A nickel-doped cuprous phosphide catalyst for detecting hydrogen sulfide gas, a self-powered gas sensor and application

Abstract

The application discloses a nickel-doped copper phosphide catalyst for detecting hydrogen sulfide gas, a self-powered gas sensor and application, and belongs to the technical field of gas detection. The self-powered gas sensor comprises a zinc negative electrode, a solid-state electrolyte and an air positive electrode; the air positive electrode comprises a conductive substrate and a nickel-doped copper phosphide catalyst loaded on the conductive substrate; the nickel-doped copper phosphide catalyst comprises Cu3P and Ni doped in the Cu3P crystal lattice at a molar doping ratio of 5%; a copper source and a nickel source are dissolved in deionized water, a phosphorus source is added and stirred, a hydrothermal reaction is carried out, and the product is collected, washed and dried to obtain the nickel-doped copper phosphide catalyst. The application utilizes the excellent oxygen reduction catalytic capacity of Cu3P, uses the same as a zinc-air battery positive electrode catalytic material, enables H2S to form a Cu-S bond after adsorption and occupy oxygen reduction active sites, thus causing the output voltage of the battery to change, and realizes H2S detection without an external power supply.

Description

Technical Field

[0001] This invention relates to the field of gas detection technology, specifically to a nickel-doped copper phosphide catalyst for detecting hydrogen sulfide gas, a self-powered gas sensor, and its applications. Background Technology

[0002] Gas sensors, as crucial devices for environmental safety monitoring, industrial process control, and human health assessment, have wide applications in hazardous gas early warning and disease-aided diagnosis. Hydrogen sulfide (H2S), a highly irritating and toxic reducing gas, is widely present in industrial environments such as petrochemicals, wastewater treatment, and mining, and can harm the human respiratory and nervous systems even at low concentrations. Currently, H2S gas detection mainly relies on electrochemical sensors, semiconductor metal oxide sensors, optical sensors, and field-effect transistor sensors. Among these, gas sensors based on metal oxide semiconductor materials (such as ZnO, SnO2, and WO3) have attracted widespread attention due to their mature fabrication processes, fast response speeds, and high detection sensitivity. However, traditional metal oxide gas sensors typically require high temperatures to promote gas molecule adsorption, desorption, and surface oxygen activation, resulting in high energy consumption. Furthermore, the high-temperature operating environment not only increases device complexity but also limits their application in wearable devices, portable monitoring equipment, and flammable and explosive environments. In addition, some traditional sensors suffer from insufficient selectivity, decreased long-term stability, and difficulty in achieving self-powered operation.

[0003] In recent years, with the development of self-powered electronic devices, self-powered gas sensors that utilize the battery system itself to output electrical energy and simultaneously achieve sensing functions have gradually attracted attention. Among them, zinc-air batteries (ZABs) are considered an ideal platform for constructing flexible self-powered sensors due to their high theoretical energy density, environmental friendliness, and structural designability. During the operation of ZABs, the oxygen reduction reaction (ORR) on the air electrode determines the battery's output performance, while the interaction between gas molecules and the electrode catalyst surface can change the reaction kinetics on the electrode surface, thereby causing changes in the battery's output voltage, current, or power. Therefore, by controlling the specific interaction between the air electrode catalyst and the target gas, gas detection without external power supply can be achieved. However, current ZAB-based gas sensors still face problems such as insufficient sensitivity, a single response mechanism, and limited room temperature detection performance. Since the gas sensing process mainly occurs at the three-phase interface of the catalyst, electrolyte, and gas, the structure and electronic properties of the air cathode catalyst directly determine the sensor's detection performance. Developing novel air electrode materials with high catalytic activity, high gas adsorption capacity, and excellent charge transport capability is key to improving the self-powered gas sensing performance of ZABs.

