Clay-based 2D nanofluidics are potential candidates to drive the practical implementation of osmotic energy collection because they are economical and easy to prepare on a large scale. However, they usually suffer from inadequate ionic selectivity and low mechanical strength.
Study: 2D nanofluidics based on nanofiber-reinforced clay for the collection of highly efficient osmotic energy. Image credit: David Prado Perucha / Shutterstock.com
In research published in the journal Nano Energy, a nanofiber reinforcement technique is suggested to overcome these two main problems with nanofiber-based 2D nanofluidics reinforced with nanofibers to achieve extremely effective results.
An introduction to osmotic energy
One of the most critical global issues in addressing the fossil fuel crisis and environmental pollution has been the search for clean, renewable energy. Blue energy, abundant in nature, can be found in rivers and oceans. Due to its high efficiency and pure electricity supply, the energy obtained from the difference in salinity between fresh water and salt by osmosis is a possible source of blue energy.
The reverse electrodialysis (RED) technique, which relies heavily on an ion selective membrane (ISM), is generally used to capture this energy. ISM could specifically conduct individual ions (anions or cations) and generate net ion current under the transmembrane salinity gradient as the main component for blue energy collection.
The ionic flux and ionic selectivity of the ISM define energy performance. Due to the configuration of the nanofluidic membrane, which relies on surplus surface charges and dense nanochannels, leading to robust ionic selectivity and high ion flux, new opportunities have recently emerged to produce ideal ISMs.
Two-dimensional nanofluidics for osmotic energy collection
Stacking two-dimensional (2D) nanowires makes it relatively easier to produce larger amounts of membranes with nanoconfined channels and functional modifications.
2D nanofluidic membranes have received increasing attention in the application of osmosis-produced collection energy as a result.
Graphene oxide and MXenes are the two most widely used 2D materials for the manufacture of 2D nanofluidics. Despite having exceptional ionic selectivity, their practical uses are limited by the complicated and expensive procedure of manufacturing or disassembling the material.
Therefore, it is preferable to expand the selection of economical 2D raw materials and establish feasible and easy preparation or purification techniques to achieve mass production of 2D nanofluidics to achieve the desired output.
Limitations of clay-based 2D nanofluidics and how to improve them
The clay-based nanosheet is a strong candidate to create 2D nanofluidic membranes for its low cost, simple preparation method and abundant raw materials. More importantly, when 2D nanofluidic is incorporated, the electrified clay substrate naturally facilitates the obtaining of ionic selectivity.
Although they can be used in blue energy collection systems, 2D nanofluidic membranes reinforced with clay-based nanofibers have low ionic selectivity and low mechanical performance. From here, a proper change of the functional part is required to improve the fundamental functionality of these nanofluidics towards a highly efficient energy collection.
Many researchers have recently produced a variety of high-performance 2D nanofluids (BN, GO, MXene) reinforced with nanofibers such as Kevlar and cellulose. The intercalated alteration of nanofibers greatly improved the mechanical power of 2D nanofluidic membranes, providing benefits for applications using osmosis energy.
In addition, the charged groups of the nanofibers would increase the charge density in the nanoconfined region of the 2D nanofluidic, improving the ionic selectivity and therefore the output of osmotic energy. Therefore, nanofiber reinforcement is expected to improve the fundamental capacity of nanofluidic-based 2D nanofluidics to highly efficient and large-scale osmotic energy harvesting.
Main conclusions of the study
In this study, a strong 2D nanofluidic membrane based on nanofiber reinforcement was produced for the first time to successfully collect osmotic energy. The mechanical potency of the MMT lamellar membrane, which was found to be Young’s modulus was almost three orders of magnitude larger than the pure MMT membrane, was significantly increased by ANF intercalation.
The addition of negatively charged ANFs also increased the excess charge density within the 2D nanofluidic channels, resulting in better cation selectivity for highly efficient osmotic energy collection.
Systems for the collection of osmotic energy could generate an effective energy production of 5.16 Wm-2 in KCl system with the difference in salinity between the river and the sea, based on such well-designed 2D nanofluidics. The energy conversion performance was significantly higher than all previously reported 2D clay nanofluidics based on nanofibers.
ANF-reinforced MMT nanofluidics could generate a constant and significant amount of output power in a variety of environments, including those with extreme pH scales, fluctuating temperatures, and natural salinity gradients.
ANF-reinforced MMT nanofluidics showed excellent potential for practical applications in large-scale harvesting of osmotic energy along with features that include simple preparation and low cost. The design approach presented in this work is expected to be applied to different clay materials to produce improved performance 2D nanofluidics.
Reference
Qin, R., Tang, J. et al. (2022). 2D nanofluidic clay-based nanofiber reinforced for highly efficient osmotic energy collection. Nanoenergy. Available at: https://doi.org/10.1016/j.nanoen.2022.107526
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