On-line free radical detection device and on-line free radical detection method thereof

Abstract

The invention discloses an on-line free radical detection device and an on-line free radical detection method, the device comprises a gas diffusion electrode flow cell, a cathode liquid flow channel plate is provided with a micro-channel for circulation of an electrolyte containing a free radical trapping agent and a liquid storage cavity; the cathode gas diffusion electrode is a working electrode; the electron paramagnetic resonance spectrometer is used for detecting free radical signals in the electrolyte; the electrochemical workstation is used for applying control potential to the working electrode; the temperature control module is used for controlling the working temperature of the gas diffusion electrode flow cell; and the data processing module is in electric connection or signal connection with the electron paramagnetic resonance spectrometer and is used for processing the free radical signal and obtaining the relative concentration or generation rate of the free radicals. According to the invention, in-situ capture and on-line detection can be carried out on short-life free radicals generated in the electrochemical reaction process under the condition of simulating the actual working condition of the fuel cell.

Description

Technical Field

[0001] This invention relates to the field of electrochemical detection technology, and in particular to an online free radical detection device and its online free radical detection method. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are highly efficient and clean energy conversion devices. Non-precious metal catalysts (such as Fe-NC catalysts) have become a research hotspot due to their low cost and high activity. However, the durability of PEMFCs in practical applications is far from meeting commercial requirements. Numerous studies have shown that during fuel cell operation, especially during the oxygen reduction reaction (ORR) via the two-electron pathway, reactive oxygen species (ROS) are generated, such as hydrogen peroxide (H₂O₂) and hydroxyl radicals (•OH). •OH exhibits extremely high reactivity, attacking the active sites of the catalyst, leading to metal dissolution and corrosion of the carbon support, and is a key factor causing catalyst structural damage and performance degradation. Therefore, accurate detection and quantification of these free radicals are crucial for understanding the catalyst degradation mechanism.

[0003] Currently, commonly used detection methods are ultraviolet-visible absorption spectroscopy and fluorescence spectroscopy. The general procedure for these methods is as follows: after the electrochemical reaction is complete, the stable adduct formed by the reaction of the scavenging agent with the free radical is extracted and subjected to offline spectroscopic analysis. However, these methods have significant limitations, making them unsuitable for studying catalyst degradation mechanisms under real-world operating conditions. (1) Unable to monitor in real time: Because it relies on non-in-situ analysis of the sample after the reaction, the above method can only provide information on the cumulative concentration of free radicals after the reaction ends, and cannot capture the instantaneous changes in the concentration of free radicals during the reaction.

[0004] (2) Insufficient detection sensitivity, making accurate quantification difficult: The above methods have the technical characteristics of high detection limits. For low concentration and short lifespan •OH, the detection signal is weak and the signal-to-noise ratio is poor, making it difficult to accurately quantify and analyze free radicals, and the sensitivity cannot meet the requirements.

[0005] (3) The test environment differs from the actual working conditions: Existing methods are usually tested in a simple solution-phase electrolytic cell, which makes it impossible to simulate the gas-liquid-solid three-phase reaction interface unique to the gas diffusion electrode in a fuel cell, as well as the acidic working environment of about 80°C. The test results under these simplified conditions cannot truly reflect the free radical generation behavior and decay mechanism of the catalyst in the actual device, resulting in limited guiding significance of the research conclusions.

[0006] Electron paramagnetic resonance (EPR) spectroscopy is the most powerful tool for directly detecting paramagnetic substances containing unpaired electrons (such as free radicals). However, conventional EPR sample cells (such as flat cells) cannot simultaneously apply precise electrochemical potential control and simulate the three-phase reaction environment of fuel cells, making them unsuitable for studying free radical generation in real electrocatalytic reaction processes.

[0007] Therefore, developing a device and method for online monitoring of free radicals generated during electrocatalytic reactions under simulated fuel cell operating conditions has significant scientific value and application potential.

[0008] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art. Summary of the Invention

[0009] The purpose of this invention is to provide an online free radical detection device and its online free radical detection method, which can capture and detect short-lived free radicals generated during electrochemical reactions (oxygen reduction reactions) in situ and online under simulated PEMFC working conditions, thereby studying the potential dependence and time dependence of free radical generation and providing direct experimental evidence for catalyst degradation mechanisms.

[0010] To achieve the above objectives, the present invention provides an online free radical detection device, comprising: A gas diffusion electrode flow cell is used to simulate the working environment of a fuel cell. The gas diffusion electrode flow cell comprises, in sequence, an anode heating end plate, an anode current collector, an anode flow field plate, an anode gas diffusion electrode, a proton exchange membrane, a cathode liquid flow channel plate, a cathode gas diffusion electrode, a cathode flow field plate, a cathode current collector, and a cathode heating end plate. The cathode liquid flow channel plate is provided with microchannels and a storage chamber for the flow of electrolyte containing a free radical scavenger. The cathode gas diffusion electrode is the working electrode. An electron paramagnetic resonance spectrometer includes a detection chamber, the inlet of which is connected to the outlet of the cathode liquid flow channel plate, for detecting free radical signals in the electrolyte; An electrochemical workstation, wherein the working electrode lead is connected to the cathode current collector and the counter electrode lead is connected to the anode current collector, is used to apply a control potential to the working electrode; A temperature control module, which is connected to the anode heating end plate and the cathode heating end plate, is used to control the working temperature of the gas diffusion electrode flow cell. The data processing module, which is electrically or signal-connected to the electron paramagnetic resonance spectrometer, is used to process the free radical signal transmitted from the electron paramagnetic resonance spectrometer to obtain the relative concentration or generation rate of free radicals.

