Nanomesh Electrodes Research Articles

Conformal Electrodeposition of Mesoporous Silica over High Aspect Ratio (AR>100) Nanomesh Electrodes

The high surface area provided by the nanopores of ordered mesoporous silica thin films enables a wide range of electrochemical applications such as sensors, catalysis, energy storage and ion-selective membranes. Further improvements are possible by coating such thin films on large surface area electrodes with high aspect ratios (> 100) to increase the active surface area. Atomic layer deposition (ALD) is often preferred to deposit conformal thin film oxides on high aspect ratio structures. Such vapor-phase depositions are limited by the available surface reactive sites to deposit thin films of thickness ranging from sub-nanometer to few tens of nanometer. However, there is a tradeoff in terms of deposition time/cycles to achieve quality films especially when high aspect ratios (>100) substrates are introduced. Electrochemistry offers an alternative, versatile method to conformally coat layers on 3D electrode surfaces. The electrochemically assisted self-assembly (EASA) of mesoporous silica, utilizes electrochemical reactions to locally increase the pH near the electrode surface, which in turn catalyzes the silica gelation and surfactant self-assembly, thus causing the controlled growth of mesoporous silica thin films [1]. Recently, our group has shown that good quality mesoporous silica films with thickness between 20-2000 nm could be achieved by controlling the hydrodynamic layer in a rotating disc electrode setup [2]. Moreover, EASA of mesoporous silica offers meso-channels that are aligned perpendicular to the underlaying conductive substrate which is optimal for mass-transport.In this follow-up work, we demonstrate a reliable, electrochemically controlled, conformal deposition of mesoporous silica onto large surface area nanomesh electrodes with an aspect ratio close to 100. Nanomesh electrodes developed in our group at imec, is built up of a regularly spaced (50 nm), inter-connected network of vertical and horizontal nanowires of diameter ~40 nm. These electrodes offer an 80x area enhancement (80 cm2 per geometric cm2) while maintaining a porosity close to 75%. We show that, the extent of silica deposition over these nanomesh electrodes can be electrochemically controlled from conformal coatings (~10 nm thick) uniformly coating the whole nanomesh architecture to complete fill and overfill of the nanomesh electrodes (~4 µm thick). Furthermore, excellent mass-transport properties of various silica coated nanomesh electrodes has been demonstrated using a ruthenium hexaammine redox probe. Finally, the area enhancement offered by the silica coated Ni nanomesh is demonstrated using the characteristic accumulation of a positively charged [Ru(NH3)6]3+ probe within the negatively charged silica nanochannels, which shows 55x increase for the amount of charge from the probe stored in the coated nanomesh, compared to a planar silica layer, consistent with the expected surface area enhancement of the 4 µm thick nanomesh electrodes.

Highly Transparent Ka-/W-Band Electromagnetic Shielding Films Based on Double-Layered Metal Meshes.

An electromagnetic (EM) wave-shielding film exhibiting high performance in high-frequency bands, such as the Ka- and W-bands, was fabricated by using double-layered metal meshes. The double-layered shielding (DLS) film consists of metallic micromesh and nanomesh electrodes (NMEs) on the upper and lower surfaces of a poly(ethylene terephthalate) (PET) film, respectively. The micromesh electrodes (MMEs) were fabricated such that they possessed a thickness higher than the line width, and they thus exhibited excellent electromagnetic wave-shielding performance in addition to optical transmittance. Moreover, the nanomesh electrodes helped prevent the deterioration of the shielding performance owing to the increase in frequency, which was possible by decreasing the aperture size of the mesh-type electrodes. The shielding effectiveness (SE) of the double-layered metal-mesh film was evaluated by using a shielding measurement system that is optimized for high frequencies. In addition, optical transmittance and flexibility tests were conducted. The results confirm that the double-layered shielding film exhibited a shielding effectiveness of more than 50 dB at an optical transmittance of 90% and a stable bending resistance of up to 5000 cycles at a radius of curvature of 6 mm. Double-layered metal-mesh films with such excellent performance are expected to be widely used in diverse applications such as the automobile, medical, and military industries.

