Low-Power and Eco-Friendly Temperature Sensor Based on Gelatin Nanocomposite

Abstract

An environmentally-friendly temperature sensor has been fabricated by using a low-cost water-processable nanocomposite material based on gelatin and graphene. The temperature dependence of the electrochemical properties has been investigated by using cyclic voltammetry, chronopotentiometry and impedance spectroscopy measurements. The simple symmetric device, composed of a sandwich structure between two metal foils and a printable graphene–gelatin blend, exhibits a dependence on the open-circuit voltage in a range between 260 and 310 K. Additionally, at subzero temperature, the device is able to detect the ice/frost formation. The thermally-induced phenomena occur at the electrode/gel interface with a bias current of a few tens of μA. The occurrence of dissociation reactions within the sensor causes limiting-current phenomena in the gelatin electrolyte. A detailed model describing the charge carrier accumulation, the faradaic charge transfer and diffusion processes within the device under the current-controlled has been proposed. In order to increase the cycle stability of the temperature sensor and reduce its voltage drift and offset of the output electrical signal, a driving circuit has been designed. The eco-friendly sensor shows a temperature sensitivity of about −19 mV/K, long-term stability, fast response and low-power consumption in the range of microwatts suitable for environmental monitoring for indoor applications.

Electrochemical Performance of Biopolymer-Based Hydrogel Electrolyte for Supercapacitors with Eco-Friendly Binders

“…All the electrodes display relatively homogeneous and dense surfaces without significant holes or cracks, except for the casein where a micro-cracks are evident [ 32 ]. The blend between gelatin and water–glycerol molecule acts as an intrinsic protonic conductor with an ionic conductivity value ranging between 0.4 and 0.7 mS/cm [ 3 , 33 ]. The addition of the NaCl salt to the pristine gelatin blend increases the value.…”

“…The addition of the NaCl salt to the pristine gelatin blend increases the value. From the impedance spectra, the bulk ionic conductivity can be estimated by , where is the real part of impedance when the phase angle goes to zero, is the thickness of the gel layer and is the area of the device [ 3 ]. Figure S1b reports the impedance spectra measured for the hydrogels as a function of NaCl content.…”

“…The cell structure is shown in the inset of Figure 1 d. As can be noted, the addition of the NaCl salt leads to an enhancement of the bulk conductivity reaching a value of about 50 mS/cm at 2 M. This value is in good agreement with what has been found in the literature for gel polymer electrolytes [ 33 , 34 ]. Since the gelatin-based electrolyte exhibits a temperature dependence of the value, all the measurements have been performed at 300 K [ 3 , 35 ].…”

“…The technological advances in consumer electronics and the rapid diffusion of related products in our daily lives increase energy demands [ 1 ]. Electrochemical energy storage, including batteries and supercapacitors, is the most practical and flexible strategy for portable power devices for a plethora of applications and the industry is focused on developing more efficient and cost-effective products [ 2 , 3 , 4 ]. The state-of-the-art Lithium-Ion Batteries deliver a high specific energy density of 250–270 Wh kg −1 and a relatively low specific power density (<350 W kg −1 ) [ 5 ].…”

Impact of Acetate‐Based Hydrogel Electrolyte on Electrical Performance and Stability of Eco‐Friendly Supercapacitors

“…[23,24] Recently, hydrogel based on gelatin has been used as an electrolyte in eco-friendly energy storage devices and low-power sensors for IoT applications. [5,[25][26][27][28] In this paper, the fabrication of symmetric carbon-based SCs, with natural polymers employed both in the electrode slurry and electrolyte system has been reported. The latter is a hydrogel containing sodium acetate (CH 3 COONa) as a highly soluble, and widely available salt, and has already demonstrated to be a beneficial aqueous electrolyte for SCs [29,30] but has been applied for the first time within a GPE.…”