[0011] Optionally, the device further includes a fluid delivery system, wherein the inlet and outlet of the cathode liquid flow channel plate are respectively connected to the fluid delivery system, for inputting the electrolyte into the inlet of the cathode liquid flow channel plate and delivering the electrolyte from the outlet of the cathode liquid flow channel plate to the detection chamber of the electron paramagnetic resonance spectrometer.

[0012] Optionally, the gas diffusion electrode flow cell further includes a reference electrode, which is connected to the inlet of the cathode liquid flow channel plate via a salt bridge or through-hole; the reference electrode is connected to the reference electrode lead of the electrochemical workstation.

[0013] Optionally, the cathode gas diffusion electrode includes a stacked catalytic layer and a gas diffusion layer; the catalytic layer faces the cathode liquid flow channel plate, and the gas diffusion layer faces the cathode flow field plate.

[0014] Optionally, the inner diameter of the microchannels in the cathode liquid flow channel plate is 0.5 mm to 2 mm, and the volume of the liquid storage chamber is 0.1 cm³. 3 ~0.5cm 3 .

[0015] Optionally, the operating temperature of the gas diffusion electrode flow cell is 20℃~90℃.

[0016] Accordingly, the present invention also provides a method for online free radical detection using the above-described online free radical detection device, comprising the following steps: The catalyst to be tested was prepared as a cathode gas diffusion electrode and used as the working electrode, which was then placed into the flow cell of the gas diffusion electrode. An electrolyte containing a free radical scavenger is introduced into the cathode liquid flow channel plate, oxygen is introduced into the cathode flow field plate, and hydrogen is introduced into the anode flow field plate. The temperature of the anode heating end plate and the cathode heating end plate is controlled by the temperature control module so that the gas diffusion electrode flow cell is maintained at the set temperature. An electrochemical workstation is used to apply a controlled potential to the working electrode, causing an electrochemical reaction on the surface of the working electrode to generate free radicals. The free radicals are then instantly captured by a free radical scavenger to form an electrolyte containing the free radicals. The electrolyte containing the captured free radicals is transported from the cathode gas diffusion electrode to the electron paramagnetic resonance spectrometer via a fluid delivery system; The electrolyte containing the captured free radicals is detected in real time using an electron paramagnetic resonance spectrometer to obtain the free radical signal, and the free radical signal is transmitted to the data processing module. The data processing module collects and processes the free radical signal to obtain the relative concentration or generation rate of the free radical.

[0017] Optionally, the free radical scavenger is 5,5-dimethyl-1-pyrrolline-N-oxide, and the concentration of 5,5-dimethyl-1-pyrrolline-N-oxide is 0.01 mol / L to 0.1 mol / L.

[0018] Optionally, the electrolyte is an acidic electrolyte, specifically a 0.1 mol / L HClO4 solution.

[0019] Optionally, the control potential is 0.2V to 0.9V relative to the reversible hydrogen electrode.

[0020] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects: In the device provided by this invention, on the one hand, the gas diffusion electrode flow cell constructs a three-phase reaction interface and proton conduction channel of gas (reacting gas), liquid (electrolyte), and solid (catalyst) through the gas diffusion electrode, flow field plate, cathode liquid flow channel plate, and proton exchange membrane. The integrated temperature control module maintains the reaction system at a preset temperature (actual operating temperature), realistically simulating the actual working environment of PEMFC and overcoming the shortcomings of unrealistic testing environments in existing technologies. On the other hand, the microchannels within the cathode liquid flow channel plate allow the electrolyte containing free radical scavengers to adhere closely to the working electrode. The flow of the cathode gas diffusion electrode enables immediate in-situ capture of free radicals after their generation. The electrolyte after capturing free radicals can be continuously and rapidly transported to an electron paramagnetic resonance spectrometer for real-time detection, thereby enabling the dynamic capture of the instantaneous evolution of short-lived free radicals (hydroxyl radicals) during potential or time changes. Furthermore, by applying a step or constant control potential to the working electrode through an electrochemical workstation, the potential dependence of free radical generation can be systematically studied, directly linking the free radical generation rate to specific electrochemical reaction conditions, which can be applied to the study of catalyst degradation mechanisms. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of an online free radical detection device provided by the present invention.

[0022] Figure 2 An exploded view of a gas diffusion electrode flow cell 20 provided by the present invention.

[0023] Figure 3 This is a schematic diagram of the structure of a cathode liquid flow channel plate provided by the present invention.

[0024] Figure 4 The flowchart illustrates an online free radical detection method provided by this invention.

