Application of nickel-based composite electrode based on electrochemical regulation in hydrogel sensor

Abstract

The application is application of a nickel-based composite electrode based on electrochemical regulation in a hydrogel sensor. A hydrogel solution is placed in a mold with a manganese dioxide foam nickel at the bottom, and a manganese dioxide foam nickel-hydrogel sensor is obtained through freeze-thaw treatment. The sensitivity and energy storage capacity of the manganese dioxide foam nickel-hydrogel sensor are regulated by an electrochemical regulation method of an external voltage. The positive end of the manganese dioxide foam nickel-hydrogel sensor is connected to the working electrode of an electrochemical workstation, and the negative end is connected to the reference electrode and the counter electrode. The manganese dioxide foam nickel-hydrogel sensor indeed has energy storage capacity. The use of manganese dioxide foam nickel as a substrate and electrochemical regulation significantly improves the capacitance response and sensitivity. The sensing and energy storage performance of the hydrogel sensor is regulated in this way, and the hydrogel sensor after regulation has good effect in human body detection.

Description

Technical Field

[0001] This invention relates to the application of an electrochemically controlled nickel-based composite electrode in a hydrogel sensor. The hydrogel sensor has dual functions of force sensing and energy storage. The control method can effectively improve the sensing performance and energy storage performance of the hydrogel sensor, and the controlled hydrogel sensor has good results in human body detection. Background Technology

[0002] Flexible sensors have attracted research interest due to their potential applications in wearable devices, human-computer interaction, and smart textiles. Over the past few decades, researchers have designed a wide variety of dielectric layer materials to improve sensor performance and enhance their applications. (Qingyang Yu et al., Yu, Qingyang, and Jian Zhang. "Flexible capacitive pressure sensor based on a double-sided microstructure porous dielectric layer.") Micromachines14.1 (2022): 111.) A flexible capacitive pressure sensor with a double-sided microstructure porous dielectric layer was designed using silicone rubber (SR) / NaCl / carbon black (CB). Its sensing unit and array are suitable for large-area pressure sensing and object recognition. Lei Wu et al. (Wu, Lei, et al. "Beetle‐inspired gradient slant structures for capacitive pressure sensor with a broad linear response range." Advanced Functional Materials 34.26 (2024):2312370.) proposed a novel beetle-inspired gradient slant structure (GSS) dielectric layer, which endows the capacitive sensor with a wide linear range and excellent sensor stability. Lei Wang et al. (Wang, Lei, et al. "Studyon Highly Sensitive Capacitive Pressure Sensor Based on Silk Fibroin-LigninNanoparticles Hydrogel." Biomacromolecules 26.2 (2025): 1044-1052.) introduced lignin nanoparticles (LNPs) into silk fibroin (SF), resulting in a modified hydrogel sensor exhibiting high stress sensitivity, fast response speed, and excellent cycling stability.

[0003] Current technologies rely on adding nanoporous materials or structural design to increase the specific surface area inside the hydrogel. Increased contact area leads to increased capacitance, and theoretically, increased sensitivity to capacitance changes, thereby improving hydrogel performance. However, these traditional methods involve material selection and topology optimization of the material structure, making the process quite complex.

[0004] This invention targets hydrogel capacitive pressure sensors. Based on an existing structure, the sensitivity and internal capacitance of the hydrogel sensor can be adjusted by an external voltage, enabling it to not only function as a sensor but also possess a certain energy storage capacity. During operation, an electrochemical workstation is used to apply a voltage to the sensor electrodes, allowing for further control over both sensing and energy storage capabilities. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an application of an electrochemically controlled nickel-based composite electrode in hydrogel sensors. By employing electrochemical methods and cyclic voltammetry, a relatively stable voltage range for the hydrogel sensor is determined. Then, by applying an external voltage, the sensing and energy storage performance of the hydrogel sensor is significantly improved.

[0006] The technical solution adopted by the present invention to solve the aforementioned technical problem is as follows:

[0007] An application of an electrochemically controlled nickel-based composite electrode in a hydrogel sensor involves placing a hydrogel solution in a mold with manganese dioxide nickel foam at the bottom, followed by freeze-thaw treatment to obtain a manganese dioxide nickel foam-hydrogel sensor.

