Engineered Cellulose Nanofiber Membranes with Ultrathin Low-Dimensional Carbon Material Layers for Photothermal-Enhanced Osmotic Energy Conversion.

As a promising clean energy source, membrane-based osmotic energy harvesting has been widely investigated and developed through optimizing the membrane structure in recent years. For chasing higher energy conversion performance, various external stimuli have been introduced into the osmotic energy harvesting systems as assistant factors. Light as a renewable and well-tunable energy form has drawn great attention. Normally, it needs massive photoresponsive materials for improving the energy conversion performance and this hinders its wide applications. Herein, we fabricate a cellulose nanofiber (CNF) membrane with an ultrathin layer of low-dimensional carbon materials (LDCMs) for photothermal-enhanced osmotic energy conversion. The ultralow loading carbon quantum dot, carbon nanotube, and graphene oxide (LDCM/CNF = 1:200 wt) are used for light-to-heat conversion to build the heat gradient across the membrane. The output power density of the osmotic energy generator has increased from ∼3.55 to ∼7.67 W/m under a 50-fold concentration gradient with light irradiation. This work shows the great potential of the CNF as a nanofluidic platform and the photothermal enhancement in osmotic energy conversion, and the ultralow loading design provides a practical and economical way to fully utilize other energy resources for enhancing osmotic energy conversion.