Electrospray Deposition Technique Research Articles

Investigation of the catalyst ink compositions for a uniform microporous catalyst layer preparation via electrospray deposition technique and MEA assembling conditions in PEMFC specific

High utilization of catalyst and preserving evenly distributed pores for Proton Exchange Membrane Fuel Cell (PEMFC) electrodes were optimized using an in-house designed electrospray system. In order to hold the porous electrode structure prepared through the electrospray technique by varying ink compositions. Using optimized electrodes and commercially available Nafion-212 membrane, a series of membrane-electrode assemblies (MEAs) were fabricated by varying the hot-pressing parameters of pressure, temperature, and time for evaluating the performance at 60 °C to 80 °C with varying relative humidity. The MEAs were hot-pressed at 8 MPa for 390 s at a temperature of 150 °C generating a maximum peak power density of 903 mW cm−2 and current density of 1040 mA cm−2 at 0.6 V and calculated electrochemical surface area (ECSA) is 23.96 m2/gPt. In contrast, the MEAs hot-pressed for the same length of time at the same temperature but with a lower pressure of 2.67 MPa generated higher peak power density of 1130 mW cm−2, higher current density of 1320 mA cm−2 at 0.6 V, despite having a lower ECSA of 19.18 m2/gPt. Overall, results in this study present that low hot-pressing pressure and a high pressing temperature enable a negative effect on the porous structure of electrospray electrodes for producing the high achievement of MEA performance.

Investigating Nano-Sized Dispersity and High Crystallinity of Perfluoro-Sulfonic Acidionomer in Polymer Electrolyte Fuel Cell Electrodes Via Electrospray Deposition

Polymer electrolyte fuel cells (PEFCs) hold great promise for mitigating the worldwide climate crisis by tapping into the potential of producing clean energy from renewable sources. However, widespread commercial adoption of PEFCs requires addressing the challenges associated with PEFC performance and durability, particularly concerning electrode materials and design. The PEFC electrode is a crucial component of PEFC performance, with the ionomer playing a vital role as both an electrode binder and proton conductor. Nano-sized dispersity and high crystallinity of the ionomer are vital properties that are crucial for achieving enhanced performance and durability. However, existing methods for fabricating PEFC electrodes have been unable to attain these desirable ionomer characteristics. In this work, we propose a novel approach to fabricating PEFC electrode architectures with ionomers possessing nano-sized dispersity and high crystallinity using the electrospray deposition (ESD) technique. In the ESD process, a precursor solution is atomized into charged droplets, while evaporating the solvent, and results in the formation of advanced electrode with vertical architecture that exhibits high crystallinity of ionomer, in contrast to much lower crystallinity of those fabricated by conventional decal methods. The ionomer characteristics significantly impact the overall fuel cell performance and durability. Therefore, controlling the residual solvent content during the ESD process is a crucial aspect that is vital for achieving the desired ionomer characteristics. The residual solvent content is tuned by investigating the initial mixed solvent ratio, substrate temperature, and distance between the nozzle to substrate. By fine-tuning the residual solvent content and optimizing the deposition parameters, the ESD technique can overcome the limitations of traditional fabrication methods, resulting in PEFC electrodes that offer enhanced performance, increased durability, and improved energy efficiency. The electrospray deposition (ESD) technique provides precise control over the amount of residual solvent required for deposition, making it a scalable technique. This work shows that the residual solvent content of PEFC electrodes significantly impacts the ionomer crystallinity and the electrode architecture using a well-controlled and optimized electrospray technique, without the use of any additives or special ionomer. In summary, this work demonstrates a novel approach to fabricating PEFC electrode architectures with ionomers possessing nano-sized dispersity and high crystallinity using the electrospray deposition technique. This approach provides precise control over the residual solvent content, allowing for enhanced performance and increased durability of PEFC electrodes due to the high-crystallinity of the ionomer. These findings have important implications for the development of sustainable energy technologies and contribute to the ongoing efforts towards mitigating the worldwide climate crisis.

