A self-powered, sliding electrification based triboelectric sensor was developed for detecting PH value from a periodic contact/separation motion. This innovative, cost-effective, simply designed sensor is composed of a fluorinated ethylene propylene thin film and an array of electrodes underneath. The operation of the TENG (triboelectric nanogenerator) sensor relies on a repetitive emerging-submerging process with traveling solution waves, in which the coupling between triboelectrification and electrostatic induction gives rise to alternating flows of electrons between electrodes. On the basis of coupling effect between triboelectrification and electrostatic induction, the sensor generates electric output signals which are associated with PH value. Experimental results show that the output voltage of the TENG sensor increases with the increasing PH value, which indicate that the PH value of different solution can be real-time monitored. This work not only demonstrates a new principle in the field of PH value measurement but also greatly expands the applicability of triboelectric nanogenerator (TENG) as self-powered sensors.
As one of the analytical devices, pH sensors play an important role in many fields such as environment monitors, biological analyses, blood monitors, and medical detection [
The presented self-powered PH sensor has a fork-finger structure, which is shown in Figure
Structural design of the TENG sensor. (a) Schematic diagram of the fabricated sensor. (b) Photograph of the prepared TENG sensor.
The operation of the TENG sensor involves a repetitive emerging-submerging process with traveling solution waves, which result in the coupling between triboelectrification and electrostatic induction between the TENG sensor and solution buffer and thus give rise to alternating flows of electrons. The electricity-generating process is described through a basic unit in Figure
Working mechanism of the fabricated TENG sensor. (a) Electrode A is partially submerged. (b) The water surface levels with the middle point of the device. (c) Electrode B is being covered by water, (d) electrode B is partially exposed, (d) electrode B is completely exposed, and (f) electrode A is partially exposed.
In the previous research, nanowire-based modification from polymer nanowires plays a key role in increasing the output power [
Electric measurement results of factors that influence the electric output. (a) Open-circuit voltage with increasing velocity. (b) Open-circuit voltage with increasing aspect ratio of the device.
For the fixed TENG surface area, more surface triboelectric charges and thus higher electric output will be produced accordingly for a narrower TENG with a higher aspect ratio has a shorter interaction distance with the solution, which was illustrated by the increasing
To demonstrate applications of the TENG for self-powered PH measurement, we mounted the sensor onto the linear motor to ensure reciprocating motion through the motor-controlling program for monitoring the PH value of the container in real-time.
Figure
Open-circuit voltage results as the TENG is repetitively submerged into buffer solution.
The buffer solution was driven by linear motor mounted with the TENG sensor to form a repeated wave motion. According to the measurement results plotted in Figure
Relationship between output voltage and PH value.
In summary, a self-powered sensor for PH measurement using triboelectrification was firstly demonstrated. The sensor has a fork-finger structure composed of FEP material and metal electrodes, as well as PET as the substrate. The reciprocating motion between TENG sensor and buffer solution leads to charge transfer between the adjacent Cu bottom electrodes, generating AC voltage in the external circuit. The output voltage of the TENG sensor varies with the buffer solution with different PH value due to the different ion concentration. And the PH value of buffer solution can be actively monitored in real-time by reading the output voltage. This work not only presents a new principle in the field of PH measurement but also greatly expands the applicability of TENGs as self-powered sensors. The electricity was generated through triboelectric effect at the solid-liquid interface upon directly interacting with ambient buffer solution, showing a practically feasible technology for water quality monitoring and environment protection.
A 1.5 mm thick acrylic sheet was cut into a hollow mask by precision laser cutting. The patterns in the mask were the same as electrodes. Then the mask was mounted onto the FEP film. The Cu layer was deposited onto the exposed PET surface by physical vapour deposition (PVD) to prepare the parallel electrode. Lead wires were connected to the electrodes as output terminals with one-to-one correspondence. Subsequently, a 75 mm thick FEP film was attached to the PET substrate.
TENG sensor was mounted vertically on the electrical linear motor. The sheet was immersed into the different PH buffer solution and perpendicular to the solution surface. The moving direction of the motor was perpendicular to the array of strip-shaped electrodes. A container filled with buffer solution was placed under the device with the water level adjacent to the device edge. The reciprocating motion of the TENG sensor was achieved through the motor-controlling program. The reciprocating motion of the linear motor forms waves of tap solution in the container. The output leads of TENG sensor were connected to Keithly 6514.
The authors declare no competing financial interest.
Ying Wu and Yuanjie Su contributed equally to this work.
This work was supported in part by the Research Foundation of Chongqing Municipal Education Committee (Grant no. KJ1401333) and Research Foundation of Chongqing University of Science & Technology (Grant no. CK2011Z08 and Grant no. CK2011Z09).