[0008] The sensitivity and energy storage capacity of the manganese dioxide nickel foam hydrogel sensor are controlled by electrochemical regulation of applied voltage. The positive terminal of the manganese dioxide nickel foam hydrogel sensor is connected to the working electrode of the electrochemical workstation, and the negative terminal is connected to the reference electrode and the counter electrode.

[0009] Furthermore, the process of controlling the sensitivity and energy storage capacity of the manganese dioxide nickel foam-hydrogel sensor through electrochemical modulation of applied voltage is as follows:

[0010] The CV curve of the manganese dioxide foam nickel-hydrogel sensor is obtained by cyclic voltammetry. If the CV curve has a rectangular trend, the highest and lowest potential values ​​of the CV curve are obtained, and the flat voltage range in the positive voltage range between the highest and lowest potentials is determined.

[0011] Within the flat voltage range, the initial capacitance and sensitivity at different voltages were tested, and the voltage that combines both sensitivity and initial capacitance was selected as the operating voltage of the manganese dioxide foam nickel-hydrogel sensor.

[0012] Furthermore, no redox reaction occurred within the flattened voltage range. Specifically, the flattened voltage range was determined by obtaining the peak slope k from the CV curve. peak If the slope of the CV curve at different voltage points in the positive voltage segment is less than 0.3k... peak If a point is a flat point, then it is called a flat point. The voltage range formed by consecutive flat points is called the smooth voltage range.

[0013] Further, the preparation process of the manganese dioxide nickel foam hydrogel sensor is as follows: Prepare analytically pure polyvinyl alcohol (PVA) particles, chitosan powder, and a 45% phytic acid solution. The mass ratio of each substance is: deionized water: polyvinyl alcohol: chitosan: 45% phytic acid solution = 10:1:0.05~0.2:0.009. Mix the phytic acid solution dropwise into the deionized water. Then weigh the polyvinyl alcohol particles and chitosan powder and pour them into the mixture of phytic acid and deionized water. Heat the mixture in a water bath at 90℃~96℃ for 1h~2h. Then pour the mixture into a mold with manganese dioxide nickel foam at the bottom and freeze it at -20℃~-30℃ for 24h~48h. Finally, thaw it at room temperature for 1h~2h to obtain the manganese dioxide nickel foam hydrogel sensor.

[0014] Furthermore, the preparation process of the manganese dioxide foamed nickel is as follows: first, a mixed solution of 0.5 mol / L Na2SO4 and 0.5 mol / L MnSO4 is prepared, and then MnO2 is electrochemically deposited on the foamed nickel;

[0015] The electrochemical deposition process of MnO2 is as follows: using nickel foam as the working electrode, platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode, the parameters of the cyclic voltammetry electrochemical workstation are set as follows: scan rate 0.01V / s; maximum potential 1.5V; minimum potential 0V; and 3 cycles are run.

[0016] Furthermore, the sensitivity of the manganese dioxide foam nickel-hydrogel sensor is improved by no less than 400%, and the capacity loss is controlled within 10% during 500 charge-discharge cycles.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] 1. This invention enables the regulation of the sensitivity of a hydrogel sensor by applying an external voltage. In sensor performance tests after applying a working potential, the sensitivity was improved by approximately 400% (compared to hydrogel sensor A). Furthermore, the implementation method is more convenient; the sensor sensitivity can be increased simply by changing the parameters of the electrochemical workstation. It is also noteworthy that this invention improves both sensing performance and the internal capacitance of the hydrogel, maintaining good energy storage performance even after 500 charge-discharge cycles.

[0019] 2. This invention improves sensing and energy storage performance by applying an external voltage to induce ion adsorption between the electrode material and the hydrogel, forming an ion layer at the interface with a potential different from the applied voltage, thus creating an electrical double-layer structure. The electrochemical method of finding a suitable voltage range to control the hydrogel is fundamentally different from traditional methods that involve designing contact area and replacing active materials. This invention only requires an external voltage to modify performance, eliminating the cumbersome steps of re-preparation.