[0004] Transition metal phosphides (TMPs) are considered important candidate materials to replace traditional noble metal catalysts due to their electronic structure similar to noble metals, high electrical conductivity, and excellent electrocatalytic activity. Among them, cuprous phosphide (Cu3P) has abundant copper active sites and good ORR catalytic ability, showing good application potential in the field of zinc-air batteries. Existing studies have shown that by constructing Cu3P-based heterostructures or adjusting its electronic structure, the adsorption energy of oxygen intermediates can be effectively improved, the ORR reaction kinetics can be enhanced, and thus the output performance of zinc-air batteries can be improved. However, existing Cu3P materials are mainly used to improve oxygen reduction catalytic performance, and their ability to recognize specific gas molecules still needs to be improved. Therefore, developing a novel catalytic material that can effectively adjust the electronic structure of Cu3P, enhance H2S adsorption capacity, and improve gas-induced electrochemical response, and constructing a self-powered H2S gas sensor with high sensitivity, low power consumption, and flexibility based on this material, is of great significance for promoting the development of next-generation portable gas detection technology. Summary of the Invention

[0005] To address the aforementioned limitations of existing technologies, the present invention aims to provide a nickel-doped copper phosphide catalyst, a self-powered gas sensor, and its applications for detecting hydrogen sulfide gas. This invention employs Ni ions to dope and regulate the Cu3P crystal structure, thereby altering the surface electronic structure and the d-band center position to enhance Cu3P's adsorption capacity for H2S molecules and its interfacial charge transfer efficiency. Simultaneously, leveraging Cu3P's excellent oxygen reduction catalytic ability, it is used as the positive electrode catalyst material in a zinc-air battery. This allows H2S adsorption to form Cu-S bonds, which then occupy oxygen reduction active sites, resulting in a change in the battery's output voltage and enabling H2S detection without an external power source.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a nickel-doped copper phosphide catalyst (NCP) for detecting hydrogen sulfide gas, comprising Cu3P and Ni doped in the Cu3P lattice; the nickel-doped copper phosphide catalyst is prepared by the following method: Copper and nickel sources were dissolved in deionized water, and then phosphorus source was added and stirred to carry out a hydrothermal reaction. The product was collected, washed, and dried to obtain nickel-doped copper phosphide catalyst. The copper source is CuCl2·6H2O; the nickel source is NiCl2·6H2O; and the phosphorus source is red phosphorus.

[0007] Preferably, the molar ratio of Cu, Ni, and P contained in CuCl2·6H2O, NiCl2·6H2O, and red phosphorus is 0.95:0.05:5.

[0008] The molar doping amount of Ni is 5%. The molar doping amount of Ni refers to the amount of Ni in the nickel source being 5% of the total molar amount of Ni in the nickel source and Cu in the copper source.

[0009] Preferably, the hydrothermal reaction is carried out at a temperature of 200°C for 36 hours.

[0010] Preferably, the washing is performed by alternating centrifugal washing with water and anhydrous ethanol; the drying is performed by vacuum drying at 60°C for 24 hours.

[0011] A second aspect of the present invention provides a self-powered gas sensor for detecting hydrogen sulfide gas, comprising a zinc negative electrode, a solid electrolyte, and an air positive electrode; the air positive electrode comprises a conductive substrate and a nickel-doped copper phosphide catalyst supported on the conductive substrate.

[0012] Preferably, the solid electrolyte is a Zn(OTf)2 / PAM hydrogel; the conductive substrate is carbon paper; and the air positive electrode is prepared by the following method: CMC was dissolved in deionized water, nickel-doped copper phosphide catalyst was added and stirred, and then ultrasonic treatment was performed to obtain a slurry. The slurry was uniformly coated onto carbon paper and dried to obtain an air cathode.

[0013] A third aspect of the invention provides the application of a nickel-doped copper phosphide catalyst, or a self-powered gas sensor, in the detection of hydrogen sulfide gas.

[0014] Preferably, the application includes improving the sensitivity, flexibility, and environmental tolerance of hydrogen sulfide gas detection.

[0015] Preferably, the detection involves exposing an air cathode containing a nickel-doped copper phosphide catalyst to the test environment, detecting the change in the output voltage of the zinc-air battery, and determining the H2S concentration based on the change in output voltage.

[0016] Preferably, the limit of detection (LOD) of the self-powered gas sensor is 45.9 ppb.

[0017] The beneficial effects of this invention are: (1) The present invention uses Ni doping to regulate the electronic structure of Cu3P to improve the adsorption capacity of the material for H2S molecules; and utilizes the Cu-S bond formation mechanism to achieve specific H2S response and improve sensing sensitivity.

