Supramolecular Calix[n]arenes-Intercalated Graphene Oxide Membranes for Efficient Proton Conduction

Abstract

Graphene oxide (GO) membranes with 2D interlaminar channels have triggered intensive interest as ion conductors. Incorporating abundant ion-conducting sites into GO interlayers is recognized as an effective strategy to facilitate ion conduction. Herein, we designed supramolecular compounds, para-sulphonato-calix[n]arenes (p-SC[n]As), as versatile intercalators to acquire highly conductive and robust GO membranes. The SC[n]A with ultrahigh ionic exchange capacity (IEC w , 5.37 mmol g −1 ) imparts sufficient proton donors, and its rigid framework imparts strong support of adjacent nanosheets. We designed three kinds of SC [n]As with the same IEC w but different sizes as intercalators, endowing the GO/ SC[n]A membranes with increasing ion concentration and d-spacing in the order of GO/SC[4]A < GO/SC[6]A < GO/SC[8]A. Therefore, the interlayers of GO/SC[8]A membranes afforded higher density of proton donors and could accommodate more water molecules to construct more continuous H-bond networks for proton transfer. Accordingly, the proton conductivities exhibited the same increasing trend, up to 327.0 mS cm −1 of GO/ SC[8]A-30% at 80 °C, 100% RH, which was 2.80 times higher than that of the GO membrane. Moreover, the GO/SC[n]A membranes remained stable in wet state, along with a 66% elevation in mechanical performance compared to the GO membrane.

Enhanced Fuel Cell Performance Using Ultrafast, Out-of-Plane Proton-Conducting, 3D Graphene Oxide as an Electrolyte

“…The high open-circuit voltage (OCV) of above 1.0 V at 30 °C indicates low fuel crossover and hence is suitable for practical application. 30 The current−voltage (I−V) curve and the current−power density curve are shown in Figure 3. A maximum current density of 300 mA cm −2 along with a maximum power density (MPD) of 60.2 mW cm −2 were observed for a 72 μm thick 3DGO pellet.…”

“…The single-cell performance evaluation was conducted at 30 °C and 100% RH. The high open-circuit voltage (OCV) of above 1.0 V at 30 °C indicates low fuel crossover and hence is suitable for practical application . The current–voltage ( I – V ) curve and the current–power density curve are shown in Figure .…”

“…High in-plane proton conductivity of single-layer GO nanosheet was first reported by Karim et al using a comb-shaped microelectrode . Thereafter, several strategies, including multilayer stacking, increasing the oxygen content by ozonation, and intercalating different hydrophilic groups/ions onto the GO walled channels, have been applied to improve the proton conductivity of GO-based materials. − Fundamentally, GO incorporates hydrophilic functional sites consisting of epoxy, carboxylic, and hydroxyl groups that extend from the hydrophobic carbon skeleton. Under humid conditions, these hydrophilic sites can adsorb water molecules that function as the vehicle for the movement of the proton via a Grouthuss mechanism.…”

Molecular-Level Control over Ionic Conduction and Ionic Current Direction by Designing Macrocycle-Based Ionomers

“… 37 − 41 Researchers, inspired by these features, have designed synthetic fluid/ion channels 42 , 43 based on dendritic dipeptides, 44 imidazole I-quartets, 42 , 45 functionalized calix 46 /pillararenes, 42 , 43 , 47 − 49 carbon nanotubes (CNTs), 34 , 50 − 52 graphene oxide, 53 and more. 54 − 57 These artificial systems have been studied as single transport elements 46 , 48 , 49 , 51 or self-assembled features comprising several monomeric units 46 , 47 upon embedding within lipid bilayers, 46 − 48 , 51 , 54 polymers, 49 , 50 , 52 or inorganic 51 , 58 matrices. CNTs with narrow diameters allow fluid flow in a frictionless manner, 50 which is best explained by slip flow.…”

“…Macrocycles or other sub-nanometer precision materials are widely used for ion sensing, 69 , 70 host–guest interaction studies, 71 − 74 gas separation, 75 , 76 and desalination/ion-selective separations. 43 , 55 , 77 − 82 Very limited attempts have incorporated calix[ n ]arenes within inorganic 58 , 83 ion-transporting membranes, but in the monomeric form. Therefore, the incorporation of macrocyclic repeat units within the chemical structure of oligo/polymers is still a new concept in ionomer design for energy conversion/storage devices.…”