CN115575694A - Constant potential rectifier capable of detecting micro-current signal - Google Patents
Constant potential rectifier capable of detecting micro-current signal Download PDFInfo
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Abstract
The invention discloses a potentiostat capable of detecting microcurrent signals, which comprises a three-electrode test system taking a microelectrode as a working electrode, a microcontroller connected with a PC (personal computer) end and used for analyzing operation parameters of the three-electrode test system, a first low-pass filter circuit and a potentiostatic circuit which are sequentially connected between the microcontroller and a reference electrode and a counter electrode of the three-electrode test system, and a second low-pass filter circuit and a transimpedance amplifier circuit which are sequentially connected between the working electrode of the three-electrode test system and the microcontroller. Compared with the prior art, the invention has the advantages of low cost, reliable performance and convenient use and carrying, can realize the accurate detection characterization of pA-level current resolution, and provides great convenience for the research of advanced new energy nano and sub-nano materials, the detection and analysis of miniature signals and the like.
Description
Technical Field
The invention belongs to the field of advanced characterization instruments, and particularly relates to a potentiostat capable of detecting a microcurrent signal.
Background
The potentiostat is an important characterization test instrument for the research in the advanced science and technology fields of energy conversion, energy storage, corrosion, impedance and the like, can accurately characterize the electrochemical reaction in the energy conversion or storage process, and the test of a three-electrode system can independently and accurately control the absolute potential on a working electrode, thereby having important significance for promoting the advanced development of the new energy field.
The current commercial potentiostat has high cost, larger size and more biased functions to common application. The increase in demand for electrochemical detection has driven a new era in the development of personalized self-made instruments. The design ideas of the current self-made electrochemical instrument mainly comprise the following three types: 1) The portable electrochemical detection embedded system designed by Kwakye et al (Sensors and Actuators B: chemical, 2007, 123 (1): 336-343.), KAUSTat (2019 IEEE Sensors. IEEE, 2019: 1-4.) designed by Ahmad et al provides a small electrochemical instrument design for health monitoring or some other wearable and other uses; 2) ChepStat (Plos one, 2011, 6 (9): e 23783) developed by Rowe et al), a potentiostat (Biosensors and Bioelectronics, 2012, 32 (1): 309-313)) designed by Friedman et al, which is cost-effective and available on-site, and GN Meloni, which designs a cheap and versatile electrochemistry based on Arduino UNO, can be used for simple electrochemical teaching and training experiments (J. Chem. Educ. 2016, 93, 7, 1320-1322), which saves instrument cost at the expense of hardware performance; 3) Functional potentiostat circuits for specific detection or connection to other devices, including Dstat (PloS one, 2015, 10 (10): e 0140349.) developed by Michael D.M.Dryden and Aaron R.Wheeler for electrical analysis and integration, potentiostats developed by Dobbeleare for thin film battery characterization (HardwareX, 2017, 2: 34-49.), UWED (Analytical chemistry, 2018, 90 (10): 6240-6246.) manufactured by Ainla et al that can be used for smart phone wireless manipulation, and paper potentiostats designed by Taheria, mehdi et al for bacterial electrochemical research (omega, 2020, 5 (38): 24717-24723.). The above work provides many valuable designs for homemade electrochemical instruments, but all focus on electrochemical measurement on millimeter-scale electrodes, and cannot realize the test of extremely small micro-current signals, so that the intrinsic characterization of real material signals or chemical reactions cannot be realized.
Microelectrode electrochemistry provides a powerful means for people to explore the microstructure of substances, because when the size of an electrode is reduced from millimeter level to micrometer level or even nanometer level, the electrode shows many excellent electrochemical characteristics different from that of a conventional size electrode (ACS sensors, 2019, 4 (9): 2403-2411.). Microelectrodes have found numerous applications in scientific research fields such as electrochemical analysis (Environmental science & technology, 1995, 29 (3): 751-761., analytical Chemistry, 2002, 74 (6): 1322-1326.), neuroscience (Nature, 1958, 182 (4640): 962-962, MRS, 37 (6): 590-598.), cytobiochemistry (Accounts of chemical research, 2014, 47 (8): 2417-2425, omega, 2021, 6 (10): 6571-6581.), energy science (applied materials & interfaces, 2018, 10 (29): 73-245782.) and the like. Generally, in order to realize the acquisition and analysis of the micro-current, expensive import professional instruments need to be purchased, or an external circuit expansion module needs to be specially configured, so that the accurate test of the micro-current signal can be realized. Glasscott M W, verber M D developed sweet pottat (j. Chem. Educ. 2020, 97, 1, 265-270) based on a two-electrode system, microelectrode applicability, but the two-electrode system gave far less control over the working electrode potential than the three-electrode system.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a potentiostat capable of detecting micro-current signals.
The invention has the technical scheme that the potentiostat capable of detecting micro-current signals comprises a three-electrode test system taking a microelectrode as a working electrode, a microcontroller connected with a PC (personal computer) end and used for analyzing operation parameters of the three-electrode test system, a first low-pass filter circuit and a constant potential circuit which are sequentially connected between the microcontroller and a reference electrode and a counter electrode of the three-electrode test system, and a second low-pass filter circuit and a transimpedance amplifier circuit which are sequentially connected between the working electrode of the three-electrode test system and the microcontroller;
the microcontroller can provide driving signals for the reference electrode and the counter electrode sequentially through the first low-pass filter circuit and the constant potential circuit, sampling signals can be obtained from the working electrode sequentially through the second low-pass filter circuit and the transimpedance amplification circuit, and the microcontroller is in serial port communication with the PC terminal for signal analysis.
