A nanofluidic chemoelectrical generator with enhanced energy harvesting by ion-electron Coulomb drag

A nanofluidic chemoelectrical generator with enhanced energy harvesting by ion-electron Coulomb drag | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article A nanofluidic chemoelectrical generator with enhanced energy harvesting by ion-electron Coulomb drag Kai Xiao, Yisha Jiang, Tao Wang, Wenchao Liu, Yitian Wu, Tingting Mei, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3828339/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 03 Oct, 2024 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract A sufficiently high current output of nano energy harvesting devices is highly desired in practical applications, while still a challenge. Theoretical evidence has demonstrated that Coulomb drag based on the ion-electron coupling interaction, can amplify current in nanofluidic energy generation systems, resulting in enhanced energy harvesting. However, experimental validation of this concept is still lacking. Here we develop a nanofluidic chemoelectrical generator (NCEG) consisting of a carbon nanotube membrane (CNTM) sandwiched between metal electrodes, in which spontaneous redox reactions between the metal and oxygen in electrolyte solution enable movement of ions within the carbon nanotubes. Through Coulomb drag effect between moving ions in these nanotubes and electrons within the CNTM, an amplificated current of 1.2 mA·cm -2 is generated, which is 15.6 times higher than that collected without a CNTM. Meanwhile, one single NCEG unit can produce a high voltage of ~0.8 V and exhibit a linear scalable performance up to tens of volts. Different from the other Coulomb drag systems that need additional energy input, the NCEG with enhanced energy harvesting realizes the ion-electron coupling by its own redox reactions potential, which provides a possibility to drive multiple electronic devices for practical application. Physical sciences/Nanoscience and technology/Nanoscale devices/Nanofluidics Physical sciences/Chemistry/Physical chemistry/Electron transfer energy harvesting Coulomb drag nanofluidic carbon nanotube interface energy Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction The phenomenon of Coulomb drag was initially documented as electron-electron interactions between two closely spaced, yet electrically isolated conductors, referred to as “layers”. Due to long-range interactions between these two distinct layers, an electrical current flowing through one of the layers, known as the “active layer”, can induce an electrical current in the other layer, the “passive layer”. During this process, both the energy and momentum of the carriers in the “active layer” transfer to the carriers in the “passive layer”, resulting in the generation of an open circuit voltage and short circuit current through efficiently “dragging” them along. 1–3 A similar dragging effect has also been observed in nanofluidic-based devices, extending the concept of Coulomb drag to interactions between a moving ionic fluid and electrons in conductors. 4–9 It has been discovered that a nanoampere electrical current in graphene can be induced by ionic flow which is driven by applying voltage to the fluidic chamber, 10 as the flow of fluids induces electrical polarization, driving electrical currents. Conversely, electrical excitations also contribute to ions movement. By applying an externally biased voltage to the single-walled carbon nanotube (SWCNT) shell layer, an electrical current is generated which drags ions through the SWCNT nanochannels, resulting in an ionic drag current with opposite direction. 11 Recently, Xiong et al. demonstrated that this generated current originates from the confined ion-electron interactions via a nanofluidic Coulomb drag mechanism through calculations and simulations. 12 The model predicts the amplification of ionic current by the electric energy applied on the semiconductive membrane due to the significant difference between ion mass and hole mass on the semiconductive membrane, deepening the understanding of the ion-electron interactions in nanochannels and demonstrating the potential for enhancing the current output in energy harvesting. With the amplified current resulting from Coulomb drag effect, the bottleneck of low current in the practical application of nano energy generators can be addressed. 13–15 However, further experimental work is still needed to verify the amplification of ionic current. In addition, all previously reported studies on Coulomb drag effect needed an external electrical field to drive the electrons or ionic flow. 10,11 These additional energy input components increase the complexity of the energy-harvesting devices, hindering their practical application. Therefore, it is important to develop nanofluidic-based energy generators that can not only exploit the current amplification effect by Coulomb drag but also power the ionic flow itself. In this work, we present a high-performance nanofluidic chemoelectrical generator (NCEG) based on a carbon nanotube membrane (CNTM), which is fabricated by sandwiching a CNTM with an area of around 25 mm 2 between two metal electrodes. To drive the ionic flow by the NCEG itself, we utilize metal-air redox reactions that can convert chemical energy into electrical energy without external stimulation. 16–18 Through the spontaneous redox reactions, a chemical potential is established across the membrane, which provides a driving force for the migration of ions in the nanochannels of CNTM. As a result, the current coupling of ion-electron is amplified to three times larger than that of the literatures where an external voltage was applied to drive the ionic flow. 10,11 Furthermore, this device can generate a stable and sustained direct voltage of 0.8 V and a short-circuit current density of 0.8 mA·cm − 2 , with a power density of 74 µW·cm − 2 , under ambient conditions for up to 80 hours. This work firstly provides experimental evidence that ion-electron Coulomb drag interactions can amplify currents for energy harvesting and offers a scalable strategy for energy harvesting devices based on nanofluidic systems. Results and Discussions Schematic and electrical output characteristics of NCEG In general, an applied voltage is needed to drive ion movement by Coulomb drag phenomenon in the nanofluidic system. 10,11 However, for a nanofluidic-based energy generator through Coulomb drag, it is essential that the device itself can facilitate ion transport within the nanochannels without requiring additional voltage components, thereby simplifying its structure. Here, we reported a compact nanofluidic energy generator device with an active electrode, in which the redox reactions on the electrode were employed to provide chemical potential, driving the transport of ions in nanochannels, and enhancing the collected current by Coulomb drag (Fig. 1 a). As shown in Supplementary Fig. 1a, a highly arrayed porous CNTM is sandwiched between a pair of metal electrodes, which are a gold foil and a conductive carbon tape (Nissin SEM double-sided conductive carbon tape) containing an aluminum substrate, respectively. And the preparation procedure of nitrogen-doped CNTM is illustrated. With a template of porous anodic aluminum oxide (AAO), nitrogen-doped CNTM was grown through the conventional chemical vapor deposition (CVD) approach using humidified acetonitrile bubbler as the single source of both carbon and nitrogen. The optical photograph and the cross-section SEM of the CNTM are shown in Fig. 1 b. The peaks of nitrogen and carbon in X-ray photoelectron spectroscopy (XPS) of nitrogen-doped CNTM (Supplementary Fig. 2) prove the successful fabrication of nitrogen-doped CNTM on the AAO template. When only the bottom conductive carbon tape electrode and the CNTM encounter 0.1 M NaCl electrolyte, an open circuit voltage (V OC ) of approximately 0.8 V (Fig. 1 c) and a persistent current density of around 0.8 mA·cm − 2 (Fig. 1 d) can be achieved. The origin of the output voltage signal Figure 2 a shows that the output voltage signal is from the redox reactions between the metal electrode and oxygen. In the presence of the electrolyte solution, the oxidation of the bottom metal electrode occurs, generating an electrical potential, thus realizing the conversion of chemical energy into electrical energy. 