Printable Electrodes for Flexible Supercapacitors

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Electrochemical Sensors with Screen Printed Ag|AgCl|KCl Reference Electrodes

This paper presents the printed thick film Ag|AgCl|KCl reference electrodes for electrochemical or biosensors application and their electrochemical and analytical performance. The reference electrode exhibits a stable potential against standard glass reference electrode with a potential difference of 5 mV in the deionized water. The anodic and cathodic peak current of the electrode increase with the increase in scan rate in the range of 25-150 mVs-1. The open circuit potential response of thick film reference electrode in the NaCl concentrations range (30-100 mM) was measured and it shows a stable potential in each test solution. The fabricated reference electrode shows an excellent application for an electrochemical pH sensor

Stretchable pH Sensing Patch in a Hybrid Package

This work presents a novel stretchable pH sensing patch to detect the pH in body fluid which is one of the most important parameters in human health monitoring. The sensing patch is a hybrid package comprising of polyimide/gold-based stretchable interconnects and graphite composite-based flexible pH sensor. With the integration of stretchable interconnects, the patch is able to withstand external stretching up to 50% longer than its original length. Moreover, the electrical behavior of the patch does not degrade as studied by the real-time resistance investigation. In order to protect the connecting electrodes and wirings from direct contacting with solution under analysis, the sensing patch is encapsulated with elastic polymer with the active sensing area exposed. The fabricated patch reveals a high pH sensitivity of 36.2 μA/pH in the pH range between 5 and 9 which is validated through electrochemical and electroanalytical studies

Cloth Based Biocompatiable Temperature Sensor

Circular economy focussing on the reuse and recycling of materials is gaining significant interest these days as the concern for environment sustainability is increasing [1] - [3] . In this regard, printed electronics or green electronics is being promoted as alternative to conventional electronics, which requires several hazardous and toxic materials. However, there is lot to be done to align this emerging field with the requirements of circular economy [4] , [5] and one way is to identify the waste materials and transfer them into a valuable products [6] . In this regard, integration of electronics in textiles is one of the attractive directions [7] and recently flexible devices like solar cells, sensors and electronics have been successfully integrated into textiles [8] - [12] . Here we present, a temperature sensor fabricated on biodegradable cellulose cloth. The fabricated cloth based temperature sensors shows a sensitivity of 30°C/Ω in the temperature range of 25-60°C

Metal oxides based electrochemical pH sensors: Current progress and future perspectives

Electrochemical pH sensors are on high demand in numerous applications such as food processing, health monitoring, agriculture and nuclear sectors, and water quality monitoring etc., owing to their fast response (<10 s), wide pH sensing range (2–12), superior sensitivity (close to Nernstian response of 59.12 mV/pH), easy integration on wearable/flexible substrates, excellent biocompatibility and low cost of fabrication. This article presents an in-depth review of the wide range of MOx materials that have been utilized to develop pH sensors, based on various mechanisms (e.g. potentiometric, conductimetric, chemi-resistors, ion sensitive field effect transistor (ISFET) and extended-gate field effect transistor etc.). The tools and techniques such as potentiometric and electrochemical impedance spectroscopic that are commonly adopted to characterize these metal oxide-based pH sensors are also discussed in detail. Concerning materials and design of sensors for various practical application, the major challenges are toxicity of materials, interfernce of other ions or analytes, cost, and flexibility of materials. In this regard, this review also discusses the metal oxide-based composite sensing (active) material, designs of pH sensors and their applications in flexible/wearable biosensors for medical application are examined to present their suitability for these futuristic applications