Further, an analog-digital converter and a digital-analog converter are arranged in the microcontroller, and the analog-digital converter is connected to the output end of the microcontroller and is used for performing analog-digital conversion when the microcontroller provides the driving signals for the reference electrode and the counter electrode;
the digital-to-analog converter is connected to the input end of the microcontroller and is used for executing digital-to-analog conversion when the microcontroller acquires the sampling signal from the working electrode;
the microcontroller adopts at least one of a Tensy application development board, an Arduino application development board, a single chip microcomputer and a microcomputer chip externally connected with a digital-to-analog conversion chip;
further, the constant potential circuit includes: the circuit comprises an amplifier U1, an amplifier U2, an amplifier U3, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor Ro1, a resistor Rb1, a resistor R-ref, a capacitor C1 and a capacitor C2;
the non-inverting input end of the amplifier U1 is connected with the resistor R1 in series and then connected to the output end of the analog-to-digital converter, the output end of the amplifier U1 is connected with the resistor R2 and the resistor R3 in series in sequence and then connected to the inverting input end of the amplifier U2, the non-inverting input end of the amplifier U2 is connected with the resistor Rb1 in series and then grounded, and the output end of the amplifier U2 is connected to the counter electrode, the non-inverting input end of the amplifier U3 is connected with the reference electrode in series after being connected with the resistor R-ref in series, the output end of the amplifier U4 is connected between the resistor R3 and the inverting input end of the amplifier U2 in series and then the inverting input end of the amplifier U3 is connected to the output end of the amplifier U3;
one end of the capacitor C1 is connected between the resistor R1 and the non-inverting input end of the amplifier U, and the other end of the capacitor C1 is grounded;
one end of the capacitor C2 is connected between the resistor R2 and the resistor R3, and the other end of the capacitor C is grounded;
one end of the resistor Ro1 is connected between the resistor R3 and the inverting input end of the amplifier U2, and the other end of the resistor Ro1 is connected to a set voltage-Offset.
Further, the transimpedance amplifier circuit includes a high-gain transimpedance amplifier circuit, the high-gain transimpedance amplifier circuit is connected to the second low-pass filter circuit, and the high-gain transimpedance amplifier circuit and the second low-pass filter circuit include: the circuit comprises an amplifier U4, an amplifier U5, a resistor R6, a resistor R7, a resistor Rf1, a resistor Rf2, a resistor Ro2, a capacitor Cf1 and a capacitor C3;
the inverting input end of the amplifier U4 is connected to the working electrode, the non-inverting input end of the amplifier U4 is grounded, the output end of the amplifier U4 is connected to the inverting input end of the amplifier U5 after being sequentially connected with a resistor R7 and a capacitor C3 in series, the non-inverting input end of the amplifier U5 is grounded, and the output end of the amplifier U5 is connected to the microcontroller;
one end of the resistor Rf1 is connected to the inverting input end of the amplifier U4, the other end of the resistor Rf1 is connected to the output end of the amplifier U4, and the capacitor Cf1 is connected in series with the resistor R5 and then connected in parallel to two ends of the resistor Rf 1;
the resistor R6 has one end connected between the output end of the amplifier U4 and the resistor R7 and the other end connected between the capacitor C3 and the inverting input end of the amplifier U5, the resistor Ro2 has one end connected between the inverting input end of the amplifier U5 and the capacitor C3 and the other end connected to a set voltage-Offset, and the resistor Rf2 has one end connected to the inverting input end of the amplifier U5 and the other end connected to the output end of the amplifier U5.
Further, the transimpedance amplification circuit further includes a low-gain transimpedance amplification circuit, the low-gain transimpedance amplification circuit is connected to the second low-pass filter circuit, and the low-gain transimpedance amplification circuit and the second low-pass filter circuit include: the circuit comprises an amplifier U6, an amplifier U7, a resistor Ro3, a resistor Rb2, a resistor Rf3 and a capacitor Cf2;
the inverting input end of the amplifier U6 is connected to the working electrode, the non-inverting input end of the amplifier U6 is connected in series with the resistor Rb2 and then is grounded, the output end of the amplifier U7 is connected to the non-inverting input end of the amplifier U7, the output end of the amplifier U7 is connected to the microcontroller, and the inverting input end of the amplifier U7 is connected to the output end of the amplifier U7;
one end of the resistor Ro3 is connected between the inverting input terminal of the amplifier U6 and the working electrode, and the other end is connected to a set voltage-Offset, one end of the resistor Rf3 is connected to the inverting input terminal of the amplifier U6, and the other end is connected to the output terminal of the amplifier U6, and the capacitor Cf2 is connected in parallel across the resistor Rf 3.
The potentiometer further comprises a compensation circuit connected with the constant potential circuit and the transimpedance amplification circuit, and the compensation circuit is used for providing a set voltage-Offset for the constant potential circuit and the transimpedance amplification circuit so as to expand the test range of the potentiostat.
Further, the potentiostat further comprises a power supply module for supplying power to circuits in the potentiostat, wherein the power supply module comprises an AC/DC module for converting 220V alternating current into 12V direct current, a first DC/DC module for converting 12V direct current into 5V direct current, and a second DC/DC module for converting 12V direct current into 9V direct current.
Furthermore, the AC/DC module adopts an IRM-20-12 chip, an AC/L port of the IRM-20-12 chip is connected with a live wire of a 220V alternating current power grid, an AC/N port is connected with a zero wire of the 220V alternating current power grid, and a + V end outputs 12V direct current voltage and a-V end is grounded;
the first DC/DC module comprises a constant voltage module REG1, a constant voltage module REG2, a capacitor EC1 and a capacitor EC2;
the first end of the constant voltage module REG2 is connected to 12V dc voltage, the second end is grounded, the third end outputs-5V dc voltage, the first end of the constant voltage module REG1 is connected to 12V dc voltage, the second end outputs +5V dc voltage, the third end is grounded, the capacitor EC1 is connected between the first end and the third end of the constant voltage module REG2, and the capacitor EC2 is connected between the second end and the third end of the constant voltage module REG 2;
the second DC/DC module comprises a constant voltage module REG3, a constant voltage module REG4, a capacitor EC3 and a capacitor EC4;
the first end of the constant voltage module REG4 is connected to 12V dc voltage, the second end is grounded, the third end outputs a set voltage-Offset, the first end of the constant voltage module REG3 is connected to 12V dc voltage, the second end outputs an auxiliary voltage Vsup, the third end is grounded, the capacitor EC3 is connected between the first end and the third end of the constant voltage module REG4, the capacitor EC4 is connected between the second end and the third end of the constant voltage module REG4, the set voltage-Offset is-9V dc voltage, and the auxiliary voltage is +9V dc voltage.