19–21 The output voltage can drive ions in nanochannels transporting, which then couple electrons from CNTM moving and will be explained later. To confirm the origin of the output voltage signal, position variations of the electrolyte solution were explored. As shown in Fig. 2 b, no significant voltage output can be observed when the electrolyte solution only contacts with the bottom of the CNTM. In this case, the necessary conditions for redox reactions are not sufficient. With the contact between the electrolyte solution and the bottom electrode on the CNTM, the redox reactions occurred and a potential difference between the conductive carbon tape electrode and O 2 in the electrolyte was built, resulting in a V OC of around 0.8 V. However, the V OC of the generator decreased sharply to 0 V when the electrolyte submerged both the bottom and top electrodes, which can be ascribed to the counteraction of the primary battery potential between the two electrodes. Furthermore, the sign of output voltage can be controlled by changing the reaction electrode. As shown in Fig. 2 c, a V OC of 0.8 V is generated when the electrolyte contacts with the bottom electrode, while a voltage of -0.8 V results from the contact between the electrolyte and the top electrode. To exclude the effect from CNTM, two different connection statuses between the electrode and CNTM were explored (Fig. 2 d). In both cases, the output voltages have no obvious difference, which can further confirm that the output voltage in the nanofluidic chemoelectrical generator is only related to the redox potential between the metal electrode and O 2 in the electrolyte. The redox reactions that occurred between the metal electrode and oxygen are summarized as following: \({\text{O}}_{2}+4{e}^{-}+2{H}_{2}O\to 4{OH}^{-}\) (cathode electrode) ( 1 ) \(M\to {M}^{n+}+n{e}^{-}\) (anode electrode) ( 2 ) where M represents the metal electrode. In these reactions, the pH of the electrolyte 22–24 and electrode activity 25–28 have significant effects on output voltage. The output voltage shows a higher value up to 1.2 V but decays gradually when the neutral NaCl electrolyte solution was substituted by a strong acid or alkaline (Fig. 2 e), indicating the accelerated redox reactions caused by the more reactive electrolyte solutions. 29 The presence of bubbles at the reaction interface (Supplementary Fig. 3) also confirmed the chemical reactions, as evidenced by chemical equations ( 3 ) and ( 4 ) below: $$M+HCl\to {MCl}_{n}+{H}_{2}\uparrow$$ 3 $$M+NaOH\to {NaMO}_{2}+{H}_{2}\uparrow$$ 4 The decayed output voltage can be attributed to the corrosive depletion of the bottom electrode. 30–32 The electrode activities of various metals determine the potentials in the redox reactions. 33 As shown in Fig. 2 f, the output voltages are highly correlated with the electrode activities, in which more active electrodes result in higher output voltages. After the redox reactions, the metal ions (Zn 2+ as an example) will be released from Zn electrode and can be driven to move from the bottom reaction site to the top layer (Supplementary Fig. 4), which can further confirm the redox reactions and the generation of transmembrane potential. Current amplification via ion-electron Coulomb drag For ions transport in a nanofluidic device, free electrons can be induced to migrate via ionic Coulomb drag when the cations of the electrolytes move along the solid channel surface benefiting from the ionic selectivity in surface charged nanochannel. 8–12 Theoretical study has demonstrated the potential utilization of Coulomb drag between ions within nanochannels and electrons/holes on semiconductors to amplify ionic current, due to a significant disparity between the ion mass and the effective mass of electrons/holes. 12 In the previous part, it has been proved that the redox reactions were employed to power the ionic transport in the nanochannels of CNTM. As a result, an amplified current density of 1.2 mA·cm − 2 can be observed in the CEG device, which is 15.6 times higher than the current collected by the primary cell without CNTM (Fig. 3 a). To further validate the mechanism of the current amplification induced by the ionic flow in the nanochannels, we conducted a comparison of the current in the NCEG with and without the presence of an electrolyte solution (0.1 M NaCl). In this case, all the electrodes in the NCEG were replaced as gold electrodes to avoid the potential difference. The output voltage of the redox reactions was replaced by an external voltage applied via a waveform generator to power the ionic flow. As shown in Fig. 3 b, under different voltage output, including ± 2, ±1, and ± 0.5 V, the current densities detected with NaCl electrolyte are consistently higher than those without NaCl electrolyte. This can be attributed to the reduction of electrical resistance with electrolyte and the Coulomb drag effect within nanochannels. As schemed in Fig. 3 d i, without the addition of electrolyte solution, the electrons powered by external voltage can only transfer in the semiconductor, CNTM, whose electrical resistance is much higher than that of electrolyte solution, resulting in a low current. Once the electrolyte solution is added, an ion pathway is established in parallel as depicted in the equivalent circuit on the right of Fig. 3 d iii, enabling the charges from the redox reactions to be transported via the cations and anions in the electrolyte solution (Fig. 3 d ii). Figure 3 e and 3 f confirm the ionic flow along the nanochannels of NCEG, where both sodium and chloride were detected on the top surface of the CNTM by EDS in the case that the bottom surface of CNTM was only in contact with the electrolyte solution. With the ionic flow along the nanochannels of NCEG, the Coulomb drag effect between the ionic flow in the nanochannels and electrons in the CNTM occurs, significantly contributing to the amplification of the current density. Figure 3 d iii illustrates the interactions between the electrons in the CNTM and the ions flowing in the nanochannels. Based on the principle of momentum conservation and the fact that the typical mass ratio between the ions and the holes is of the order of 10 5 to 10 6 , 12 the ion transport in the nanochannels promotes the number of electrons in the CNTM and therefore a remarkably amplified current can be achieved. Figure 3 b also shows that the deviation between the current density values with and without electrolyte solution increases with the increase of the loading external voltages. The increase of current density ( ΔJ SC1 ) exhibited an exponential enhancement with the increase of external voltage (Supplementary Fig. 5), indicating that with the increase of current in the circuit, the number of ions moving in the nanochannels is sharply increased, leading to more electrons transferring in the CNTM (Fig. 3 d iii). A similar effect was also observed when different external resistances were loaded in the circuit. As the circuit diagram illustrated in the inset of Fig. 3 c, under a fixed voltage of 0.8 V provided by the redox reactions, the increase of loaded resistance leads to a drop in the circuit current density, which was calculated as J SC−theoretical in Fig. 3 c. As shown in Supplementary Fig. 6, the current density difference ( ΔJ SC2 ) decreases with the increase of the loading external resistances. Strikingly, the measured circuit currents are much higher than the theoretical values of the current, showing the current amplification caused by the ionic Coulomb drag. Enhanced output energy power and application Figure 4 a and 4 b display the energy outputs with different resistive load conditions. With a 25 mm 2 working area of the