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Micromachines
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Microelectrodes and Microdevices for Electrochemical Applications
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Microelectrodes and Microdevices for Electrochemical Applications

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "C：Chemistry".

Deadline for manuscript submissions: closed (30 October 2024) | Viewed by 11451

Special Issue Editors

Dr. Chen Peng

E-Mail Website
Guest Editor
School of Chemical Engineering and Advanced Materials, The University of Adelaide, Adelaide, SA 5005, Australia
Interests: electrochemical CO2/CO reduction; rechargeable batteries
Dr. Pengtang Wang

E-Mail Website
Guest Editor
School of Chemical Engineering and Advanced Materials, The University of Adelaide, Adelaide, SA 5005, Australia
Interests: design of cost-effective nanocatalysts for small-molecule conversion and green fuel production

Special Issue Information

Dear Colleagues,

Currently, microelectrodes are among the most important structures in microdevices and are widely employed in electrochemical applications. Several factors need to be considered when designing and fabricating an efficient microelectrode, including its component, structure and morphology, as well as the interphase between it and the targeted molecules (i.e., the dissolved CO2). They are strongly associated with the transfer rate of both the mass (i.e., H+ in acidic electrolyte) and electron, and the adsorption/desorption strength of the initial targeted molecules, subsequent intermediates and final product, thus significantly influencing the performance of the entire microdevice. In recent years, numerous studies have focused on the design and optimization of microelectrodes in order to improve the mass/electron transfer and adsorption/desorption strength of intermediates, and have made many breakthroughs in electrochemical applications, such as electrolysis, electrosynthesis, batteries and sensors. Of course, there are also significant challenges facing these fields, including precisely constructing unique, or manufacturing homogeneous, microelectrodes and microdevices. Accordingly, this Special Issue seeks to showcase research papers, communications, and review articles that focus on the novel design, fabrication and modeling of microelectrodes and microdevices in electrochemical applications, including electrocatalysis, electrosynthesis, batteries, sensors, chips and so on.

Dr. Chen Peng
Dr. Pengtang Wang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • microelectrode
  • microdevices
  • electrochemical applications
  • electrocatalysis
  • electrosynthesis
  • batteries
  • sensors
  • chips

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Published Papers (7 papers)

