Patent Description:
Electronic and ionic conductivity are one of the most important phenomena in the fields of energy materials, sensor devices, biological systems and so on. It is not only important for the efficiency of charge transport, but also relates to the chemical and electrochemical reaction mechanism and rates within the systems. At the meantime, it is also one of the determinative factors for the construction of electrochemical boundaries, and then dominates the performance, cost, and durability of the applied devices. In the fields of advanced energy technologies, including fuel cells, metal-air batteries and lithium ion batteries, the synergy of electron and ion transport is the key factor limiting the development. Therefore, efficient detection of ionic conductivity and electronic conductivity, as well as effective analysis of charge transport channels, is one of the key technologies for synthesis of electrode materials and structures.

The traditional measurements of electronic and ionic conductivity include the two-electrode and four-electrode ohms or electrochemical methods. With years of development, these techniques have been evolved as mature detection systems, and gained success in theoretical and applied aspects. However, in the current electrochemical systems including fuel cells, lithium ion batteries, and electrochemical sensors, the functions of electronic and ionic conductance usually exist synchronously in the microstructure of the electrode in the form of compound channels to ensure the high efficiency and utilization of the electrochemical boundaries and active components. Therefore, in the systems integrated with both the electronic and ion conductivity, it was found difficult to separate ionic conductance from the complicated series and parallel connections of electronic and ionic conductors with the traditional measurement equipped with metal probes. Specifically, the electronic conductivity of the electrode is usually greater than <NUM>/cm, generally up to <NUM>-<NUM><NUM> S/cm, much higher than the ionic conductivity in the magnitude order of <NUM>-<NUM>-<NUM>-<NUM> S/cm range. Conventional conductivity testing methods could hide signals of the ion conductance, and then render it impossible to separate efficiently. For this reason, finding a way to effectively separate the electronic conductance from the ionic conductance is critical to the development of advanced materials. On the other hand, the traditional ionic conductance detections are usually performed in the aqueous solution, which obviously differ from the applied environment in the electrode system and hardly reflect the convincible property of the ionic conductance. Therefore, the design and preparation of an conductivity testing instrument with controllable temperature and humidity could lay the foundation of analytical techniques for the development of electrode materials.

<CIT> describes a device for measuring the conductivity in a controlled environment and method thereof. and <CIT> describes an environmental humidity control device.

To aim at the deficiencies of the prior art, this invention has been devised as an ion conductive polymer modified four-probe detection apparatus to separate ion-/electron-conductance from the composite conductive materials. This detection apparatus includes an ion-conductive polymer modified probe and the ambient temperature and humidity controlling system, effectively solving the difficulty of the ion-/electron-conductance separation and the problem of environmental differences between measurement and applied status. This invention could accurately detect ionic conductance from the composite conductor materials, with precisely controlled temperature/humidity, increased reproducibility, simplified testing procedures, and enhanced measurement efficiency.

The invention adopts the following specific schemes:
An ionic conductance measuring device comprises a voltage/current detection part and a test electrode; wherein the test electrode consists of a block of substrate, four linearly arranged through holes in the block of substrate, four platinum wires inserted in the holes with the upper tips of the platinum wires extended outside the block of substrate and the opposite tips withdrawn inside the block of substrate. An ion conductive polymer fills the gaps between the lower end surfaces of the platinum wires and the block of substrate. The axes of the mentioned Pt wire are aligned parallel in the same plane. The upper tips of the second and third platinum wires counted from the left in the test electrode are connected with a voltage control terminal of the voltage/current detection part, and the uppers tips of the first and fourth platinum wires counted from the left in the test electrode are connected with a current control terminal of the voltage/current detection part. A distance between the lower end surface of the platinum wires and a bottom surface of the block of substrate is <NUM>-<NUM>. In use, a sample may be measured by pressing the sample on a bottom end of the test electrode block of substrate.

The voltage/current detection part is one of a potentiostat, ohmmeter, ammeter, constant voltage power supply, and a constant current meter.

The distance between the adjacent Pt wires is equal, and the diameters of the Pt wires are equal.

The substrate material is one of polytetrafluoroethylene, polyether ether ketone and polyethylene;.

Probes of the voltage/current detection part and the test electrode are arranged in the testing chamber.

