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

Abstract

Despite the considerable in-plane proton conductivity of graphene oxide (GO) nanosheets, inadequate single-cell performance in a polymer exchange membrane fuel cell (PEMFC) occurred on incorporating a vacuum-filtration-prepared GO membrane between the electrodes. In particular, the proton transfer between the electrodes in the PEMFC single cell is in the out-of-plane direction of the GO membrane and was found to be significantly lower than for the in-plane direction due to the presence of proton conduction barriers arising from turbostratic stacking of the GO layers. Therefore, the structural transformation of GO nanosheets into an ultrafast, out-of-plane proton conductor is key to boosting GO-based PEMFC performance. Here, we report the use of a freeze-dried route to three-dimensional (3D) graphene oxide (3DGO) exhibiting a 3D interconnected network and significant interlayer void space. The out-of-plane direction proton conductivity of 3DGO was calculated to be 3.5 × 10–2 S cm–1 at 343 K and 100% relative humidity (RH), which is about 175 times higher than that for the GO membrane. The 3DGO was incorporated as a solid electrolyte in a PEMFC single cell, and a maximum power density of 60.2 mW cm–2 was obtained at 30 °C. This high proton conductivity and PEMFC performance of the 3DGO are correlated with the facile proton conduction pathway and higher water uptake in the 3D porous architecture of 3DGO.

Enhanced mixed proton and electron conductor at room temperature from chemically modified single-wall carbon nanotubes

“…Very recently, the freeze-dried route-driven 3D GO was found to show significantly higher proton conductivity compared to the traditional vacuum dried 2D GO. 29 Herein, we also observed that the freeze-drying process of oxidized SWCNT can improve the proton conductivity over Ox-SWCNT-OD. The probable cause is explained in ESI.…”

Synergistic Strengthening in Graphene Oxide and Oxidized Single‐walled Carbon Nanotube Hybrid Material for use as Electrolytes in Proton Exchange Membrane Fuel Cells

“…The maximum power density obtained using 3DGO-CNTOX1 is the highest literature value so far reported for a GO-based PEMFC and even higher than that obtained for a Nafion based PEMFC under identical experimental conditions (see Table S2). [31,45,46,49,50]…”

“…[30] Furthermore, the application of the simple and efficient freeze-drying synthetic procedure promotes the formation of numerous pores and ion transport nanochannels. [31] Nevertheless, the resulting higher porosity weakens the structural integrity giving rise to lower mechanical strength in conjunction with an increase in the number of non-connected ion conduction channels. [32] Clearly, for optimum application as electrolyte in a PEMFC, sequentiallyarranged, multiple proton-conduction channels, with short pathways are required.…”

High Proton Conductivity of 3D Graphene Oxide Intercalated with Aromatic Sulfonic Acids

“…[24] To circumnavigate this, the use of 3D graphene oxide (3DGO) appeared highly attractive since it has a highly porous structure and thus provides numerous channels for the propagation of protons in different directions while resulting in the mean proton conduction pathway being significantly shortened. [41] However, maintaining the high performance of a PEMFC, especially under higher temperature and lower humidity conditions, while also ensuring a long lifetime, is exceedingly challenging. In a further approach, PEMFC efficiency has been demonstrated to be enhanced by incorporation of a dopant containing both hydrophilic and hydrophobic domains, as occurs in aromatic sulfonic acids (Scheme 1).…”