[0020] 3. In this invention, chitosan and nickel manganese dioxide foam were added to the original polyvinyl alcohol / phytic acid hydrogel to increase the capacitance content of the hydrogel. Compared with oxides such as TiO2 (dense anatase structure), ZnO (close-packed hexagonal structure), and Fe3O4 (partially open interstitial structure), MnO2 has a layered crystal structure with more open ion channels. The high specific surface area and abundant surface functional groups (such as hydroxyl groups) of MnO2 can increase the number of active sites and promote the transport of ions and electrons. Surface defects (such as oxygen vacancies) can act as electron traps to improve conductivity. When MnO2 is combined with conductive materials, MnO2 has better dispersion and shorter electron transport paths. As a result, the surface charge density is greater during the formation of the electric double layer, which provides a larger electric double layer capacitance. Therefore, the hydrogel with added nickel manganese dioxide foam shows significant advantages in terms of initial capacitance and sensitivity.

[0021] 4. The hydrogel sensor prepared by the present invention using an electrochemically controlled nickel-based composite electrode can be used with high sensitivity in the detection of daily human activities. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the fabrication process of a hydrogel sensor according to an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the structure of an experimental platform according to an embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram illustrating the discharge performance of a manganese dioxide foam nickel-hydrogel sensor according to one embodiment.

[0025] Figure 4 This is a schematic diagram illustrating the response of a hydrogel sensor to pressure under different voltages, according to one embodiment.

[0026] Figure 5 This is a schematic diagram showing the response of a nickel foam-hydrogel sensor to pressure under different voltages.

[0027] Figure 6 This is a schematic diagram showing the response of a manganese dioxide foam nickel-hydrogel sensor to pressure under different voltages.

[0028] Figure 7 A bar chart comparing the sensitivity of three sensors at different voltages.

[0029] Figure 8 A bar chart comparing the initial capacitance of three sensors at different voltages.

[0030] Figure 9 The graphs show the CV curves of the three sensors.

[0031] Figure 10 Application effect and actual installation diagram of manganese dioxide foam nickel-hydrogel sensor attached to finger joint for finger bending detection.

[0032] Figure 11 This image shows the application effect and physical installation diagram of the manganese dioxide foam nickel-hydrogel sensor in voice recognition and swallowing action detection.

[0033] In the figure, 1 is the electrochemical workstation, 2 is the digital bridge, and 3 is the hydrogel sensor. Detailed Implementation

[0034] The present invention will be further explained below with reference to the embodiments and accompanying drawings, but this is not intended to limit the scope of protection of this application.

[0035] The experimental platform used in this invention includes: an electrochemical workstation 1, an electronic universal testing machine (not shown in the figure), and a digital bridge 2, wherein:

[0036] An electrochemical workstation is used to apply an external voltage to the hydrogel sensor 3. The highest and lowest potential voltage values ​​are set using cyclic voltammetry. A relatively flat range in the CV curve is selected as the working voltage range. Subsequently, an external voltage is applied to the hydrogel sensor within the selected working voltage range. In this embodiment, the range from the lowest to the highest voltage set by cyclic voltammetry is -1.5V to 1.5V.

[0037] Electronic universal testing machine for applying external pressure loads to hydrogel sensors;

[0038] A digital bridge is used to read the capacitance of the hydrogel sensor and record the capacitance signal of the hydrogel sensor under each voltage and pressure, providing raw data for subsequent plotting.

[0039] This invention can improve sensor sensitivity and initial capacitance by controlling the electrode surface potential. By utilizing the double-layer characteristics of the electrode-hydrogel interface, the distribution of anions and cations is regulated by applying an external voltage, thereby increasing the double-layer capacitance formed at the interface and achieving the purpose of improving sensing and energy storage performance.