Further, the potential of the working electrode relative to the reference electrode is
；
Wherein, the first and the second end of the pipe are connected with each other,
is the potential of the working electrode relative to a reference electrode
The voltage output by the microcontroller after digital-to-analog conversion,
is the resistance value of the resistor Ro1,
is the resistance value of the resistor R2,
is the resistance value of the resistor R3,
is the resistance value of the resistor R4,
is the set voltage-Offset in the potentiostat circuit.
Further, the current magnitude of the sampling signal is:
；
wherein the content of the first and second substances,
is the current magnitude of the sampled signal,
is a set voltage-Offset in the transimpedance amplification circuit,
is the magnitude of the voltage received by the microcontroller,
is the resistance value of the resistor Ro2,
is a resistance value of the resistance Rf1,
is the resistance value of the resistor R6,
is the resistance value of the resistor Rf 2.
Compared with the prior art, the invention has at least the following beneficial effects:
by adopting the microcontroller, the invention develops the miniature potentiostat with compact structure, powerful function, accurate control and accurate reading, and can realize the detection of current signals as small as pA level. Through circuit board circuit design, shell shielding design need not external extra little current module, makes its performance accuracy reach the level of commercial high-end potentiostat. The system has low cost, reliable performance and convenient use and carrying, and provides great convenience for the research of leading-edge nano and sub-nano materials, the detection and analysis of micro signals, the research of the energy conversion and storage fields and the like.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.
FIG. 1 shows a schematic diagram of an implementation of the present invention;
FIG. 2 shows a potentiostat circuit schematic of the miniature potentiostat;
FIG. 3 shows a schematic diagram of a low pass filtering and high gain transimpedance amplification circuit of the miniature potentiostat;
FIG. 4 shows a schematic diagram of a low pass filtering and low gain transimpedance amplification circuit of the miniature potentiostat;
FIG. 5 shows a power signal processing circuit schematic;
FIG. 6 shows a schematic of the connection circuit of Arduino DUE to the present invention;
FIG. 7 shows an analog voltage signal output by the ADC1 port of Arduino DUE;
FIG. 8 shows potential signals at the reference electrode port and the working electrode port when a three electrode system is used in the present invention;
FIG. 9 shows cyclic voltammograms of a solution of ruthenium hexaammine trichloride at 2mmol/L using microelectrodes according to the invention;
FIG. 10 shows cyclic voltammograms of a 1mmol/L solution of ruthenium hexaammine trichloride using a microelectrode according to the invention;
FIG. 11 shows cyclic voltammograms of a solution of ruthenium hexaammine trichloride at 0.2mmol/L using microelectrodes according to the invention;
FIG. 12 shows a graph of steady state current versus solution concentration for FIGS. 7-9;
FIG. 13 shows the I-V characteristic of the present invention using a two-electrode system to measure a 500M Ω resistance;
FIG. 14 shows the cyclic voltammogram of a 0.2mmol/L ruthenium trichloride solution at a sweep rate of 50mV/s using a conventional electrode in accordance with the present invention;
FIG. 15 shows the cyclic voltammogram of the present invention in a 0.2mmol/L ruthenium hexaammine trichloride solution at a sweep rate of 100mV/s using a conventional electrode;
FIG. 16 shows the cyclic voltammogram of the present invention in a 0.2mmol/L ruthenium hexaammine trichloride solution using a conventional electrode at a sweep rate of 200 mV/s;
fig. 17 shows a plot of the reduction peak current versus the square root of the sweep rate for the cyclic voltammograms of fig. 13-15.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.
Thus, a feature indicated in this specification will serve to explain one of the features of one embodiment of the invention and does not imply that every embodiment of the invention must have the explained feature. Further, it should be noted that this specification describes many features. Although some features may be combined to show a possible system design, these features may also be used in other combinations not explicitly described. Thus, the combinations illustrated are not intended to be limiting unless otherwise specified.
The principles and construction of the present invention will be described in detail below with reference to the drawings and examples.
Referring to fig. 1, the present invention provides a potentiostat capable of detecting microcurrent signals, which includes a three-electrode testing system, a microcontroller, a first low-pass filter circuit, a second low-pass filter circuit, a potentiostat circuit, and a transimpedance amplifier circuit.
The three-electrode test system is a detection system consisting of three electrodes and comprises a Counter Electrode (CE), a Reference Electrode (RE) and a Working Electrode (WE), wherein the working electrode adopts a microelectrode. When the electrochemical cell is detected, a driving signal needs to be sent to a counter electrode and a reference electrode of a three-electrode testing system through a microcontroller, then the three-electrode testing system can generate a sampling signal, namely a micro-current, on a working electrode of the three-electrode testing system, and the micro-current signal can be reversely calculated through the signal received by the microcontroller, so that the electrochemical cell is analyzed.
In the invention, a first low-pass filter circuit and a constant potential circuit are sequentially connected between a reference electrode and a counter electrode of a microcontroller to three-electrode testing system, and a second low-pass filter circuit and a transimpedance amplification circuit are sequentially connected between a working electrode of the three-electrode testing system and the microcontroller. Through the mutual cooperation of a plurality of circuits and the circuit principle, the microcontroller can calculate the voltage of a driving signal received by the three-electrode testing system from an excitation signal sent by the microcontroller, and can reversely calculate the micro-current generated by a working electrode on the three-electrode testing system according to the received signal, so as to be used for analyzing the electrochemical cell.