A gas inlet-A and a dry gas outlet are fixed on the dry gas chamber, and the inside of the dry gas chamber is filled with dehydration material; a gas inlet-B and a wet gas outlet are fixed on the wet gas chamber, and the deionized water is contained in the wet gas chamber; The gas outlets of the dry and wet gas chambers are connected to the testing chamber by tubes, and the inlets are connected to an gas supply source by gas flow meters.

The dry gas outlet and the wet gas outlet are connected with a pipeline of the testing chamber through a three-way valve, and three ports of the three-way valve are respectively connected with the testing chamber, the dry gas outlet and the wet gas outlet; and the gas flow meters are selected from one of rotor flow rate meters, electromagnetic flow meters, and differential pressure flow meters.

The bottom of the testing chamber is set with a water outlet, and the water outlet is set with a valve, and the water outlet can be opened or closed, and the water outlet can be opened to discharge liquid water into the testing chamber.

The testing chamber is provided with a sample test table, and the sample test table is drilled with several through holes, which can drain the liquid water to the bottom of the testing chamber. The upper side of the test chamber is provided with a switchable sample taking-out port.

The humidity controllable testing box is provided with a heat keeping device outside, and the dry gas chamber, wet gas chamber and testing chamber are all covered by the heat keeping device.

The heat keeping device is one of a thermostatic water bath and an electric heating jacket.

The dry gas chamber, the wet gas chamber and the testing chamber are made of moisture resistant and heat resistant materials, and the moisture resistant and heat resistant material is one of organic glasses, polytetrafluoroethylene and stainless steel.

The method for measuring ionic conductivity using the testing device involves the followed steps:.

The ionic resistivity ρ of the test sample is calculated by ρ=Cd, where C is the correction factor and is calculated as follow: <MAT>.

Where S<NUM>, S<NUM> and S<NUM> are the distance between the first Pt wire and the second Pt wire, the second Pt wire and the third Pt wire, the third Pt wire and the fourth Pt wire, respectively. And the conductivity of the sample to be measured is <NUM>/ρ.

The applied voltage range in step (<NUM>) is -1V to 1V.

When the length of the test sample on the vertical scale to the Pt wires is more than <NUM> times of the distance between the Pt wires, it could be considered to meet the semi-infinite boundary condition, and the conductivity value can be calculated directly from the above equation.

When the distance between adjacent platinum wires is equal, and the diameters of the platinum wires are equal, the ratio of the sample thickness and the distance between the Pt wires is less than <NUM>, a correction curve is provided by testing a series of samples to evaluate the relationships between the sample thickness and the testing positions.

The ionic conductivity test method can be used to measure the ionic conductivity of samples as carbon paper, carbon powder, carbon fiber, semiconductor, metal, or polymers.

The flow ratio QA: QB is equal to X:(<NUM>-X), where X is the preset humidity, <NUM>≤X≤<NUM>%; and the flow of gases through the gas inlet A and the gas inlet B is simultaneously introduced;.

The gas is one of nitrogen, argon, air, and oxygen.

The invention solves the problem that the ionic conductivity mixed in the electronic conductor is difficult to measure in the prior art. By adopting this method, the ionic conductance of the electronic conductors could be precisely measured and the ion migration of the materials could also be investigated. This measurement possesses the multi advantages of testing accuracy, stability of temperature and humidity, data reproducibility, simplified procedures and enhanced testing efficiency.

As shown in <FIG> and <FIG> of the schematic of the test device, the cylindrical PTFE block with diameter of <NUM> is drilled along the axis out four linear through-holes with the diameter of <NUM> and the adjacent distance of <NUM>. Four Pt wires of the same diameters as the holes were fixed in the holes, and the end surface of the Pt wires was <NUM> from the end surface of the PTFE block. The <NUM>% Nafion ionomer solution was applied dropwise onto the end surfaces of the Pt wires. After drying, the coating was repeatedly applied until the Nafion polymer solid completely covered the end surfaces of the Pt wires.

The middle two Pt wires of the test circuit are connected to the voltage test terminals (reference electrode <NUM> and <NUM>) of the potentiometer, and the outer two Pt wires are connected to the current test terminal (working electrode and counter electrode).

A dried Nafion <NUM> film with a size of <NUM> x <NUM><NUM> is closely contacted with the Nafion ionomer modified end of the test electrode. The potential signals were applied to the voltage test terminals with a voltage range of -<NUM> to <NUM> V, and the current response signals were then recorded at the current test terminals.

The above measured current data are set as the abscissa, and the voltage data are set as the ordinate, and an approximate linear curve could be obtained as shown in <FIG>. The linear fitting of the curve near the zero potential is performed, and the slope d of the fitting curve is the test ion resistance of the sample.

