▎ 摘　　要

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 x 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 degrees 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.