High-Performance Ionic Diode Membrane for Salinity Gradient Power Generation

Abstract

Salinity difference between seawater and river water is a sustainable energy resource that catches eyes of the public and the investors in the background of energy crisis. To capture this energy, interdisciplinary efforts from chemistry, materials science, environmental science, and nanotechnology have been made to create efficient and economically viable energy conversion methods and materials. Beyond conventional membrane-based processes, technological breakthroughs in harvesting salinity gradient power from natural waters are expected to emerge from the novel fluidic transport phenomena on the nanoscale. A major challenge toward real-world applications is to extrapolate existing single-channel devices to macroscopic materials. Here, we report a membrane-scale nanofluidic device with asymmetric structure, chemical composition, and surface charge polarity, termed ionic diode membrane (IDM), for harvesting electric power from salinity gradient. The IDM comprises heterojunctions between mesoporous carbon (pore size ∼7 nm, negatively charged) and macroporous alumina (pore size ∼80 nm, positively charged). The meso-/macroporous membrane rectifies the ionic current with distinctly high ratio of ca. 450 and keeps on rectifying in high-concentration electrolytes, even in saturated solution. The selective and rectified ion transport furthermore sheds light on salinity-gradient power generation. By mixing artificial seawater and river water through the IDM, substantially high power density of up to 3.46 W/m(2) is discovered, which largely outperforms some commercial ion-exchange membranes. A theoretical model based on coupled Poisson and Nernst-Planck equations is established to quantitatively explain the experimental observations and get insights into the underlying mechanism. The macroscopic and asymmetric nanofluidic structure anticipates wide potentials for sustainable power generation, water purification, and desalination.

Bioinspired Energy Conversion in Nanofluidics: A Paradigm of Material Evolution

“…[41] They fabricated a membrane-scale heterostructured nanofluidic device, termed an "ionic diode membrane" (IDM), which comprises asymmetric heterojunctions between mesoporous carbon and a macroporous alumina array. The multiple heterojunctions in pore size, surface charge polarity, and chemical composition result in highly rectified ion transport with rectification ratio of up to ≈450 and distinct cation selectivity (Figure 2e).…”

Smart Bioinspired Nanochannels and their Applications in Energy‐Conversion Systems

“…By mixing artificial seawater and river water though the heterostructured membrane, a substantially high power density of up to 3.46 W·m −2 was obtained, which largely outperforms some commercial ion exchange membranes. [34] Very recently, Wen and co workers constructed another salinity gradient energy harvesting system by integrating a porous BCP membrane with a conically porous PET membrane (Figure 5b). This asymmetric heterogeneous membrane could output a maxi mum power density of 0.35 W·m −2 by using 0.5 m NaCl and 0.01 m NaCl solutions.…”

“…a) Reproduced with permission. [34] Copyright 2014, American Chemical Society. b) Reproduced with permission.…”

“…450, which is beneficial for salinity gradient power generation. [34] Liu and co workers demon strated TiO 2 /Al 2 O 3 heterogeneous nanochan nels (Figure 2b) that exhibited light tuned ion gating and ion rectification characteristics. [35] Wen and co workers developed a series of heterogeneous membranes composed of a block copolymer (BCP) membrane and a porous PET membrane (Figure 2c,d).…”

Two-dimensional ion channel based soft-matter piezoelectricity

“…In addition, compared with other layered nanocomposites, the 2D building blocks provide unparalleled high packing density of the asformed nanochannels [10]. This strategy shows an advance from fabrication of individual nano-sized devices to largescale and low-cost manufacture of 2D yet bulky materials, boosting its application in ultrafiltration, energy storage and conversion, catalysis, and sensing [11,12].The structural inspiration stems from the nacre, an inner layer of mollusc shells, showing excellent mechanical strength and toughness [13,14]. The structural biomaterial consists of alternatively arranged hard matter (aragonite platelets) as backbone, and soft matter (proteins and poly- Figure 1 Fluidic transport in layered graphene membrane is confined only in the normal direction of the channel wall, termed 2D nanofluidics.…”