[0018] (2) This invention integrates catalytic materials, energy devices and gas sensing functions to achieve self-powered detection without external power supply; Ni-doped Cu3P has a porous nanosheet structure, which can provide more gas adsorption sites and improve response performance; the device has flexibility, repeatability and long-term stability, and is suitable for portable environmental monitoring; even under repeated bending deformation or different geometric shapes, the sensor can still maintain a stable response value.

[0019] (3) The Ni doping of this invention can effectively regulate the electronic structure of Cu3P and change its original morphological characteristics. Compared with other metal doping, the NCP catalyst exhibits the best sensing performance. It not only has a low LOD (45.9 ppb) for H2S, but also shows excellent selectivity and good environmental tolerance, while also possessing excellent mechanical flexibility and long-term stability. Attached Figure Description

[0020] Figure 1 (a) Material preparation process, (b) XRD pattern of Co-doped Cu3P, (c) XRD pattern of Fe-doped Cu3P, (d) XRD pattern of Ni-doped Cu3P; Figure 2(a) SEM image of NCP catalyst, (b) TEM image of NCP catalyst, (c) HRTEM image of NCP catalyst, (d) EDS spectrum and related elemental mapping image of NCP catalyst; Figure 3 (a) XRD patterns of CP and NCP, (b) XRD patterns of NCP-1, NCP-2, and NCP-3, (c) XPS total spectrum of CP and NCP, (d) Cu 2p spectrum of CP and NCP, (e) Ni 2p spectrum of CP and NCP, (f) P 2p spectrum of CP and NCP; Figure 4 Raman spectra of NCP catalysts; Figure 5 (a) Gas-sensitive response curve of FCP sensor to H2S concentration range of 10-50 ppm, (b) Gas-sensitive response curve of NCP-3 sensor to H2S concentration range of 10-50 ppm, (c) Gas-sensitive response curve of CCP sensor to H2S concentration range of 10-50 ppm, (d) Performance comparison of FCP sensor, NCP-3 sensor and CCP sensor; Figure 6 (a) Response curve of CP to H2S gas at a concentration of 10-50 ppm, (b) Response curve of NCP to H2S gas at a concentration of 10-50 ppm, (c) Response curve of NCP-1 to H2S gas at a concentration of 10-50 ppm, (d) Response curve of NCP-2 to H2S gas at a concentration of 10-50 ppm, (e) Response curve of NCP-3 to H2S gas at a concentration of 10-50 ppm, (f) Performance comparison of the above five catalysts; Figure 7 (a) Response recovery time of CP, (b) Response recovery time of NCP sensor, (c) Stability of voltage output of NCP sensor in air, (d) LOD of NCP sensor, (e) Selectivity of NCP sensor, (f) Humidity resistance of NCP sensor, (g) Low temperature resistance of NCP sensor, (h) Repeatability of NCP sensor, (i) Long-term stability of NCP sensor; Figure 8(a) Response curve of NCP sensor at 0° bending in 30 ppm H2S; (b) Response curve of NCP sensor at 45° bending in 30 ppm H2S; (c) Response curve of NCP sensor at 90° bending in 30 ppm H2S; (d) Performance comparison of NCP sensor at different bending angles; (e) Response curve of NCP sensor at 20 ppm H2S after 0 bending cycles; (f) Response curve of NCP sensor at 20 ppm H2S after 30 bending cycles; (g) Response curve of NCP sensor at 20 ppm H2S after 60 bending cycles; (h) Response curve of NCP sensor at 20 ppm H2S after 90 bending cycles; (i) Response curve of NCP sensor at 20 ppm H2S after being configured as a circular device; (j) Response curve of NCP sensor at 20 ppm H2S after being configured as a triangular device; (k) Response curve of NCP sensor at 20 ppm H2S after being configured as a pentagonal device. H2S response curve; (l) Performance comparison of NCP sensor under different shapes; Figure 9 (a) Adsorption energy of H2S on pure CP and NCP surfaces; (b) PDOS of CP catalyst; (c) PDOS of NCP catalyst; (d) PDOS of H2S adsorbed on CP surface; (e) PDOS of H2S adsorbed on NCP surface; (f) Differential charge density distribution on NCP and H2S-NCP (NCP after H2S adsorption) surfaces. Detailed Implementation