[0040] Example:

[0041] In this embodiment, the hydrogel sensor is prepared using polyvinyl alcohol, phytic acid, and chitosan as raw materials. At the same time, the hydrogel is placed in different molds to obtain hydrogel sensors with different positive terminals. The performance of the hydrogel sensor can be improved by changing the potential. The three different hydrogel sensors are referred to as: hydrogel sensor A (polyvinyl alcohol-phytic acid-chitosan), nickel foam-hydrogel sensor B (nickel foam-polyvinyl alcohol-phytic acid-chitosan), and manganese dioxide nickel foam-hydrogel sensor C (manganese dioxide nickel foam-polyvinyl alcohol-phytic acid-chitosan).

[0042] Different potentials were applied to the best-performing hydrogel sensor, and the performance of the hydrogel sensor under different potentials was compared with that of the hydrogel sensor without applied potential.

[0043] First, it should be emphasized that all experiments in this embodiment were conducted at room temperature using the electronic universal testing machine of Xiangjie Instruments and the Tonghui TH2817B+ digital bridge, and the potential was controlled by the Chenhua electrochemical workstation CHI760E. In this embodiment, the capacitance signals were all read by the Tonghui TH2817H+ at 1V level and 100Hz, and the data are presented in the form of charts.

[0044] Preparation of manganese dioxide nickel foam: First, a mixed solution of 0.5 mol / L Na2SO4 and 0.5 mol / L MnSO4 was prepared, and MnO2 was electrochemically deposited on the nickel foam. Specific parameters for the electrochemical deposition of MnO2 included:

[0045] Electrode setup: Nickel foam is used as the working electrode, platinum sheet is used as the counter electrode, and Ag / AgCl is used as the reference electrode.

[0046] The parameters of the cyclic voltammetry electrochemical workstation were set as follows: scan rate 0.01 V / s; maximum potential 1.5 V; minimum potential 0 V; 3 cycles.

[0047] Manganese dioxide nickel foam was obtained.

[0048] Fabrication of hydrogel sensors (see) Figure 1Prepare 99.9% pure PVA (polyvinyl alcohol) particles, chitosan powder, and a 45% phytic acid solution. Use a pipette to take 40 μL of phytic acid (PA) solution and add it to 20 mL of deionized water for mixing. Then weigh 2 g of polyvinyl alcohol particles and 0.3 g of chitosan (CS) powder and pour them into the mixture of phytic acid and deionized water. Heat the mixture at 95°C for 1.5 h using a water bath method. Then pour the mixture into a custom mold and freeze it at -24°C for 24 h. In this embodiment, there are three types of molds: an empty mold, a mold with nickel foam at the bottom, and a mold with manganese dioxide nickel foam at the bottom. After thawing at room temperature for 1 h, three types of hydrogel sensors A, B, and C can be obtained.

[0049] The nickel foam used in this embodiment was obtained directly from commercial sources; it was 100ppi nickel foam.

[0050] The three types of hydrogel sensors, after molding, were placed on an electronic universal testing machine. Electrochemical workstation 1 was connected to the electrode of hydrogel sensor 3, and a digital bridge was used to record the capacitance signal of the hydrogel sensor, such as... Figure 2 As shown.

[0051] The energy storage performance of hydrogels was tested using a constant current charge-discharge method. Figure 3 The charge-discharge performance of the manganese dioxide foam nickel-hydrogel sensor C is shown, and it still has good energy storage capacity after 500 charge-discharge cycles, which also proves that the hydrogel sensor has energy storage performance.

[0052] Simultaneously, 500 cycles were used in the cyclic voltammetry to obtain the CV curve of the sensor, as shown below. Figure 9 As shown, all three hydrogel sensors exhibit a roughly rectangular shape, with a relatively flat middle section and peaks at both ends. The highest and lowest potentials are 1.5V and -1.5V, respectively. Figure 9 Find the flat voltage range within the positive voltage range, where the parameters of the cyclic voltammetry are set as follows: scan rate 0.02V / s; highest potential 1.5V; lowest potential -1.5V; run 500 cycles.