The ionic resistivity of the material is corrected by ρ=Cd, and C is the correction factor. When the spacing S between the probes is equal, <MAT>.

The measured ionic conductivity of the non-humidified Nafion <NUM> membrane is about <NUM>±<NUM> cm-<NUM>.

The experiment is carried out by the unmodified four-probe method. The cylindrical PTFE block with diameter of <NUM> is drilled along the axis out four linear through-holes with the diameter of <NUM> and the adjacent distance of <NUM>. Four Pt wires of the same diameters as the holes were fixed in the holes, and the end surface of the Pt wires was <NUM> reaching out from the end surface of the PTFE block.

The above measured current data are set as the abscissa, and the voltage data are set as the ordinate, and an approximate linear curve could be obtained. The linear fitting of the curve near the zero potential is performed, and the slope d of the fitting curve is the test ion resistance of the sample.

The measured ionic conductivity of the non-humidified Nafion <NUM> membrane is about <NUM>±<NUM> cm-<NUM>. This result is similar to that of the Example <NUM>, and indicates the convincing test results of the measurement.

A piece of dry Cu foil, Al foil, carbon paper, gas diffusion layer(GDL), porous PTFE, porous PTFE/Nafion ionomer with a size of <NUM> x <NUM><NUM> is closely contacted with the Nafion ionomer modified end of the test electrode. The potential signals were applied to the voltage test terminals with a voltage range of -<NUM> to <NUM> V, and the current response signals were then recorded at the current test terminals.

The measured ionic conductivity of the samples is shown in <FIG>.

The measured ionic conductivity of the samples is shown in <FIG>. As demonstrated by the results, this measurement effectively blocks the conductance of electrons, while maintains the conductance of ions, which can successfully separate ionic conductance from electronic conductors.

The testing instrument is the same as Example <NUM>.

A humidified Nafion <NUM> film with a size of <NUM> x <NUM><NUM> is closely contacted with the Nafion ionomer modified end of the test electrode. The potential signals were applied to the voltage test terminals with a voltage range of -<NUM> to <NUM> V, and the current response signals were then recorded at the current test terminals.

The measured ionic conductivity of the humidified Nafion <NUM> membrane is about <NUM>±<NUM> cm-<NUM>.

A carbon paper with a size of <NUM> x <NUM><NUM> is closely contacted with the Nafion ionomer modified end of the test electrode. The potential signals were applied to the voltage test terminals with a voltage range of -<NUM> to <NUM> V, and the current response signals were then recorded at the current test terminals.

The measured ionic conductivity of the carbon paper is about <NUM>±<NUM> cm-<NUM>, which indicates that the influence of the electronic conductance is largely separated.

A carbon paper dipped with <NUM>% Nafion ionomer with a size of <NUM> x <NUM><NUM> is closely contacted with the Nafion ionomer modified end of the test electrode. The potential signals were applied to the voltage test terminals with a voltage range of -<NUM> to <NUM> V, and the current response signals were then recorded at the current test terminals.

Claim 1:
An ionic conductance measuring device comprising a voltage/current detection part and a test electrode; characterized in that the test electrode consists of:
a block of substrate (<NUM>),
four linearly arranged through holes in the block of substrate (<NUM>),
four platinum wires (<NUM>) inserted in the holes with upper tips of the platinum wires (<NUM>) extended outside the block of substrate (<NUM>), and opposite tips of the platinum wires (<NUM>) withdrawn inside the block of substrate (<NUM>),
an ion conductive polymer (<NUM>) that fills the gaps between the lower end surfaces of the platinum wires (<NUM>) and the block of substrate (<NUM>),
wherein axes of the mentioned through holes, as well as the platinum wires (<NUM>), are aligned parallel in the same plane,
the upper tips of the second and third platinum wires (<NUM>) counted from the left in the test electrode are connected with a voltage control terminal (<NUM>) of the voltage/current detection part, and the upper tips of the first and fourth platinum wires (<NUM>) counted from the left in the test electrode are connected with a current control terminal (<NUM>) of the voltage/current detection part,
a distance between a lower end surface of the platinum wires (<NUM>) and a bottom surface of the block of substrate (<NUM>) is <NUM>-<NUM>, and
such that in use a sample may be measured by pressing the sample on a bottom end of the test electrode block of substrate (<NUM>).