[0021] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0022] As introduced in the background section, cuprous phosphide (Cu3P) possesses abundant copper active sites and excellent ORR catalytic activity, demonstrating promising application potential in zinc-air batteries. Previous studies have shown that constructing Cu3P-based heterostructures or adjusting its electronic structure can effectively improve the adsorption energy of oxygen intermediates, enhance ORR reaction kinetics, and thus improve the output performance of zinc-air batteries. However, existing Cu3P materials are mainly used to improve oxygen reduction catalytic performance, and their ability to recognize specific gas molecules still needs improvement.

[0023] Based on this, the purpose of this invention is to provide a nickel-doped copper phosphide catalyst, a self-powered gas sensor, and its application for detecting hydrogen sulfide gas. This application uses a Ni-modified Cu3P-based catalyst, wherein Ni exists in the form of lattice doping, surface coordination, or defect regulation, with a molar doping ratio of 5%. This invention overcomes the overall performance bottleneck of the sensor through the synergistic effect of Ni-induced electron delocalization, electronic band reconstruction, and electrochemical reaction kinetic regulation. In terms of sensitivity, the doping effect of Ni atoms brings the energy band of the Ni-doped Cu3P catalyst closer to the Fermi level, optimizing carrier concentration and transport efficiency. By inducing local lattice distortion, a large number of unsaturated active sites are exposed. Combined with the catalytic effect of Ni's highly active centers, the dissociation activation energy of H2S molecules is significantly reduced, thereby amplifying the charge exchange capacity of the gas-sensitive interface and further improving the sensor's response amplitude. In terms of selectivity, based on the extremely strong specific chemical affinity between Ni atoms with incomplete 3d orbitals and sulfur atoms, the surface of the Ni-doped Cu3P catalyst material forms more favorable binding sites and electrochemical reaction kinetic channels for H2S molecules, resulting in better thermal... The dual screening of mechanical and electrochemical reaction kinetics effectively reduces the adsorption barrier and electrochemical reaction energy barrier of H2S, thus giving H2S superior adsorption and electrochemical reaction capabilities at the gas-sensitive interface compared to other background gases, thereby improving the selectivity of the sensor. In terms of stability, Ni doping induces lattice distortion, which hinders the thermal sintering and agglomeration of nanocrystals during preparation. This gives the Ni-doped Cu3P catalyst more active sites and specific surface area. By regulating the local electron density, the balance between the electrochemical reaction of H2S and H2S adsorption-desorption is effectively controlled, thus endowing the sensor with excellent structural integrity and baseline reversibility during long-term adsorption-desorption cycles.

[0024] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0025] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0026] Example 1: Preparation of nickel-doped copper phosphide catalyst 18.24 mmol CuCl₂·6H₂O and 0.96 mmol NiCl₂·6H₂O were completely dissolved in 52 mL of deionized water. 96 mmol red phosphorus (P) was added to the solution and the mixture was magnetically stirred for 0.5 hours. The mixture was transferred to a 100 mL polytetrafluoroethylene (PTFE) reactor and reacted at 200 °C for 36 hours. The resulting product was collected and washed alternately by centrifugation with deionized water and anhydrous ethanol. The centrifuged product was dried in a vacuum drying oven at 60 °C for 24 hours to obtain a Ni-Cu₃P catalyst with a doping molar ratio of 5%, denoted as NCP.