[0025] Figure 5 The electron paramagnetic resonance (EPR) spectra obtained by online detection of the generation behavior of hydroxyl radicals under different control potentials in Example 1 are shown below. The inset at the top right corner of each EPR sub-spectrum represents the relative concentration of hydroxyl radicals at the corresponding control potential.

[0026] Figure 6 This is a schematic diagram showing the relationship between the concentration of hydroxyl radicals and the current density as a function of potential in Example 1.

[0027] Figure 7 This is a schematic diagram comparing the evolution characteristics and stability changes of the two test catalysts (Fe-NC and Pt3Fe-Fe-NC) over time in Example 2; where (a) represents the curve of the current density of the two test catalysts changing over time; and (b) represents the curve of the concentration of hydroxyl radicals generated by the two test catalysts changing over time.

[0028] Attached image labels: Electrolyte storage tank 10; Gas diffusion electrode flow cell 20; anode insulating protective plate 201; anode heating end plate 202; anode insulating gasket 203; anode current collector 204; anode flow field plate 205; anode sealing gasket 206; anode gas diffusion electrode 207; proton exchange membrane 208; cathode liquid flow channel plate 209; cathode gas diffusion electrode 210; cathode sealing gasket 211; cathode flow field plate 212; cathode current collector 213; cathode insulating gasket 214; cathode heating end plate 215; cathode insulating protective plate 216; reference electrode 217. Microchannel 2091; Liquid storage chamber 2092; Inlet of cathode liquid flow channel plate 2093; Outlet of cathode liquid flow channel plate 2094; Perfluoroether rubber O-ring 2095; Bolt 2096; Inlet auxiliary plate 2097; Outlet auxiliary plate 2098; Electron paramagnetic resonance spectrometer 30; Electrochemical workstation 40; Temperature control module 50; Data processing module 60; Fluid delivery system 70, peristaltic pump 71, connecting pipeline 72. Detailed Implementation

[0029] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a further detailed explanation of the online free radical detection device and method proposed in this invention. The advantages and features of this invention will become clearer from the following description. It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions, used only to facilitate and clearly illustrate the embodiments of this invention. Please refer to the accompanying drawings to make the objectives, features, and advantages of this invention more apparent and understandable. It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings are only for illustrative purposes to aid those skilled in the art and are not intended to limit the implementation conditions of this invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by this invention, should still fall within the scope of the technical content disclosed in this invention.

[0030] The chemical reaction formula for the "oxygen reduction reaction via a two-electron pathway" described in this article is: O₂ + 2H₂O + + 2e - →H2O2, this reaction differs from the ideal four-electron pathway oxygen reduction reaction in a fuel cell: O2 + 4H + + 4e - →2H₂O. The H₂O₂ generated by the "two-electron-path oxygen reduction reaction" will release trace amounts of transition metal ions (e.g., Fe) from the catalyst's active sites. 2+ Cu 2+ The Fenton reaction occurs, generating hydroxyl radicals (•OH).

[0031] The “Fe-NC catalyst” described in this article is a type of non-precious metal electrocatalyst based on iron (Fe), nitrogen (N) co-doped carbon (C) materials.

[0032] The "Fenton reaction" mentioned in this article refers to the chemical reaction in which transition metal ions react with H2O2 under acidic conditions to generate hydroxyl radicals (•OH).

[0033] As described in the background section, existing free radical detection methods for studying the degradation mechanism of catalysts during fuel cell operation suffer from problems such as the inability to monitor the instantaneous changes of free radicals in real time, the difficulty in quantifying low-concentration, short-lived free radicals, and the inability to simulate real operating conditions, resulting in limited guiding significance of the detection results.

[0034] To address this, the present invention provides an online free radical detection device and method, which combines a Gas Diffusion Electrode Flow Cell (GDE-FC) with an electron paramagnetic resonance spectrometer to achieve in-situ capture and real-time analysis of free radicals generated by electrochemical reactions while simulating real fuel cell operating conditions. Specifically, the present invention uses a GDE-FC with an added cathode liquid flow channel plate to provide a gas-liquid-solid three-phase interface, simulating the fuel cell environment for electrochemical reactions. The generated free radicals can be instantly captured by the electrolyte (containing free radical scavengers) flowing within the cathode liquid flow channel plate, forming adducts. These adducts are then continuously transported by a flow delivery system (e.g., a peristaltic pump) to the detection cavity (or resonant cavity) of the electron paramagnetic resonance spectrometer for detection, thereby overcoming the limitations of traditional non-in-situ methods.

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] like Figure 1 As shown, the present invention provides an online free radical detection device, comprising a gas diffusion electrode flow cell 20, an electron paramagnetic resonance spectrometer 30, an electrochemical workstation 40, a temperature control module 50, and a data processing module 60.

