Method for measuring phosphoric acid content in exhaust of high-temperature polymer fuel cell

Abstract

The application discloses a method for measuring phosphoric acid content in high-temperature polymer fuel cell tail exhaust, comprising the following steps: (1) cleaning, drying and then plating Ni-PTFE coating on the inlet and outlet port interface pipe fittings of the end plate; (2) coating the dispersion liquid of graphite and polymer on the surface of the polar plate, and then drying; (3) assembling the treated polar plate and end plate into the fuel cell; (4) placing the cathode outlet and anode outlet of the fuel cell into the tail exhaust collection liquid respectively, and then performing normal operation; (5) after a period of operation, quantifying the P element in the tail exhaust collection liquid, and calculating the loss amount of phosphoric acid. Compared with the prior art, the method can more accurately quantify the loss amount of phosphoric acid, so that the service life of the high-temperature fuel cell under different working conditions can be accurately predicted.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature polymer fuel cells, and specifically relates to a method for determining the phosphoric acid content in the exhaust gas during the operation of a high-temperature polymer fuel cell. Background Technology

[0002] Compared to low-temperature polymer fuel cells, high-temperature polymer fuel cells have become a research hotspot due to their stronger CO tolerance (CO content in the fuel can reach 5%). However, the lifespan of high-temperature polymer fuel cells remains one of the key factors limiting their widespread application. Phosphoric acid loss is considered one of the main causes of performance degradation in high-temperature polymer fuel cells. Currently, the method of detecting phosphoric acid content in the exhaust gas is commonly used to analyze the phosphoric acid loss rate during fuel cell operation. This can determine the impact of phosphoric acid loss on fuel cell polarization and predict the lifespan of high-temperature fuel cells by determining the phosphoric acid content in the exhaust gas. However, current research typically uses water absorption to collect phosphoric acid in the exhaust gas. Due to the residual phosphoric acid in the pipeline and incomplete water collection, the assessment of phosphoric acid loss is very inaccurate. This not only leads to errors or even failures in lifespan prediction but also affects the accurate identification of key factors in fuel cell performance degradation, ultimately hindering the development of effective solutions to extend fuel cell lifespan. Summary of the Invention

[0003] To address the above problems, the purpose of this invention is to provide an accurate method for determining the phosphoric acid content in the exhaust gas during the operation of a high-temperature polymer fuel cell.

[0004] The specific technical solution of this invention is as follows:

[0005] A method for determining the phosphoric acid content in the exhaust gas of a high-temperature polymer fuel cell during operation includes the following steps:

[0006] (1) Clean and dry the end plate inlet and outlet pipe fittings, and then electroplate Ni-PTFE coating.

[0007] (2) Coat the surface of the electrode plate with a dispersion of graphite and polymer and dry it;

[0008] (3) The processed electrode plates and end plates are assembled into the fuel cell. A sealing gasket is provided between the electrode plates and the membrane electrode of the fuel cell. After assembly, the thickness of the membrane electrode is compressed to 75-93% of that before assembly.

[0009] (4) Place the cathode outlet and anode outlet of the fuel cell into the tail discharge collection liquid respectively, and the fuel cell will start to operate normally. The tail discharge collection liquid includes alkaline solution and deionized water placed in sequence. The temperature of the deionized water is 0-5℃. The cathode outlet and anode outlet are connected to the alkaline solution and deionized water placed in sequence by PTFE pipes, and the connection is insulated. The insulation temperature is controlled at 50-70℃.

[0010] (5) After running for a period of time, the amount of phosphoric acid lost was calculated by quantitatively analyzing the phosphoric acid in the tail discharge collection liquid.

[0011] Based on the above scheme, preferably, the method for determining the phosphate content in the tail section specifically includes the following steps:

[0012] (1) Protection of end plate air outlet (and air inlet) fittings

[0013] To avoid corrosion and adsorption of phosphoric acid on the metal interface fittings of the end plate outlet and inlet, which would reduce the amount of phosphoric acid in the tail discharge and cause inaccurate phosphoric acid content measurements, the metal interface fittings of the outlet and inlet (especially the outlet) are first protected. The outlet (and inlet) metal interface fittings are ultrasonically immersed in acetone or ethanol for 5-30 minutes, then ultrasonically immersed in 0.01-1 mol / L sodium hydroxide solution or immersed at room temperature -50°C for 0.05-2 hours. After thorough washing with water, they are dried at 50-120°C. Finally, a Ni-PTFE coating is applied to the washed fittings using a composite electroplating technique.