[0027] Example 2: Fabrication of a self-powered gas sensor Weigh 10 mg of carboxymethyl cellulose (C6H7O2(OH)2CH2COONa, CMC) and add it to 1 mL of deionized water, stirring continuously until completely dissolved. Add 90 mg of NCP sample to the above solution, stir continuously for 1 hour, and then sonicate for 30 minutes. Using a four-sided wet film preparation device, uniformly coat the slurry onto carbon paper with a gap of 150 μm (carbon paper area is 1.5 cm × 1.5 cm, catalyst loading is 1.35 mg × cm). -2 Subsequently, the carbon paper was placed in an oven at 60°C and dried for 30 minutes before being removed. 6 g of acrylamide (PAM) and 6 mg of N,N'-methylenebisacrylamide (MBA) were dissolved in 20 mL of deionized water, and 0.02 mol of zinc trifluoromethanesulfonate (Zn(OTf)2) was weighed and dissolved in 20 mL of deionized water. The two solutions were mixed, and 75 mg of ammonium persulfate (APS) was added. The mixture was magnetically stirred for 1 hour. The thoroughly mixed solution was poured into a mold and reacted in an oven at 70°C for 1 hour to obtain a Zn(OTf)2 / PAM hydrogel. Using the Zn(OTf)2 / PAM hydrogel as the solid electrolyte, carbon paper coated with an NCP catalyst as the positive current collector, and a zinc sheet as the negative electrode, a sensor was assembled.

[0028] Comparative Example 1: Preparation of Copper Phosphide Catalyst 19.2 mmol CuCl₂·6H₂O was completely dissolved in 52 mL of deionized water. 96 mmol of red phosphorus was added to the solution and the mixture was magnetically stirred for 0.5 hours. The mixture was transferred to a 100 mL polytetrafluoroethylene (PTFE) reactor and reacted at 200 °C for 36 hours. The product was collected and washed alternately by centrifugation with water and anhydrous ethanol. The centrifuged product was then placed in a vacuum drying oven for 24 hours to obtain pure Cu₃P, denoted as CP.

[0029] Comparative Example 2: Different Doping Ratios (1) The difference from Example 1 is that the amount of CuCl2·6H2O and NiCl2·6H2O is adjusted so that the molar doping ratio of Ni is 3%, 7% and 10%, respectively. The Ni-Cu3P finally prepared is referred to as NCP-1, NCP-2 and NCP-3, respectively.

[0030] (2) The difference from Example 2 is that NCP is replaced with equal amounts of NCP-1, NCP-2, and NCP-3 respectively. Finally, NCP-1, NCP-2, and NCP-3 sensors are prepared.

[0031] Comparative Example 3: Sensors fabricated using copper phosphide with different metal doping (1) The difference from Example 1 is that NiCl2·6H2O is replaced with FeCl3·6H2O and CoCl2·6H2O respectively, and the amount of CuCl2·6H2O and FeCl3·6H2O and CoCl2·6H2O is adjusted so that the molar ratio of Fe to Ni doping is 10%. Finally, Fe-Cu3P catalyst and Co-Cu3P catalyst are prepared, which are denoted as FCP and CCP respectively.

[0032] (2) The difference from Example 2 is that NCP is replaced with an equal amount of FCP or CCP respectively. Finally, FCP sensor and CCP sensor are prepared.

[0033] Example 3: Characterization (1) XRD tests were performed on CCP, FCP and NCP, and the results are as follows: Figure 1 (b) Figure 1 As shown in (d), all samples exhibited sharp and strong characteristic diffraction peaks at 2θ values ​​of 35.98°, 39.08°, 41.56°, 45.08°, and 46.14°. The positions of these diffraction peaks perfectly match the crystal planes (112), (202), (211), (300), and (113) in the Cu3P standard card (ICDD NO. 97-001-5056), indicating that Cu3P was successfully prepared and that doping did not alter the crystal structure of Cu3P. Furthermore, no other obvious impurity peaks were observed in the spectra, indicating that all catalysts possessed high phase purity and crystallinity.

[0034] (2) Figure 2 (a) and Figure 2 Image (b) shows SEM and TEM images of the NCP catalyst, revealing a porous nanosheet assembly structure. This structure provides numerous active sites for gas molecule adsorption, facilitating interaction between gas molecules and the material surface and significantly improving the sensor's response performance. Furthermore, HRTEM observations of the NCP catalyst yielded the following results: Figure 2As shown in (c), the interplanar spacings are 0.173 nm and 0.201 nm, respectively, which correspond to the (220) and (300) crystal planes of Cu3P, confirming the successful preparation of the NCP catalyst. Figure 2 The EDS and related elemental mapping results in (d) reveal the presence and uniform distribution of Cu, Ni, and P elements in the NCP catalyst, confirming the successful incorporation of Ni into Cu3P.