[0037] The gas diffusion electrode flow cell 20 is used to provide a three-phase reaction interface of gas (reactant gas), liquid (electrolyte), and solid (catalyst) to simulate the working environment of a fuel cell. Figure 2As shown, in this embodiment, the gas diffusion electrode flow cell 20 includes, in sequence, an anode insulating protective plate 201, an anode heating end plate 202, an anode insulating gasket 203, an anode current collector 204, an anode flow field plate 205, an anode sealing gasket 206, an anode gas diffusion electrode 207, a proton exchange membrane 208, a cathode liquid flow channel plate 209, a cathode gas diffusion electrode 210, a cathode sealing gasket 211, a cathode flow field plate 212, a cathode current collector 213, a cathode heating end plate 215, a cathode insulating gasket 214, and a cathode insulating protective plate 216. The anode insulating protective plate 201 and cathode insulating protective plate 216 are the outermost structural components of the gas diffusion electrode flow cell 20, providing mechanical support and insulation protection. The anode heating end plate 202 and cathode heating end plate 215 have embedded heating elements (e.g., heating rods), controlled by the temperature control module 50, used to transfer heat to the internal components, allowing the gas diffusion electrode flow cell 20 to reach a preset temperature. The anode insulating gasket 203 and cathode insulating gasket 214 prevent heat and current from being lost or conducted to the outside. The anode current collector 204 and cathode current collector 213 can be made of highly conductive materials (e.g., gold-plated copper plates), collecting the current generated on the anode and cathode sides respectively, and connecting with the electrochemical workstation 40. The electrodes are connected to form a current loop; the anode flow field plate 205 and cathode flow field plate 212 can be made of graphite and have flow channels (e.g., serpentine flow channels) on their surfaces. The anode flow field plate 205 and cathode flow field plate 212 are used to guide hydrogen and oxygen to be evenly distributed to the surfaces of the anode gas diffusion electrode 207 and cathode gas diffusion electrode 210, respectively, and at the same time, assist in current conduction; the anode sealing gasket 206 and cathode sealing gasket 211 are used to prevent hydrogen and oxygen from leaking from the anode chamber and cathode chamber, respectively; the anode gas diffusion electrode 207 is composed of a gas diffusion layer (carbon paper) coated with an anode catalyst (e.g., Pt / C), and the anode gas diffusion electrode 207 is the site where hydrogen undergoes oxidation reaction, producing protons (H). + The free radicals are conducted to the cathode side through the proton exchange membrane 208; the cathode gas diffusion electrode 210 is the working electrode of the online free radical detection device of the present invention. In this embodiment, the cathode gas diffusion electrode 210 is composed of a gas diffusion layer (carbon paper) coated with the catalyst to be tested (e.g., Fe-NC). The cathode gas diffusion electrode 210 is the site where oxygen undergoes a reduction reaction. Some oxygen generates free radicals such as H2O2 and •OH through the oxygen reduction reaction via two electron paths; the cathode liquid flow channel plate 209 is used to circulate the electrolyte containing the free radical scavenger, providing a site for in-situ capture of the free radicals generated immediately.

[0038] Furthermore, such as Figure 3As shown, the cathode liquid flow channel plate 209 is provided with interconnected microchannels 2091 and a storage cavity 2092. In this embodiment, the microchannels 2091 are located inside the plate body of the cathode liquid flow channel plate 209 and are channels used to guide the directional flow of electrolyte; the storage cavity 2092 is a hollow cavity on the cathode liquid flow channel plate 209. When the proton exchange membrane 208, the cathode flow channel plate 209 and the cathode gas diffusion electrode 210 are pressed together, one wall of the storage cavity 2092 is defined by the proton exchange membrane 208, the opposite wall is defined by the surface of the cathode gas diffusion electrode 210 coated with the catalyst to be tested, and the four sides are defined by the plate body of the cathode liquid flow channel plate 209, forming a closed cavity for temporarily storing electrolyte containing free radical scavengers. The inlet 2093 of the cathode liquid flow channel plate 209 is connected to the inlet (not shown) of the microchannel 2091, and the outlet (not shown) of the microchannel 2091 is connected to the outlet 2094 of the cathode liquid flow channel plate 209. In this embodiment, the online free radical detection device further includes an electrolyte storage tank 10, which is connected to the inlet 2093 of the cathode liquid flow channel plate 209 and is used to introduce electrolyte into the microchannel 2091.

[0039] In some embodiments, the inner diameter of the microchannel 2091 of the cathode liquid flow channel plate 209 is 0.5 mm to 2 mm, and the volume of the liquid storage chamber 2092 is 0.1 cm³. 3 ~0.5cm 3 .

[0040] In some embodiments, an inlet auxiliary plate 2097 and an outlet auxiliary plate 2098 are respectively provided at the inlet 2093 and outlet 2094 of the cathode liquid flow channel plate 209. Since the inner diameter of the external connecting pipe 72 and the microchannel 2091 may be different, the inlet auxiliary plate 2097 and the outlet auxiliary plate 2098 serve as transitional connectors to achieve a stable and sealed connection between the external connecting pipe and the microchannel 2091.

