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From China:Progress has been made in the research of self-assembled monolayer COF membrane in The National Nanocentre

Recently, zhiyong Tang and Lianshan Li of the National Center for Nanoscience, Chinese Academy of Sciences have made important progress in the research of single-molecule COF membrane for salt difference energy conversion. Advancing Osmotic Power Generation by Covalent Organic Framework Monolayer Published online in Nature Nanotechnology. A review article on Harnessing Blue Energy with COF MEMBRANES was published in Nature Nanotechnology.  

  Osmotic energy, also known as salt differential energy, is an important clean energy source obtained by mixing seawater and river water. The key of salt difference energy conversion is to realize the selectivity of positive and negative ions and the selectivity of low resistance transmission through the membrane, that is, when positive and negative ions pass through the membrane at different speeds driven by the concentration gradient, the potential difference between the high concentration side and the low concentration side will be generated, so as to generate a current in the external circuit. Conventional polymer ion-exchange membranes typically achieve highly selective transport of positive and negative ions, but their high membrane resistance makes the ion flow rate and current density low, making it difficult for the energy output power density to exceed the minimum standard 5 WM-2 for commercial applications. Therefore, the key to solve the problem is to improve the membrane conductivity and ion transport rate while maintaining the positive and negative ion selectivity.

The low film resistance due to the ultra-thin thickness of two-dimensional materials makes them ideal materials to solve this problem. For example, the single nanopore on the monolayer of molybdenum sulfide exhibits extremely high output power density. However, traditional monolayer films, such as monolayer of molybdenum sulfide and graphene, have two defects in reducing film resistance: it is difficult to build high-density and uniform nanopore through top-down physical drilling; Membrane resistance caused by the low concentration polarization phenomena make the performance of the single nanopore difficult to linear extrapolation to the porous system, namely when the density is very high, make the film difficult to keep the effective concentration difference on both sides, leading to the sharp decline in current and voltage, this phenomenon is caused by the single span to the performance of the porous system attenuation makes people once questioned the feasibility of poor salt can convert.

In order to solve this problem, the research team constructed a large area of covalent organic framework (COF) monolayer film through preassembly interfacial polymerization reaction, which can reduce the film resistance and effectively restrain the voltage and current drop caused by concentration polarization through the pore-hole coupling effect caused by low pore spacing. The inherent high pore density and monolayer thickness of COF materials reduce the mass transfer resistance to the limit, thus improving the conductivity and current density of the film. The novel pore-hole coupling effect caused by high pore density and low pore spacing in this unique system is the key to solve the performance attenuation caused by concentration polarization, that is, the charged nanopores in COF film affect the adjacent nanopores, thus counteracting the current and voltage drop caused by concentration polarization. This material design increases the salt-differential energy conversion output power density to 135 WM-2. Furthermore, by regulating the metal center of porphyrin molecules in the COF framework, the output power density higher than 300 WM-2 under the real seawater/river salt gradient can be achieved. Theoretical simulation shows that the pore-hole coupling effect only occurs when the pore spacing is as low as 4.5 nm, which is a unique feature of COF membrane materials with high pore density and low pore spacing, and provides a new theoretical support for the calculation of new salt difference energy conversion materials.

The research work was supported by the National Key RESEARCH and Development Program, national Natural Science Foundation of China, the Strategic Priority Science and Technology Special Project of THE Chinese Academy of Sciences (Class B), etc.

The strong pore-hole coupling effect of single layer COF membrane with low pore spacing is used for salt difference energy conversion. (a) Synthesis and pore structure of monolayer COF films; (b) Thickness of single-layer COF film; (c, d) structure characterization of ordered pores; (e) Salt difference energy conversion performance; Theoretical simulation of (F, G) Hole-hole coupling effect & NBSP;

  Recently, zhiyong Tang and Lianshan Li of the National Center for Nanoscience, Chinese Academy of Sciences have made important progress in the research of single-molecule COF membrane for salt difference energy conversion. Advancing Osmotic Power Generation by Covalent Organic Framework Monolayer Published online in Nature Nanotechnology. A review article on Harnessing Blue Energy with COF MEMBRANES was published in Nature Nanotechnology.

Osmotic energy, also known as salt differential energy, is an important clean energy source obtained by mixing seawater and river water. The key of salt difference energy conversion is to realize the selectivity of positive and negative ions and the selectivity of low resistance transmission through the membrane, that is, when positive and negative ions pass through the membrane at different speeds driven by the concentration gradient, the potential difference between the high concentration side and the low concentration side will be generated, so as to generate a current in the external circuit. Conventional polymer ion-exchange membranes typically achieve highly selective transport of positive and negative ions, but their high membrane resistance makes the ion flow rate and current density low, making it difficult for the energy output power density to exceed the minimum standard 5 WM-2 for commercial applications. Therefore, the key to solve the problem is to improve the membrane conductivity and ion transport rate while maintaining the positive and negative ion selectivity.

The low film resistance due to the ultra-thin thickness of two-dimensional materials makes them ideal materials to solve this problem. For example, the single nanopore on the monolayer of molybdenum sulfide exhibits extremely high output power density. However, traditional monolayer films, such as monolayer of molybdenum sulfide and graphene, have two defects in reducing film resistance: it is difficult to build high-density and uniform nanopore through top-down physical drilling; Membrane resistance caused by the low concentration polarization phenomena make the performance of the single nanopore difficult to linear extrapolation to the porous system, namely when the density is very high, make the film difficult to keep the effective concentration difference on both sides, leading to the sharp decline in current and voltage, this phenomenon is caused by the single span to the performance of the porous system attenuation makes people once questioned the feasibility of poor salt can convert.

In order to solve this problem, the research team constructed a large area of covalent organic framework (COF) monolayer film through preassembly interfacial polymerization reaction, which can reduce the film resistance and effectively restrain the voltage and current drop caused by concentration polarization through the pore-hole coupling effect caused by low pore spacing. The inherent high pore density and monolayer thickness of COF materials reduce the mass transfer resistance to the limit, thus improving the conductivity and current density of the film. The novel pore-hole coupling effect caused by high pore density and low pore spacing in this unique system is the key to solve the performance attenuation caused by concentration polarization, that is, the charged nanopores in COF film affect the adjacent nanopores, thus counteracting the current and voltage drop caused by concentration polarization. This material design increases the salt-differential energy conversion output power density to 135 WM-2. Furthermore, by regulating the metal center of porphyrin molecules in the COF framework, the output power density higher than 300 WM-2 under the real seawater/river salt gradient can be achieved. Theoretical simulation shows that the pore-hole coupling effect only occurs when the pore spacing is as low as 4.5 nm, which is a unique feature of COF membrane materials with high pore density and low pore spacing, and provides a new theoretical support for the calculation of new salt difference energy conversion materials.

The research work was supported by the National Key RESEARCH and Development Program, national Natural Science Foundation of China, the Strategic Priority Science and Technology Special Project of THE Chinese Academy of Sciences (Class B), etc.

The strong pore-hole coupling effect of single layer COF membrane with low pore spacing is used for salt difference energy conversion. (a) Synthesis and pore structure of monolayer COF films; (b) Thickness of single-layer COF film; (c, d) structure characterization of ordered pores; (e) Salt difference energy conversion performance; Theoretical simulation of (F, G) Hole-hole coupling effect & NBSP;

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