[0035] (3) Figure 3 (a) shows the XRD pattern of the CP catalyst prepared in Comparative Example 1. It exhibits distinct diffraction peaks at 35.98°, 39.08°, 41.56°, 45.08°, and 46.14°, which highly match the standard Cu3P card (ICCD NO. 97-001-5056), corresponding to the (112), (202), (211), (300), and (113) crystal planes, respectively. Furthermore, the XRD pattern of the NCP catalyst is basically consistent with the characteristic peak positions of the Cu3P standard card, and compared to the CP catalyst, the diffraction peaks of NCP show a slight shift, which can be attributed to Ni. 2+ (0.69 Å) Cu substitution 2+ (0.78 Å). The smaller radius of the Ni ion causes lattice contraction. According to Bragg's law of diffraction, the decrease in interplanar spacing will cause the diffraction peaks to shift towards higher angles. Figure 3 As shown in (b), other catalysts with different doping ratios also highly matched the standard card of Cu3P, and no obvious impurity phase diffraction peaks were observed, indicating that Ni doping did not introduce new phases and the system still maintained the pure phase Cu3P crystal structure. Figure 3 (c) shows the XPS full spectrum of the CP and NCP catalysts, which also confirms the presence of Ni, further demonstrating the successful doping of Ni. Figure 3 The Cu 2p spectrum of the NCP catalyst in (d) shows two prominent peaks at binding energies of 932.2 eV and 952 eV, which are attributed to the Cu 2p of the Cu-P bond, respectively. 3 / 2 and Cu 2p 1 / 2 Furthermore, the peaks at binding energies of 943.3 eV and 962.5 eV are satellite peaks. Compared with the Cu 2p spectrum of the CP catalyst, the peak positions of the NCP catalyst shift towards higher binding energies. This is because Ni doping can modulate the Cu 2p binding energy. d It adds a center, altering its electronic structure. Figure 3 The Ni 2p spectrum of the (e) NCP catalyst exhibits two distinct main peaks at binding energies of 855.85 eV and 873.85 eV, which are attributed to Ni, respectively. 2+ Ni 2p 3 / 2 and Ni 2p 1 / 2Characteristic peaks, accompanied by typical satellite peaks, indicate the presence of partially oxidized nickel species on the catalyst surface. Furthermore, another set of double peaks observed at binding energies of 852.95 eV and 870.06 eV can be attributed to the Ni 2p bonds in Ni2P. 3 / 2 and Ni 2p 1 / 2 Based on the peak area integral fitting results of the high-resolution spectrum, the peak area attributable to Ni-P bonds is approximately 24.3%, while the surface oxidized Ni... 2+ The proportion of the main peak and satellite peaks combined is approximately 75.7%. This result indicates that although the outermost layer undergoes slight oxidation due to unavoidable air contact, the clear manifestation of the 24.3% metallic Ni-P peak still provides direct and strong spectroscopic evidence that Ni ions have been successfully embedded in the Cu3P lattice to form a stable Ni-P coordination structure. These embedded active sites are the core of regulating the catalytic activity of the material surface.

[0036] The results show that nickel in the NCP catalyst mainly exists in the phosphating state, with a small amount of thin oxide layer on the surface. In contrast, no significant Ni signal was detected in the undoped CP sample. Furthermore, the slight shift of the Ni 2p peak relative to the standard value indicates significant electronic interactions and charge transfer between the doped Ni and Cu sites. Figure 3 Figure (f) shows the high-resolution XPS analysis results of P 2p peaks for CP and NCP catalysts. The P 2p peak of the NCP catalyst can be decomposed into two main spin orbital splitting peaks: P 2p 3 / 2 and P 2p 1 / 2 These two peaks are located at binding energies of approximately 129.4 eV and 130.5 eV, respectively. Additionally, a distinct peak was observed at approximately 133.8 eV, a characteristic peak of the PO bond, further confirming oxidation on the catalyst surface. Notably, the P 2p binding energy of the NCP sample is slightly lower than that of the CP sample, which is likely due to changes in the electronic structure caused by Ni doping. Ni incorporation increases the electron cloud density around the P atom, thereby lowering its binding energy.