[0041] In some embodiments, the gas diffusion electrode flow cell 20 further includes a reference electrode 217 for providing a stable potential reference during testing. In this embodiment, the reference electrode 217 is a saturated calomel electrode (SCE). To achieve accurate potential measurement and avoid interference with the fluid, the reference electrode 217 can be connected to the flow channel at the inlet 2093 of the cathode liquid flow channel plate 209 via a salt bridge or through-hole structure. Specifically, a tiny connecting channel (i.e., through-hole) can be provided near the inlet 2093 of the cathode liquid flow channel plate 209, or it can be connected from the outside of the cathode liquid flow channel plate 209 via a Luggin capillary (as a salt bridge), so that the reference electrode 217 can establish a stable ionic conductivity pathway with the electrolyte working in the microchannel 2091. The lead end of the reference electrode 217 is connected to the reference electrode (RE) interface of the electrochemical workstation 40, thereby forming a closed electrochemical circuit with the working electrode. This allows the electrochemical workstation to precisely control the potential of the cathode gas diffusion electrode 210 (working electrode) relative to the reference electrode 217. In this embodiment, the reference electrode 217 is disposed on the inlet auxiliary plate 2097.

[0042] In some embodiments, the gas diffusion electrode flow cell 20 further includes a sealing structure (not shown) to ensure the sealing performance of the gas diffusion electrode flow cell 20 during long-term operation in high-temperature and acidic environments. For example... Figure 3 As shown, in this embodiment, the cathode liquid flow channel plate 209 is provided with the sealing structure to ensure that the electrolyte will not leak under high temperature and acidic conditions. The sealing structure is specifically configured as follows: at the interface between the reference electrode 217 and the inlet auxiliary plate 2097 of the cathode liquid flow channel plate 209, a perfluoroether rubber (FFKM) O-ring 2095 is provided, and it is tightened by applying uniform torque with bolts 2096 to achieve a reliable seal.

[0043] When the gas diffusion electrode flow cell 20 is in operation, a reaction occurs at the anode gas diffusion electrode 207: H2 → 2H2O + + 2e - The generated H + The protons migrate through the proton exchange membrane 208 into the reservoir 2092, where they mix with the electrolyte containing a free radical scavenger. This electrolyte then contacts the catalytic layer surface (the surface coated with the cathode catalyst) of the cathode gas diffusion electrode 209. + Ultimately, it participates in the oxygen reduction reaction at the cathode gas diffusion electrode 210.

[0044] The electron paramagnetic resonance spectrometer 30 includes a detection chamber (not shown in the figure). The inlet of the detection chamber is connected to the outlet 2094 of the cathode liquid flow channel plate 209. The electrolyte flowing out of the cathode liquid flow channel plate 209 flows into the detection chamber of the electron paramagnetic resonance spectrometer 30 to detect the free radical signal captured by the free radical scavenger in the electrolyte in real time.

[0045] The working electrode lead of the electrochemical workstation 40 is connected to the cathode current collector 213, and the counter electrode lead is connected to the anode current collector 204, for applying a control potential relative to the reference electrode to the working electrode (cathode gas diffusion electrode 210). The control potential drives the occurrence of the electrochemical reaction.

[0046] The temperature control module 50 is connected to the anode heating end plate 202 and the cathode heating end plate 215, and is used to control the operating temperature of the gas diffusion electrode flow cell 20 to simulate the temperature conditions consistent with the working environment of a real fuel cell. In this embodiment, the anode heating end plate 202 and the cathode heating end plate 215 have cylindrical grooves (not shown in the figure) for mounting heating rods. The temperature control module 50 controls the temperature of the heating rods to perform temperature control on the gas diffusion electrode flow cell 20, and the operating temperature of the gas diffusion electrode flow cell 20 is 20℃~90℃.

[0047] The data processing module 60 is electrically or signal-connected to the electron paramagnetic resonance spectrometer 30, and is used to process the free radical signal transmitted from the electron paramagnetic resonance spectrometer 30 to obtain the relative concentration or generation rate of free radicals.

[0048] In some embodiments, the online free radical detection device further includes a fluid delivery system 70. In this embodiment, the fluid delivery system 70 includes a peristaltic pump 71 and a connecting pipe 72. The electrolyte storage tank 10 is connected to the peristaltic pump 71 and the inlet 2093 of the cathode liquid flow channel plate 209 in sequence through the connecting pipe 72, for pumping the electrolyte from the electrolyte storage tank 10 to the inlet 2093 of the cathode liquid flow channel plate 209, thereby entering the storage chamber 2092 through the microchannel 2091. The outlet 2094 of the cathode liquid flow channel plate 209 is connected to the peristaltic pump (not shown in the figure) and the resonant cavity inlet of the electron paramagnetic resonance spectrometer 30 in sequence through the connecting pipe 72, for pumping the electrolyte from the outlet 2094 of the cathode liquid flow channel plate 209 into the resonant cavity of the electron paramagnetic resonance spectrometer 30. The connecting pipe 72 can be a quartz glass capillary. The quartz glass material can retain the intensity of free radical signals to the maximum extent, ensuring the sensitivity of detection, and is resistant to high temperature and acidic environment, avoiding contamination of electrolyte.

[0049] This invention also provides a method for online free radical detection using the above-described online free radical detection device, such as... Figure 4As shown, it includes the following steps: Step 1: Prepare the catalyst to be tested into a cathode gas diffusion electrode, which is then used as the working electrode and placed into the flow cell of the gas diffusion electrode.

[0050] In some embodiments, the anode gas diffusion electrode may be prepared using a commercial Pt / C catalyst.

