Composite GO@Silk membrane for capillary-driven energy conversion

Abstract

Capillary-driven energy conversion based on saline electrolytes has attracted significant interest in recent years. The use of two-dimensional (2D) layer-by-layer membranes on this purpose have been widely reported, due to the sub-nanometer channels in such membranes provide a good capillary effect. The present study provides novel insights into the capillary-driven energy conversion performance of a 2D composite membrane consisting of a graphene oxide (GO) matrix and natural silk fibers. Notably, the composite structure of the GO@silk membrane results in a greater physical robustness, while the silk fibers increase the charge density of the 2D layers and hence improve their ion selectivity. Under the combined effects of capillary-driven flow in the layer channel and an overlapped electrical double layer (EDL) at the interface between the electrolyte and the negatively charged GO@silk structure, counter-ions (i.e., Na+) are readily attracted and transferred to the layer spacing of the membrane, resulting in the formation of an electrical voltage and current. We numerically and experimentally investigate the contribution of the silk mass ratio on the performance of the composite membrane. The electrolyte and tilt angle are found to show significant effect on output voltage and current. The experimental results show that the voltage and current have high values of 0.22 V and 12 μA, respectively. Overall, the present results suggest the feasibility of utilizing a stack of composite membrane structures to perform environmental energy conversion on a larger scale.