[0037] (4) Figure 4 The Raman spectrum of the NCP catalyst at room temperature is presented. Three main characteristic peaks are clearly observed in the spectrum, located at 213 cm⁻¹. -1 420 cm -1 and 614 cm -1 Among them, the one located at 213 cm -1 The strong peak at 420 cm⁻¹ belongs to the intrinsic lattice vibration mode of Cu₃P, confirming the successful preparation of copper phosphide.-1 The characteristic peak was attributed to the antisymmetric bending vibration (F2) of the PO bond in the phosphate species formed by surface oxidation. This is likely due to the formation of a phosphorus-containing oxide layer on the material surface, and its local coordination environment leading to a characteristic shift in the vibrational frequency relative to the standard tetrahedral phosphate group. Furthermore, at 614 cm⁻¹... -1 The sharp peak at that point corresponds to the B-O bond in monoclinic CuO. g The stretching vibration mode also indicates that the catalyst surface is oxidized.

[0038] Experimental example: Gas sensitivity detection The gases used in this experiment—hydrogen sulfide (H2S), nitrogen dioxide (NO2), carbon dioxide (CO2), sulfur dioxide (SO2), carbon monoxide (CO), and ammonia (NH3)—were all commercially available dry gases stored in steel cylinders, purchased from Jinan Deyang Gas Co., Ltd., China. The NO2 concentration was 10% (with nitrogen (N2) as the balance gas); the concentrations of CO, SO2, and H2S were all 5% (with nitrogen (N2) as the balance gas); CO2 and NH3 were commercially available high-purity standard gases with a concentration of 99%. The gas sensitivity testing conditions were room temperature (25℃) and relative humidity of 40%.

[0039] (1) Gas sensitivity detection was performed on the NCP-3 sensor in Comparative Example 2 and the sensor prepared in Comparative Example 3. The gas-sensing performance testing system mainly consists of a Keithley 2600S digital source meter, a 5 L gas chamber, and a data acquisition system. Post-processing and plotting analysis of the test data were performed using Origin software. During the gas-sensing test, FCP, NCP-3, and CCP sensors were placed in the gas chamber and connected to the digital source meter via wires. The sensor output voltage was acquired by the Keithley 2600S digital source meter. Before the target gas was injected, the voltage of the sensor during stable operation in air was the air baseline voltage V. gas The calculated amount of dry gas (nitrogen balanced) was then drawn from a commercial standard cylinder using a syringe and injected into a 5 L test chamber initially filled with air. The required concentration of the target gas was calculated using formula (1): (1); In the formula: V x (μL) is the volume of gas extracted; V (L) is the chamber volume; C is the required concentration of the target gas (ppm); T r At room temperature; T bThe temperature is the chamber temperature. Based on this formula, to prepare target H2S concentrations of 10 ppm, 20 ppm, 30 ppm, 40 ppm, and 50 ppm respectively within the test chamber, the calculated required standard gas volumes are 1 mL, 2 mL, 3 mL, 4 mL, and 5 mL, respectively. Subsequently, a small fan is used to uniformly mix the gas within the chamber. The sensor's output voltage V after contact with the H2S gas is... gas Data acquired using a Keithley 2600S digital source meter. The sensor response value is defined as V. gas -V air V gas With V air These represent the sensor voltage in the target gas atmosphere and the air atmosphere, respectively. Response time and recovery time are defined as follows: the time required for the voltage change to reach 90% of its maximum value after H2S is introduced is the response time; the time required for the voltage change to return to 90% of its maximum value after H2S is removed is the recovery time.

[0040] Figure 5 (a) ~ Figure 5 Figure (c) shows the response curves of the FCP, NCP-3, and CCP sensors under H2S exposure at concentrations of 10–50 ppm. It can be seen that all three exhibit a consistent response pattern: when exposed to an H2S atmosphere, the sensor's OCV drops rapidly, but recovers after air purging, indicating that the sensing system has good repeatability and reversibility. Furthermore, the response values ​​of all sensors increase significantly with increasing H2S concentration, exhibiting a clear concentration-dependent characteristic. Figure 5 Figure (d) compares the performance of the three sensors. The FCP sensor has the highest baseline voltage (1.08 V), but its response to H2S is the worst. The NCP-3 sensor exhibits the best sensing performance, with a response value of 0.1 V at 50 ppm H2S.