[0051] The anode insulating protective plate, anode heating end plate, anode insulating gasket, anode current collector, anode flow field plate, anode sealing gasket, anode gas diffusion electrode, proton exchange membrane, cathode liquid flow channel plate, cathode gas diffusion electrode, cathode sealing gasket, cathode flow field plate, cathode current collector, cathode heating end plate, cathode insulating gasket, and cathode insulating protective plate are sequentially stacked and assembled, and then fastened to form a complete gas diffusion electrode flow cell. After assembling the gas diffusion electrode flow cell, the above-mentioned online free radical detection device is assembled.

[0052] Step 2: Introduce an electrolyte containing a free radical scavenger into the cathode liquid flow channel plate, introduce oxygen into the cathode flow field plate, and introduce hydrogen into the anode flow field plate.

[0053] In some embodiments, the free radical scavenger is 5,5-dimethyl-1-pyrrolline-N-oxide (DMPO, CAS: 3317-61-1), and the concentration of 5,5-dimethyl-1-pyrrolline-N-oxide is 0.01 mol / L to 0.1 mol / L. Taking •OH as an example, DMPO can rapidly react with •OH (a short-lived free radical): DMPO + •OH → DMPO-OH adduct, forming a relatively stable DMPO-OH adduct. The DMPO-OH adduct contains unpaired electrons and can be detected by electron paramagnetic resonance (EPR) spectroscopy. The DMPO-OH adduct produces a typical 1:2:2:1 quartet in the EPR spectrum, and therefore, data processing can be performed using this characteristic peak to obtain the relative concentration or generation rate of •OH.

[0054] In some embodiments, the electrolyte is an acidic electrolyte, specifically a 0.1 mol / L HClO4 solution. The operating environment inside a fuel cell is typically strongly acidic (pH < 1). The activity and stability of the catalyst, reaction pathways (e.g., the selectivity of the oxygen reduction reaction), and degradation mechanisms (e.g., corrosion of the carbon support, dissolution of metal ions) all depend on this acidic environment. Therefore, an acidic electrolyte is used to simulate the real operating environment of a fuel cell.

[0055] Step 3: Control the temperature of the anode heating end plate and the cathode heating end plate through the temperature control module so that the gas diffusion electrode flow cell is maintained at the set temperature.

[0056] In some embodiments, the set temperature is 20°C to 90°C.

[0057] Step 4: Apply a controlled potential to the working electrode using an electrochemical workstation to cause an electrochemical reaction on the surface of the working electrode, generating free radicals; the free radicals are immediately captured by a free radical scavenger to form an electrolyte containing the free radicals.

[0058] In some embodiments, the control potential is 0.2V to 0.9V relative to the reversible hydrogen electrode (RHE) to study the potential dependence of hydroxyl radical generation in the oxygen reduction reaction via a two-electron pathway.

[0059] Step 5: The electrolyte containing the captured free radicals is transported from the cathode gas diffusion electrode to the electron paramagnetic resonance spectrometer via a fluid transport system.

[0060] In this embodiment, the free radicals generated in the electrochemical reaction are captured immediately by the free radical scavenger to form adducts. The adducts are transported along with the electrolyte from the outlet of the cathode liquid flow channel plate to the detection chamber of the electron paramagnetic resonance spectrometer through the connecting pipeline.

[0061] Step 6: The electrolyte containing the captured free radicals is detected in real time using an electron paramagnetic resonance spectrometer to obtain the free radical signal, and the free radical signal is transmitted to the data processing module.

[0062] Step 7: The free radical signal is acquired and processed by the data processing module to obtain the relative concentration or generation rate of the free radical.

[0063] In this embodiment, the free radical signal intensity is obtained by baseline correction and quadratic integration of the electron paramagnetic resonance spectrum (EPR spectrum), and the relative concentration or generation rate of free radicals is calculated based on the free radical signal intensity.

[0064] Example 1 Reference Figure 2 A gas diffusion electrode flow cell was assembled. Both the cathode and anode flow field plates were made of high-purity graphite and incorporated a serpentine flow field. The cathode liquid flow channel plate was made of polytetrafluoroethylene (PTFE), with a thickness of 2 mm and an internal microchannel diameter of 1 mm. The solvent in the storage chamber was 0.1 cm³. 3 The proton exchange membrane used is a Nafion 211 membrane. The anode and cathode are sealed with perfluoroether rubber (FFKM) O-rings, tightened with bolts using uniform torque. The cathode gas diffusion electrode (working electrode) contains the Fe-NC catalyst to be tested (loading 2.0 mg / cm³). 2 The electrode was prepared by coating a commercial Pt / C catalyst (Pt loading 0.4 mg / cm³) onto carbon paper. 2The electrolyte was prepared by coating carbon paper. A reference electrode (saturated calomel electrode, SCE) was connected to the inlet channel of the cathode liquid flow channel plate. The outlet of the cathode liquid flow channel plate was connected to the resonant cavity inlet of a Bruker E500 series electron paramagnetic resonance (EPR) spectrometer via a quartz glass capillary tube (0.5 mm inner diameter). A peristaltic pump was used to control the electrolyte flow rate at 0.1 mL / min. The temperature of the anode heating plate and the cathode heating plate was stabilized at 80 ± 0.5 °C using a temperature control module.