Enhanced Oxygen Evolution Reaction Activity of Fe-Doped Lithium Nickel-Based Metal Oxide through Modification of Nickel Oxidation State

The oxygen evolution reaction (OER) involves the four-electron transfer process of water oxidation to produce oxygen gas and protons. However, this reaction is kinetically sluggish and requires high overpotential compared to hydrogen evolution reaction (HER). Herein, we have fabricated Fe-doped LiNiO2 using electrospray deposition (ESD) technique. With this technique, we can modify the electronic structure of LiNiO2 by controlling amounts of Fe, and the morphology can be controlled with various parameters such as applied voltage, spray rate, and substrate temperature. The synergistic effect of iron doping can modify the electronic structure of the surface Ni ions and increase oxidation state of Ni2+ to Ni3+. Through this oxidation state change, Ni becomes more electrophilic and then adsorbed oxygen in the M – O step, which is considered as rate-determining step in OER, easily reacts with OH ions. In electrochemical analysis, the optimized Fe-doped LiNiO2 showed improved OER performance compared to LiNiO2. The surface chemical compositions of the Fe-doped LiNiO2 electrode were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). From our result, we can improve OER performance and stability with simple control of ESD technique parameters and electronic structure modification by Fe doping.

Mass Transport Impedance in a PEMFC with Superhydrophobic Catalyst Layers

Hydrogen transport in the anode of a proton-exchange membrane fuel cell (PEMFC) with superhydrophobic catalyst layer has been studied with Current-modulated Hydrogen-flowrate Spectroscopy (CH2S). The catalyst layers of Pt/C catalyst and ionomer (Nafion) are prepared by the electrospray deposition technique, with macroporous morphology and superhydrophobic pores walls. Transport properties are studied under different operating conditions in a PEMFC, including humidification, temperature, and cell current. Features of the CH2S spectra are compared for electrosprayed and commercial –hydrophilic- catalyst layers, reflecting different transport properties. The electrosprayed layers show enhanced hydrogen transport properties.

Electrospray Deposition of PEDOT:PSS on Carbon Yarn Electrodes for Solid-State Flexible Supercapacitors.

The increasing demand for flexible electronic devices has risen due to the high interest in electronic textiles (e-textiles). Consequently, the urge to power e-textiles has sparked enormous interest in flexible energy storage devices. One-dimensional (1D) configuration supercapacitors are the most promising technology for textile applications, but often their production involves complex synthesis techniques and expensive materials. This work unveils the use of the novel electrospray deposition (ESD) technique for the deposition of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS). This deposition methodology on conductive carbon yarns creates flexible electrodes with a high surface area. The deposition conditions of PEDOT:PSS were optimized, and their influence on the electrochemical performance of a 1D symmetric supercapacitor with a cellulose-based gel as an electrolyte and a separator was evaluated. The tests herein reported show that these capacitors exhibited a high specific capacitance of 72 mF g-1, an excellent cyclability of more than 85% capacitance retention after 1500 cycles, and an outstanding capability of bending.

Improved reuse and storage performances at room temperature of a new environmentally friendly lactate oxidase biosensor prepared by ambient electrospray immobilization

A new, environmentally friendly lactate oxidase (LOX) based biosensor for lactate detection, with unprecedented reuse and storage capabilities at room temperature, has been manufactured using the ambient electrospray deposition (ESD) technique.

Flexible Solid Supercapacitors of Novel Nanostructured Electrodes Outperform Most Supercapacitors.

Sustainable and scalable fabrication of electrode materials with high energy and power densities is paramount for the development of future electrochemical energy storage devices. The electrode material of a supercapacitor should have high electrical conductivity, good thermal and chemical stability, and a high surface area per unit volume (or per unit mass). Researchers have made great efforts to use two-dimensional (2D) nanomaterials, but the separated 2D plates are re-stacked during processing for electrode fabrication, impeding the transport of ions and reducing the number of active sites. We developed a novel process for manufacturing thin and flexible electrodes using a 2D material (MXene,Ti3AlC2) and a conducting polymer (poly(3,4-ethylenedioxythiophene), PEDOT). Because the PEDOT layer is electrochemically synthesized, it does not contain the activator poly(styrene sulfonate). The electrospray deposition technique solves the restacking problem and facilitates the infilling of the gel electrolyte by forming a highly porous open structure across the entire electrode. In the PEDOT/MXene multilayered electrode, the double-layer capacitance increased substantially because of a dramatic increase in the number of accessible sites through the MXene layer. Although applied to solid supercapacitors, these new supercapacitors outperform most aqueous electrolyte supercapacitors as well as other solid supercapacitors.