[0053] Quantitative indicators for the smooth voltage range: In this embodiment, for the manganese dioxide foam nickel-hydrogel sensor C, the peak slope is 2e -3 Let the slope of the peak region be denoted as k. peak The criterion is k < 0.3 × k peak When it is slow, it is recorded as flat. Figure 9 The slope of the lower part of the manganese dioxide foam nickel at 0.5V is 1.55e. -4 Less than 0.3k peakTherefore, it is still considered to be flat. The flat voltage range is 0.4~1.1V. No redox reaction occurs in this range, and the capacitance is dominated by the electric double layer capacitance. Therefore, the voltage range of 0.4~1.1V is chosen. This electric double layer voltage range may be different for different materials.

[0054] For hydrogel sensor A, one side of the hydrogel is connected to the working electrode, and the other side is connected to the counter electrode and the reference electrode. For nickel foam-hydrogel sensor B and manganese dioxide nickel foam-hydrogel sensor C, the nickel foam and manganese dioxide nickel foam sides are connected to the working electrode, and the opposite side is connected to the counter electrode and the reference electrode.

[0055] Record the capacitance and pressure data of the hydrogel sensor within the pressure range of 0~1kPa; Figures 4-6 The capacitive responses of three different hydrogel sensors to external pressure at different potentials were shown. It can be seen that regardless of whether the hydrogel is combined with other materials, the capacitive response after being energized is much higher than that without being energized.

[0056] Different external voltages (0.4–1.1 V in a gradual voltage range) were applied to the hydrogel sensor using an electrochemical workstation. The capacitance and pressure data of the hydrogel sensor within the 0–1 kPa pressure range were recorded at different voltages to obtain the sensitivity and initial capacitance at different voltages. Figure 7 and Figure 8 As shown.

[0057] Figure 7 and Figure 8 The diagram shows a comparison of the sensitivity and initial capacitance of three hydrogel sensors at different voltages. It clearly demonstrates that the sensitivity and initial capacitance of hydrogel sensors A, B, and C are higher after being energized than those without. However, unlike capacitance, the sensitivity decreases at 0.9V. Combined with the CV curve, this is attributed to the oxygen evolution reaction occurring at 0.9V, where internal bubbles interfere with the sensing performance of the hydrogel. Furthermore, excessively high voltages can cause polarization in the hydrogel, leading to deterioration in electrochemical performance and negatively impacting sensor performance.

[0058] An external voltage is applied to the sensor at the operating voltage for high-sensitivity pressure detection. A manganese dioxide foam nickel-hydrogel sensor is selected, which has a high initial capacitance (1.1 × e) at an operating voltage of 0.8V. -5 F), possessing good energy storage capacity and sensitivity greater than 0.8 kPa. -1 It is more sensitive to pressure detection.

[0059] Figure 10The system demonstrates the capacitive response characteristics of attaching the manganese dioxide foam nickel-hydrogel sensor to the back of a finger joint under different finger bending angles (0°, 30°, 45°, 60°). Figure 10 (as shown in Figure (a)) and actual application scenarios ( Figure 10 As shown in Figure (b), the capacitance change is obvious, and it has a relatively sensitive detection limit in human finger movements. Figure 11 The system demonstrates the performance of the manganese dioxide foam nickel-hydrogel sensor in speech recognition and swallowing motion detection. When applied to the throat, it exhibits noticeable capacitance changes during greetings and swallowing, with different responses to different pitches (see [link]). Figure 11 The first image in the first row of the middle section can distinguish human swallowing movements (see...). Figure 11 The first figure in the second row (in the middle) illustrates that the manganese dioxide foam nickel-hydrogel sensor has a good effect in detecting daily human activities.

[0060] In addition, the present invention also selects aluminum sheets and nickel sheets as substrates and places them in a mold to prepare hydrogel sensors under the same conditions. Experimental tests show that the sensitivity and initial capacitance are even worse than those of empty molds. Manganese dioxide foam nickel as substrate has the best sensing and energy storage performance.

[0061] In summary, in the embodiments of the present invention, the manganese dioxide nickel foam hydrogel sensor does indeed possess energy storage capabilities. By using manganese dioxide nickel foam as a substrate and combining it with electrochemical regulation, the capacitive response and sensitivity can be significantly improved, thereby regulating the sensing and energy storage performance of the hydrogel sensor.