[0014] (2) Coat a layer of material onto a composite graphite electrode with an existing flow field;

[0015] (3) Assemble a single cell for testing: Place the treated electrode plate on the end plate, aligning its air inlet and outlet with the air inlet and outlet of the end plate. Place a sealing gasket of a certain thickness on the electrode plate, then place the prepared MEA, and secure it with bolts to assemble the single cell or fuel cell stack. Test the single cell or fuel cell stack on a test bench.

[0016] (4) Place the cathode and anode outlets in a series of tanks to collect phosphoric acid thoroughly;

[0017] (5) The P element in the tail discharge collection liquid is quantitatively analyzed by ICP technology, and the final concentration of phosphoric acid is converted into mg / L. Combined with the volume V (L) of the collection liquid, the total mass of lost phosphoric acid is calculated, and the rate and degree of phosphoric acid loss are compared to predict the limit of the operating life of high temperature fuel cells caused by phosphoric acid loss.

[0018] Preferably, in step (1), the composite electroplating technology uses cell pulverization technology to process the PTFE particles for more than 1 hour to ensure that the PTFE particles are fully and uniformly dispersed in the plating solution; the cell pulverization technology process requires the addition of ice to cool down.

[0019] Preferably, the mass ratio of PTFE in the plating solution to nickel salt in the electroless nickel plating solution in step (1) is 0.1-0.5.

[0020] Preferably, in order to improve the dispersion and uniformity of PTFE particles in the plating solution, the total mass ratio of PTFE and nickel salt in step (1) is 5-30%.

[0021] Preferably, the electroplating method in step (1) is double-anode electroplating, with the steel pipe as the cathode, and the electroplating temperature is 50-70℃; the electroplating current is 91-130 mA / cm². -2 During electroplating, the solution is stirred to promote uniform plating and prevent PTFE deposition. To prevent stirring from affecting Ni / PTFE deposition, the distance between the workpiece and the bottom of the container holding the plating solution is ≥8cm. The workpiece is rotated during the electroplating process at a speed of 2 minutes per revolution. When electroplating the outer layer of the workpiece, the workpiece is parallel to the anode, and when electroplating the inner layer of the workpiece, the workpiece is perpendicular to the anode. The electroplating time for the outer or inner layer of the workpiece is ≥20 minutes.

[0022] Preferably, in step (2), the coating substance is a dispersion of graphite and polymer; the polymer is PTFE, perfluorosulfonic acid resin, polysulfone, polyetherketone, polybenzimidazole, or a positively charged polymer.

[0023] Preferably, the main chain of the positively charged polymer in step (2) is polybiphenylpiperidine, biphenylpiperidine-trifluorophenylethyl biphenyl copolymer, all-phenyl, or poly(styrene-ethylene-butene) block copolymer; the positive charge of the positively charged polymer is quaternary ammonium salt, piperidine, pyrrolidine, or imidazole.

[0024] Preferably, the solvent used for the coating material in step (2) is one or more of ethanol, water, DMF, DMAc, DMSO, THF, chloroform, and tetrachloroethane.

[0025] Preferably, in order to balance the conductivity, acid resistance, adhesion and phosphoric acid adsorption resistance of the coating material, the polymer content in the coating material in step (2) is 0.5-20%; the total proportion of graphite and polymer in the coating material is 30-60%, thereby achieving uniformity and reliability of the coating layer.

[0026] Preferably, the sealing gasket material in step (3) is PTFE, PET, FEP, PVDF, or fluororubber; the thickness of the sealing gasket can be controlled to be 75-93% of the thickness before assembly after membrane electrode assembly, so as to avoid the influence of compression ratio on battery performance, uniformity and acid redistribution.

[0027] Preferably, in step (4), three or more tanks are placed at the cathode and anode outlets of the fuel cell; the tank directly connected to the cathode and anode outlets contains alkaline solution, while the other tanks contain deionized water, which enters the tank through the vent hole and is below the liquid level; in order to fully absorb phosphoric acid and ensure the reliability of the test, the alkaline solution is a NaOH or KOH solution with a concentration of 0.5-3 mol / L, and the volume of the liquid in the tank is 0.2-0.5 L; the cathode and anode outlets are connected to the tanks, and the tanks are connected to each other using PTFE pipes.