[0065] An electrolyte solution containing 0.05 mol / L DMPO and 0.1 mol / L HClO4 was prepared and pumped into the cathode liquid flow channel plate using a peristaltic pump. High-purity O2 (100 mL / min) was introduced into the cathode flow channel plate, and high-purity H2 (100 mL / min) was introduced into the anode flow channel plate. After the system temperature and EPR baseline stabilized, the electrochemical workstation (model: CHI 760E) was started, and potential step tests were performed on the working electrodes: starting from 0.9 V (vs. RHE), the potentials were gradually stepped to 0.2 V in 0.1 V steps, and each potential was held for 3 minutes. The current response and free radical signal (EPR signal) at each control potential were recorded in real time.

[0066] The acquired EPR signals are automatically processed and analyzed using a data processing module: First, the characteristic 1:2:2:1 quartet signal of the DMPO-OH adduct is identified; then, baseline correction and double integral calculation of the signal intensity are performed on the characteristic peaks to obtain the hydroxyl radical concentration at each potential. Finally, the relative concentration of hydroxyl radicals at different control potentials is correlated with the corresponding electrochemical current signal to plot a curve of the hydroxyl radical generation rate (or concentration) as a function of the control potential.

[0067] Figure 5 A series of EPR spectra show the results of online detection of hydroxyl radical (•OH) generation behavior at different control potentials using the online free radical detection device of the present invention. Figure 5 In this context, "GDE-Blank" refers to the background signal measured when only electrolyte and reactant gas are introduced without applying any control potential. For example... Figure 5 As shown, the characteristic 1:2:2:1 quartet signal intensity (Intensity / au) of the DMPO-OH adduct detected by EPR exhibits a significant and regular increase. Figure 5 Each subplot at each potential clearly shows the characteristic peaks that highly match the experimental data points with the theoretical fitting curve, and the inset in the upper right corner quantitatively depicts the hydroxyl radical concentration (C) calculated from the free radical signal (EPR signal). •OH / μmol·L -1 The trend is that it increases as the control potential decreases. Figure 6 The variation of hydroxyl radical concentration with control potential (E) and oxygen reduction reaction current density (J / mA·cm) were further shown. -2 The curve shows the change in oxygen reduction reaction (ORR) with control potential (E). When a control potential gradually decreased from 0.9 V (relative to the reversible hydrogen electrode) to 0.2 V was applied to the cathode gas diffusion electrode, the ORR current recorded by the electrochemical workstation gradually increased, indicating an acceleration of the overall electrochemical reaction rate. The hydroxyl radical concentration can be obtained by performing a double integration of the EPR signal to obtain its signal intensity; the signal intensity value can then be converted into hydroxyl radical concentration by comparison with a standard sample of known concentration or through calibration.

[0068] Figure 5 and Figure 6 This study demonstrates that as the control potential decreases, the rate of H2O2 formation via the two-electron pathway and subsequent •OH production via the Fenton reaction during the oxygen reduction reaction significantly increases. This finding reveals the radical generation behavior of the studied catalyst (Fe-NC catalyst) at different control potentials: at higher potential ranges (e.g., close to 0.9 V vs. RHE), the oxygen reduction reaction tends to follow the four-electron pathway for direct H2O formation, resulting in a relatively "clean" reaction process and a lower •OH yield. Conversely, at lower control potentials (e.g., close to 0.2 V vs. RHE), the Fe-NC catalyst exhibits lower stability and is more prone to undergoing the two-electron pathway for H2O2 formation, thus generating more •OH via the Fenton reaction. Therefore, this invention verifies the attenuation mechanism of the Fe-NC catalyst's primary H2O2 formation via the two-electron pathway and subsequent •OH production via the Fenton reaction at low potentials.

[0069] Example 2 The difference between this embodiment and Example 1 is that Fe-NC catalyst and Pt3Fe-Fe-NC catalyst were used as the research objects, and continuous testing was conducted for up to 10 hours at a constant potential of 0.6 V (vs. RHE). The time-varying behavior of free radical concentration was monitored in real time using the device of this invention. The Pt3Fe-Fe-NC catalyst is a composite catalyst, which is composed of alloy nanoparticles formed by Pt and Fe in an atomic ratio of 3:1, which are uniformly dispersed in the Fe-NC matrix as a modifying component.

[0070] like Figure 7 As shown in (a) and (b), the hydroxyl radical concentration (C) of the Fe-NC catalyst in the initial 1 hour is... •OH / μmol·L -1 The oxygen reduction reaction current density (J / mA·cm) increases sharply. -2The current decay rate of the Pt3Fe-Fe-NC catalyst exceeded 40%. However, the concentration of hydroxyl radicals remained at a low level throughout the entire test, and the current decay rate was only 17%. This directly proves that the introduction of Pt nanoparticles can effectively improve the stability of the catalyst by quenching hydroxyl radicals, and verifies the practical value of the device and method of the present invention in evaluating the durability of different catalysts.