Performance study of novel PES membrane using electrospray deposition method for organic contaminants separation

The aim of this study is to design and fabricate a new kind of membrane that could be used effectively in wastewater treatment. In this study, a novel type of electrosprayed thin membrane was synthesized via electrospray deposition technique and its properties were compared with electrospun membrane in terms of structure and separation efficiency. The electrosprayed thin membrane was developed using dope solution composed of 20 wt. % polyethersulfone (PES) and 80 wt. % n-methyle-2-pyrrolidone/dimethylformamide mixture. The electrosprayed PES membrane exhibited water flux of up to 100 Lm−2h−1 at 2 bar with porosity of 76 % which is very similar to the electrospun membranes. The electrosprayed PES membrane also showed an excellent tensile strength up to 4.5 MPa and demonstrated about 81 % and 63 % rejection rate against humic acid (HA) and bovine serum albumin (BSA), respectively when tested at 2 bar. The fouling of the membrane was further studied using FTIR, TGA and XPS analysis and the results confirmed that the membrane did not suffer from substantial fouling. Moreover, a high flux recovery was recorded, indicating low fouling tendency of the membrane. Overall, the findings showed that the electrosprayed thin PES membrane performed better than the electrospun PES membrane for wastewater treatment.

Fabrication of multilayer film with graphene oxide of different surface charge through electrospray deposition

Due to its notable mechanical and electrical properties, graphene has high-value-added applications in future flexible electronics. The preparation of ultrathin uniform graphene oxide (GO) multilayer film through simple and cost-effective technique still is concern. Herein, we have demonstrated the electrospray deposition (ESD) method to prepare the uniform alternative GO multilayer film with controlled thickness by alternatively depositing the different surface charge. It is a solution-processed technique that can be applied in a variety of practical applications due to low-cost and high-speed processing time. Colloidal nanoparticles, which is deposited through ESD technique, have different physical and optical properties based on surface charge. Owing to the electrostatic repulsion between the functional groups, GO can be well soluble, homogeneous and stable dispersion. The prepared alternated rGO films enhanced the sheet resistance because of improving electrical conductivity. Furthermore, alternated rGO film is utilized in the symmetric supercapacitor and the device exhibit a larger capacitance of 103.5 F/g at 0.5 A/g and good cycling stability (94%) on the account of high conductivity than that of other prepared rGO based films. These attributes of ultra-thin rGO film underscore the potential of the current method towards the understanding of film-based supercapacitors in a numerous energy storage applications.

Multilayer films of exfoliated 2D oxide nanosheets by electrospray deposition

The potential of the electrospray deposition technique as new method to make nanosheet-based multilayer films is evaluated. Densely packed nanosheet-based films with thicknesses of 1–20 nm with rms roughnesses of 2.1–2.4 nm were fabricated on samples of 1 cm2 size with a growth rate of 0.5 nm/min. Electrosprayed Ti0.87O2 nanosheet films were successfully used as oriented growth templates for 40 nm perovskite SrRuO3 thin films grown by pulsed laser deposition. The electrospray method provides a fast and easy alternative to the more commonly used Langmuir–Blodgett (LB) deposition method for nanosheet films.

Electrospray deposition of AlN-PVA composite coating as thermal interface material

In this study, aluminum nitride (AlN)-polyvinyl alcohol (PVA) composite coatings as a novel thermal interface material for electronic applications were fabricated by using the electrospray deposition (ESD) technique at room temperature. The influence of deposition time on the morphology and the thermal behavior of AlN-PVA composite coatings was investigated. The microstructural inspections indicate that homogeneous, highly dense, and paste-like AlN-PVA coatings were formed. Increasing the deposition time from 15 min to 30 min reduced the surface roughness of the AlN-PVA coating. Infrared thermography images revealed that the deposition of AlN-PVA composite coatings on aluminum alloy substrates dramatically improved its thermal effusivity. The thermal diffusivity of 15 min (38.767 mm2/s) and 30 min (37.485 mm2/s) coated samples were approximately 30% higher than the uncoated substrate (26.638 mm2/s).

Atomic Layer Deposition Reinforcement of Methylcellulose Nanowire Forests

Micro‐ and nanostructured surfaces are widely used as functional surfaces in various fields including the maritime and medical industries. Many micro‐ and nanocoating technologies are delicate processes that have high costs at scale. Herein, an electrospray deposition (ESD) technique is investigated as an affordable method for obtaining micro/nanostructured surfaces. When processed via ESD from water:ethanol blends, methylcellulose (MC), a fibril gel former, can form nanowire coatings. These nanowires are formed via enhanced gelation by shear forces and surface charges that lead to electrospinning on a drop‐by‐drop basis. However, these ESD MC nanostructures can be easily destroyed upon water exposure. In this work, conformal coating of these MC nanostructures with atomic layer deposition (ALD) of Al2O3 is explored to impart further stability. Upon subsequent heating of the ALD‐coated MC nanostructures, superhydrophobicity can be obtained. It is found that the final ALD‐coated structures exhibit a trade‐off between mechanical stability and hydrophobicity depending on MC nanowire size, with smaller wires being more mechanically robust and larger wires being more hydrophobic.