In order to facilitate data processing, an analog-to-digital converter and a digital-to-analog converter are arranged in the microcontroller, the analog-to-digital converter is used for performing analog-to-digital conversion on an excitation signal output by the microcontroller, and the digital-to-analog converter is used for performing digital-to-analog conversion on a signal received by the microcontroller. The specific model can adopt an application development board or a single chip microcomputer with an analog-digital converter, a digital-analog converter or Teensy, arduino and the like capable of outputting pulse width modulation signals, or can adopt one or a plurality of combinations in a microcomputer chip externally connected with a digital-analog conversion chip.
The working principle of the invention is as follows: the microcontroller is communicated with the PC end through the USB serial port, and parameters such as a voltage scanning interval, a voltage scanning speed, the number of sampling points, a sampling interval and the like required by the three-electrode testing system are set from the PC end;
after receiving the instruction, the microcontroller outputs the excitation signal through the analog-to-digital converter, the excitation signal is filtered by the first low-pass filter circuit to obtain a low-noise voltage signal and is transmitted to the constant voltage circuit, and the constant voltage circuit converts the signal into a voltage signal negative value set by the PC end and outputs the voltage signal negative value at the reference electrode;
the working electrode is a microelectrode, and one end of the working electrode is connected with the virtual point of the operational amplifier, so that the signal of the working electrode is compared with the signal of the reference electrode, namely the voltage signal set by the PC end (namely the driving signal in the foregoing). Because the electrochemical reaction occurs due to the voltage difference applied to the working electrode, almost no current flows through the reference electrode, and thus the current of the electrochemical reaction flows from the working electrode to the counter electrode.
The current signal is extremely weak, is subjected to noise reduction through a second low-pass filter circuit, is converted into a corresponding voltage signal through a transimpedance amplification circuit, is input into a microcontroller through a digital-to-analog converter, and is transmitted back to a PC (personal computer) end through a USB (universal serial bus) serial port for analysis.
The working mode can respectively aim at an extremely-small micro-current reaction scene and a microampere current reaction scene, and can realize detection of an electrode electrochemical signal and detection of common electrochemistry.
Referring to fig. 2, the constant potential circuit according to the present invention includes: the circuit comprises an amplifier U1, an amplifier U2, an amplifier U3, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor Ro1, a resistor Rb1, a resistor R-ref, a capacitor C1 and a capacitor C2;
the non-inverting input end of the amplifier U1 is connected with the output end of the analog-to-digital converter after being connected with the resistor R1 in series, the output end is connected with the resistor R2 in series in sequence, the resistor R3 is connected with the inverting input end of the amplifier U2, the inverting input end is connected with the output end of the amplifier U1, the non-inverting input end of the amplifier U2 is connected with the ground after being connected with the resistor Rb1 in series, the output end is connected with the counter electrode, the non-inverting input end of the amplifier U3 is connected with the reference electrode after being connected with the resistor R-ref in series, the output end is connected between the resistor R3 and the inverting input end of the amplifier U2 after being connected with the resistor R4 in series, and the inverting input end is connected with the output end of the amplifier U3;
one end of the capacitor C1 is connected between the resistor R1 and the non-inverting input end of the amplifier U, and the other end of the capacitor C1 is grounded;
one end of the capacitor C2 is connected between the resistor R2 and the resistor R3, and the other end of the capacitor C is grounded;
the resistor Ro1 has one end connected between the resistor R3 and the inverting input terminal of the amplifier U2 and the other end connected to the set voltage-Offset.
After the set voltage Offest is input into the constant potential circuit, the voltage output by the microcontroller after passing through the analog-to-digital converter can be converted into the voltage range set by the PC end, and therefore tight detection and measurement are achieved.
Further, the transimpedance amplifier circuit includes a high-gain transimpedance amplifier circuit and a low-gain transimpedance amplifier circuit, which are both connected to the second low-pass filter circuit, as shown in fig. 3, the high-gain transimpedance amplifier circuit and the second low-pass filter circuit include: the circuit comprises an amplifier U4, an amplifier U5, a resistor R6, a resistor R7, a resistor Rf1, a resistor Rf2, a resistor Ro2, a capacitor Cf1 and a capacitor C3;
the inverting input end of the amplifier U4 is connected to the working electrode, the non-inverting input end of the amplifier U4 is grounded, the output end of the amplifier U4 is connected to the inverting input end of the amplifier U5 after being sequentially connected with the resistor R7 and the capacitor C3 in series, the non-inverting input end of the amplifier U5 is grounded, and the output end of the amplifier U5 is connected to the microcontroller;
one end of a resistor Rf1 is connected to the inverting input end of the amplifier U4, the other end of the resistor Rf1 is connected to the output end of the amplifier U4, and a capacitor Cf1 is connected in series with a resistor R5 and then connected in parallel to two ends of the resistor Rf 1;
one end of a resistor R6 is connected between the output end of the amplifier U4 and the resistor R7, the other end of the resistor R is connected between the capacitor C3 and the inverting input end of the amplifier U5, one end of a resistor Ro2 is connected between the inverting input end of the amplifier U5 and the capacitor C3, the other end of the resistor Ro2 is grounded, one end of a resistor Rf2 is connected to the inverting input end of the amplifier U5, and the other end of the resistor Rf2 is connected to the output end of the amplifier U5.