CNTM, the maximum volumetric power density can reach 74 µW·cm − 2 when an optimal resistance of 10 KΩ was connected with the NCEG. A long-term stability measurement shows that the NCEG can work steadily for 80 hours with a negligible output V OC decay (Fig. 4 c). Moreover, airflow disturbances and varied light environment have limited influence on the voltage outputs of the NCEG (Supplementary Fig. 7). To measure the scalable performance of the NCEG, one, two, and three NCEG units were connected in series connection and output voltages of ~ 1.0 V, ~ 1.8 V and ~ 2.9 V, can be obtained, respectively (Fig. 4 d). Similarly, the short-circuit current increased to ~ 0.4 mA with three cells connected in parallel (Fig. 4 e). With further increasing the number of devices in series to fourteen, an output voltage of ~ 10 V can be achieved (Supplementary Fig. 8) and a linear relationship between series number and output voltage were obtained (Fig. 4 f). With three NCEG units connected in series, an electronic timer can be powered as shown in inset of the Fig. 4 f. Compared with the reported hydroelectric devices, the NCEG presents a huge advantage on the current density resulting from the Coulomb drag effect (Supplementary Table S1 ). Conclusions In this work, a NCEG that can achieve a milliampere-level current output was designed by sandwiching a CNTM between two metal electrodes. It has been demonstrated that the redox reactions between active metal and oxygen provide sufficient power to drive ionic flow within the nanochannels in the CNTM. Meanwhile, the theory that Coulomb drag induced by the movement of ions in the nanochannels can be used to amplify the current output is validated. The developed NCEG device exhibits constant and stable electrical output with high environmental tolerance, achieving an output power density of 74 µW·cm − 2 . We anticipate that this approach of amplifying the current output of NCEG not only enhances our fundamental understanding of energy harvesting principle in nanofluidic systems but also facilitates the development of new-generation energy generators in practical applications. Materials and Methods Materials: The anodic aluminum oxide AAO membranes with a thickness of 60 µm, a top pore size of 200 nm, and a bottom pore size of 30 nm were purchased from Sterlitech Corporation, Germany. Different metal electrodes (Al, Zn, Cu, Fe, and Au) were purchased from Taizhou Sennuo Material Technology Co. Ltd, China. The aluminum base conductive carbon tape (Nissin SEM double-sided carbon conductive tape) and non-woven substrate conductive carbon tape (conductive carbon fiber cloth) were purchased from Guangzhou Li-ge Technology Co, Ltd, China. Acetonitrile was purchased from J&K Scientific China. Fabrication of nitrogen-doped CNTM: An asymmetric porous AAO membrane was used as a template to fabricate the CNTM through the conventional chemical vapor deposition (CVD) process. In the CVD process, acetonitrile was employed as the carbon source precursor. Typically, the AAO substrate was first placed into the horizontal growth chamber of a standard atmospheric pressure CVD system. To conduct a reduction treatment on the AAO substrate, the temperature of the chamber was heated up to 1000°C with a gas mixture (Ar, 100 standard cubic centimeters per minute, sccm and H 2 , 50 sccm) for 0.5 h. Afterward, the carbon precursor was introduced to implement the growth step with a humidified acetonitrile bubbler. After 1.0 h of growth, the system was cooled down to room temperature under Ar protection. Design of NCEG: The NCEG device was simply built by attaching two electrodes on the upside and downside of the CNTM, respectively. Typically, aluminum-based conductive carbon tape (Nissin SEM double-sided carbon conductive tape) was used as the bottom electrode, and Au works as the top electrode. To investigate the effect of the potential difference in the redox reactions process, various materials, including Al, Zn, Cu, Fe, Au, and conductive carbon fiber cloth were used as the bottom electrode. Characterizations: Scanning electron microscope (SEM) (Hitachi-SU8220) was used to characterize the morphologies of AAO substrate and CNTM grown of AAO template. X-ray photoelectron spectroscopy (XPS) (PHI 5000 VersaProbe, ULVAC-PHI, Inc) was used to analyze the surface element composition of CNTM and AAO. X-ray energy dispersion spectroscopy (EDS) (OXFORD X-Max 80) was used to characterize the elemental composition of the CNTM before and after electrical output measurement. Electrical output measurement: The open-circuit voltage (V OC ) and the short-circuit current (I SC ) of the device were recorded using the digit multimeter (Keithley DMM7510). To confirm the source of the voltage output signal, the positions where the electrolyte solution contacted the CNTM were manipulated and the corresponding voltage output was recorded. To explore the important role of the ionic flow within nanochannels in the current amplification, the currents with and without ionic flow were compared. Since the chemical voltage on the NCEG only generates when the electrolyte solution contacts with the CNTM, a waveform generator (SDG1000X, Shenzhen Dingyang Technology, China) was applied to provide external bias voltage, including ± 0.1 V, ± 0.3 V, ± 0.5 V, ± 0.7 V, ± 1 V, ± 1.5 V, and ± 2 V. The top and bottom electrodes in the NCEG device were both replaced as gold electrodes to get rid of the voltage generated by the chemical difference. The currents of the NCEG with and without the contact of electrolyte solution (0.1 M NaCl) were compared following the equation: $$\varDelta {J}_{SC1} \left(mA·{cm}^{-2}\right)={J}_{SC-electrolyte}-{J}_{SC-without electrolyte}$$ $$={(I}_{electrolyte}-{I}_{without electrolyte})/S$$ 5 where the I electrolyte is the real-time current when the electrolyte contacted the device, I without electrolyte is the real-time current when the device connected to the circuit at the corresponding external voltage without electrolyte, and S = 0.25 cm − 2 is the working area of the device. To further explore the effect of the circuit current on the current amplification, the circuit current on the NCEG device was adjusted via loading different electrical resistances, including 100, 500, 1000, 3000, 5000, and 10000 Ω. The theoretical current of the circuit with different loads of resistances can be calculated based on the equation below: $${J}_{SC-theoretical} (mA·{cm}^{-2})=\frac{U}{{R}_{S}+{R}_{L}}/S$$ 6 Where U = 0.8 V is the average voltage output of the NCEG device, R S = 10000 Ω is the internal resistance of the device, determined by the maximum power output when the external resistance is equal to the internal resistance (Fig. 4 a), and the R L is the load resistance. To exhibit the significance of Coulomb drag in the nanochannels, the differences between the measured current and the theoretical current were calculated following the equation: $$\varDelta {J}_{SC2} (mA·{cm}^{-2})={{J}_{SC-measured}-{J}_{SC-theoretical}=(I}_{measured}-\frac{U}{{R}_{S}+{R}_{L}})/S$$ 7 Where I measured is the current measured. Declarations Data availability All data generated or analyzed during this study are included in the paper and its Supplementary Information, and from the corresponding author on request. Acknowledgments We acknowledge the help from Xiaoliu Wen in drawing the schemes including Figures 1a, 2a, and 3d. This work was financially supported by the National Key Technologies R&D Program of China （Grant No. 2023YFC2415900）, the National Natural Science Foundation of China(No.22275079), Shenzhen Science and Innovation Committee (20220815164834003), Shenzhen Science and Technology Program (KQTD20221101093559017), Guangdong Provincial Key Laboratory of Advanced Biomaterials (2022B1212010003) and Starting Grant from Southern University of Science and Technology (SUSTech). We also acknowledge the assistance of technical support from SUSTech Core Research Facilities. Author contributions K.X. conceived and supervised the project. Y. S. J. and T. W. designed the experiments, discussed the results, and wrote the paper. Y. S. J. fabricated devices, carried out experiments, and performed data analysis. W. C. L. explored and directed the synthesis of CNTM material samples. 