[0062] Furthermore, it should be understood that although the present invention is described according to embodiments, not every embodiment contains only one independent technical solution. This way of describing the invention is merely for clarity. Those skilled in the art should regard the invention as a whole, and the various technical solutions can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0063] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. The application of electrochemically regulated nickel-based composite electrodes in hydrogel sensors, characterized in that, The hydrogel solution was placed in a mold with manganese dioxide nickel foam at the bottom, and the manganese dioxide nickel foam-hydrogel sensor was obtained by freezing and thawing. The sensitivity and energy storage capacity of the manganese dioxide nickel foam hydrogel sensor are controlled by electrochemical regulation of applied voltage. The positive terminal of the manganese dioxide nickel foam hydrogel sensor is connected to the working electrode of the electrochemical workstation, and the negative terminal is connected to the reference electrode and the counter electrode. The process of controlling the sensitivity and energy storage capacity of the manganese dioxide nickel foam-hydrogel sensor by means of electrochemical regulation of applied voltage is as follows: The CV curve of the manganese dioxide nickel foam-hydrogel sensor is obtained by cyclic voltammetry. If the CV curve has a rectangular trend, the highest and lowest potential values ​​of the CV curve are obtained, and a flat voltage range is selected within the positive voltage range between the highest and lowest potentials. Within the flat voltage range, the initial capacitance and sensitivity at different voltages were tested, and the voltage that combines both sensitivity and initial capacitance was selected as the operating voltage of the manganese dioxide foam nickel-hydrogel sensor.

2. The application of the electrochemically controlled nickel-based composite electrode in hydrogel sensors according to claim 1, characterized in that, No redox reactions occurred within the flat voltage range. Specifically, the flat voltage range was determined by obtaining the peak slope k from the CV curve. peak If the slope of the CV curve at different voltage points in the positive voltage segment is less than 0.3k... peak If a point is a flat point, then it is called a flat point. The voltage range formed by consecutive flat points is called the smooth voltage range.

3. The application of the electrochemically controlled nickel-based composite electrode in hydrogel sensors according to claim 1, characterized in that, The preparation process of the manganese dioxide nickel foam hydrogel sensor is as follows: Prepare analytically pure polyvinyl alcohol (PVA) particles, chitosan powder, and a 45% phytic acid solution. The mass ratio of each substance is: deionized water: polyvinyl alcohol: chitosan: 45% phytic acid solution = 10:1:0.05~0.2:0.

009. Mix the phytic acid solution dropwise into the deionized water. Then weigh the polyvinyl alcohol particles and chitosan powder and pour them into the mixture of phytic acid and deionized water. Heat the mixture at 100℃ for 1-2 hours using a water bath method. Pour the mixture into a mold with manganese dioxide nickel foam at the bottom and freeze it at -20℃ to -30℃ for 24-48 hours. Thaw the mixture at room temperature for 1-2 hours to obtain the manganese dioxide nickel foam hydrogel sensor.

4. The application of the electrochemically controlled nickel-based composite electrode according to claim 1 in hydrogel sensors, characterized in that, The preparation process of the manganese dioxide nickel foam is as follows: first, a mixed solution of 0.5 mol / L Na2SO4 and 0.5 mol / L MnSO4 is prepared, and then MnO2 is electrochemically deposited on the nickel foam. The electrochemical deposition process of MnO2 is as follows: using nickel foam as the working electrode, platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode, electrodeposition is performed using cyclic voltammetry. The specific electrochemical workstation parameters are set as follows: scan rate 0.01 V / s; maximum potential 1.5 V; minimum potential 0 V; and 3 cycles are run.

5. The application of the electrochemically controlled nickel-based composite electrode according to any one of claims 1-4 in hydrogel sensors, characterized in that, The sensitivity of the manganese dioxide foam nickel-hydrogel sensor is improved by no less than 400%, and the capacity loss is controlled within 10% during 500 charge-discharge cycles.

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