-BHT from 50 mK to 300 K; (e) Temperature dependence of R(T)/R(300 K) of Cu-BHT near TC in constant applied magnetic fields up to 2 500 Oe[25]
图 5 (a) ab initio算法计算的HKUST-1-TCNQ复合物最低能量构型; (b) 未经处理(红色)、插入TCNQ(绿色)、插入F4-TCNQ(金色)以及插入H4-TCNQ(紫色)的HKUST-1的I-V曲线[26]
Figure 5 (a) Minimum-energy configuration for TCNQ@Cu3(BTC)2 obtained from ab initio calculations; (b) I-V curves before (red) and after infiltration with TCNQ (green), F4-TCNQ (gold), or H4-TCNQ (purple)[26]
图 6 (a) Cu3(HHTP)2-聚吡咯复合物合成过程示意图; (b) Cu3(HHTP)2-聚吡咯复合物吸收电磁波原理; (c) 质量分数均为30%的Cu3(HHTP)2、PPy和Cu3(HHTP)2@PPy的电导率; (d~f) 质量分数均为30%的Cu3(HHTP)2、PPy和Cu3(HHTP)2@PPy在不同厚度下反射损耗的频率依赖性[27]
Figure 6 (a) Synthetic route of Cu3(HHTP)2@PPy; (b) Schematic mechanism of electromagnetic wave absorption for Cu3(HHTP)2@PPy; (c) Electrical conductivity of Cu3(HHTP)2, PPy, Cu3(HHTP)2@PPy in the same mass ratio of 30%; (d-f) Frequency-dependence of 2D reflection loss of Cu3(HHTP)2, PPy, Cu3(HHTP)2@PPy in 30% mass ratio with different thickness[27]
图 8 四点法电路连接示意图: (a) 待测材料为规则条状, (b) 待测材料为均匀片状或薄膜[28]; (c) 使用四点法测量插入客体前(蓝线)后(绿线)MOF薄膜(插图)的I-V曲线[29]
Figure 8 Schematic diagram of a four-point probe setup for (a) symmetrical rod or (b) even flake or film[28]; (c) I-V relationships of MOF devices (inset) before (blue line) and after (green line) doped with guest molecules[29]
图 10 (a) DDA-Cu的晶体结构; (b) DDA-Cu电容器在不同电压扫描速率下的循环伏安(CV)图; (c) DDA-Cu电容器在不同电流密度下的比电容; (d) DDA-Cu电容器的循环稳定性[14]; (e) Ni-HHTP@Co(OH)2、Ni-HHTP@CoP和N-HHTP@Co3O4在不同电流密度下的倍率性能; (f) Ni-HHTP@Co(OH)2和Ni-HHTP@CoP在电流密度为3 A·g-1时, 循环5 000次的稳定性; (g) 拉贡图表示的一系列基于Co(OH)2/MOF的电容器的能量和功率密度[36]
Figure 10 (a) Crystal structure of DDA-Cu; (b) Cyclic voltammetry (CV) curves of the symmetrical supercapacitor at different scan rates; (c) Calculated specific gravimetric capacitance at different current densities; (d) Cycling stability of the device[14]; (e) Rate performance of Ni-HHTP@Co(OH)2, Ni-HHTP@CoP, and Ni-HHTP@Co3O4 at different current densities; (f) Cycling stability of Ni-HHTP@Co(OH)2 and Ni-HHTP@CoP at 3 A·g-1 after 5 000 cycles; (g) Ragone plots illustrated energy and power density of some Co(OH)2/MOF-based devices[36]
图 11 (a) Ni-HAB的结构; (b) Ni-HAB和对应离子的氧化还原反应示意图; (c) 扫描速率为0.1 mV·s-1时, 不同电势窗口下Ni-HAB的CV图[42]; (d) Cu-TAC的合成与结构示意图; (e) 电导率随温度的变化曲线; (f) 几种cMOFs制成锂离子电池的容量对比[43]
Figure 11 (a) Chemical structure of Ni-HAB; (b) Illustration of the redox reactions of Ni-HAB with respective counter ions; (c) Cyclic voltammograms of Ni-HAB at 0.1 mV·s-1 in various potential windows[42]; (d) Synthetic and structure scheme of Cu-TAC; (e) Temperature-dependent conductivity of Cu-TAC; (f) Comparison of capacity of Cu-TAC to other 2D cMOF anodes for LIBs[43]