Referring to fig. 4, the low-gain transimpedance amplifier circuit and the second low-pass filter circuit include: the circuit comprises an amplifier U6, an amplifier U7, a resistor Ro3, a resistor Rb2, a resistor Rf3 and a capacitor Cf2;
the inverting input end of the amplifier U6 is connected to the working electrode, the non-inverting input end of the amplifier U6 is connected with the resistor Rb2 in series and then is grounded, the output end of the amplifier U7 is connected to the non-inverting input end of the amplifier U7, the output end of the amplifier U7 is connected to the microcontroller, and the inverting input end of the amplifier U7 is connected to the output end of the amplifier U7;
one end of the resistor Ro3 is connected between the inverting input end of the amplifier U6 and the working electrode, the other end is connected to a set voltage-Offset, one end of the resistor Rf3 is connected to the inverting input end of the amplifier U6, the other end is connected to the output end of the amplifier U6, and the capacitor Cf2 is connected in parallel to two ends of the resistor Rf 3.
Through the arrangement of the low-gain trans-impedance amplifying circuit and the high-gain trans-impedance amplifying circuit, a tiny current signal can be converted into a range which can be identified by the microcontroller, and therefore the effect of detecting tiny micro-current by the simple microcontroller is achieved.
Referring to fig. 1, the present invention further includes a compensation circuit connected to the constant potential circuit and the transimpedance amplifier circuit, where the compensation circuit can provide a set voltage for the constant potential circuit and the transimpedance amplifier circuit, respectively, so as to be used for detection and calculation analysis of the micro-current, and at the same time, the set voltage is provided to the constant potential circuit and can also be used for setting the measurement range of the present invention.
Referring to fig. 5, the present invention further includes a power module for supplying power to each circuit in the potentiostat, wherein the power module includes an AC/DC module for converting 220V AC power into 12V DC power, a first DC/DC module for converting 12V DC power into 5V DC power, and a second DC/DC module for converting 12V DC power into 9V DC power. Through the arrangement of the power supply module, the invention can get electricity from an alternating current power grid and ensure the normal work of circuits of all parts in the potentiostat.
As shown in fig. 5, the first circuit diagram is a connection schematic diagram of an AC/DC module, which employs an IRM-20-12 chip, an AC/L port of the IRM-20-12 chip is connected to a live wire of a 220V AC power grid, an AC/N port is connected to a zero line of the 220V AC power grid, a + V end outputs 12V DC voltage, and an-V end is grounded;
the second circuit diagram in fig. 5 is a connection schematic diagram of the first DC/DC module, which includes a constant voltage module REG1, a constant voltage module REG2, a capacitor EC1, and a capacitor EC2;
the first end of the constant voltage module REG2 is connected with 12V direct current voltage, the second end is grounded, the third end outputs-5V direct current voltage, the first end of the constant voltage module REG1 is connected with 12V direct current voltage, the second end outputs +5V direct current voltage, and the third end is grounded, the capacitor EC1 is respectively connected between the first end and the third end of the constant voltage module REG2, and the capacitor EC2 is respectively connected between the second end and the third end of the constant voltage module REG 2;
the third circuit diagram in fig. 5 is a connection schematic diagram of the second DC/DC module, which includes the constant voltage module REG3, the constant voltage module REG4, the capacitor EC3, and the capacitor EC4;
the first end of the constant voltage module REG4 is connected to 12V dc voltage, the second end is grounded, and the third end outputs a set voltage-Offset, the first end of the constant voltage module REG3 is connected to 12V dc voltage, the second end outputs an auxiliary voltage Vsup, and the third end is grounded, the capacitor EC3 is connected between the first end and the third end of the constant voltage module REG4, and the capacitor EC4 is connected between the second end and the third end of the constant voltage module REG 4.
Further, since the working electrode is connected to the virtual ground, the potential of the working electrode compared to the reference electrode, i.e. the voltage of the voltage signal (i.e. the driving signal) set for the PC terminal, is:
wherein the content of the first and second substances,
is the potential of the working electrode relative to a reference electrode
Is the voltage output by the microcontroller after digital-to-analog conversion,
is the resistance value of the resistor Ro1,
is the resistance value of the resistor R2,
is the resistance value of the resistor R3,
is the resistance value of the resistor R4,
is the set voltage-Offset in the potentiostatic circuit.
Here, RE, i.e. the reference electrode,
is the potential on the reference electrode, which is the potential compared to groundWE is a working electrode, and because the working electrode is connected to a virtual ground, the potential of the working electrode on the reference electrode satisfies the following conditions:
wherein
Is the potential of the reference electrode compared to ground.
Further, the current flowing through the working electrode (i.e. the current of the sampling signal) in the present invention is:
wherein, the first and the second end of the pipe are connected with each other,
in order to sample the magnitude of the current of the signal,
for setting voltage-Offset in transimpedance amplifier circuit
Is the magnitude of the voltage received by the microcontroller,
is the resistance value of the resistor Ro2,
as the resistance value of the resistor Rf1,
is the resistance value of the resistor R6,
is the resistance value of the resistor Rf 2.
Therefore, the current on the working electrode can be reversely calculated by utilizing the voltage signal received by the microcontroller by utilizing the formula, and then the current is transmitted to the PC terminal for analysis.
Therefore, the invention can realize advanced analysis and test methods such as cyclic voltammetry test, chronoamperometry test, nano-collision test and the like of micro-current signals, and can be applied to the fields of energy conversion, energy storage, current-voltage test, electrochemical analysis, nano-material characterization and the like.
The size of the whole body is not more than 10cm and not more than 5cm, the whole structure is compact, and the portable type solar water heater is convenient to use and carry.
Referring to fig. 6, which is a schematic diagram of the connection between the present invention and Arduino DUE, in one embodiment of the present invention, arduino DUE is used as a microcontroller, and a voltage of 9V is applied to Vin, and Arduino DUE and all circuits 0V are grounded.
