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Design of nanochannel interfaces is a key point in energy utilization

(Nanowerk Spotlight) The ability of nanochannels to regulate transported substances in confined spaces is of great research interest in innovative applications, such as high-resolution sensing, filtering, and high-efficiency energy utilization.
In the last area, research on nanochannels in energy-related areas continues to face challenges such as low efficiencies, complex preparation processes, and high fabrication costs. Overcoming these challenges is an important and difficult task in the field of energy conversion, energy conservation, and energy recovery.
Creating nanochannels for energy utilization that are efficient, low-cost, and easy to prepare would lead the way to the development of clean and renewable energy resources.
The energy utilization process in nanochannels is affected by the interactions between the nanochannel's inner surface and flowing fluids. Consequently, the physicochemical properties of the interface inside nanochannels have a profound influence on the flowing liquid, which thereby affects energy utilization.
A Perspective article in ACS Nano ("Interface Design of Nanochannels for Energy Utilization") highlights the interface design and applications of nanochannels and addresses relevant issues and challenges.
Illustration of interface design in nanochannels for energy utilization in energy conversion, energy conservation, and energy recovery
Illustration of interface design in nanochannels for energy utilization in energy conversion, energy conservation, and energy recovery. (Top left) Pressure-driven flow through a nanochannel induces a flow of counter charges in the double layer at the channel walls, thus generating an electrical current, which converts mechanical energy into electrical energy. (Top right) With a concentration gradient, the ions diffuse spontaneously across the nanochannel, converting Gibbs free energy in the form of a salinity gradient into electricity. (Bottom left) The slip interface is formed at the inner wall of nanochannels by modifying the interface with an additive bilayer, and the total streaming current generation from nanochannels is related to the slip of additive molecules. (Bottom right) Optimized interface design could improve the energy recovery efficiency in a capacitive deionization system for water desalination. (© American Chemical Society) (click on image to enlarge)

Energy Conversion

Energy conversion from pressure, osmotic potential, or photo energy, etc. to electrical energy through nanochannel-based devices – such as pressure-driven energy conversion, salinity-gradient power conversion, or photoelectric conversion – has become a hotspot recently because of nanochannelsí green energy character.
Although energy-conversion-related nanochannels have been widely studied, most researchers have focused on the material structures and concentration of electrolytes. However, the properties at the interfaces of nanochannels play important roles in ion transport during energy conversion.

Energy Conservation

The interface design of nanochannels can be used not only for energy conversion but also for energy conservation. For example, slip interfaces enable liquid flowing near the inner wall of a nanochannel to move relative to the inner surface of the nanochannel. This effect contributes to increases in the advection of counterions and decreases in dissipative loss at the interface between the liquid phase and the solid-state inner wall of the nanochannel.
Current research on energy conservation of nanochannels has focused on the solid materials, which are subject to problems such as fouling, physical damage, and limited lifetime. These drawbacks give rise to energetic losses. Fabrication of the slip interface in nanochannels is an efficient approach for improving fluid power generation efficiency.
Additionally, the dynamic multiphase transport and separation under steady-state applied pressure has great benefits for membrane science but has not yet been realized.

Energy Recovery

For the purpose of energy recovery, highly conductive electrodes and ion-exchange membranes have been developed because of their ability to reduce electrical resistance.
However, the interface between the ion-exchange membrane consisting of nanopores and the salt solution also affects energy recovery because the physicochemical properties of the seawater-solid porous membrane interface influences the amount of energy stored for the next desalination process. Energy recovery efficiency can likely be varied by changing the properties of the nanopore surfaces.
Thus, optimizing the interface design of the membranes could produce even higher energy recovery.
Collectively, current methods related to energy production based on nanochannels give rise to problems such as complex preparation processes, high fabrication costs, fouling, and low efficiency.
The authors conclude that interface design of nanochannels is one of the most promising, economical ways for targeting high-energy efficiency for real-world applications such as pressure-driven energy devices, salinity-gradient power cells, and desalination apparatuses.
As for the functionalization of the interfaces of nanochannels, emerging modification strategies such as bio-inspired design, dynamic liquid interface design, and symmetric/asymmetric design provide possible approaches to realize new avenues in energy utilization.
By Michael is author of two books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology and Nanotechnology: The Future is Tiny. Copyright © Nanowerk

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