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Research

16 pages, 9287 KiB  
Article
One-Step Fabrication of 2.5D CuMoOx Interdigital Microelectrodes Using Numerically Controlled Electric Discharge Machining for Coplanar Micro-Supercapacitors
by Shunqi Yang, Ri Chen, Fu Huang, Wenxia Wang and Igor Zhitomirsky
Micromachines 2024, 15(11), 1319; https://doi.org/10.3390/mi15111319 - 29 Oct 2024
Cited by 1 | Viewed by 827
Abstract
With the increasing market demands for wearable and portable electronic devices, binary metal oxides (BMOs) with a remarkable capacity and good structure stability have been considered as a promising candidate for fabricating coplanar micro-supercapacitors (CMSCs), serving as the power source. However, the current [...] Read more.
With the increasing market demands for wearable and portable electronic devices, binary metal oxides (BMOs) with a remarkable capacity and good structure stability have been considered as a promising candidate for fabricating coplanar micro-supercapacitors (CMSCs), serving as the power source. However, the current fabrication methods for BMO microelectrodes are complex, which greatly hinder their further development and application in BMO CMSCs. Herein, the one-step fabrication of 2.5D CuMoOx-based CMSCs (CuMoCMSCs) has been realized by numerically controlled electric discharge machining (NCEDM) for the first time. In addition, the controllable capacity of CuMoCMSCs has been achieved by adjusting the NCEDM-machining voltage. The CuMoCMSCs machined by a machining voltage of 60 V (CuMoCMSCs60) showed the best performance. The fabricated CuMoCMSCs60 with binary metal oxides could operate at an ultra-high scanning rate of 10 V s−1, and gained a capacity of 40.3 mF cm−2 (1.1 mA cm−2), which is more than 4 times higher than that of MoOx-based CMSCs (MoCMSCs60) with a single metal oxide. This is because CuMoOx BMOs materials overcome the poor electroconductivity problem of the MoOx single metal oxide. This one-step and numerically controlled fabrication technique developed in this research opens a new vision for preparing BMO materials, BMO microelectrodes, and BMO microdevices in an environmental, automatic, and intelligent way. Full article
(This article belongs to the Special Issue Microelectrodes and Microdevices for Electrochemical Applications)
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14 pages, 5279 KiB  
Article
3D Binder-Free Mo@CoO Electrodes Directly Manufactured in One Step via Electric Discharge Machining for In-Plane Microsupercapacitor Application
by Shunqi Yang, Ri Chen, Fu Huang, Wenxia Wang and Igor Zhitomirsky
Micromachines 2024, 15(11), 1294; https://doi.org/10.3390/mi15111294 - 24 Oct 2024
Cited by 2 | Viewed by 942
Abstract
Cobalt oxide-based in-plane microsupercapacitors (IPMSCs) stand out as a favorable choice for various applications in energy sources for the Internet of Things (IoT) and other microelectronic devices due to their abundant natural resources and high theoretical specific capacitance. However, the low electronic conductivity [...] Read more.
Cobalt oxide-based in-plane microsupercapacitors (IPMSCs) stand out as a favorable choice for various applications in energy sources for the Internet of Things (IoT) and other microelectronic devices due to their abundant natural resources and high theoretical specific capacitance. However, the low electronic conductivity of cobalt oxide greatly hinders its further application in energy storage devices. Herein, a new manufacturing method of electric discharging machining (EDM), which is simple, safe, efficient, and environment-friendly, has been developed for synthesizing Mo-doped and oxygen-vacancy-enriched Co-CoO (Mo@Co-CoO) integrated microelectrodes for efficiently constructing Mo@Co-CoO IPMSCs with customized structures in a single step for the first time. The Mo@Co-CoO IPMSCs with three loops (IPMSCs3) exhibited a maximum areal capacitance of 30.4 mF cm−2 at 2 mV s−1. Moreover, the Mo@Co-CoO IPMSCs3 showed good capacitive behavior at a super-high scanning rate of 100 V s−1, which is around 500–1000 times higher than most reported CoO-based electrodes. It is important to note that the IPMSCs were fabricated using a one-step EDM process without any assistance of other material processing techniques, toxic chemicals, low conductivity binders, exceptional current collectors, and conductive fillers. This novel fabrication method developed in this research opens a new avenue to simplify material synthesis, providing a novel way for realizing intelligent, digital, and green manufacturing of various metal oxide materials, microelectrodes, and microdevices. Full article
(This article belongs to the Special Issue Microelectrodes and Microdevices for Electrochemical Applications)
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14 pages, 2817 KiB  
Article
Salivary Cortisol Detection with a Fully Inkjet-Printed Paper-Based Electrochemical Sensor
by Miguel Zea, Hamdi Ben Halima, Rosa Villa, Imad Abrao Nemeir, Nadia Zine, Abdelhamid Errachid and Gemma Gabriel
Micromachines 2024, 15(10), 1252; https://doi.org/10.3390/mi15101252 - 12 Oct 2024
Viewed by 1738
Abstract
Electrochemical paper-based analytical devices (ePADs) offer an innovative, low-cost, and environmentally friendly approach for real-time diagnostics. In this study, we developed a functional all-inkjet paper-based electrochemical immunosensor using gold (Au) printed ink to detect salivary cortisol. Covalent binding of the cortisol monoclonal antibody [...] Read more.