[0071] In summary, this invention provides an online free radical detection device and method. The online free radical detection device can effectively simulate the actual working state of a fuel cell gas diffusion electrode, achieving in-situ capture and online electron paramagnetic resonance detection of short-lived free radicals generated during electrochemical reactions. Using this device and method, the potential-dependent and time-dependent behavior of free radical generation can be systematically studied, thus providing direct and dynamic experimental evidence for revealing catalyst degradation mechanisms. The entire device possesses high detection sensitivity, excellent operational stability, and reliable sealing performance, making it suitable for long-term continuous testing tasks.

[0072] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0073] In the description of this invention, it should be understood that the terms "center," "height," "thickness," "upper," "lower," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0074] In the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0075] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0076] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. An online free radical detection device, characterized in that, include: A gas diffusion electrode flow cell comprises, in sequence, an anode heating end plate, an anode current collector, an anode flow field plate, an anode gas diffusion electrode, a proton exchange membrane, a cathode liquid flow channel plate, a cathode gas diffusion electrode, a cathode flow field plate, a cathode current collector, and a cathode heating end plate; wherein, the cathode liquid flow channel plate is provided with microchannels and a liquid storage chamber for the flow of electrolyte containing a free radical scavenger; the cathode gas diffusion electrode is the working electrode; An electron paramagnetic resonance spectrometer includes a detection chamber, the inlet of which is connected to the outlet of the cathode liquid flow channel plate, for detecting free radical signals in the electrolyte; An electrochemical workstation, wherein the working electrode lead is connected to the cathode current collector and the counter electrode lead is connected to the anode current collector, is used to apply a control potential to the working electrode; A temperature control module, which is connected to the anode heating end plate and the cathode heating end plate, is used to control the working temperature of the gas diffusion electrode flow cell. The data processing module, which is electrically or signal-connected to the electron paramagnetic resonance spectrometer, is used to process the free radical signal transmitted from the electron paramagnetic resonance spectrometer to obtain the relative concentration or generation rate of free radicals.

2. The online free radical detection device as described in claim 1, characterized in that, It also includes: a fluid delivery system, wherein the inlet and outlet of the cathode liquid flow channel plate are respectively connected to the fluid delivery system, for inputting the electrolyte into the inlet of the cathode liquid flow channel plate and delivering the electrolyte from the outlet of the cathode liquid flow channel plate to the detection chamber of the electron paramagnetic resonance spectrometer.

3. The online free radical detection device as described in claim 1, characterized in that, The gas diffusion electrode flow cell also includes a reference electrode, which is connected to the inlet of the cathode liquid flow channel plate via a salt bridge or through-hole; the reference electrode is connected to the reference electrode lead of the electrochemical workstation.

4. The online free radical detection device as described in claim 1, characterized in that, The cathode gas diffusion electrode includes a stacked catalytic layer and a gas diffusion layer; the catalytic layer faces the cathode liquid flow channel plate, and the gas diffusion layer faces the cathode flow field plate.

5. The online free radical detection device as described in claim 1, characterized in that, The inner diameter of the microchannels in the cathode liquid flow channel plate is 0.5mm~2mm, and the volume of the liquid storage chamber is 0.1cm³. 3 ~0.5cm 3 .

6. The online free radical detection device as described in claim 1, characterized in that, The operating temperature of the gas diffusion electrode flow cell is 20℃~90℃.

7. A method for online free radical detection using the online free radical detection device as described in any one of claims 1 to 6, characterized in that, Includes the following steps: The catalyst to be tested was prepared as a cathode gas diffusion electrode and used as the working electrode, which was then placed into the flow cell of the gas diffusion electrode. An electrolyte containing a free radical scavenger is introduced into the cathode liquid flow channel plate, oxygen is introduced into the cathode flow field plate, and hydrogen is introduced into the anode flow field plate. The temperature of the anode heating end plate and the cathode heating end plate is controlled by the temperature control module so that the gas diffusion electrode flow cell is maintained at the set temperature. An electrochemical workstation is used to apply a controlled potential to the working electrode, causing an electrochemical reaction on the surface of the working electrode to generate free radicals. The free radicals are instantly captured by the free radical scavenger, forming an electrolyte containing the captured free radicals; The electrolyte containing the captured free radicals is transported from the cathode gas diffusion electrode to the electron paramagnetic resonance spectrometer via a fluid delivery system; The electrolyte containing the captured free radicals is detected in real time using an electron paramagnetic resonance spectrometer to obtain the free radical signal, and the free radical signal is transmitted to the data processing module. The data processing module collects and processes the free radical signal to obtain the relative concentration or generation rate of the free radical.

8. The method as described in claim 7, characterized in that, The free radical scavenger is 5,5-dimethyl-1-pyrrolline-N-oxide, and the concentration of 5,5-dimethyl-1-pyrrolline-N-oxide is 0.01 mol / L to 0.1 mol / L.

9. The method as described in claim 7, characterized in that, The electrolyte is an acidic electrolyte, specifically a 0.1 mol / L HClO4 solution.

10. The method as described in claim 7, characterized in that, The control potential is 0.2V to 0.9V relative to the reversible hydrogen electrode.

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