The voltage signals subjected to digital-to-analog conversion are output at the DAC1 interface of the Arduino DUE board, and the voltage signal range is shown in FIG. 7. The voltage signal is sent to the RE reference electrode through the filter circuit and the voltage control circuit, the RE potential is negative value of the set value of the PC end compared with the WE (namely, the ground) potential, and the potential of the working electrode can be calculated by the following formula:
wherein the content of the first and second substances,
which is the potential of the reference electrode compared to ground, the schematic diagram of the circuit is shown in figure 2,
for the output voltage at the DAC port to be,
ro1, R2, R3, R4 are resistance values of the resistors at various places in FIG. 2 for the voltage at-Offset.
In this embodiment, the excitation potential provided by Arduino DUE is shown in fig. 6, and the voltage variation range of the working electrode compared to the reference electrode is shown in fig. 8.
The RE reference electrode is connected with an SCE standard electrode, the CE counter electrode is connected with a platinum column counter electrode, RE, CE and WE are placed in beakers containing hexaammine ruthenium trichloride with certain concentration and 0.1M KCl electrolyte solution, and the WE working electrode is a gold microdisk electrode with the diameter of 25 um.
The micro potentiostat selects a Microelectrode mode through a current mode switch.
The working range of the micro potentiostat is controlled to be 0.2V to-0.6V on the PC, the sweeping speed is 10mV/s, an electrochemical reaction occurs on a WE working electrode, a current signal is converted into a corresponding voltage signal through a filter circuit, a transimpedance amplification circuit and the like, and the corresponding voltage signal is received by an A1 port OUTPUT1 of the Arduino DUE.
The current of the WE working electrode can be deduced according to the voltage value measured by OUTPUT 1:
；
wherein the content of the first and second substances,
is the current that flows through the working electrode,
the voltage of the-offset bit in figure 3,
for the voltage output by the circuit to the microcontroller module,
、
、
、
the resistance values of the resistors in fig. 3 are shown.
FIG. 9 shows a comparison of CV curves of the present invention and commercial electrochemical working Bio-logic SP-200 in a 2mmol/L solution of ruthenium hexaammine trichloride, and it can be seen that the present invention is comparable to commercial instrumentation performance. FIGS. 10 and 11 show the cyclic voltammograms of the invention measured at concentrations of ruthenium hexaammine tetrachloride of 1mmol/L and 0.2mmol/L, respectively, with a current of-0.3V vs. SCE at which a steady state is reached. Therefore, the system can realize accurate and stable test of the pA level current signal.
In order to verify the accuracy of the test result, according to theoretical calculation, the steady-state current of the microdisk electrode obeys the formula:
wherein
Is the steady state current, F is the Faraday constant,
is the diffusion coefficient of ruthenium (III) hexammine,
is the concentration of the ruthenium (III) hexamine in the bulk solution,
the radius of the microdisk electrode. FIG. 12 is a plot of steady state current versus solution concentration as shown in FIGS. 9-11, with a linear fit having a slope of-0.0032A/(mol. About. L) -1 ) The diffusion coefficient of ruthenium (III) hexammine, D0=8.43 × 10, is reported in the literature -10 m 2 s -1 According to the equation, the radius of the WE working electrode used in the experiment can be calculated to be 9.87um, and the result is equivalent to the size of the mark radius of the purchased microelectrode of 12.5um, so that the micro potentiostat has higher accuracy in detecting a micro-current signal.
Furthermore, in another embodiment of the present invention, the RE reference electrode and the CE counter electrode of the present invention are connected, which is compatible with the detection of a two-electrode system, and can be used for conventional electrical detection for detecting resistance values of megaohm-level resistors or other nanoampere and picoampere-level currents. The Arduino DUE is also used as a microcontroller, a voltage of 9V is connected to Vin, and the Arduino DUE and all circuits of 0V are grounded.
The voltage signal after digital-to-analog conversion is output at the DAC1 interface of the Arduino DUE plate, the voltage signal is transmitted to an RE reference electrode and a CE counter electrode through a filter circuit and a voltage control circuit, the RE potential is a negative value of a set value of a PC end compared with the WE (namely, ground) potential, and the potential of a working electrode can be calculated through the following formula:
wherein the content of the first and second substances,
which is the potential of the reference electrode compared to ground, the schematic diagram of the circuit is shown in figure 2,
for the DAC port output voltage, vo is the voltage at Offset,
、
、
、
the resistance values of the resistors in fig. 2 are shown.
The RE reference electrode and the CE counter electrode are connected with one end of a 500M omega resistor, and the WE working electrode is connected with the other end of the resistor to be detected;
the micro potentiostat selects a Microelectrode mode through a current mode switch.
The working range of the micro potentiostat is controlled on the PC to be-1V to 1V, the sweep speed is 10mV/s, and the current signals are converted into corresponding voltage signals through a filter circuit, a transimpedance amplification circuit and the like and received by an A1 port OUTPUT1 of the Arduino DUE.
The current of the WE working electrode can be deduced according to the voltage value measured by OUTPUT 1:
wherein the content of the first and second substances,
is the current flowing through the working electrode,
the voltage of the-offset bit in figure 3,
for the voltage output by the circuit to the microcontroller module,
、
、
、
the resistance values of the resistors in fig. 3 are shown.
FIG. 13 shows the electrical characteristic curve of the 500M omega resistor detected by the double-electrode system, and the slope of the characteristic curve is 1919.24pA/V according to the linear fitting result, so that the resistance value of the resistor can be calculated to be 520.92M omega, which is equivalent to the labeled value of the measured resistor, and the micro-current signal detected by the micro-potentiostat has higher accuracy.
Further, in another embodiment of the present invention, the Arduino DUE is also used as a microcontroller, and the voltage of 9V is applied to Vin, and the Arduino DUE and all the circuits 0V are grounded. The system is also internally provided with a series circuit capable of testing a conventional electrochemical current signal, and a circuit selection switch of the micro potentiostat is arranged on the conventional electrochemical circuit.