Fabrication of a New, Low-Cost, and Environment-Friendly Laccase-Based Biosensor by Electrospray Immobilization with Unprecedented Reuse and Storage Performances.

The fabrication of enzyme-based biosensors has received much attention for their selectivity and sensitivity. In particular, laccase-based biosensors have attracted a lot of interest for their capacity to detect highly toxic molecules in the environment, becoming essential tools in the fields of white biotechnology and green chemistry. The manufacturing of a new, metal-free, laccase-based biosensor with unprecedented reuse and storage capabilities has been achieved in this work through the application of the electrospray deposition (ESD) methodology as the enzyme immobilization technique. Electrospray ionization (ESI) has been used for ambient soft-landing of laccase enzymes on a carbon substrate, employing sustainable chemistry. This study shows how the ESD technique can be successfully exploited for the fabrication of a new promising environment-friendly electrochemical amperometric laccase-based biosensor, with storage capability up to two months without any particular care and reuse performance up to 63 measurements on the same electrode just prepared and 20 measurements on the one-year-old electrode subjected to redeposition. The laccase-based biosensor has been tested for catechol detection in the linear range 2–100 μM, with a limit of detection of 1.7 μM, without interference from chrome, cadmium, arsenic, and zinc and without any memory effects.

Electrospray Deposition of Multiwalled Carbon Nanotubes-OH/ Polyvinylidene Fluoride Nanocomposites for Volatile Organic Compounds (VOCs) Detection

In this work, we report on the synthesis and performance evaluation of electrosprayed multi-walled carbon nanotubes (MWCNTs)/ Polyvinylidene Fluoride (PVDF) nanocomposite materials for gas detection of volatile organic compounds. MWCNTs are characterized by a hollow structure, large surface area and several unique properties that make them potentially excellent for gas sensing. However, in order to improve their sensitivity, stability and reproducibility effects, the carbon nanotubes were doped with PVDF polymer in a minimal concentration such that it utilizes its strong binding effect with interconnected nanotubes and the substrate and further, the polymer does not affect the dominance of MWCNTs on the surface as observed from SEM characterization. The electrospray deposition technique, combined with sonication, was used to ensure the MWCNT was dispersed evenly in the polymer matrix, as MWCNTs tend to aggregate due to their strong Van der Waals forces. The sensing mechanism and the kinetic adsorption of gases on the sensors were studied and the experimental result shows that MWCNT-OH/PVDF sensor revealed a larger sensitivity than that of MWCNT-OH sensor to tested VOCs at room temperature.

Evaluation of electrosprayed graphene oxide coatings for elemental analysis by thin film microextraction followed by Laser-induced Breakdown Spectroscopy detection

In this work, a solid phase microextraction procedure, denoted as Thin Film Microextraction (TFME), was combined with Laser-induced Breakdown Spectroscopy for the detection of several analytes in aqueous solutions (Cu, Cr, Ni and Pb). The adsorbent films, consisting of a thin layer of graphene oxide deposited on glass substrates, were generated by using the electrospray deposition technique (ESD). Several parameters affecting the quality and shape of the films resulting from the ESD process were studied, and the morphology and adsorption capacity of the films were evaluated. The generated films were used for extraction of the target analytes from aqueous solutions and, after extraction, the analytes-enriched adsorbents were analysed by LIBS without the need of any desorption or elution step. In order to assess the analytical capability of the TFME-LIBS procedure, different analytical figures of merit of the proposed TFME-LIBS methodology were evaluated. The obtained limits of detection were 14 μg kg−1 for Pb and 15 μg kg−1 for the rest of the tested analytes. Measurement repeatability was better than 4% RSD at low concentration level (20 μg kg−1) but deteriorated by increasing the concentration level at 100 μg kg−1, with %RSD ranging from 3.6% (Cr) to 24% (Pb). Method trueness, evaluated from the analysis of a real sample of bottled water, led to recovery values in the range 85%–106%.

Electrospray Deposition: A Breakthrough Technique for Proton Exchange Membrane Fuel Cell Catalyst Layer Fabrication

This Spotlight article presents the state-of-the-art of electrospray deposition technique applied to the fabrication of proton exchange membrane fuel cell (PEMFC) components, mainly focusing on catalyst layers in gas diffusion electrodes. The atomization of a suspension of particles over a substrate under the influence of a strong electric field results in the growth of a film with macroporous morphology and many interesting properties. This so-called electrospray deposition has reported many noteworthy beneficial effects for the fabrication of the catalyst layers of gas diffusion electrodes of PEMFCs. The electrosprayed catalyst layers prepared from suspensions of catalyst particles and ionomers present a dendritic macroporous morphology with superhydrophobic character that improves the water management inside the cell and increases the performance by ∼20% with respect to standard electrodes prepared by airbrushing. Other interesting effects observed with electrosprayed catalyst layers are increased catalyst utilization and water absorption capabilities of the ionomer, improved performance under nonhumidified conditions, and a reduction in catalyst degradation. In addition, the electrospray deposition decreases platinum losses during fabrication thanks to the attractive electrostatic forces between the ion mist and the substrate compared with regular ink-based spray methods.

