Research Progress in Covalent Organic Frameworks for Energy Storage and Conversion

Abstract

Covalent organic frameworks (COFs) are a class of porous crystalline materials consisting of organic units connected through covalent bonds. Due to their low density, high surface area and high thermal stability, COFs have found interesting applications in many fields, including molecular adsorption and separation, sensing, catalysis and optoelectronics devices. In particular, two-dimensional (2D) COFs have attracted increasing attention in energy fields. In this perspective, the applications of 2D COFs in energy storage (lithium ion batteries, lithium-sulfur batteries, supercapacitor and fuel cells) and energy conversion (water splitting and reduction of carbon dioxide) are reviewed. In addition, we will also discuss the remaining challenging issues. Keywords covalent organic frameworks; rechargeable batteries; supercapacitor; fuel cells; water splitting; CO 2 reduction 1 引言 共 价 有 机 框 架 (Covalent Organic Frameworks, COFs)是一类由有机结构单元通过共价键连接形成的晶 态有机多孔材料 [1] , 具有比表面积大、结晶性好、孔隙 率高等特点, 受到科研人员的广泛关注. 与其它有机多 孔材料如共轭微孔聚合物 [2] (CMP)、多孔芳香骨架 [3] (PAF)、超交联聚合物 [4] (HCP)等相比, COFs 具有有序的 堆积结构和良好的结晶性 [1c] . 依据 "框架化学" (Reticular Chemistry), 研究人员可对 COFs 材料的骨架和孔道进 行设计, 并对其结构与功能进行更加精确的调控 [1a,1d] . 自 2005 年 Yaghi 等 [5] 报道首例 COF 以来, COFs 受到研 究人员的广泛关注. 目前 COFs 已被应用于气体存储与 分离 [6] 、传感 [7] 、催化 [8] 、光电器件 [9] 等诸多领域, 并取 得了一系列重要进展.

Covalent‐Organic Frameworks (COFs) as Proton Conductors

“…[ 108 ] This high range of superior properties and excellent compatibility provides sufficient fuel to the researchers for the rapid exploration of COFs in the enormous fields of application, starting from energy to the environment such as sensor materials, [ 114–121 ] heterogeneous catalysis, [ 122–126 ] ionic conduction, [ 127–129 ] environmental remediation, [ 130–131 ] separation applications, [ 132–134 ] and so on. [ 135–138 ] Inspiring from these superior properties along with excellent stability and easy pore surface modifiability of COFs, from 2014, they have been employed extensively toward proton conduction application domain which demands a summarization of the recent progress for at a glance rapid visualizations ( Figure 2 ). [ 34,139–163 ] It is known that the preparation process in the form of film/membrane highly depends upon the compatibility of the substrate with other organic materials.…”

“…By thorough literature survey, we have found quite a few review reports on COFs based on their several applications such as luminescence and photophysical properties, [117] catalytic activities, [122][123][124][125][126] several separation applications, [132][133][134] sensing, [114][115][116][117][118][119][120][121] optoelectronics, [164][165][166] energy storage, [167][168] and so on. [135][136][137][138] Though a considerable number of COFs have been reported since 2014 for their potential applications in PEMFC as proton conductors, a comprehensive review on the rational design strategies to induce the proton conduction property of COFs is still lacking in literature. While Jiang and co-workers recently outlined the proton conduction property of COFs in a chapter briefly with the prime focus given on design, synthesis and various other functional properties of COFs, [108] Li and coworkers summarized quite a few proton-conducting COFs constructed by various linkages (CC, CC, CN, etc.)…”

Preparation and Photocatalytic Hydrogen Production of B, N Co-doped In2O3/TiO2

“…自从 1972 年 Fujishima 与 Honda [1] 发表了 TiO 2 作为 光催化剂实现光电催化分解水产氢/氧的工作以来, 光 催化制氢一直被认为是制备氢气这种清洁能源最有潜 力的方法之一 [2] . 由于 TiO 2 具有出色的生物、化学稳定 性与光化学稳定性以及合适的电势电位, 因此受到了科 研人员的广泛关注, 其在光催化降解有机污染物 [3][4][5] 、光 催化制氢 [6][7][8][9] 、 有害气体的探测与净化领域 [10][11] 都有潜在 的应用前景. 然而由于 TiO 2 本征带隙较宽(E g ＝3.1～3.2 eV), 只对紫外光有响应, 而对可见光部分几乎毫无响 应, 这限制了其在实际应用中对太阳能的高效利用 [12] ; 同时, TiO 2 吸收光后激发产生的载流子-电子和空穴容 易发生复合, 使得可以传输到催化剂表面参与反应的载 流子数目减少, 降低催化效率 [13] .…”

Fabrication of a Novel Covalent Organic Framework Membrane and Its Gas Separation Performance

“…Because of its outstanding characteristics, the novel DMTA-COF membrane is expected to be widely used in the field of H 2 purification and separation. Keywords covalent organic framework; crystal structure; membranes; gas separation; H 2 purification 成 [10][11][12][13][14][15] . 有序的且可调控的孔结构, 大的比表面积和永 久的孔隙率, 功能的多样性以及超高的热稳定性和化学 稳定性以及特殊的吸附亲和力等独特的性质使得 COFs 有望成为具有高的气体分离选择性的膜材料 [16][17][18] .…”

“…而 且层层堆叠方法通常用于 2D COF 膜的制备, 这就使得 该方法具有很大的局限性. 人们虽然利用界面聚合的方 法在气-固 [25] 、气-液 [26] 以及水-有机 [27] [15,31] , 这比气体分子的动力学直径(0.25～0. [33] , 这主要归因于 N 2 吸附过程中在压力增加 下由客体分子诱导的 COF 结构转变和客体分子在 COF 骨架中的重新定向堆积 [33][34][35] 其中 x i , x j 分别为渗透端气体 i 和气体 j 的摩尔分数; y i , y j 分别为残留端气体 i 和 j 的摩尔分数.…”