Nanochannels are nanoscale structures that enable controlled ion and electron transport. They offer an effective approach to improving the efficiency, capacity, and durability of energy storage systems, including batteries, supercapacitors, and fuel cells.1
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In electrochemical power sources—essential for high-energy-density devices and portable electronics—uncontrolled ionic transport, particularly unwanted anion transfer, can degrade performance. By managing ionic transport, nanochannels help optimize the efficiency of electrochemical energy storage and conversion.1
Mechanism of Action
Nanochannels serve as precisely engineered pathways that enhance ion and electron transport in energy storage devices. Their nanoscale dimensions impart unique physicochemical properties at the interface, which significantly influence ion mobility and charge transfer, introducing specific ionic transport behaviors. These channels exhibit ion selectivity—allowing only certain ions to pass—and ion rectification, where ions preferentially move in a single direction.2
The ability of nanochannels to regulate ionic transport is primarily due to their nanoscale aperture and the excess charge on their interior surfaces. When in contact with an electrolyte, the surface charge attracts counter-ions (ions with an opposite charge) to form an electric double layer (EDL) that maintains charge balance.3
When the pore size of nanochannels is comparable to or smaller than the EDL thickness, the EDLs overlap, filling the entire channel. This overlap means that ionic transport within the nanochannel is governed by the surface charge, producing distinctive ionic transport characteristics unlike those in bulk solutions.1 These properties enhance ion mobility and charge transfer in batteries and supercapacitors, contributing to higher energy and power densities.
Applications in Energy Storage Systems
Nanochannels are applied across various types of energy storage systems, each benefiting in specific ways from their integration.
Lithium-Ion Batteries
In lithium-ion batteries (LIBs), the rapid transfer of Li+ ions between the cathode and anode is essential for maintaining optimal performance. If this ion transfer is delayed, electrons may accumulate at the anode, resulting in reduced voltage and diminished discharge capacity, especially during high-current discharge.4
Although anions in the electrolyte generally do not participate in the lithiation and delithiation processes, they have greater mobility than Li+. Excessive anion transport can reduce the Li+ transference number.5
Recent studies have shown that uncontrolled anion transfer can cause unwanted Joule heating, side reactions, and battery polarization, all of which significantly shorten battery life.4 Therefore, achieving high Li+ conductivity and a high Li+ transference number is critical for efficient ionic transport in LIBs.
Negatively charged nanochannels within electrode materials or separators can facilitate the rapid movement of Li+ due to strong electrostatic interactions, which helps mitigate issues related to uncontrolled anion transport and enhances the overall electrochemical performance of the batteries.6
2D nanoarchitectures are highly effective for fast Li+ transport due to their large active surface area, short diffusion paths, and excellent structural stability.1 Surface-charged 2D nanofluidic structures, known for their ion selectivity and high ionic transport, are particularly well-suited for LIBs.4
For example, C. Yan and colleagues developed stacked ultrathin Co3O4 nanosheets with surface functionalization (SUCNs-SF), which exhibited rapid Li+ transport, reduced structural stress, and minimized diffusion paths.6
When used as anodes in LIBs, SUCNs-SF demonstrated significantly higher discharge capacity compared to thicker Co3O4 nanosheets and bulk counterparts. This enhancement is attributed to the presence of negatively charged functional groups and the capacitive surface storage provided by the 2D nanofluidic channels.
Supercapacitors
Advancements in nanochannel-based supercapacitors have focused on materials with high conductivity and chemical stability, such as graphene and metal-organic frameworks (MOFs). These materials are structurally robust and offer a large surface area, which, combined with nanochannels, supports efficient ion transport and charge storage.
Research highlights the use of two-dimensional graphene oxide (GO) nanochannels infused with deep eutectic solvents (DES), which improve ion transport efficiency and conductivity.7 For instance, X. Wang et al. (2023) developed GO-DES membranes that demonstrated a 64-fold increase in ionic conductivity compared to bulk DES, attributed to the orderly ion transport within the nanochannels—this increased conductivity led to improved electrochemical performance, with energy density gains of up to 50.88 %.7
In another study, Pei Tang et al. incorporated MOFs, such as the zeolitic-imidazolate framework (ZIF-7), which effectively leveraged non-linear ion transport within nanochannels to boost ionic conductivity and create a “memory effect.”8 This dynamic ion movement enhanced capacitance and retention, making MOF-based supercapacitors highly stable and efficient. This makes nanochannels valuable for future energy storage innovations.