Enhanced flexural strength of carbon nanotubes‐glass fiber epoxy composite laminates using an electrospray deposition technique

AbstractThe electrospray deposition technique (ESD) was used to coat carbon nanotubes (CNTs) uniformly on the surface of glass fiber (GF) and to increase the flexural strength of CNTs‐GF epoxy composite laminate. The deposition of CNTs on the GF surface has been optimized by the applied voltage and spray time. The deposited CNTs on the GF surface showed a well dispersed and homogeneous coating. Implementing optimized ESD in the fabrication of composite laminate caused a 25.26% to 59.28% improvement of flexural performance in CNTs‐GF composite laminate. The dispersion of CNTs was characterized by using a digital microscope, a field emission scanning electron microscope (FESEM), and a transmission electron microscope (TEM). The result revealed that the applied voltage had an impact on the well‐dispersed coated CNTs, while the spray time affected the flexural output.

Reliable sensors based on graphene textile with negative resistance variation in three dimensions

The weft-knitted reduced graphene oxide (r-GO) textile that is made up of many conductive r-GO coated fibers was successfully prepared dependent on the electrospray deposition technique. Interestingly, the r-GO textile presents negative resistance variation not only in axial direction as the pressure increases but also in transverse direction as the lateral stretch increases which makes it has the advantage to fabricate the reliable sensors based on strain-resistance effect. The transverse-strain and pressure sensors based on the r-GO textiles all show the excellent sensing characteristics such as high sensitivity, reliability, and good durability, etc. The maximum gauge factors (GF) of the transverse-sensor are 27.1 and 153.5 in the x- and y-direction, respectively. And the practical detection range can up to 40% in the x-direction and 35% in the y-direction, respectively. The r-GO textile pressure sensor also shows high sensitivity for a broad pressure range that with a GF up to 716.8 kPa−1 for less than 4.5 kPa region and still has more sensitive pressure sensing characteristics even the pressure goes up to 14 kPa. Based on those good performances of r-GO textile sensors, its potential applications in human body states monitoring have been studied.

Binder‐Free High‐Performance MXene Supercapacitors Fabricated by a Simple Electrospray Deposition Technique

AbstractIn this work, an electrospray deposition (ESD) technique is applied to fabricate binder‐free porous 2D MXene (Ti3C2Tx) electrodes for supercapacitor applications. As a result of the crumpling of MXene flakes induced by the capillary force during drying, a porous structure is formed between MXene flakes within the electrode which leads to the formation of channels for rapid ion‐diffusion. Together with binder‐free networks of highly electrical conductive MXene sheets, these ion diffusion channels greatly improve the rate capability of the electrospray MXene electrode. Cyclic voltammetry measurements show that micron‐thickness electrodes retain their capacitive rectangular‐shaped curves even at a very high scan rate of 10 000 mV s−1 in KOH electrolyte. A specific capacitance as high as 400 F g−1 is also recorded in H2SO4 electrolyte and this high specific capacitance maintains 85% of its value when the scan rate is increased to 1000 mV s−1. Furthermore, the electrospray MXene electrode shows good cycle stability in H2SO4 without a binder. About 90% of the capacitance is maintained after 10 000 charge–discharge cycles at a current density of 15 A g−1. All of these results show that the ESD MXene electrodes are a promising candidate for supercapacitor applications that require both high capacitance and enhanced rate capability.

Fabrication of thermally reduced graphene micro-tube and its electronic transport properties

Graphene-based micro-tubes (μ-GTs) with good tubular structure were successfully fabricated from commercial graphene oxide dispersion by the electrospray deposition technique and thermal reduction. As a result of the structural changes, the electrical conductivity of the μ-GTs clearly increased as the annealing temperature increased. In particular, the μ-GTs with lower annealing temperatures exhibited distinct semiconductor properties. The electrical conduction mechanism can be explained by the 2-D variable-range hopping model. Furthermore, a transition from semiconductor to semi-metal was found to occur when the annealing temperature exceeded 900 °C, and the electrical conduction mechanism follows the exponential law of temperature in this condition.