National University of Singapore Jiang Donglin \”Nature Communications\”: COF power proton conduction efficiency breakthroughs!
high proton conductivity is not only vital to maintain the physiological functions of the art has an important role, are sensing, catalysis, energy conduction and storage, and the like. When the one-dimensional proton passage hole is sufficiently small, it can cause proton superfluid. However, as proton conductive materials must have a high density one-dimensional channel, rather than a single hole dimension. In the synthetic material, the conductive material is generally proton-proton conductive material and an aqueous fraction anhydrous proton conductive material. The aqueous proton conductive typically only work below 100 ℃. Anhydrous proton conducting systems are usually based on pure acid and heterocyclyl, it requires a very high stability of the porous material, and low conduction velocity. Thus design a material having both high stability and good proton conductivity is a very significant challenge. 
Recently, Professor Jiang Donglin National University of Singapore team on the \”Nature Communication\” reported based on COF developed a meet material efficiency requires both high stability and high proton conductivity. COF selected as the reason of the frame are three: First, in the COF covalently layer connected between a strong force so that a layer structure with sufficient stability. Second, a stable conductive network through hydrogen bonding proton proton COF network and the channel wall anchoring effect is achieved. Third, the guide topology design polygon skeleton COF may be achieved with a high density and high dimensional orientation passage can adjust the shape, size, capacity and transmission channels simultaneously. Based on the concept paper, the authors guide topology design, the use of C3 symmetry of 1,3,5-tri (4-aminophenyl) benzene (TPB) as a node having C2 symmetry 2,5-dimethylterephthalaldehyde (DMeTP) as channel segments connected together to build a diameter of 3.36 nm TPB-DMeTP-COF material (FIG. 1a). In which two methyl groups on the benzene ring is DmeTP very clever design. This causes two methyl Hyperconjugation and the inductive effect of weakening the polarity of C = N bond, diminished interlayer rejection, more conducive to a stable structure. FIG. (1b-1d), each pass TPB-DMeTP-COF materialThe channel has a C = N unit 6 inward, such units may be anchored entire network protons. After building a one-dimensional channel, the selection of phosphoric acid as a proton carrier. Because the non-volatile non-toxic acid having a high proton conductivity and can construct a network of hydrogen bonds formed by intermolecular hydrogen bonds with phosphoric acid. Phosphate, hydrogen bonding network in the passage TPB-DMeTP-COF, it is possible to C = N means a nitrogen atom in the hydrogen bonding anchor. Such stabilizing effect COF dual network with the network such that the phosphoric acid materials have very good stability.
Application of Fourier Transform Infrared (FTIR) spectroscopy to characterize the chemical structure and TPB-DMeTP-COF of the solid-state 13C NMR magic angle pulse (CP / MASNMR). Crystal structure TPB-DMeTP-COF is by powder X-ray diffraction (PXRD) and tight binding is calculated based on the density functional theory (DFTB +) is determined (FIG. 2a, 2b, 2c). On further confirmed TPB-DMeTP-COF with a good and uniform gap passage by a thermostat nitrogen adsorption test, a single channel radius of 3.36 nm and the void volume per unit mass of up to 1.60 cm 3 g -1 [ Langmuir 123], having a 2894 m 2 g -1 BET specific surface area, and 4596 m 2 g -1 the specific surface area (FIG. 2d, 2e). TPB-DMeTP-COF having a excellent stability , in tetrahydrofuran, acetonitrile, water and a solvent such as phosphoric acid solution, 12M concentrated hydrochloric acid, sodium hydroxide solution for 7 days 14M can still maintain a good crystal and a porous structure characteristic.
FIG. 2. (a) TPB-DMeTP-COF of PXRD spectra, the original red data, green data intensive blue analogdata. (B) and (c) are a top view and a plan view TPB-DMeTP-COF structure. (D) a nitrogen temperature TPB-DMeTP-COF at a temperature of 77 Kelvin adsorption curve. (E) the distribution of the void (circles) and the void volume (block).Proton characteristics superfluid , of application of vacuum infusion approach, phosphoric acid is annexed to the TPB-DMeTP-COF channel obtained H3PO4 @ TPB-DMeTP-COF (FIG. 3a, 3b). X-ray photoelectron spectroscopy (XPS) proved the existence of H3PO4 @ TPB-DMeTP-COF of elemental phosphorus, FTIR spectrum confirmed the acid with hydrogen TPB-DMeTP-COF nitrogen atom of the channel walls. Molecular dynamics calculation shows that a single layer structure contains 57 COF acid molecules by hydrogen bonding and spreading itself in the channel.
FIG. 3 (a) and (b) are top and side views H3PO4 @ TPB-DMeTP-COF structure.-11 S cm -1 ), but it is a good proton conductor (proton conductivity of 1.91 * 10 -1 S cm -1 ). It is worth emphasizing, H3PO4 @ TPB-DMeTP-COF proton conductivity of the order of 2-8 higher than the current grade anhydrous proton conducting system. Moreover, H3PO4 @ TPB-DMeTP-COF at 100 ℃ – within a temperature range of 160 ℃ exhibit both good proton conductivity, and continuously operate at a temperature of 160 ℃ of 20 hours, there was no performance degradation.
FIG. 4, (a) – (g) H3PO4 @ TPB-DMeTP-COF at different operating temperatures of proton conductivity. (H) at 160 ℃, H3PO4 @ TPB-DMeTP-COF 20 work child proton conductivity. (I) the amount of different acid-carrying TPB-DMeTP-COF proton conductivity, 100% annexed red, blue annexed 75%, 50% black annexed.