Photovoltaic–Electrolyzer System Operated at >50 mA cm−2 by Combining Large‐Area Shingled Silicon Photovoltaic Module with High Surface Area Nickel Electrodes for Low‐Cost Green H2 Generation

Green hydrogen plays an important role in the energy transition as a renewable energy vector for long‐duration energy storage and as feedstock chemical for the industry. To reduce the price below 1.5 € kg−1 H2, competitive to production from fossil fuels, silicon photovoltaic (PV)‐powered efficient anion‐exchange membrane (AEM) water electrolysis is a promising combination. Practical implementation of such a photovoltaic–electrolyzer (PV–EC) technology requires standard area‐sized solar cells and electrolyzers operating at large current densities. Nonetheless, state‐of‐the‐art research often employs <10 cm2 PV devices and electrolyzers operated at <10 mA cm−2. Herein, a commercially relevant PV–EC system combining shingled standard silicon technology with efficient low‐cost AEM electrolysis using high‐surface‐area (26 m2 cm−3) nickel nanomesh electrodes is presented. The produced H2, operating current, and voltage are in situ monitored over >20 h yielding a stable solar‐to‐hydrogen efficiency (ηSTH) of 10% at electrolyzer current densities ≈60 mA cm−2 and dynamic load testing up to 300 mA cm−2 results in stable performance. Based on the measured PV–EC system data, best practices to accurately determine the ηSTH for PV‐powered water‐splitting devices and the validation of this benchmark against important component parameters for practical implementation of this technology are discussed.

An epifluidic electronic patch with spiking sweat clearance for event-driven perspiration monitoring

Sensory neurons generate spike patterns upon receiving external stimuli and encode key information to the spike patterns, enabling energy-efficient external information processing. Herein, we report an epifluidic electronic patch with spiking sweat clearance using a sensor containing a vertical sweat-collecting channel for event-driven, energy-efficient, long-term wireless monitoring of epidermal perspiration dynamics. Our sweat sensor contains nanomesh electrodes on its inner wall of the channel and unique sweat-clearing structures. During perspiration, repeated filling and abrupt emptying of the vertical sweat-collecting channel generate electrical spike patterns with the sweat rate and ionic conductivity proportional to the spike frequency and amplitude over a wide dynamic range and long time (> 8 h). With such ‘spiking’ sweat clearance and corresponding electronic spike patterns, the epifluidic wireless patch successfully decodes epidermal perspiration dynamics in an event-driven manner at different skin locations during exercise, consuming less than 0.6% of the energy required for continuous data transmission. Our patch could integrate various on-skin sensors and emerging edge computing technologies for energy-efficient, intelligent digital healthcare.

Freestanding μm-thin nanomesh electrodes exceeding 100x current density enhancement for high-throughput electrochemical applications

Nanomeshes (NMs), regularly interconnected 3D nanowire-networks, obtained from electroplating in rationally designed alumina templates, are attractive for numerous fields due to their extremely high surface area and porosity. Until now, non-porous support substrates were required to provide sufficient mechanical robustness to the highly porous NM. However, to exploit these compelling nano-architectures as freestanding electrodes in electrochemical flow cells, e.g. water electrolysis, it is essential that the nanowire-network is accessible from all sides requiring a porous support structure. To demonstrate the advantage of the high volumetric NM surface area of 26 m2/cm3 for water electrolysis up to 1 A/cm2, we monolithically integrated a nickel NM with an open support grid in a facile and up-scalable fabrication flow. The freestanding NM electrodes show beyond state-of-the-art performance for the alkaline hydrogen- and oxygen evolution reaction (HER and OER), with over 100x enhanced current densities in respect to planar nickel. Interestingly, the regular nano-architecture of the electrodes causes an intrinsic catalytic effect for the HER. The high potential of these novel 4 μm thin electrodes toward high-throughput electrochemical applications is shown by the significant 400 mV lower overpotential compared to commercial 1.6 mm thick nickel foams (<0.01 m2/cm3) in the alkaline anion-exchange membrane water electrolysis.