Electrochemical paper-based analytical devices (ePADs) offer an innovative, low-cost, and environmentally friendly approach for real-time diagnostics. In this study, we developed a functional all-inkjet paper-based electrochemical immunosensor using gold (Au) printed ink to detect salivary cortisol. Covalent binding of the cortisol monoclonal antibody onto the printed Au surface was achieved through electrodeposition of 4-carboxymethylaniline (CMA), with ethanolamine passivation to prevent non-specific binding. The ePAD exhibited a linear response within the physiological cortisol range (5–20 ng/mL), with sensitivities of 25, 23, and 19 Ω·ng/mL and R2 values of 0.995, 0.979, and 0.99, respectively. Additionally, interference studies against tumor necrosis factor-α (TNF-α) and N-terminal pro-B-type natriuretic peptide (NT-proBNP) yielded excellent results. This novel ePAD, fabricated using inkjet printing technology on paper, simplifies the process, reduces environmental impact, and lowers fabrication costs. Full article
(This article belongs to the Special Issue Microelectrodes and Microdevices for Electrochemical Applications)
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9 pages, 31124 KiB  
Article
Fabrication of Two-Layer Microfluidic Devices with Porous Electrodes Using Printed Sacrificial Layers
by Kosuke Ino, An Konno, Yoshinobu Utagawa, Taiyo Kanno, Kazuyuki Iwase, Hiroya Abe and Hitoshi Shiku
Micromachines 2024, 15(8), 1054; https://doi.org/10.3390/mi15081054 - 22 Aug 2024
Viewed by 1503
Abstract
Two-layer microfluidic devices with porous membranes have been widely used in bioapplications such as microphysiological systems (MPS). Porous electrodes, instead of membranes, have recently been incorporated into devices for electrochemical cell analysis. Generally, microfluidic channels are prepared using soft lithography and assembled into [...] Read more.
Two-layer microfluidic devices with porous membranes have been widely used in bioapplications such as microphysiological systems (MPS). Porous electrodes, instead of membranes, have recently been incorporated into devices for electrochemical cell analysis. Generally, microfluidic channels are prepared using soft lithography and assembled into two-layer microfluidic devices. In addition to soft lithography, three-dimensional (3D) printing has been widely used for the direct fabrication of microfluidic devices because of its high flexibility. However, this technique has not yet been applied to the fabrication of two-layer microfluidic devices with porous electrodes. This paper proposes a novel fabrication process for this type of device. In brief, Pluronic F-127 ink was three-dimensionally printed in the form of sacrificial layers. A porous Au electrode, fabricated by sputtering Au on track-etched polyethylene terephthalate membranes, was placed between the top and bottom sacrificial layers. After covering with polydimethylsiloxane, the sacrificial layers were removed by flushing with a cold solution. To the best of our knowledge, this is the first report on the sacrificial approach-based fabrication of two-layer microfluidic devices with a porous electrode. Furthermore, the device was used for electrochemical assays of serotonin and could successfully measure concentrations up to 5 µM. In the future, this device can be used for MPS applications. Full article
(This article belongs to the Special Issue Microelectrodes and Microdevices for Electrochemical Applications)
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17 pages, 4690 KiB  
Article
Development of Light-Scribing Process Using L-Ascorbic Acid for Graphene Micro-Supercapacitor
by Seorin Park, Da Young Lee and Sunghun Cho
Micromachines 2024, 15(7), 858; https://doi.org/10.3390/mi15070858 - 30 Jun 2024
Cited by 1 | Viewed by 1081
Abstract
The rapid development of smart technologies is accelerating the growing demand for microscale energy storage devices. This work reports a facile and practical approach to fabricating interdigitated graphene micro-patterns through the LSC process accompanied by the l-ascorbic acid (L-AA) and preheating treatment. Our [...] Read more.
The rapid development of smart technologies is accelerating the growing demand for microscale energy storage devices. This work reports a facile and practical approach to fabricating interdigitated graphene micro-patterns through the LSC process accompanied by the l-ascorbic acid (L-AA) and preheating treatment. Our work offered a higher degree of GO reduction than the conventional microfabrication. It significantly shortened the overall processing time to obtain the micro-patterns with improved electrical and electrochemical performances. The interdigitated MSC composed of 16 electrodes exhibited a high capacitance of 14.1 F/cm3, energy density of 1.78 mWh/cm3, and power density of 69.9 mW/cm3. Furthermore, the fabricated MSC device demonstrated excellent cycling stability of 88.2% after 10,000 GCD cycles and a high rate capability of 81.1% at a current density of 1.00 A/cm3. The fabrication process provides an effective means for producing high-performance MSCs for miniaturized electronic devices. Full article
(This article belongs to the Special Issue Microelectrodes and Microdevices for Electrochemical Applications)
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11 pages, 5760 KiB  
Article
Deposition of FeOOH Layer on Ultrathin Hematite Nanoflakes to Promote Photoelectrochemical Water Splitting
