and global climate-change crises. [1] In theory, mixing river water with seawater can release energy up to 0.8 kWh m −3 , equivalent to the energy obtained from water falling from a dam at a height of 280 m. [2] The total amount of this "blue energy" in the world has been estimated to be 1.4−2.6 TW, ranking it as the second largest marine-based energy source. [3][4][5] Compared with other renewable but intermittent energy sources, such as wind and solar power, osmotic energy features the advantage of minimal variability in power output. [6] To date, numerous methodologies have been proposed to capture this energy, among which reverse electrodialysis (RED) has been considered as the most promising one since it can convert osmotic energy to electricity directly, which dramatically streamlines processes and allows such system easier to popularize. [7] In a typical setup of RED, an ionselective membrane is placed between salty and fresh water to allow selective transport of cations or anions and therefore produce a transmembrane potential that can be harnessed as a battery. [8] Conventional RED systems are usually based on commercial ion-exchange membranes, but even with arrays or stacks of these membranes in series, [9] their maximum power density only reaches up to 2.2 W m −2 , which is far from commercial benchmark of 5 W m −2 for industrial development. [10] This is mainly related to insufficient ion selectivity and large transport resistance within these membrane materials. To achieve a high power density, advances in the design of membrane components to give dedicated architectures and physicochemical properties for efficient ionic transport are highly desirable. [11,12] In nature, biological ion channels feature rapid ion transport with extremely high selectivity and lay the foundation for almost all physiological processes. [13][14][15] Design elements learned from these natural systems have spawned a series of artificial nanofluidic porous membranes in which spatially confined surface charges contribute to excellent ion selectivity and high ion throughput. [16][17][18] These exciting progresses potentially open new avenues of high-performance membrane components for RED systems. [19][20][21] In particular, a giant increase in the power output of osmotic energy harvesting has been Two-dimensional nanofluidic membranes offer great opportunities for developing efficient and robust devices for ionic/water-nexus energy harvesting. However, low counterion concentration and long pathway through limited ionic flux restrict their output performance. Herein, it is demonstrated that rapid diffusion kinetics can be realized in two-dimensional nanofluidic membranes by introducing in-plane holes across nanosheets, which not only increase counterion concentration but also shorten pathway length through the membranes. Thus, the holey membranes exhibited an enhanced performance relative to the pristine ones in terms of osmotic energy conversion. In particular, a biomimetic multilayered membrane sequentially assembled from pr...
The emergence of lamellar nanofluidic membranes offers feasible routes for developing highly efficient, mechanically robust, and large‐scale devices for osmotic energy harvesting. However, inferior ion permeability associated with their relatively long channels limits ionic flux and restricts their output performance. Herein, a superstructured graphene oxide membrane is developed to allow programmable topological variation in local geometry and contain laminar spaces inside. Such deliberate design offers excess specific area as well as nanofluidic channels to modulate transmembrane ionic transportation while concomitantly retaining similar nanoconfined environment in contrast to planar ones, leading to considerable enhancement of ionic permeability without compromising selectivity. This can be highly favorable in terms of osmotic energy harvesting, where the superstructured membranes offer a power output much higher than those of conventional planar ones. Besides, the superstructure design also endows the resulting membranes with benign biofouling resistance, which can be crucial to their long‐term usage in converting osmotic energy. This study highlights the importance of membrane topographies and presents a general design concept that could be extended to other nanoporous membranes to develop high‐performance nanofluidic devices.
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