High Surface Area 3D Copper Nanowire Networks for High-Throughput Electrochemical CO2 Reduction

An attractive solution towards net-zero carbon emission is the electrocatalytic CO2 reduction with its ability to convert the greenhouse gas CO2 with renewable electricity and appropriate catalytic materials to useful chemicals and fuels to store energy. Depending on the number of electrons transferred a variety of oxygenates and hydrocarbons can be obtained. Among used catalytic materials, such as metals, alloys or composites, copper has shown the unique property to electrocatalytically convert CO2 into a wide variety of valuable C2+ products such as ethylene or alcohols.Apart from the high potential to reshape our carbon economy the electrocatalytic CO2 reduction is still in its early development stage compared to the more mature water electrolysis, with high-throughput operation at practical current densities as well as long-term stability of the catalysts being only scarcely demonstrated. Additionally, selectivity towards high-value (beyond C1) products using copper catalysts has proven to be challenging and many research efforts are directed towards improving product selectivity. For this purpose, mainly nanostructured porous Cu electrodes either based on randomly ordered nanoparticles loaded on porous (carbon-based) supports or low-surface area metal foams, meshes or felts with high porosity are commonly used. While the former electrode architecture typically shows poor long-term stability with often weak adhesion between the nanoparticles and the porous support, the latter electrodes have a low electrochemical surface area and hence are not suitable for high-throughput CO2 reduction at high current densities.In this work we present novel high-surface area porous copper electrodes, so-called copper nanomeshes, that are regular 3D-networks of interconnected Cu nanowires. These unique few µm-thin electrodes show a large surface area enhancement (compared to planar Cu) by a factor of ~80, while providing a high porosity of ~70% together with sufficient mechanical stability, an important aspect towards their practical implementation in electrocatalytic flow cells. Cu nanomesh electrodes with a thickness of 4µm were fabricated through electrochemically plating in 3D-porous anodic aluminum oxide templates and show a mixed surface texture of (111), (100) and (110) Cu. We demonstrate the high potential toward high-throughput CO2 electrolysis of these novel electrodes in comparison to planar copper electrodes in various CO2-containing electrolyte solutions. The CO2 reduction product analysis showed a significant difference in selectivity between planar (polycrystalline or with preferential 111 or 200 texture) and the polycrystalline Cu nanomesh electrodes with CO or C2H4 as major reduction products depending on the potential applied. The beneficial effect of the high electrochemical surface area was demonstrated by a significant increase in the current density on the nanostructured Cu electrodes. Additionally, we characterized the copper nanomesh electrodes before, during and after CO2 reduction with complementary techniques to gain insights on the reaction mechanism and on the electrode stability. Figure 1

Electromyogram-strain synergetic intelligent artificial throat

Assisting the disabled to speak is a meaningful activity and attracts much attention in the recent years. In this work, an intelligent artificial throat has been realized based on the nanomesh, which can not only emit the sound, but also detect the voice or throat vibration generated by using the electromyogram (EMG)-strain synergetic method. The Au/PVA nanomesh with good thermoacoustic effect can be used as sound source. By theorical analyzing, the porous nanomesh structure plays an important role during the sound emitting process. The Au/PU nanomesh can also be used as the strain sensor, which shows high sensitivity, large work range, and good stability. A finite element model containing six paralleled resistance layers was proposed to explain the performance of strain sensor, which reveals the nonlinear origin of the device. The Au nanomesh can be applied as the physiological electrodes whose impendence is even lower than the commercial gel electrodes, which can be used to detect the electrocardiogram and EMG signal. In addition, the nanomesh has good water permeability, stability, and conformal property with skin. Finally, a synergetic convolution neural network (SCNN) algorithm built by ResNet18 (EMG part) and two-layers CNN (strain part) is demonstrated to distinguish the transitory voice signals detected by the nanomesh strain sensor and electrodes with the high accuracy of 98.9%. This work has great potential in the language function reconstruction.

High-performance transparent heater with Ag paste-based nanomesh electrodes

Transparent heaters have attracted significant attention in recent years because of their wide range of potential applications, including defogging and defrosting windshields, thermochromic smart windows, and wearable heating devices. This paper presents a comparison of the performances of a transparent heater with nanomesh electrodes and that with micromesh electrodes. Both transparent heaters exhibit excellent basic characteristics, with an optical transmittance of more than 90%, and sheet resistance of less than 2 Ω/□. From the thermal response time tests, we observed a shorter thermal response time of 30 s for the nanomesh heater. This is because the heater must warm the transparent area; hence, the smaller transparent area of the nanomesh is more advantageous for a transparent heater. Furthermore, the nanomesh transparent heater exhibited excellent heating stability and performance at various sizes. The promising results of this study can facilitate significant and practical applications of transparent heaters, such as windshields for vehicles.