[0028] Beneficial effects

[0029] 1. Compared with the prior art, the present invention can more accurately quantify the loss of phosphoric acid, thereby accurately predicting the service life of high-temperature fuel cells under different operating conditions.

[0030] 2. The present invention first protects the metal interface pipe fittings of the end plate inlet and outlet, thus avoiding the problem of inaccurate phosphoric acid content measurement caused by the corrosion and adsorption of phosphoric acid on the metal interface pipe fittings.

[0031] 3. The present invention coats the surface of the electrode plate with graphite and polymer to improve the electrode plate's resistance to phosphoric acid adsorption.

[0032] 4. By setting a sealing gasket between the electrode plate and the membrane electrode, the present invention can control the thickness of the membrane electrode after assembly to be 75-93% of that before assembly, so as to avoid the influence of compression ratio on battery performance, uniformity and acid redistribution.

[0033] 5. This invention uses insulated PTFE pipe fittings to connect the cathode and anode outlets to the tank and between tanks, and combines this with the control of the solution in the tank, the amount of solution, and the temperature to effectively avoid phosphoric acid residue, thereby achieving full absorption of phosphoric acid and improving the accuracy of phosphoric acid quantification. Detailed Implementation

[0034] Example 1

[0035] Using BASF P1000 45cm 2 Experimental studies were conducted on a membrane electrode assembly battery, during which the battery was compressed to 85% of its original size. The battery was tested at 160℃ and 200 mA / cm². -2 After activation for 48 hours, the cathode and anode tail sections were placed in 0.2L and 0.4L of 3mol / L NaOH solution, respectively. Then, two deionized water tanks at 0℃ were connected to each tank. The temperature of the PTFE tubing was controlled at 60-65℃. The battery operated at a current density of 200 mA / cm². -2Operating in constant current start-stop mode, after 1000 hours of continuous operation, the tail-out solution was collected for ICP quantification. The total amount of phosphoric acid lost from the anode and cathode was determined to be 0.965 mg, and the phosphoric acid loss rate was calculated to be 21.4 ng / cm³. -2 h -1 .

[0036] Comparative Example 1

[0037] Using the same BASF P100045cm as in the example 2 The membrane electrode assembly battery was compressed to 85% of its original size. The battery was also subjected to 160°C and 200 mA / cm² temperature. -2 After activating for 48 hours, the cathode and anode tail sections were placed in deionized water, and then connected to two separate deionized water tanks at 0°C. The temperature of the PTFE tubing was controlled at 60-65°C. The battery's operating condition was: a current density of 200 mA / cm². -2 Operating in constant current start-stop mode, after 1000 hours of continuous operation, the tail-out solution was collected for ICP quantification. The total amount of phosphoric acid lost from the anode and cathode was determined to be 0.566 mg, and the phosphoric acid loss rate was calculated to be 12.5 ng / cm³. -2 h -1 The amount of phosphate absorbed was reduced by 41% compared to the examples.

[0038] Comparative Example 2

[0039] Using the same membrane electrode and operating conditions and other control methods as in Example 1, except that a deionized water tank was installed and cryogenic operation was not performed, the total amount of phosphoric acid lost from the anode and cathode was measured to be 0.786 mg, and the phosphoric acid loss rate was calculated to be 17.4 ng / cm³. -2 h -1 The amount of phosphate absorbed is reduced by approximately 19% compared to the examples.

[0040] Comparative Example 3

[0041] Using the same conditions and methods as in Example 1, but without temperature control of the PTFE fittings, the measured amount of phosphoric acid was reduced by approximately 12% compared to the example.

[0042] Comparative Example 4

[0043] Using composite graphite plates without post-processing, after 1000 hours of testing of the membrane electrode, the phosphoric acid content in the graphite plates was found to be approximately 20% of the total phosphoric acid loss, and the amount of collected phosphoric acid was reduced by approximately 20%.

[0044] Comparative Example 5

[0045] Similarly, without post-processing of the inlet and outlet pipe fittings, the amount of phosphoric acid collected is reduced by approximately 7%.