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Supplementary Files SupportingInformation.docx Cite Share Download PDF Status: Published Journal Publication published 03 Oct, 2024 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3828339","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":267844272,"identity":"f90aabc5-9c68-430d-a091-e8d4c6d73b25","order_by":0,"name":"Kai Xiao","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA00lEQVRIiWNgGAWjYDACZgYGxgYGCTk2krUYk6CFAayFIbGBaOUGx5kfPpxRY5Hex3744ccfDHbyDOxnD+DVItnMZmy44ZhEbhtPmrE0D0OyYQNPXgJeLfzMDGaSD9iAWiR4GKSBXktgkOAxwKuFjZn9m+SDfxLpbBI8zD9/MNQT1sLPzGMmubFNIgGoBYgYDhPWItnMU2w4s0/CEOgXM2seg+NARg5+LQbnj2982POtTl6+/fDjmz8qquX52c/g14JuAtB3pKgfBaNgFIyCUYAdAACbHjQszPSfSgAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0001-9829-2707","institution":"Southern University of Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"Kai","middleName":"","lastName":"Xiao","suffix":""},{"id":267844273,"identity":"43b09865-fe08-4b9a-a534-2d15d25fa049","order_by":1,"name":"Yisha Jiang","email":"","orcid":"","institution":"Southern University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Yisha","middleName":"","lastName":"Jiang","suffix":""},{"id":267844274,"identity":"5cc246cf-1f14-4100-8f4d-a60030934d35","order_by":2,"name":"Tao Wang","email":"","orcid":"","institution":"Southern University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Tao","middleName":"","lastName":"Wang","suffix":""},{"id":267844275,"identity":"0a223f7e-11ee-4e0c-b9bd-21901456f4f8","order_by":3,"name":"Wenchao Liu","email":"","orcid":"","institution":"Southern University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Wenchao","middleName":"","lastName":"Liu","suffix":""},{"id":267844276,"identity":"11b4aab6-06e1-47c7-b585-61adc8c6b70a","order_by":4,"name":"Yitian Wu","email":"","orcid":"","institution":"Southern University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Yitian","middleName":"","lastName":"Wu","suffix":""},{"id":267844277,"identity":"6b1b5da4-fcd5-4555-9472-7e3e1784526a","order_by":5,"name":"Tingting Mei","email":"","orcid":"","institution":"Southern University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Tingting","middleName":"","lastName":"Mei","suffix":""},{"id":267844278,"identity":"8b762424-d62e-44e4-ab35-8896a62b8c48","order_by":6,"name":"Li Wang","email":"","orcid":"","institution":"East China Normal University","correspondingAuthor":false,"prefix":"","firstName":"Li","middleName":"","lastName":"Wang","suffix":""},{"id":267844279,"identity":"40021e1a-9555-4967-b7be-4b607a050f93","order_by":7,"name":"Guoheng Xu","email":"","orcid":"","institution":"Southern University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Guoheng","middleName":"","lastName":"Xu","suffix":""},{"id":267844280,"identity":"8e845317-d745-493f-873f-745ec2e3c2ad","order_by":8,"name":"Nannan Liu","email":"","orcid":"https://orcid.org/0000-0001-9235-2633","institution":"Wenzhou University","correspondingAuthor":false,"prefix":"","firstName":"Nannan","middleName":"","lastName":"Liu","suffix":""},{"id":267844281,"identity":"1b5d14f0-4674-456d-a882-c36b8587d4f8","order_by":9,"name":"Yude Wang","email":"","orcid":"","institution":"Yunnan University","correspondingAuthor":false,"prefix":"","firstName":"Yude","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2024-01-02 02:25:27","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3828339/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3828339/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-024-52892-4","type":"published","date":"2024-10-03T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":49847706,"identity":"8b1ef438-a787-46d7-8f79-032cac8f337f","added_by":"auto","created_at":"2024-01-19 03:56:58","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1815816,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSchematic and electrical output characteristics of NCEG.\u003c/strong\u003e a) Schematic depiction of the energy harvesting process in the NCEG; b) The optical photograph and the cross-view SEM of the CNTM; c) Measured continuous voltage and d) current density generated when the bottom of the generator was immersed in 0.1 M NaCl electrolyte. The insets indicate the sensitive signal response once the electrolyte solution is added.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3828339/v1/dffe3b6f995edc7ab54c35bf.png"},{"id":49847594,"identity":"83ed62e5-4140-45d4-81e8-df47c21c0a95","added_by":"auto","created_at":"2024-01-19 03:48:58","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":825776,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe origin of the output voltage signal.\u003c/strong\u003e a) The metal-oxygen redox reactions occurred in the NCEG; b) and c) The voltage output signals with different positions where the electrolyte solution contacted the device. Both the bottom and top electrodes are aluminum-based carbon conductive tape; d) The voltage of the device when the aluminum-based carbon conductive tape electrode was disconnected/connected to the CNTM; e) The voltage of the NCEG when 0.1 M NaCl solution was replaced by the acidic and alkaline electrolyte solutions; f) The voltage output signals with different metals working as the bottom electrode including conductive carbon fiber cloth (CFC), gold (Au), iron (Fe), copper (Cu), aluminum (Al), and conductive carbon tape (CT).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3828339/v1/4d434c2a1ea99cb38dc94c13.png"},{"id":49847595,"identity":"110a69d5-0e9f-40f4-b52f-a768378dbcc8","added_by":"auto","created_at":"2024-01-19 03:48:58","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1528231,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCurrent amplification via the ion-electron Coulomb drag. \u003c/strong\u003ea) The current density collected by the device without and with the CNTM in the electrolyte solution (0.1 M NaCl); b) The current density of the NCEG with and without the contact of electrolyte solution (0.1 M NaCl) as a function of external voltages. Both the bottom and top electrodes in the NCEG are replaced with gold electrodes to avoid the potential difference; c) The current density change of the NCEG when different external resistances are loaded in the circuit. A fixed voltage of 0.8 V was provided by the redox reactions on the electrodes; d) Schematic illustrations of the ion-electron coupling interactions via ionic Coulomb drag within CNTM nanochannels. The electrical current that flows through the CNTM nanochannels is manipulated by applying external voltage or connecting an external load resistor to the circuit. The transport of cations within the nanochannels is enhanced with higher electrical current and thus more electrons within the CNTM are generated due to Coulomb drag between ionic flow and electrons in CNTM. e) EDS mapping of the bottom and f) top section of CNTM after 1 hour testing (scale bar 25 μm).\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3828339/v1/df0179b4f0b7ea313b69e6fe.png"},{"id":49847597,"identity":"24bd6cea-4626-4f26-b614-ef842c00cd5f","added_by":"auto","created_at":"2024-01-19 03:48:58","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":774398,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEnhanced output energy power and application.\u003c/strong\u003e a) Output voltage and current change under different load resistances for NCEG with an area of around 25 mm\u003csup\u003e2\u003c/sup\u003e; b) Corresponding changes in output power density with different load resistances, and the best output performance can be achieved when the external resistance is 10 KΩ; c) Long-term performance of the NCEG measured with 0.1 M NaCl; d) Voltage output with one, two and three NCEGs connected in series; e) Short-circuit current with one, two, and three NCEGs connected in parallel; f) The open-circuit voltage when different number of devices are connected in series. The inset image is an optical photograph of the electronic timer powered by three NCEGs connected in series.