Enhanced ion transport by graphene oxide/cellulose nanofibers assembled membranes for high-performance osmotic energy harvesting

Abstract

As an emerging potential energy source to address the energy crisis, osmotic energy has attracted increasing attention. Fast ion transport is essential for this blue energy and for other membrane-based energy systems to achieve low membrane resistance and high ion selectivity for power density. However, the current nanochannel membranes suffer from a high energy barrier for ion transmembrane movement because of the narrow channel size and the low charge density, which results in low current and undesirable power density. Here, an elaborate graphene oxide (GO) nanosheets/cellulose nanofibers (CNFs) assembled membrane is reported to improve confined ion transport for high-performance osmotic energy conversion. CNFs, the most abundant natural nanomaterial with highly anisotropic properties and a high density of functional groups, not only enlarge the original narrow channel, which reduces the energy barrier for ion transport, but also introduce space charge between pristine GO nanosheets to maintain ion selectivity. Benefiting from the effective assembly of GO and CNFs, a high power density of 4.19 W m⁻² with an improved current is obtained by mixing artificial seawater and river water. Moreover, a power density of 7.20 W m⁻², which is higher than the standard for commercialization, is achieved at 323 K. The osmotic energy conversion shows a nonlinear thermal dependence relationship at high temperatures due to bubble nucleation. This material design strategy can provide an alternative concept to effectively enhance ion transport in membrane-based fields such as separations, desalination, flow batteries and fuel cells.