Highly Precise, Continuous, Long-Term Monitoring of Skin Electrical Resistance by Nanomesh Electrodes.

The transepidermal water loss has been widely used as a method for directly evaluating the barrier function of the stratum corneum of the skin. However, transepidermal water loss could not be measured continuously for a long period of time, and there were no reports of continuous monitoring of skin barrier functions. Here, a method is reported to continuously monitor the skin electrical resistance by nanomesh electrodes for a long period of time while maintaining the natural skin condition that does not inhibit water evaporation. Simultaneous measurements of the skin electrical resistance by nanomesh electrodes and transepidermal water loss exhibits a linear fit with a high negative correlation. Furthermore, dynamics of skin physiological functions are successfully visualized by monitoring of the skin electrical resistance by nanomesh electrodes for 30 h in daily life.

Haze-enhanced ZnO/Ag/ZnO nanomesh electrode for flexible, high-efficiency indoor organic photovoltaics

An oxide/metal/oxide multilayer electrode is employed to improve the mechanical flexibility as well as power conversion efficiency of organic photovoltaics. However, its performance needs to be further improved to provide a higher conversion efficiency and better environmental compatibility with curved indoor electronics. In this study, ZnO/Ag/ZnO nanomesh electrodes are incorporated into the inverted non-fullerene organic photovoltaics to enhance the efficiency under indoor and outdoor lighting illumination in a flexible mode. The opto-electrical properties of the perforated ZnO/Ag/ZnO nanomesh electrode with different hole sizes are compared with those of the planar ZnO/Ag/ZnO and indium tin oxide electrodes. The micro-cavity effect and haze effect, which plays a crucial role in determining the performance of the organic photovoltaics, are directly related to the hole diameter. Despite higher transmittance of indium tin oxide, organic photovoltaics using ZnO/Ag/ZnO nanomesh electrodes with a hole diameter of 350 nm exhibits an average conversion efficiency of 15.7% under a 1000 lux light-emitting diode lamp; this efficiency is 45.3% and 27.6% greater than those of organic photovoltaics using indium tin oxide and planar ZnO/Ag/ZnO electrodes, respectively. Furthermore, all ZnO/Ag/ZnO nanomesh-based organic photovoltaics show much higher mechanical flexible properties than those of the planar ZnO/Ag/ZnO-based organic photovoltaics. • ZnO/Ag/ZnO nanomesh is employed as a cathode for flexible organic photovoltaics. • Opto-electrical properties of the ZnO/Ag/ZnO nanomesh electrode are optimized. • As the hole size decreases, optical haze and micro-cavity effect are found to increase. • Fabricated photovoltaic shows a 15.7% efficiency under 1000 lux LED light. • Fabricated photovoltaic also exhibits an excellent mechanical flexibility.

Skin Impedance Measurements with Nanomesh Electrodes for Monitoring Skin Hydration.

The importance of continuous monitoring of skin hydration in daily life, to aid in the diagnosis of skin diseases, is rising. Electrodes that can be worn directly on the skin are attracting attention as an effective means. However, they should not inhibit natural water evaporation from the skin and should not cause inflammation or irritation even if they are attached to the body for long periods of time. In this study, nanomesh electrodes that have previously been reported to exhibit high biocompatibility are also found to exhibit high water vapor permeability, resulting in properties that prevent skin dampness. Furthermore, the skin impedance measured using nanomesh electrodes is found to correlate with the hydration level of skin measured using existing medical equipment. This study provides a new approach to measure skin hydration in conditions close to bare skin.