图 13 (a) Ni3(HITP)2和Ni3(Ni3HAHATN)2的电催化析氢反应极化曲线; (b) 几种不同(M2)3((M1)3HAHATN)2样品的电催化析氢反应极化曲线以及(c) 对应的Tafel图; (d) Ni3(Ni3HAHATN)2纳米薄层电催化水分解示意图[48]
Figure 13 (a) HER polarization curves of Ni3(HITP)2 and Ni3(Ni3HAHATN)2; (b) Polarization curves of the various (M2)3((M1)3HAHATN)2 samples and (c) the corresponding Tafel plots; (d) Electrocatalytic diagram of Ni3(Ni3HAHATN)2 nanosheets toward HER[48]
图 14 (a) NiPc-NiO4催化CO2RR机理示意图; (b) 几种MOFs材料的转换频率(TOF)和最大CO偏电流密度对比; (c) NiPc-NiO4和NiPc-OH对CO的FE[49]; (d) 平面和垂直扩展结构的二维MOFs示意图; (e) 2D-vc-MOF(Cu)的合成和结构模型(C、O、Cu分别为灰色、红色和蓝色, H原子省略); (f) 2D-vc-MOF(Cu)的线性扫描伏安图; (g) 2D-vc-MOF(Cu)与Cu3(HHTP)2对甲烷的FE对比[51]
Figure 14 (a) Illustration of the mechanism of CO2RR reaction catalyzed by NiPc-NiO4; (b) Comparison of the turnover frequencies (TOFs) and maximum CO partial current densities of reported MOF catalysts; (c) FEs of CO for NiPc-NiO4 and NiPc-OH[49]; (d) Schematic illustration of planarly/vertically extended structures in 2D MOFs; (e) Synthesis and structural model of 2D-vc-MOF(Cu) (Grey, red, and blue spheres represent C, O, and Cu, respectively, and H atoms are omitted); (f) Linear sweep voltammetry (LSV) curves of 2D-vc-MOF(Cu); (g) Comparison of FEs of CH4 for 2D-vc-MOF and Cu3(HHTP)2[51]
图 15 PPy HF/Ni-CAT-NWs柔性超级电容器的(a) 结构示意图和(b) CV曲线; (c) Ni-CAT/Ni-CAT-NWs柔性超级电容器在不同弯折程度下的CV曲线; (d) Ni-CAT/Ni-CAT-NWs柔性超级电容器在不同弯折次数的容量保持率和CV曲线[53]; (e) Ni3HHTP2汗液传感器结构示意图; (f) Ni3HHTP2汗液传感器对维生素C的检测结果与高效液相色谱对比; (g) 检测数据由传感器无线传输到手机的过程示意图[54]; (h) Ni3(HITP)2-NUS-8复合材料的合成策略及其在传感器上的应用; (i) Ni3(HITP)2/NUS-8传感器对H2S响应的信号强度与H2S浓度的关系曲线[55]
Figure 15 (a) Schematic illustration and (b) CV curves of the symmetric flexible supercapacitor based on PPy HF/Ni⁃CAT⁃NWs; (c) CV curves of the supercapacitor at different bending angles; (d) Capacitance retention and CV curves of the supercapacitor at different cycles of continuous bending[53]; (e) Configuration of the layered film sensor; (f) Comparison of the vitamin C concentrations of five sweat samples detected using the cMOF⁃based sweat sensor and HPLC; (g) Illustration of the wireless transmission from the sensors to a mobile phone[54]; (h) Schematic diagram on the synthesis strategy of Ni3(HITP)2/NUS⁃8 and its application for multiple detection; (i) Linear plots of response vs concentration of H2S for the Ni3(HITP)2/NUS⁃8 coated sensors[55]
表 1 Fe2(DOBDC)、Fe2(DSBDC)、Mn2(DOBDC)和Mn2(DSBDC)的导电性[17]
Table 1. Conductivity of Fe2(DOBDC), Fe2(DSBDC), Mn2(DOBDC) and Mn2(DSBDC)[17]
cMOF Conductivity / (S·cm-1) σas-synthesized σguest free Fe2(DSBDC) 3.9×10-6 5.8×10-7 Mn2(DSBDC) 2.5×10-12 1.2×10-12 Fe2(DOBDC) 3.2×10-7 4.8×10-8 Mn2(DOBDC) 3.9×10-13 3.0×10-13 