by Wenyao Zhang, Ya Zhang, Xiao Miao, Ling Zhao and Changqing Zhu
Micromachines 2024, 15(3), 387; https://doi.org/10.3390/mi15030387 - 13 Mar 2024
Cited by 2 | Viewed by 1522
Abstract
Hematite is one of the most promising photoanode materials for the study of photoelectrochemical (PEC) water splitting because of its ideal bandgap with sufficient visible light absorption and stability in alkaline electrolytes. However, owing to the intrinsically high electron-hole recombination, the PEC performance [...] Read more.
Hematite is one of the most promising photoanode materials for the study of photoelectrochemical (PEC) water splitting because of its ideal bandgap with sufficient visible light absorption and stability in alkaline electrolytes. However, owing to the intrinsically high electron-hole recombination, the PEC performance of hematite is still far below that expected. The efficient charge separation can be achieved via growth of FeOOH on hematite photoanode. In this study, hematite nanostructures were successfully grown on the surface of iron foil by the simple immersion deposition method and thermal oxidation treatment. Furthermore, cocatalyst FeOOH was successfully added to the hematite nanostructure surface to improve charge separation and charge transfer, and thus promote the photoelectrochemical water splitting. By utilizing the FeOOH overlayer as a cocatalyst, the photocurrent density of hematite exhibited a substantial 86% increase under 1.5 VRHE, while the onset potential showed an apparent shift towards the cathodic direction. This can be ascribed to the high reaction area for the nanostructured morphology and high electrocatalytic activity of FeOOH that enhanced the amount of photogenerated holes and accelerated the kinetics of water splitting. Full article
(This article belongs to the Special Issue Microelectrodes and Microdevices for Electrochemical Applications)
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12 pages, 2631 KiB  
Article
Gold Nanoparticle-Modified Carbon-Fiber Microelectrodes for the Electrochemical Detection of Cd2+ via Fast-Scan Cyclic Voltammetry
by Noel Manring, Miriam Strini, Gene Koifman, Jessica L. Smeltz and Pavithra Pathirathna
Micromachines 2024, 15(3), 294; https://doi.org/10.3390/mi15030294 - 21 Feb 2024
Viewed by 2673
Abstract
Neurotoxic heavy metals, such as Cd2+, pose a significant global health concern due to their increased environmental contamination and subsequent detrimental health hazards they pose to human beings. These metal ions can breach the blood-brain barrierblood–brain barrier, leading to severe and [...] Read more.
Neurotoxic heavy metals, such as Cd2+, pose a significant global health concern due to their increased environmental contamination and subsequent detrimental health hazards they pose to human beings. These metal ions can breach the blood-brain barrierblood–brain barrier, leading to severe and often irreversible damage to the central nervous system and other vital organs. Therefore, developing a highly sensitive, robust, and rapid in vivo detection method for these hazardous heavy metal ions is of the utmost importance for early detection, thus initiating timely therapeutics. Detecting ultra-low levels of toxic metal ions in vivo and obtaining accurate speciation information remains a challenge with conventional analytical techniques. In this study, we fabricated a novel carbon carbon-fiber microelectrode (CFM)-based sensor that can detect Cd2+ ions using fast-scan cyclic voltammetry by electrodepositing gold nanoparticles (AuNP). We optimized electrochemical parameters that generate a unique cyclic voltammogram (CV) of Cd2+ at a temporal resolution of 100 ms with our novel sensor. All our experiments were performed in tris buffer that mimics the artificial cerebellum fluid. We established a calibration curve resulting in a limit of detection (LOD) of 0.01 µM with a corresponding sensitivity of 418.02 nA/ µM. The sensor’s selectivity was evaluated in the presence of other metal ions, and it was noteworthy to observe that the sensor retained its ability to produce the distinctive Cd2+ CV, even when the concentration of other metal ions was 200 times higher than that of Cd2+. We also found that our sensor could detect free Cd2+ ions in the presence of complexing agents. Furthermore, we analyzed the solution chemistry of each of those Cd2+–ligand solutions using a geochemical model, PHREEQC. The concentrations of free Cd2+ ions determined through our electrochemical data align well with geochemical modeling data, thus validating the response of our novel sensor. Furthermore, we reassessed our sensor’s LOD in tris buffer based on the concentration of free Cd2+ ions determined through PHREEQC analysis, revealing an LOD of 0.00132 µM. We also demonstrated the capability of our sensor to detect Cd2+ ions in artificial urine samples, showcasing its potential for application in actual biological samples. To the best of our knowledge, this is the first AuNP-modified, CFM-based Cd2+ sensor capable of detecting ultra-low concentrations of free Cd2+ ions in different complex matrices, including artificial urine at a temporal resolution of 100 ms, making it an excellent analytical tool for future real-time, in vivo detection, particularly in the brain. Full article
(This article belongs to the Special Issue Microelectrodes and Microdevices for Electrochemical Applications)
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