Conduction Mechanism in Graphene Oxide Membranes with Varied Water Content: From Proton Hopping Dominant to Ion Diffusion Dominant

Abstract

Proton conductors, particularly hydrated solid membranes, have various applications in sensors, fuel cells, and cellular biological systems. Unraveling the intrinsic proton transfer mechanism is critical for establishing the foundation of proton conduction. Two scenarios on electrical conduction, the Grotthuss and the vehicle mechanisms, have been reported by experiments and simulations. But separating and quantifying the contributions of these two components from experiments is difficult. Here, we present the conductive behavior of a two-dimensional layered proton conductor, graphene oxide membrane (GOM), and find that proton hopping is dominant at low water content, while ion diffusion prevails with increasing water content. This change in the conduction mechanism is attributable to the layers of water molecules in GOM nanosheets. The overall conductivity is greatly improved by forming one layer of water molecules. It reaches the maximum with two layers of water molecules, resulting from creating a complete hydrogen-bond network within GOM. When more than two layers of water molecules enter the GOM nanosheets, inducing the breakage of the ordered lamellar structure, protons spread in both in-plane and out-of-plane directions inside the GOM. Our results validate the existence of two conduction mechanisms and show their distinct contributions to the overall conductivity. Furthermore, these findings provide an optimization strategy for the design of realizing the fast proton transfer in materials with water participation.

Controlled Assembly of a Dawson-like Antimoniotungstate-Supported Trefoil-type Trimer with Good Proton Conductivity Performance

“…With different humidity varying from 55 to 80%, the conductivity (σ) of compound 1 gradually climbed up from 3.28 × 10 –5 to 4.50 × 10 –3 S cm –1 (Figure a,c), demonstrating a dramatic increase with relative humidity increasing, which may be due to the fact that more mobile proton transfer sites are provided by water molecules . On the other hand, the results are consistent with the water absorption isotherm, and the absorption of a large number of water molecules by compound 1 at high humidity to form hydrogen bonds with a large number of surface oxygen atoms in the interlayer also accelerates the proton transfer. − In addition, as another crucial influence factor, temperature-dependent proton conductivity measurements also were probed by using the same sample 1 . As shown in Figure b, as the temperature rose from 30 to 75 °C under 80% RH, the conductivity increased continuously to 3.07 × 10 –2 S cm –1 , which was attributed to the acceleration of proton transfer with the temperature rising up (Figure b) .…”

Anchoring of Fe-MIL-101-NH2 to the Polymer Membrane Matrix through the Hinsberg Reaction to Promote Conductivity of SPEEK Membranes

“…Likewise, the water molecules in its pores can form hydrogen bonds with the sulfonamide groups formed in the composite membrane, which serve as a proton transfer pathway, thus making the proton transport rate faster and the proton conductivity higher. The calculated activation energies of SCPEEK@MOF-2 and SPEEK/MOF-2 composite films are 0.35 and 0.22 eV, respectively, indicating that both proton conduction mechanisms are Grotthuss mechanisms (Figure c). − The proton binds to a water molecule to form a hydronium ion and forms a hydrogen bond with a sulfonamide bond to transfer the proton to the next water molecule, thus forming the proton transport pathway (Figure ). Finally, the proton conductivity of SCPEEK@MOF-2 was tested at different RHs of 298 K (Figure S12).…”

Insight into the role of oxygen-containing groups in the proton conductivity of graphdiyne oxides

“…5,6 In this case, research into the proton conduction mechanism of carbon proton conductors continues to be an area of intense investigation. [7][8][9][10] Two-dimensional (2D) oxidized carbons have been widely used as proton conductors because of their lamellar structure enabling excellent integrated compatibility, and chemical, thermal and mechanical stability. As a result, they have been used as a prototypical platform for the investigation of the proton transport mechanism of carbon-based proton conductors.…”