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3828339/v1/141f530a4d95b2e27349f5ff.png"},{"id":65898594,"identity":"3ff97f60-cf34-4d46-ac4f-084a206b7c25","added_by":"auto","created_at":"2024-10-04 07:08:06","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6809227,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3828339/v1/98abf092-dc9b-4d4a-9688-bb421ec834dc.pdf"},{"id":49847598,"identity":"09a8c39e-6196-4ff4-98d1-7c21cf798116","added_by":"auto","created_at":"2024-01-19 03:49:00","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":16276477,"visible":true,"origin":"","legend":"","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-3828339/v1/4d24c9f2565c83c02c2e6698.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"A nanofluidic chemoelectrical generator with enhanced energy harvesting by ion-electron Coulomb drag","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe phenomenon of Coulomb drag was initially documented as electron-electron interactions between two closely spaced, yet electrically isolated conductors, referred to as \u0026ldquo;layers\u0026rdquo;. Due to long-range interactions between these two distinct layers, an electrical current flowing through one of the layers, known as the \u0026ldquo;active layer\u0026rdquo;, can induce an electrical current in the other layer, the \u0026ldquo;passive layer\u0026rdquo;. During this process, both the energy and momentum of the carriers in the \u0026ldquo;active layer\u0026rdquo; transfer to the carriers in the \u0026ldquo;passive layer\u0026rdquo;, resulting in the generation of an open circuit voltage and short circuit current through efficiently \u0026ldquo;dragging\u0026rdquo; them along.\u003csup\u003e1\u0026ndash;3\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eA similar dragging effect has also been observed in nanofluidic-based devices, extending the concept of Coulomb drag to interactions between a moving ionic fluid and electrons in conductors.\u003csup\u003e4\u0026ndash;9\u003c/sup\u003e It has been discovered that a nanoampere electrical current in graphene can be induced by ionic flow which is driven by applying voltage to the fluidic chamber,\u003csup\u003e10\u003c/sup\u003e as the flow of fluids induces electrical polarization, driving electrical currents. Conversely, electrical excitations also contribute to ions movement. By applying an externally biased voltage to the single-walled carbon nanotube (SWCNT) shell layer, an electrical current is generated which drags ions through the SWCNT nanochannels, resulting in an ionic drag current with opposite direction.\u003csup\u003e11\u003c/sup\u003e Recently, Xiong et al. demonstrated that this generated current originates from the confined ion-electron interactions via a nanofluidic Coulomb drag mechanism through calculations and simulations.\u003csup\u003e12\u003c/sup\u003e The model predicts the amplification of ionic current by the electric energy applied on the semiconductive membrane due to the significant difference between ion mass and hole mass on the semiconductive membrane, deepening the understanding of the ion-electron interactions in nanochannels and demonstrating the potential for enhancing the current output in energy harvesting. With the amplified current resulting from Coulomb drag effect, the bottleneck of low current in the practical application of nano energy generators can be addressed.\u003csup\u003e13\u0026ndash;15\u003c/sup\u003e However, further experimental work is still needed to verify the amplification of ionic current. In addition, all previously reported studies on Coulomb drag effect needed an external electrical field to drive the electrons or ionic flow.\u003csup\u003e10,11\u003c/sup\u003e These additional energy input components increase the complexity of the energy-harvesting devices, hindering their practical application. Therefore, it is important to develop nanofluidic-based energy generators that can not only exploit the current amplification effect by Coulomb drag but also power the ionic flow itself.\u003c/p\u003e \u003cp\u003eIn this work, we present a high-performance nanofluidic chemoelectrical generator (NCEG) based on a carbon nanotube membrane (CNTM), which is fabricated by sandwiching a CNTM with an area of around 25 mm\u003csup\u003e2\u003c/sup\u003e between two metal electrodes. To drive the ionic flow by the NCEG itself, we utilize metal-air redox reactions that can convert chemical energy into electrical energy without external stimulation.\u003csup\u003e16\u0026ndash;18\u003c/sup\u003e Through the spontaneous redox reactions, a chemical potential is established across the membrane, which provides a driving force for the migration of ions in the nanochannels of CNTM. As a result, the current coupling of ion-electron is amplified to three times larger than that of the literatures where an external voltage was applied to drive the ionic flow.\u003csup\u003e10,11\u003c/sup\u003e Furthermore, this device can generate a stable and sustained direct voltage of 0.8 V and a short-circuit current density of 0.8 mA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, with a power density of 74 \u0026micro;W\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, under ambient conditions for up to 80 hours. This work firstly provides experimental evidence that ion-electron Coulomb drag interactions can amplify currents for energy harvesting and offers a scalable strategy for energy harvesting devices based on nanofluidic systems.\u003c/p\u003e"},{"header":"Results and Discussions","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eSchematic and electrical output characteristics of NCEG\u003c/h2\u003e \u003cp\u003eIn general, an applied voltage is needed to drive ion movement by Coulomb drag phenomenon in the nanofluidic system.\u003csup\u003e10,11\u003c/sup\u003e However, for a nanofluidic-based energy generator through Coulomb drag, it is essential that the device itself can facilitate ion transport within the nanochannels without requiring additional voltage components, thereby simplifying its structure. Here, we reported a compact nanofluidic energy generator device with an active electrode, in which the redox reactions on the electrode were employed to provide chemical potential, driving the transport of ions in nanochannels, and enhancing the collected current by Coulomb drag (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). As shown in Supplementary Fig.\u0026nbsp;1a, a highly arrayed porous CNTM is sandwiched between a pair of metal electrodes, which are a gold foil and a conductive carbon tape (Nissin SEM double-sided conductive carbon tape) containing an aluminum substrate, respectively. And the preparation procedure of nitrogen-doped CNTM is illustrated. With a template of porous anodic aluminum oxide (AAO), nitrogen-doped CNTM was grown through the conventional chemical vapor deposition (CVD) approach using humidified acetonitrile bubbler as the single source of both carbon and nitrogen. The optical photograph and the cross-section SEM of the CNTM are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb. The peaks of nitrogen and carbon in X-ray photoelectron spectroscopy (XPS) of nitrogen-doped CNTM (Supplementary Fig.\u0026nbsp;2) prove the successful fabrication of nitrogen-doped CNTM on the AAO template. When only the bottom conductive carbon tape electrode and the CNTM encounter 0.1 M NaCl electrolyte, an open circuit voltage (V\u003csub\u003eOC\u003c/sub\u003e) of approximately 0.8 V (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec) and a persistent current density of around 0.8 mA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed) can be achieved.