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表 2 Ln4(INA)3(GA)3的电导率(σ)与π-π堆积距离(d)的关系[21]
Table 2. Relationship between conductivity (σ) and distance of π-π stacking (d) of Ln4(INA)3(GA)3[21]
Compound d / nm σ / (S·cm-1) Tm4(INA)3(GA)3 0.332 2×10-6 Lu4(INA)3(GA)3 0.334 1×10-6 Gd4(INA)3(GA)3 0.335 5×10-7
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表 3 cMOFs的组成及性能参数
Table 3. Compositions and characteristics of cMOFs
Material Ligand σ / (S·cm-1) Measurement method Strategy SBET* / (m2·g-1) Reference Cu[Cu(pdt)2] 6×10-4 Through bond [16] Mn2[Ni(dbg)2] 8×10-8 Single crystal, two-point
probeThrough space 543.2 [56] 1×10-9 Pellet, two-point probe Zn2[Ni(dbg)2] 8×10-11 Pellet, two-point probe Through space 539.8 [56] Cd2[Ni(dbg)2] 6×10-7 Single crystal, two-point
probeThrough space 486.7 [56] 1×10-11 Pellet, two-point probe Ni-PTC 9 Pellet, four-point probe Extended conjugation [57] Co-PTC 455 Pellet, four-point probe Extended conjugation [58] 2D-vc-MOF(Cu) 2.25×10-5 Pellet, four-point probe Extended conjugation 556 [51] Ni3(HAB)2 (Ni3(HIB)2) 0.7 Pellet, four-point probe Extended conjugation 180-350 [59] Cu3(HAB)2 (Cu3(HIB)2) 0.11 Pellet, four-point probe Extended conjugation 180-350 [59] Co3(HAB)2 (Co3(HIB)2) 15.23 Pellet, four-point probe Extended conjugation [60] Zn3(HAB)2 (Zn3(HIB)2) 8.6×10-4 Pellet, van der Pauw Extended conjugation 145 [61] Ni3(HITP)2 2 Pellet, two-point probe Extended conjugation 766 [24, 62] 40/58.8 Film, van der Pauw Cu3(HITP)2 0.2 Pellet, two-point probe Extended conjugation [44] Co3(HITP)2 67.796 6 Pellet, four-point probe Extended conjugation 856, 2 338 [63] Mn3(HITP)2 44.923 6 Pellet, four-point probe Extended conjugation 843, 2 302 [63] Cu-BHT 2 500 Film, four-point probe Extended conjugation [25, 64] Ag3BHT2 363 Pellet, four-point probe Extended conjugation [65] Au3BHT2 9.15×10-5 Pellet, four-point probe Extended conjugation [65] Tm4(INA)3(GA)3 2×10-6 Single crystal, two-point
probeThrough space [21] Lu4(INA)3(GA)3 1×10-6 Single crystal, two-point
probeThrough space [21] Gd4(INA)3(GA)3 5×10-7 Single crystal, two-point
probeThrough space 312 [21] Cu3(HHB)2 7.3×10-8 Pellet, van der Pauw Through space 158 [66] (Cu3(HOB)2) Cu-TAC 3.2×10-5 Pellet, two-point probe Extended conjugation 114 [43] DDA-Cu 9.4×10-2 Film, two-point probe Extended conjugation,
Through space127.3 [14] Cu3(HHTP)2 1×10-4 Extended conjugation 334 [67-68] 0.02 Film, two-point probe LaHHTP 9×10-4 Pellet, two-point probe Through space 325 [69] NdHHTP 8×10-4 Pellet, two-point probe Through space 513 [69] HoHHTP 0.05 Pellet, two-point probe Through space 208 [69] YbHHTP 0.01 Pellet, two-point probe Through space 452 [69] M6(μ6-NO3)(HOTP)2