The voltage signal after digital-to-analog conversion is output at the DAC1 interface of the Arduino DUE board, the voltage signal is transmitted to an RE reference electrode through a filter circuit and a voltage control circuit, the RE potential is a negative value of a set value of a PC end compared with the WE (namely, ground) potential, and the potential of a working electrode can be calculated through the following formula:
wherein, the first and the second end of the pipe are connected with each other,
which is the potential of the reference electrode compared to ground, the schematic circuit diagram of which is shown in figure 2,
for the output of the voltage at the DAC port,
is the voltage at-Offset and is,
、
、
、
the resistance values of the resistors in fig. 2 are shown.
The RE reference electrode is connected with an SCE standard electrode, the CE counter electrode is connected with a platinum column counter electrode, the RE, the CE and the WE are all placed in a beaker containing 2mM ruthenium hexammine trichloride solution, and the WE electrode is a glassy carbon electrode with the diameter of 3 mM.
The current mode switch of the micro potentiostat selects the macroectrode mode.
Electrochemical reaction occurs on the WE working electrode, and the current signal is converted into a corresponding voltage signal through a filter circuit, a transimpedance amplification circuit and the like and is received by the A7 port OUTPUT2 of the Arduino DUE. The current of the WE working electrode can be deduced according to the voltage value measured by OUTPUT 2:
the principle is shown in FIG. 4, wherein
Is the current that flows through the working electrode,
the voltage of the-offset bit in figure 4,
for the voltage output by the circuit to the microcontroller module,
、
the resistances are shown in fig. 4.
Fig. 14-16 show the cyclic voltammetry test results of this experiment, and the peak current value increases with the increase of the scanning speed. FIG. 17 is a plot of the square root of the restored peak current values versus the corresponding scan speeds for the curves of FIGS. 14-16, having a slope of-117.64 uA/(V/s) 0.5 The relation between the two satisfies Randles-Sevcik equation:
wherein F is the Faraday constant and R is a gasThe constant, T is the experimental temperature, n is the reaction electron transfer number, A is the electrode surface area, D0 is the diffusion coefficient of ruthenium (III) hexaammine, C0 is the concentration of ruthenium (III) hexaammine in the bulk solution, and v is the scanning speed of cyclic voltammetry. The diffusion coefficient of ruthenium (III) hexamine used in this experiment was calculated to be 9.5732 m/s according to the Randles-Sevcik equation 2 The value is close to the report of the literature (Journal of electrochemical Chemistry, 2011, 652 (1-2): 13-17.), and the micro potentiostat is proved to have higher accuracy in detecting the conventional electrochemical signal.
In conclusion, compared with the prior art, the micro potentiostat has the advantages that the micro potentiostat is developed by adopting the microcontroller, the structure is compact, the function is strong, the control is accurate, and the reading is accurate, so that the current signal detection of the level as small as pA can be realized. Through circuit board circuit design, shell shielding design need not external extra little current module, makes its performance accuracy reach the level of commercial high-end potentiostat. The system has low cost, reliable performance and convenient use and carrying, and provides great convenience for the research of leading-edge nano and sub-nano materials, the detection and analysis of micro signals, the research of the energy conversion and storage fields and the like.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. A potentiostat capable of detecting micro-current signals comprises a three-electrode test system taking a microelectrode as a working electrode, a microcontroller connected with a PC (personal computer) end and used for analyzing operation parameters of the three-electrode test system, and is characterized by further comprising a first low-pass filter circuit and a constant potential circuit which are sequentially connected between the microcontroller and a reference electrode and a counter electrode of the three-electrode test system, and a second low-pass filter circuit and a transimpedance amplifier circuit which are sequentially connected between the working electrode of the three-electrode test system and the microcontroller;
the microcontroller can provide driving signals for the reference electrode and the counter electrode sequentially through the first low-pass filter circuit and the constant potential circuit, and can obtain sampling signals from the working electrode sequentially through the second low-pass filter circuit and the transimpedance amplification circuit, and the microcontroller is in serial port communication with the PC (personal computer) end and used for signal analysis.
2. The potentiostat of claim 1, wherein the microcontroller houses an analog-to-digital converter and a digital-to-analog converter, and the analog-to-digital converter is connected at the output of the microcontroller for performing analog-to-digital conversion when the microcontroller provides the drive signal to the reference electrode and the counter electrode;
the digital-to-analog converter is connected to the input end of the microcontroller and is used for executing digital-to-analog conversion when the microcontroller acquires the sampling signal from the working electrode;
the microcontroller adopts at least one of a Teensy application development board, an Arduino application development board, a single chip microcomputer and a microcomputer chip externally connected with a digital-to-analog conversion chip.
3. The potentiostat of claim 2, wherein the potentiostat circuit comprises: the circuit comprises an amplifier U1, an amplifier U2, an amplifier U3, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor Ro1, a resistor Rb1, a resistor R-ref, a capacitor C1 and a capacitor C2;
the non-inverting input end of the amplifier U1 is connected with the resistor R1 in series and then connected to the output end of the analog-to-digital converter, the output end of the amplifier U1 is connected with the resistor R2 and the resistor R3 in series in sequence and then connected to the inverting input end of the amplifier U2, the non-inverting input end of the amplifier U2 is connected with the resistor Rb1 in series and then grounded, and the output end of the amplifier U2 is connected to the counter electrode, the non-inverting input end of the amplifier U3 is connected with the reference electrode in series after being connected with the resistor R-ref in series, the output end of the amplifier U4 is connected between the resistor R3 and the inverting input end of the amplifier U2 in series and then the inverting input end of the amplifier U3 is connected to the output end of the amplifier U3;
one end of the capacitor C1 is connected between the resistor R1 and the non-inverting input end of the amplifier U, and the other end of the capacitor C1 is grounded;
one end of the capacitor C2 is connected between the resistor R2 and the resistor R3, and the other end of the capacitor C is grounded;
one end of the resistor Ro1 is connected between the resistor R3 and the inverting input end of the amplifier U2, and the other end of the resistor Ro1 is connected to a set voltage-Offset.