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eThe origin of the output voltage signal\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea shows that the output voltage signal is from the redox reactions between the metal electrode and oxygen. In the presence of the electrolyte solution, the oxidation of the bottom metal electrode occurs, generating an electrical potential, thus realizing the conversion of chemical energy into electrical energy.\u003csup\u003e19\u0026ndash;21\u003c/sup\u003e The output voltage can drive ions in nanochannels transporting, which then couple electrons from CNTM moving and will be explained later. To confirm the origin of the output voltage signal, position variations of the electrolyte solution were explored. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, no significant voltage output can be observed when the electrolyte solution only contacts with the bottom of the CNTM. In this case, the necessary conditions for redox reactions are not sufficient. With the contact between the electrolyte solution and the bottom electrode on the CNTM, the redox reactions occurred and a potential difference between the conductive carbon tape electrode and O\u003csub\u003e2\u003c/sub\u003e in the electrolyte was built, resulting in a V\u003csub\u003eOC\u003c/sub\u003e of around 0.8 V. However, the V\u003csub\u003eOC\u003c/sub\u003e of the generator decreased sharply to 0 V when the electrolyte submerged both the bottom and top electrodes, which can be ascribed to the counteraction of the primary battery potential between the two electrodes. Furthermore, the sign of output voltage can be controlled by changing the reaction electrode. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, a V\u003csub\u003eOC\u003c/sub\u003e of 0.8 V is generated when the electrolyte contacts with the bottom electrode, while a voltage of -0.8 V results from the contact between the electrolyte and the top electrode. To exclude the effect from CNTM, two different connection statuses between the electrode and CNTM were explored (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). In both cases, the output voltages have no obvious difference, which can further confirm that the output voltage in the nanofluidic chemoelectrical generator is only related to the redox potential between the metal electrode and O\u003csub\u003e2\u003c/sub\u003e in the electrolyte. The redox reactions that occurred between the metal electrode and oxygen are summarized as following:\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\({\\text{O}}_{2}+4{e}^{-}+2{H}_{2}O\\to 4{OH}^{-}\\)\u003c/span\u003e \u003c/span\u003e (cathode electrode) (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(M\\to {M}^{n+}+n{e}^{-}\\)\u003c/span\u003e \u003c/span\u003e (anode electrode) (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e)\u003c/p\u003e \u003cp\u003ewhere M represents the metal electrode.\u003c/p\u003e \u003cp\u003eIn these reactions, the pH of the electrolyte\u003csup\u003e22\u0026ndash;24\u003c/sup\u003e and electrode activity\u003csup\u003e25\u0026ndash;28\u003c/sup\u003e have significant effects on output voltage. The output voltage shows a higher value up to 1.2 V but decays gradually when the neutral NaCl electrolyte solution was substituted by a strong acid or alkaline (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee), indicating the accelerated redox reactions caused by the more reactive electrolyte solutions.\u003csup\u003e29\u003c/sup\u003e The presence of bubbles at the reaction interface (Supplementary Fig.\u0026nbsp;3) also confirmed the chemical reactions, as evidenced by chemical equations (\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e3\u003c/span\u003e) and (\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e4\u003c/span\u003e) below:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$M+HCl\\to {MCl}_{n}+{H}_{2}\\uparrow$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$M+NaOH\\to {NaMO}_{2}+{H}_{2}\\uparrow$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe decayed output voltage can be attributed to the corrosive depletion of the bottom electrode.\u003csup\u003e30\u0026ndash;32\u003c/sup\u003e The electrode activities of various metals determine the potentials in the redox reactions.\u003csup\u003e33\u003c/sup\u003e As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef, the output voltages are highly correlated with the electrode activities, in which more active electrodes result in higher output voltages. After the redox reactions, the metal ions (Zn\u003csup\u003e2+\u003c/sup\u003e as an example) will be released from Zn electrode and can be driven to move from the bottom reaction site to the top layer (Supplementary Fig.\u0026nbsp;4), which can further confirm the redox reactions and the generation of transmembrane potential.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eCurrent amplification via ion-electron Coulomb drag\u003c/h2\u003e \u003cp\u003eFor ions transport in a nanofluidic device, free electrons can be induced to migrate via ionic Coulomb drag when the cations of the electrolytes move along the solid channel surface benefiting from the ionic selectivity in surface charged nanochannel.\u003csup\u003e8\u0026ndash;12\u003c/sup\u003e Theoretical study has demonstrated the potential utilization of Coulomb drag between ions within nanochannels and electrons/holes on semiconductors to amplify ionic current, due to a significant disparity between the ion mass and the effective mass of electrons/holes.\u003csup\u003e12\u003c/sup\u003e In the previous part, it has been proved that the redox reactions were employed to power the ionic transport in the nanochannels of CNTM. As a result, an amplified current density of 1.2 mA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e can be observed in the CEG device, which is 15.6 times higher than the current collected by the primary cell without CNTM (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo further validate the mechanism of the current amplification induced by the ionic flow in the nanochannels, we conducted a comparison of the current in the NCEG with and without the presence of an electrolyte solution (0.1 M NaCl). In this case, all the electrodes in the NCEG were replaced as gold electrodes to avoid the potential difference. The output voltage of the redox reactions was replaced by an external voltage applied via a waveform generator to power the ionic flow. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb, under different voltage output, including\u0026thinsp;\u0026plusmn;\u0026thinsp;2, \u0026plusmn;1, and \u0026plusmn;\u0026thinsp;0.5 V, the current densities detected with NaCl electrolyte are consistently higher than those without NaCl electrolyte. This can be attributed to the reduction of electrical resistance with electrolyte and the Coulomb drag effect within nanochannels. As schemed in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed i, without the addition of electrolyte solution, the electrons powered by external voltage can only transfer in the semiconductor, CNTM, whose electrical resistance is much higher than that of electrolyte solution, resulting in a low current. Once the electrolyte solution is added, an ion pathway is established in parallel as depicted in the equivalent circuit on the right of Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed iii, enabling the charges from the redox reactions to be transported via the cations and anions in the electrolyte solution (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed ii). Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef confirm the ionic flow along the nanochannels of NCEG, where both sodium and chloride were detected on the top surface of the CNTM by EDS in the case that the bottom surface of CNTM was only in contact with the electrolyte solution. With the ionic flow along the nanochannels of NCEG, the Coulomb drag effect between the ionic flow in the nanochannels and electrons in the CNTM occurs, significantly contributing to the amplification of the current density. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed iii illustrates the interactions between the electrons in the CNTM and the ions flowing in the nanochannels. Based on the principle of momentum conservation and the fact that the typical mass ratio between the ions and the holes is of the order of 10\u003csup\u003e5\u003c/sup\u003e to 10\u003csup\u003e6\u003c/sup\u003e,\u003csup\u003e12\u003c/sup\u003e the ion transport in the nanochannels promotes the number of electrons in the CNTM and therefore a remarkably amplified current can be achieved.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb also shows that the deviation between the current density values with and without electrolyte solution increases with the increase of the loading external voltages. The increase of current density (\u003cem\u003eΔJ\u003c/em\u003e\u003csub\u003e\u003cem\u003eSC1\u003c/em\u003e\u003c/sub\u003e) exhibited an exponential enhancement with the increase of external voltage (Supplementary Fig.\u0026nbsp;5), indicating that with the increase of current in the circuit, the number of ions moving in the nanochannels is sharply increased, leading to more electrons transferring in the CNTM (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed iii). A similar effect was also observed when different external resistances were loaded in the circuit. As the circuit diagram illustrated in the inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, under a fixed voltage of 0.8 V provided by the redox reactions, the increase of loaded resistance leads to a drop in the circuit current density, which was calculated as \u003cem\u003eJ\u003c/em\u003e\u003csub\u003e\u003cem\u003eSC\u0026minus;theoretical\u003c/em\u003e\u003c/sub\u003e in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec. As shown in Supplementary Fig.\u0026nbsp;6, the current density difference (\u003cem\u003eΔJ\u003c/em\u003e\u003csub\u003e\u003cem\u003eSC2\u003c/em\u003e\u003c/sub\u003e) decreases with the increase of the loading external resistances. Strikingly, the measured circuit currents are much higher than the theoretical values of the current, showing the current amplification caused by the ionic Coulomb drag.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eEnhanced output energy power and application\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb display the energy outputs with different resistive load conditions. With a 25 mm\u003csup\u003e2\u003c/sup\u003e working area of the CNTM, the maximum volumetric power density can reach 74 \u0026micro;W\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e when an optimal resistance of 10 KΩ was connected with the NCEG. A long-term stability measurement shows that the NCEG can work steadily for 80 hours with a negligible output V\u003csub\u003eOC\u003c/sub\u003e decay (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). Moreover, airflow disturbances and varied light environment have limited influence on the voltage outputs of the NCEG (Supplementary Fig.\u0026nbsp;7). To measure the scalable performance of the NCEG, one, two, and three NCEG units were connected in series connection and output voltages of ~\u0026thinsp;1.0 V, ~\u0026thinsp;1.8 V and ~\u0026thinsp;2.9 V, can be obtained, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed). Similarly, the short-circuit current increased to ~\u0026thinsp;0.4 mA with three cells connected in parallel (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). With further increasing the number of devices in series to fourteen, an output voltage of ~\u0026thinsp;10 V can be achieved (Supplementary Fig.\u0026nbsp;8) and a linear relationship between series number and output voltage were obtained (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef). With three NCEG units connected in series, an electronic timer can be powered as shown in inset of the Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef. Compared with the reported hydroelectric devices, the NCEG presents a huge advantage on the current density resulting from the Coulomb drag effect (Supplementary Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn this work, a NCEG that can achieve a milliampere-level current output was designed by sandwiching a CNTM between two metal electrodes. It has been demonstrated that the redox reactions between active metal and oxygen provide sufficient power to drive ionic flow within the nanochannels in the CNTM. Meanwhile, the theory that Coulomb drag induced by the movement of ions in the nanochannels can be used to amplify the current output is validated. The developed NCEG device exhibits constant and stable electrical output with high environmental tolerance, achieving an output power density of 74 \u0026micro;W\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. We anticipate that this approach of amplifying the current output of NCEG not only enhances our fundamental understanding of energy harvesting principle in nanofluidic systems but also facilitates the development of new-generation energy generators in practical applications.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003eMaterials:\u003c/h2\u003e\n \u003cp\u003eThe anodic aluminum oxide AAO membranes with a thickness of 60 \u0026micro;m, a top pore size of 200 nm, and a bottom pore size of 30 nm were purchased from Sterlitech Corporation, Germany. Different metal electrodes (Al, Zn, Cu, Fe, and Au) were purchased from Taizhou Sennuo Material Technology Co. Ltd, China. The aluminum base conductive carbon tape (Nissin SEM double-sided carbon conductive tape) and non-woven substrate conductive carbon tape (conductive carbon fiber cloth) were purchased from Guangzhou Li-ge Technology Co, Ltd, China. Acetonitrile was purchased from J\u0026amp;K Scientific China.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003eFabrication of nitrogen-doped CNTM:\u003c/h2\u003e\n \u003cp\u003eAn asymmetric porous AAO membrane was used as a template to fabricate the CNTM through the conventional chemical vapor deposition (CVD) process. In the CVD process, acetonitrile was employed as the carbon source precursor. Typically, the AAO substrate was first placed into the horizontal growth chamber of a standard atmospheric pressure CVD system. To conduct a reduction treatment on the AAO substrate, the temperature of the chamber was heated up to 1000\u0026deg;C with a gas mixture (Ar, 100 standard cubic centimeters per minute, sccm and H\u003csub\u003e2\u003c/sub\u003e, 50 sccm) for 0.5 h. Afterward, the carbon precursor was introduced to implement the growth step with a humidified acetonitrile bubbler. After 1.0 h of growth, the system was cooled down to room temperature under Ar protection.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003eDesign of NCEG:\u003c/h2\u003e\n \u003cp\u003eThe NCEG device was simply built by attaching two electrodes on the upside and downside of the CNTM, respectively. Typically, aluminum-based conductive carbon tape (Nissin SEM double-sided carbon conductive tape) was used as the bottom electrode, and Au works as the top electrode. To investigate the effect of the potential difference in the redox reactions process, various materials, including Al, Zn, Cu, Fe, Au, and conductive carbon fiber cloth were used as the bottom electrode.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003eCharacterizations:\u003c/h2\u003e\n \u003cp\u003eScanning electron microscope (SEM) (Hitachi-SU8220) was used to characterize the morphologies of AAO substrate and CNTM grown of AAO template. X-ray photoelectron spectroscopy (XPS) (PHI 5000 VersaProbe, ULVAC-PHI, Inc) was used to analyze the surface element composition of CNTM and AAO. X-ray energy dispersion spectroscopy (EDS) (OXFORD X-Max 80) was used to characterize the elemental composition of the CNTM before and after electrical output measurement.