(M=Y, La, Eu)10-5-10-6 Pellet, two-point probe Extended conjugation 780 [70] Cu3(HHTQ)2 1×10-3 Pellet, four-point probe Extended conjugation 516.99, 1 360 [71-73] (Cu3(HHTT)2) 2.74×10-5 Pellet, two-point probe Ni3(HHTQ)2 2.27×10-5 Pellet, two-point probe Extended conjugation 1 114 [72-73] (Ni3(HHTT)2) Cu3(HHTN)2 9.55×10-10 Pellet, two-point probe Extended conjugation 486 [74] (M2)3((M1)3HAHATN)2
(M=Ni, Cu, Co)2 M1=M2=Ni, pellet,
four-point probeExtended conjugation [48] Cd2(TTFTB) 4.39×10-8 Pellet, four-point probe Through space 559 [32] 2.7×10-8 Pellet, van der Pauw 1.91×10-6 Single crystal,
four-point probeLa4(HTTFTB)4 2.57×10-6 Pellet, two-point probe Through space 596 [22] La(HTTFTB) 9.4×10-7 Pellet, two-point probe Through space 454 [22] La4(TTFTB)3 1.05×10-9 Pellet, two-point probe Through space 362 [22] Yb6(TTFTB)5 9×10-7 Pellet, two-point probe Through space 400 [75] Lu6(TTFTB)5 3×10-7 Pellet, two-point probe Through space 70 [75] Co-TPHS 1×10-6 Pellet, two-point probe Extended conjugation 246 [76] Ni2[CuPc(NH)8] 8×10-3 Pellet, van der Pauw Extended conjugation 556 [60] Cu2[CuPc(NH)8] 6×10-5 Pellet, van der Pauw Extended conjugation 659 [77] Cu3(TATHB)2 1.54×10-7 Pellet, four-point probe Extended conjugation [77] (Me2NH2)2[Fe2L3]·
2H2O·6DMF1.4×10-2 Pellet, two-point probe Through bond 1 175 [78] Fe2(DOBDC) 3.2×10-7 As synthesized, pellet,
two-point probeThrough bond 241 [17] 4.8×10-2 Guest free, pellet,
two-point probeMn2(DOBDC) 3.9×10-13 As synthesized, pellet,
two-point probeThrough bond 287 [17] 3.0×10-13 Guest free, pellet,
two-point probeFe2(DSBDC) 3.9×10-6 As synthesized, pellet,
two-point probeThrough bond 54 [17] 5.8×10-7 Guest free, pellet,
two-point probeMn2(DSBDC) 2.5×10-12 As synthesized, pellet,
two-point probeThrough bond 232 [17] 1.2×10-12 Guest free, pellet,
two-point probe(NBu4)2Fe2(DHBQ)3 1.07×10-3 Pellet, four-point probe Extended conjugation 5.42 [79] {[Cu2(6-Hmna)(6-mn)]·
NH4}n10.96 Single crystal,
four-point probeThrough bond [80] NiPc-Ni 4.8×10-5 Pellet, two-point probe Extended conjugation 101 [49, 81] 7.22×10-4 Pellet, four-point probe NiPc-Cu 1.43×10-2 Pellet, four-point probe Extended conjugation 284 [81] NiNPc-Ni 1.78×10-2 Pellet, four-point probe Extended conjugation 174 [81] NiNPc-Cu 3.13×10-2 Pellet, four-point probe Extended conjugation 267 [81] * The specific surface area was determined using the Brunauer-Emmett-Teller (BET) method.
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