Flexible Printed Reference Electrodes for Electrochemical Applications

This work presents screen-printed thick film reference electrodes (REs) on a polyethylene terephthalate substrate. The ion-conducting channel of presented screen-printed thick film Ag|AgCl|KCl electrodes are made from a composite of glass–KCl powder. With this new formulation the REs exhibit negligible variation in the potential (±4 mV), when evaluated under different bending states (radius 3, 5, and 7 mm). With a stable electrode potential and in-depth electrochemical studies, the utility of the presented REs for pH-sensing and flexible supercapacitor (SC) applications is demonstrated. With amperometric studies, we have shown that for pH-sensing applications, the presented REs can exhibit a sensitivity of 9 µA pH−1. At 1 mHz, the electrochemical investigations involving presented thick film REs and graphene-based SCs demonstrate a capacitance of 75 µF cm−2. With a flexible form factor, high endurance, and a miniature size, the presented RE has distinct advantages over conventional glass-based REs, particularly for emerging applications such as flexible sensing and for characterization of materials for energy storage devices

Screen Printed Thick Film Reference Electrodes for Electrochemical Sensing

This paper presents printed thick film Ag|AgCl|KCl reference electrodes (RE) for electrochemical sensors. The screenprinted REs with 10-μm thick glass-KCl salt matrix layer exhibit a stable potential of 5 mV. Cyclic voltammetric analysis shows that the anodic and cathodic peak current of the RE increases with the scan rate in the range of 25-150 mVs -1 . The analytical performance of the REs shows a stable open circuit potential for the NaCl concentrations in the range of 30-100 mM. Testing the presented REs for electrochemical pH sensor application (with RuO 2 -based sensitive electrode) the sensitivity of 55 mV/pH was noted in the pH range of 4.5-9. Evaluating the effect of temperature on the performance of REs, a potential variation of -3.8 mV/ °C was observed. Finally, a LabVIEW interface was developed to store, analyze, and calculate the sensitivity of the sensor under different temperature conditions. The LabVIEW interface can also be used to calculate the pH-value/temperature of unknown solutions under known temperature/pH conditions

Graphene–Graphite Polyurethane Composite Based High‐Energy Density Flexible Supercapacitors

Energy autonomy is critical for wearable and portable systems and to this end storage devices with high-energy density are needed. This work presents high-energy density flexible supercapacitors (SCs), showing three times the energy density than similar type of SCs reported in the literature. The graphene–graphite polyurethane (GPU) composite based SCs have maximum energy and power densities of 10.22 µWh cm−2 and 11.15 mW cm−2, respectively, at a current density of 10 mA cm−2 and operating voltage of 2.25 V (considering the IR drop). The significant gain in the performance of SCs is due to excellent electroactive surface per unit area (surface roughness 97.6 nm) of GPU composite and high electrical conductivity (0.318 S cm−1). The fabricated SCs show stable response for more than 15 000 charging/discharging cycles at current densities of 10 mA cm−2 and operating voltage of 2.5 V (without considering the IR drop). The developed SCs are tested as energy storage devices for wide applications, namely: a) solar-powered energy-packs to operate 84 light-emitting diodes (LEDs) for more than a minute and to drive the actuators of a prosthetic limb; b) powering high-torque motors; and c) wristband for wearable sensors

Textile-Based Potentiometric Electrochemical pH Sensor for Wearable Applications

In this work, we present a potentiometric pH sensor on textile substrate for wearable applications. The sensitive (thick film graphite composite) and reference electrodes (Ag/AgCl) are printed on cellulose-polyester blend cloth. An excellent adhesion between printed electrodes allow the textile-based sensor to be washed with a reliable pH response. The developed textile-based pH sensor works on the basis of electrochemical reaction, as observed through the potentiometric, cyclic voltammetry (100 mV/s) and electrochemical impedance spectroscopic (10 mHz to 1 MHz) analysis. The electrochemical double layer formation and the ionic exchanges of the sensitive electrode-pH solution interaction are observed through the electrochemical impedance spectroscopic analysis. Potentiometric analysis reveals that the fabricated textile-based sensor exhibits a sensitivity (slope factor) of 4 mV/pH with a response time of 5 s in the pH range 6–9. The presented sensor shows stable response with a potential of 47 ± 2 mV for long time (2000 s) even after it was washed in tap water. These results indicate that the sensor can be used for wearable applications