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003eElectrical output measurement:\u003c/h2\u003e\n \u003cp\u003eThe open-circuit voltage (V\u003csub\u003eOC\u003c/sub\u003e) and the short-circuit current (I\u003csub\u003eSC\u003c/sub\u003e) of the device were recorded using the digit multimeter (Keithley DMM7510). To confirm the source of the voltage output signal, the positions where the electrolyte solution contacted the CNTM were manipulated and the corresponding voltage output was recorded. To explore the important role of the ionic flow within nanochannels in the current amplification, the currents with and without ionic flow were compared. Since the chemical voltage on the NCEG only generates when the electrolyte solution contacts with the CNTM, a waveform generator (SDG1000X, Shenzhen Dingyang Technology, China) was applied to provide external bias voltage, including\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1 V, \u0026plusmn;\u0026thinsp;0.3 V, \u0026plusmn;\u0026thinsp;0.5 V, \u0026plusmn;\u0026thinsp;0.7 V, \u0026plusmn;\u0026thinsp;1 V, \u0026plusmn;\u0026thinsp;1.5 V, and \u0026plusmn;\u0026thinsp;2 V. The top and bottom electrodes in the NCEG device were both replaced as gold electrodes to get rid of the voltage generated by the chemical difference. The currents of the NCEG with and without the contact of electrolyte solution (0.1 M NaCl) were compared following the equation:\u003c/p\u003e\n \u003cdiv id=\"Equa\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e$$\\varDelta {J}_{SC1} \\left(mA\u0026middot;{cm}^{-2}\\right)={J}_{SC-electrolyte}-{J}_{SC-without electrolyte}$$\u003c/div\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e$$={(I}_{electrolyte}-{I}_{without electrolyte})/S$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003ewhere the \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eelectrolyte\u003c/em\u003e\u003c/sub\u003e is the real-time current when the electrolyte contacted the device, \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003ewithout electrolyte\u003c/em\u003e\u003c/sub\u003e is the real-time current when the device connected to the circuit at the corresponding external voltage without electrolyte, and \u003cem\u003eS\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.25 cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e is the working area of the device. To further explore the effect of the circuit current on the current amplification, the circuit current on the NCEG device was adjusted via loading different electrical resistances, including 100, 500, 1000, 3000, 5000, and 10000 Ω. The theoretical current of the circuit with different loads of resistances can be calculated based on the equation below:\u003c/p\u003e\n \u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e$${J}_{SC-theoretical} (mA\u0026middot;{cm}^{-2})=\\frac{U}{{R}_{S}+{R}_{L}}/S$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eWhere \u003cem\u003eU\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.8 V is the average voltage output of the NCEG device, \u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003eS\u003c/em\u003e\u003c/sub\u003e = 10000 Ω is the internal resistance of the device, determined by the maximum power output when the external resistance is equal to the internal resistance (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea), and the \u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003eL\u003c/em\u003e\u003c/sub\u003e is the load resistance. To exhibit the significance of Coulomb drag in the nanochannels, the differences between the measured current and the theoretical current were calculated following the equation:\u003c/p\u003e\n \u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e$$\\varDelta {J}_{SC2} (mA\u0026middot;{cm}^{-2})={{J}_{SC-measured}-{J}_{SC-theoretical}=(I}_{measured}-\\frac{U}{{R}_{S}+{R}_{L}})/S$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e7\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eWhere \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003emeasured\u003c/em\u003e\u003c/sub\u003e is the current measured.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data generated or analyzed during this study are included in the paper and its Supplementary Information, and from the corresponding author on request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe acknowledge the help from Xiaoliu Wen in drawing the schemes including Figures 1a, 2a, and 3d. This work was financially supported by the National Key Technologies R\u0026amp;D Program of China\u0026nbsp;（Grant No. 2023YFC2415900）, the National Natural Science Foundation of China(No.22275079), Shenzhen Science and Innovation Committee (20220815164834003), Shenzhen Science and Technology Program (KQTD20221101093559017), Guangdong Provincial Key Laboratory of Advanced Biomaterials (2022B1212010003) and Starting \u0026nbsp; Grant from Southern University of Science and Technology (SUSTech). We also acknowledge the assistance of technical support from SUSTech Core Research Facilities.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eK.X. conceived and supervised the project. Y. S. J. and T. W. designed the experiments, discussed the results, and wrote the paper. Y. S. J. fabricated devices, carried out experiments, and performed data analysis. W. C. 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Commun.\u003c/em\u003e \u003cstrong\u003e13\u003c/strong\u003e, 3484-3494 (2022).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"energy harvesting, Coulomb drag, nanofluidic, carbon nanotube, interface energy","lastPublishedDoi":"10.21203/rs.3.rs-3828339/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3828339/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA sufficiently high current output of nano energy harvesting devices is highly desired in practical applications, while still a challenge. Theoretical evidence has demonstrated that Coulomb drag based on the ion-electron coupling interaction, can amplify current in nanofluidic energy generation systems, resulting in enhanced energy harvesting. However, experimental validation of this concept is still lacking. Here we develop a nanofluidic chemoelectrical generator (NCEG) consisting of a carbon nanotube membrane (CNTM) sandwiched between metal electrodes, in which spontaneous redox reactions between the metal and oxygen in electrolyte solution enable movement of ions within the carbon nanotubes. Through Coulomb drag effect between moving ions in these nanotubes and electrons within the CNTM, an amplificated current of 1.2 mA·cm\u003csup\u003e-2\u003c/sup\u003e is generated, which is 15.6 times higher than that collected without a CNTM. Meanwhile, one single NCEG unit can produce a high voltage of ~0.8 V and exhibit a linear scalable performance up to tens of volts. Different from the other Coulomb drag systems that need additional energy input, the NCEG with enhanced energy harvesting realizes the ion-electron coupling by its own redox reactions potential, which provides a possibility to drive multiple electronic devices for practical application.\u003c/p\u003e","manuscriptTitle":"A nanofluidic chemoelectrical generator with enhanced energy harvesting by ion-electron Coulomb drag","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-19 03:48:54","doi":"10.21203/rs.3.rs-3828339/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"12daaf12-7363-4152-816f-422c2f379baf","owner":[],"postedDate":"January 19th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":28223436,"name":"Physical sciences/Nanoscience and technology/Nanoscale devices/Nanofluidics"},{"id":28223437,"name":"Physical sciences/Chemistry/Physical chemistry/Electron transfer"}],"tags":[],"updatedAt":"2024-10-04T07:07:56+00:00","versionOfRecord":{"articleIdentity":"rs-3828339","link":"https://doi.org/10.1038/s41467-024-52892-4","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2024-10-03 04:00:00","publishedOnDateReadable":"October 3rd, 2024"},"versionCreatedAt":"2024-01-19 03:48:54","video":"","vorDoi":"10.1038/s41467-024-52892-4","vorDoiUrl":"https://doi.org/10.1038/s41467-024-52892-4","workflowStages":[]},"version":"v1","identity":"rs-3828339","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3828339","identity":"rs-3828339","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}