Trilayer Nanomesh Films with Tunable Wettability as Highly Transparent, Flexible, and Recyclable Electrodes

AbstractMetallic mesh materials are promising candidates to replace traditional transparent conductive oxides such as indium tin oxide (ITO) that is restricted by the limited indium resource and its brittle nature. The challenge of metal based transparent conductive networks is to achieve high transmittance, low sheet resistance, and small perforation size simultaneously, all of which significantly relate to device performances in optoelectronics. In this work, trilayer dielectric/metal/dielectric (D/M/D) nanomesh electrodes are reported with precisely controlled perforation size, wire width, and uniform hole distribution employing the nanosphere lithography technique. TiO2/Au/TiO2 nanomesh films with small hole diameter (≤700 nm) and low thickness (≤50 nm) are shown to yield high transmittance (&gt;90%), low sheet resistance (≤70 Ω sq−1), as well as outstanding flexural endurance and feasibility for large area patterning. Further, by tuning the surface wettability, these films are applied as easily recyclable flexible electrodes for electrochromic devices. The simple and cost‐effective fabrication of diverse D/M/D nanomesh transparent conductive films with tunable optoelectronic properties paves a way for the design and realization of specialized transparent electrodes in optoelectronics.

Interconnected Heat-Press-Treated Gold Nanomesh Conductors for Wearable Sensors

We report the reduction in the wire resistance of gold nanomesh electrodes caused by interconnecting mesh electrodes. The porous-structured electrodes show high resistance because of the high junct...

Narrowing Desiccating Crack Patterns by an Azeotropic Solvent for the Fabrication of Nanomesh Electrodes.

Desiccation of a colloidal layer produces crack patterns because of stress arising out of solvent evaporation. Associated with it is the rearrangement of particles, while adhesion to the substrate resists such movements. The nature of solvent, which is often overlooked, plays a key role in the process as it dictates evaporation and wetting properties of the colloidal film. Herein, we study the crack formation process by using a mixture of solvents, water, and isopropyl alcohol (IPA). Among the various ratios, a water/IPA mixture (15:85 by volume) close to the azeotropic composition possesses unusual evaporation and wetting properties, leading to narrower cracks with widths down to ∼162 nm, uncommon among the known crackle patterns. The dense and narrow crack patterns have been used as sacrificial templates to obtain metal meshes on transparent substrates for optoelectronic applications.

Electrodeposited 3D Nanomesh Electrodes: Combined High Surface Area, High Porosity and Structural Integrity and Regularity

We present a nanomesh material that is widely applicable in a variety of sustainable-applications requiring high surface area electrodes such as batteries, electrocatalytic convertors, fuel cells and hydrogen production. The nanomesh material is a three-dimensional nanowire (metal) grid structure with highly regular internal dimensions. The hexagonally organized vertical nanowires are horizontally interconnected to its three neighboring nanowires. As a result, it combines high porosity with an unprecedented surface-to-volume ratio. For each micrometer thickness, there is a 26-fold increase of available surface area. To visualize this: when filling a volume of a small can of soda, it would remain 75% empty while containing a surface area equal to the size of a football field. On top of that, the internal and external dimensions can be tuned to almost any specification, making it potentially compatible with a multitude of application requirements. The material can be quite easily manufactured through cheap anodization and electroplating processes. First, a mold is formed by anodization of aluminum foil as for the well-known Anodic Aluminum Oxide (AAO) process. The secret for the regular horizontal perforation at the nanoscale lays in the controlled doping of the aluminum metal with copper. The resulting 3D nanoporous structure acts as a mold in which a large variety of metal (compounds) can be electrodeposited. After consecutive chemical dissolution of the alumina template, a mechanically rigid nanomesh structure remains. The nanomesh can be detached from the substrate as a free-standing flexible nanomesh foil. We will show that a 3 micron thick nanomesh easily outperforms a 400 micron thick foam in surface area and electrochemical performance for hydrogen evolution reaction.