4. The potentiostat of claim 1, wherein the transimpedance amplification circuit comprises a high-gain transimpedance amplification circuit connected to the second low-pass filter circuit, and wherein the high-gain transimpedance amplification circuit and the second low-pass filter circuit comprise: the circuit comprises an amplifier U4, an amplifier U5, a resistor R6, a resistor R7, a resistor Rf1, a resistor Rf2, a resistor Ro2, a capacitor Cf1 and a capacitor C3;
the inverting input end of the amplifier U4 is connected to the working electrode, the non-inverting input end of the amplifier U4 is grounded, the output end of the amplifier U4 is connected to the inverting input end of the amplifier U5 after being sequentially connected with the resistor R7 and the capacitor C3 in series, the non-inverting input end of the amplifier U5 is grounded, and the output end of the amplifier U5 is connected to the microcontroller;
one end of the resistor Rf1 is connected to the inverting input end of the amplifier U4, the other end of the resistor Rf1 is connected to the output end of the amplifier U4, and the capacitor Cf1 is connected in series with the resistor R5 and then connected in parallel to two ends of the resistor Rf 1;
the resistor R6 has one end connected between the output end of the amplifier U4 and the resistor R7 and the other end connected between the capacitor C3 and the inverting input end of the amplifier U5, the resistor Ro2 has one end connected between the inverting input end of the amplifier U5 and the capacitor C3 and the other end connected to a set voltage-Offset, and the resistor Rf2 has one end connected to the inverting input end of the amplifier U5 and the other end connected to the output end of the amplifier U5.
5. The potentiostat of claim 1, wherein the transimpedance amplification circuit further comprises a low-gain transimpedance amplification circuit connected to the second low-pass filter circuit, and the low-gain transimpedance amplification circuit and the second low-pass filter circuit comprise: the circuit comprises an amplifier U6, an amplifier U7, a resistor Ro3, a resistor Rb2, a resistor Rf3 and a capacitor Cf2;
the inverting input end of the amplifier U6 is connected to the working electrode, the non-inverting input end of the amplifier U6 is connected in series with the resistor Rb2 and then is grounded, the output end of the amplifier U7 is connected to the non-inverting input end of the amplifier U7, the output end of the amplifier U7 is connected to the microcontroller, and the inverting input end of the amplifier U7 is connected to the output end of the amplifier U7;
one end of the resistor Ro3 is connected between the inverting input terminal of the amplifier U6 and the working electrode, and the other end is connected to a set voltage-Offset, one end of the resistor Rf3 is connected to the inverting input terminal of the amplifier U6, and the other end is connected to the output terminal of the amplifier U6, and the capacitor Cf2 is connected in parallel across the resistor Rf 3.
6. The potentiostat of claim 1, further comprising a compensation circuit connected to the potentiostat circuit and the transimpedance amplification circuit for providing a set voltage-Offset for the potentiostat circuit and the transimpedance amplification circuit for extending a test range of the potentiostat.
7. The potentiostat of claim 1, further comprising a power module for powering the circuits within the potentiostat, the power module comprising an AC/DC module for converting 220V alternating current to 12V direct current, a first DC/DC module for converting 12V direct current to 5V direct current, and a second DC/DC module for converting 12V direct current to 9V direct current.
8. The potentiostat of claim 7, wherein the AC/DC module employs an IRM-20-12 chip, the IRM-20-12 chip has an AC/L port connected to the live line of a 220V AC grid, an AC/N port connected to the neutral line of a 220V AC grid, a + V terminal outputting 12V DC voltage, and a-V terminal grounded;
the first DC/DC module comprises a constant voltage module REG1, a constant voltage module REG2, a capacitor EC1 and a capacitor EC2;
the first end of the constant voltage module REG2 is connected to 12V dc voltage, the second end is grounded, the third end outputs-5V dc voltage, the first end of the constant voltage module REG1 is connected to 12V dc voltage, the second end outputs +5V dc voltage, the third end is grounded, the capacitor EC1 is connected between the first end and the third end of the constant voltage module REG2, and the capacitor EC2 is connected between the second end and the third end of the constant voltage module REG 2;
the second DC/DC module comprises a constant voltage module REG3, a constant voltage module REG4, a capacitor EC3 and a capacitor EC4;
the first end of the constant voltage module REG4 is connected to 12V dc voltage, the second end is grounded, the third end outputs a set voltage-Offset, the first end of the constant voltage module REG3 is connected to 12V dc voltage, the second end outputs an auxiliary voltage Vsup, the third end is grounded, the capacitor EC3 is connected between the first end and the third end of the constant voltage module REG4, the capacitor EC4 is connected between the second end and the third end of the constant voltage module REG4, the set voltage-Offset is-9V dc voltage, and the auxiliary voltage is +9V dc voltage.
9. The potentiostat of claim 3, wherein the potential of the working electrode relative to the reference electrode is:
；
wherein, the first and the second end of the pipe are connected with each other,
is the potential of the working electrode relative to a reference electrode,
the voltage output by the microcontroller after digital-to-analog conversion,
is the resistance value of the resistor Ro1,
is the resistance value of the resistor R2,
is the resistance value of the resistor R3,
is the resistance value of the resistor R4,
is the set voltage-Offset in the potentiostat circuit.
10. The potentiostat of claim 4, wherein the sampled signal has a current magnitude of:
；
wherein the content of the first and second substances,
is the current magnitude of the sampled signal,
is a set voltage-Offset in the transimpedance amplification circuit,
is the magnitude of the voltage received by the microcontroller,
is the resistance value of the resistor Ro2,
is a resistance value of the resistance Rf1,
is the resistance value of the resistor R6,
is the resistance value of the resistor Rf 2.
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