Fuel Cells
Nanochannels in fuel cells offer particular benefits in proton-exchange membrane (PEM) systems, where they facilitate the efficient transport of protons from the anode to the cathode. Studies show that nanochannels within these membranes can reduce internal resistance in fuel cells, leading to higher current densities and improved energy conversion efficiency.9
Functionalized nanohybrid membranes, such as NH-g-s, demonstrate superior fuel cell performance due to their high proton conductivity, water uptake, and ion-exchange capacity.10
Recently, Om Prakash et al. found that the NH-g-s membrane shows a proton conductivity of 0.13 S/m and enhanced water uptake compared to poly (vinylidene difluoride) membrane (PVDF-g-s), attributed to abundant sulfonate groups facilitating ion transport.11 The membrane’s lower activation energy (16.54 kJ/mol) supports efficient proton movement, surpassing PVDF-g-s and nearing Nafion’s performance with improved high-temperature stability.11
When used in direct methanol fuel cells (DMFCs), NH-g-s exhibited a higher power density (45 mW/cm²) compared to PVDF-g-s and Nafion, showcasing its potential for advanced fuel cell applications due to increased sulfonation and effective ion transport. By refining the size, orientation, and composition of nanochannels, these novel membrane materials could potentially lead to fuel cells with higher energy efficiency and operational longevity.
Conclusion
Nanochannels are pivotal in advancing energy storage technologies by enhancing ion and electron transport efficiency. In LIBs, nanochannels facilitate faster lithium-ion movement, contributing to higher energy densities and improved charging rates. In supercapacitors, they offer increased surface area for charge accumulation, maximizing capacitance and power density. In fuel cells, nanochannels create efficient pathways for proton transport, boosting energy conversion efficiency.
Future research should prioritize the development of nanochannel separators to enhance conductivity, unlocking greater potential in energy storage systems. The integration of nanochannels in hybrid materials, composite electrodes, and membrane materials presents an exciting avenue for achieving high-performing and durable energy storage technologies.
The next generation of smart electronics may rely on nanochannels that can dynamically respond to external stimuli like light and temperature. This adaptability could allow precise control over ion transport, leading to advanced, responsive energy conversion devices with new functionalities.12 As research advances, nanochannels have the potential to become fundamental to energy storage technology, contributing to a more sustainable and efficient energy future.
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References and Further Reading
1. Hao, Z. et al. (2020). Nanochannels regulating ionic transport for boosting electrochemical energy storage and conversion: a review. Nanoscale. https://pubs.rsc.org/en/content/articlelanding/2020/nr/d0nr02464c
2. Zhang, Q. et al. (2018). Robust Sandwich-Structured Nanofluidic Diodes Modulating Ionic Transport for an Enhanced Electrochromic Performance. Adv. Sci. https://onlinelibrary.wiley.com/doi/full/10.1002/advs.201800163
3. Russell, WS., Lin, C.-Y. Siwy, ZS. (2022). Gating with Charge Inversion to Control Ionic Transport in Nanopores. ACS Appl. Nano Mater. https://pubs.acs.org/doi/10.1021/acsanm.2c03573
4. Zhao, H. et al. (2024). Advancing lithium-ion battery anodes towards a sustainable future: Approaches to achieve high specific capacity, rapid charging, and improved safety. Energy Storage Mater. https://www.sciencedirect.com/science/article/abs/pii/S2405829724005221
5. Zhang, C. et al. (2019). Anion-Sorbent Composite Separators for High-Rate Lithium-Ion Batteries. Adv. Mater. https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201808338
6. Yan, C. et al. (2017). Engineering 2D Nanofluidic Li-Ion Transport Channels for Superior Electrochemical Energy Storage. Adv. Mater. https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201703909
7. Wang, X. et al. (2023). A two-dimensional nanochannel facilitates ionic conductivity of a deep eutectic solvent for an efficient supercapacitor. Mater. Today Energy. https://www.sciencedirect.com/science/article/abs/pii/S2468606923000412
8. Tang, P. et al. (2024). Constructing a supercapacitor-memristor through non-linear ion transport in MOF nanochannels. Natl. Sci. Rev. https://academic.oup.com/nsr/article/11/10/nwae322/7755424
9. Xu, Z. et al. (2024). Porphyrin Helical Nanochannel‐Assembled Polybenzimidazole Membranes Doped with Phosphoric Acid for Fuel Cells Operating in a Temperature Range of 25–200° C. Adv. Funct. Mater. https://onlinelibrary.wiley.com/doi/10.1002/adfm.202310762
10. Prakash, O., Tiwari, S., Maiti, P. (2022). Fluoropolymers and Their Nanohybrids As Energy Materials: Application to Fuel Cells and Energy Harvesting. ACS omega. https://pubs.acs.org/doi/10.1021/acsomega.2c04774
11. Prakash, O. et al. (2020). Fabrication of Conducting Nanochannels Using Accelerator for Fuel Cell Membrane and Removal of Radionuclides: Role of Nanoparticles. ACS Appl. Mater. Interfaces. https://pubmed.ncbi.nlm.nih.gov/32208641/
12. Wang, Q. et al. (2023). Nanochannel‐Based Ion Transport and Its Application in Osmotic Energy Conversion: A Critical Review. Adv. Phys. Res. https://onlinelibrary.wiley.com/doi/10.1002/apxr.202300016