Vapor dealloying of ultra-thin films: a promising concept for the fabrication of highly flexible transparent conductive metal nanomesh electrodes

The booming market of flexible electronic displays has urged the development of highly flexible transparent conductive electrodes (FTCE)1–3 with the ability to replace indium tin oxide (ITO) thin films routinely used as transparent conductive electrodes in photoelectronic devices. The high cost of indium and the poor mechanical stability of ITO under deformation are the main driving forces behind the development of this research area.4 The use of metal nanomeshes as FTCE is a promising concept with a real potential to substitute ITO in photoelectronic devices.5,6 However, the development of a low-cost fabrication approach allowing producing metal nanomesh electrodes with competitive prices and a high performance remains a real bottleneck for the photoelectronic industry. In this paper, we report on a robust approach very easy to implement allowing producing highly flexible metal nanomesh electrodes with high performance at a very low cost. This approach lies on a concept consisting in applying dealloying process to ultra-thin Au-Cu alloy thin films using acidic vapors instead of a liquid phase as routinely done in the literature. Using an appropriate procedure, the nanomeshes can be transferred to any planar or curved support where they can serve as a FTCE. As a proof of concept, we demonstrate that using this approach, one can easily fabricate gold nanomesh electrodes transferred onto polyethylene terephthalate (PET) film surface with 79% of transmittance and a sheet resistance as low as 44 Ω □−1 while maintaining exceptional stability under severe mechanical deformations.

High-performance flexible transparent nanomesh electrodes

A cost-effective process for producing high-performance Ag-paste-based flexible transparent nanomesh electrodes (FTNEs) was developed by optimizing their linewidth, pitch, and height. These nanomesh electrodes, with a linewidth of several hundred nanometers and a pitch of 10–200 μm on a PET substrate, achieved wide ranges of transmittance (83.1%–98.8%) and sheet resistance (1.2–30.9 Ω/sq) and a figure of merit (992–1619) superior to those of indium tin oxide and silver nanowire (AgNW) electrodes. Our evaluation of their flexibility (testing up to 50 000 cycles) and their electromagnetic interference shielding effectiveness verifies the applicability of these FTNEs to various flexible optoelectronic devices.

Ag paste-based nanomesh electrodes for large-area touch screen panels

This study reports a novel method for fabricating a nickel nanomesh mold using phase shift lithography, suitable for use in large-area touch screen panel applications. Generally, the values of light transmittance and sheet resistance of metal mesh transparent conducting electrode (TCE) films are determined by the ratio of the aperture to metal areas. In this study, taking into consideration the optimal light transmittance, sheet resistance, and pattern visibility issues, the line width of the metal mesh pattern was ~1 µm, and the pitch of the pattern was ~100 µm. In addition, a novel method of manufacturing wiring electrodes using a phase shift lithography process was also developed and evaluated. A TCE film with a size of 370 mm × 470 mm was prepared and evaluated for its light transmittance and sheet resistance. In addition, wiring electrodes with a length of 70 mm were fabricated and their line resistances evaluated by varying their line width.

Light extraction from surface plasmon polaritons and substrate/waveguide modes in organic light-emitting devices with silver-nanomesh electrodes.

Light out-coupling of organic light-emitting diodes (OLEDs) with silver (Ag)-nanomesh electrodes was examined. Experimental results for the OLEDs with nine different nanomesh dimensions were compared with simulation results to elucidate the dimensional effect of the nanomesh on the light out-coupling behavior of the devices. The Ag-nanomesh electrodes did not only increase the transparency of the Ag electrode due to periodic nanoholes but also enhanced light extraction from surface plasmon polaritons and substrate/waveguide modes in the devices. The simulation results show similar trends with the experimental results for the optical transmittance, emission spectrum, and efficiency enhancement. With a nanomesh dimension of 480 nm period and 50% fill factor, the OLEDs with the Ag-nanomesh electrode showed 1.66 times higher efficiency than those with a planar Ag electrode did. Using our validated simulation, we construct an external quantum efficiency map in full ranges of the period and fill factor of the Ag-nanomesh electrode to find out the optimum nanomesh dimension.

Highly efficient and stable cupronickel nanomesh electrode for flexible organic photovoltaic devices

Abstract Advances in flexible optoelectronic devices have led to increasing need for developing high performance, low cost, and flexible transparent conducting electrodes. Copper-based electrodes have been unattainable due to the relatively thermal instability and poor oxidation resistance. Herein, we present oxidation-resistive CuNi nanomesh electrodes that exhibit a low sheet resistance of ∼7.5 Ω/□ and a high optical transmittance of ∼81% at 550 nm. Further, high long-term stability against the effects of oxidation, heat, and chemicals is exhibited by the CuNi nanomesh, in comparison with the behavior of a pure Cu nanomesh sample.