Claims

1. A method for determining the phosphoric acid content in the exhaust of a high temperature polymer fuel cell, said fuel cell comprising end plates, polar plates, characterized in that, The method comprises the following steps: (1) cleaning and drying the end plate gas inlet and outlet interface pipe, and then electroplating a Ni-PTFE coating; (2) coating a dispersion liquid of graphite and polymer on the surface of the polar plate and drying; (3) assembling the treated polar plate and end plate into a fuel cell, arranging a sealing gasket between the polar plate and the membrane electrode of the fuel cell, and compressing the thickness of the membrane electrode to 75-93% of the thickness before assembly; (4) placing the cathode outlet and anode outlet of the fuel cell in tail gas collection liquid respectively, starting normal operation of the fuel cell, and the tail gas collection liquid comprises alkaline solution and deionized water placed in sequence, the temperature of the deionized water is 0-5℃, the cathode outlet and anode outlet are connected with the alkaline solution and deionized water placed in sequence by PTFE pipes, and the connection part is heat-insulated, and the heat-insulating temperature is controlled to be 50-70℃; (5) after a period of operation, quantifying the P element in the tail gas collection liquid to calculate the loss amount of phosphoric acid.

2. The assay method according to claim 1, characterized by The step (1) comprises the following specific steps: placing the end plate gas inlet and outlet interface pipe in acetone or ethanol for ultrasonic treatment for 5-30 min, then ultrasonic treatment or room temperature-50℃ immersion in 0.01-1 mol / L sodium hydroxide solution for 0.05-2 h, washing with water, and then drying at 50-120℃, and then plating a Ni-PTFE coating on the dried pipe by composite electroplating technology.

3. The assay method according to claim 1, characterized by, In step (1), the plating solution is prepared by dispersing PTFE in a plating solution containing Ni, and treating by cell crushing technology for more than 1 h to obtain the plating solution; and ice is added for cooling during the cell crushing treatment.

4. The assay method according to claim 1, characterized by, In step (1), the mass ratio of PTFE to nickel salt in the plating solution is 0.1-0.5, and the total mass ratio of PTFE and nickel salt is 5-30%.

5. The assay method according to claim 1, characterized by, In step (1), the electroplating method is double anode electroplating, the steel pipe is cathode, the electroplating temperature is 50-70℃, the electroplating current is 91-130mAcm -2 , the solution is stirred during electroplating, the distance between the plated part and the bottom of the container for placing the plating solution is ≥8cm, the plated part rotates during electroplating, the rotating speed is 2 minutes / turn, the plated part is parallel to the anode when electroplating the outer layer of the plated part, the plated part is perpendicular to the anode when electroplating the inner layer of the plated part, and the electroplating time for the outer layer or the inner layer of the plated part is ≥20 minutes.

6. The assay method of claim 1, wherein In step (2), the polar plate is a composite graphite polar plate provided with a flow field; the polymer is one or more of PTFE, perfluorosulfonic acid resin, polysulfone, polyether ketone, polybenzimidazole, and positively charged polymer; the solvent of the dispersion liquid is one or more of ethanol, water, DMF, DMAc, DMSO, THF, chloroform, and tetrachloroethane; the mass fraction of the polymer in the dispersion liquid is 0.5-20 wt%; the total mass fraction of graphite and polymer in the dispersion liquid is 30-60 wt%; the main chain of the positively charged polymer is polydiphenylpiperidine, diphenylpiperidine-trifluorophenethyl biphenyl copolymer, perphenyl, or poly(styrene-ethylene-butylene) block copolymer; and the positive charge of the positively charged polymer is quaternary ammonium salt, piperidine, pyrrolidine, or imidazole.

7. The assay method according to claim 1, characterized by, In step (3), the sealing gasket material is PTFE, PET, FEP, PVDF, or fluorine-containing rubber.

8. The assay method of claim 1, wherein In step (4), the specific way of collecting phosphoric acid by tailing collection liquid is as follows: placing 3 or more than 3 tank bodies at the cathode outlet and the anode outlet of the fuel cell; placing alkali liquid in the tank bodies directly connected with the cathode outlet and the anode outlet, and placing deionized water in the other tank bodies, and the gas guide holes into the tank bodies are placed below the liquid surface, and the cathode outlet and the anode outlet are connected with the tank bodies, and the tank bodies are connected with the tank bodies by PTFE pipes.

9. The assay method according to claim 8, characterized in that, In step (4), the alkali liquid is NaOH solution or KOH solution, the concentration of the alkali liquid is 0.5-3 mol / L, and the volume of the liquid in each tank body is 0.2-0.5 L.

10. The assay method of claim 1, wherein In step (5), the ICP technology is used to quantitatively analyze the P element in the tailing collection liquid, then the concentration of phosphoric acid is converted, the total mass of the lost phosphoric acid is calculated combined with the volume of the collection liquid, and the loss rate of the phosphoric acid is obtained.