[0041] (2) To explore the H2S response performance of the sensors prepared in Example 2 and Comparative Example 2. The sensors prepared in Example 2 and Comparative Example 2 were tested using the same experimental method as in this experimental example (1).

[0042] like Figure 6 (a) ~ Figure 6As shown in (e), the gas-sensing response of sensors composed of pure Cu3P and Ni-doped Cu3P with different doping ratios all showed an increasing trend with increasing H2S concentration. This is because, with increasing H2S concentration, more H2S gas molecules adsorb onto the catalyst surface and undergo oxidation, resulting in a greater decrease in sensor voltage. Furthermore, more H2S gas molecules interact with active sites (forming Cu-S bonds), effectively covering and suppressing oxygen reduction (ORR) active sites, thus causing a more significant decrease in sensor output voltage. All of these factors ultimately contribute to the sensor exhibiting a significant enhancement in gas-sensing response with increasing H2S concentration. Moreover, with increasing Ni doping ratio, the corresponding sensor's response performance to H2S showed a trend of first increasing and then decreasing. The NCP sensor with a Ni doping ratio of 5% (the sensor prepared in Example 2) exhibited the best H2S sensing performance, with a response value of 105 mV at 20 ppm H2S. Figure 6 (f). Therefore, further performance testing of the NCP sensor is conducted to explore its specific performance.

[0043] (3) The response behavior of CP and NCP sensors to H2S was investigated.

[0044] 1) To elucidate the regulatory mechanism of Ni doping on H2S adsorption on Cu3P surfaces, DFT calculations of pure Cu3P (CP) and Ni-doped Cu3P (NCP) were compared, both based on the Vienna first-principles simulation software package (VASP). During the calculations, plane-wave basis sets were used to expand the system wavefunction. The electron exchange correlation functional was performed using the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA). To ensure sufficient convergence, the plane-wave cutoff energy was uniformly set to 600 eV. Simultaneously, full relaxation optimization was performed on the atomic coordinates and supercell structural parameters until the residual force on each atom was less than 0.01 eV / Å, and the total energy change between adjacent ion steps was less than 10. -6 eV. For the van der Waals (vdW) interactions present in the system, the DFT-D3 empirical correction method proposed by Grimme was used for relatively accurate correction. Furthermore, to avoid mutual interference between adjacent periodic mirror structures under periodic boundary conditions, a vacuum layer with a thickness of 15 Å was set in the z-axis direction.

[0045] Figure 9The adsorption energies in (a) show that the adsorption energy of H2S on NCP (-0.429 eV) is negatively shifted by 0.152 eV compared to CP (-0.277 eV), proving that Ni doping significantly enhances the adsorption capacity of Cu3P for H2S. This improvement stems from the modulation of the electronic structure of the surface active sites by Ni substitution for Cu: such as Figure 9 (b) Figure 9 PDOS analysis in (e) shows that after Ni doping, the d-band center shifts from -2.818 eV to -2.712 eV, the d-state density near the Fermi level increases, and the hybridization of the metal d orbitals with the sp orbitals in H2S is enhanced. Figure 9 The differential charge density plot in (f) visually demonstrates the significant accumulation of bonding charge between S and Ni sites after H2S adsorption, confirming the formation and strengthening of Cu-S covalent bonds. ICOHP analysis quantitatively confirms the strengthening of Cu-S bonds: the ICOHP of Cu-S bonds in NCP is -0.779 eV, a 33% negative shift compared to CP (-0.586 eV), directly indicating that Ni doping significantly enhances the covalent bonding between S and the surface metal by upregulating the d-band energy level of the active sites. Simultaneously, the Ni-P bond in NCP (-0.784 eV) is stronger than the Cu-P bond in CP (-0.555 eV), indicating that Ni atoms are firmly anchored by surrounding P atoms, ensuring the structural stability of the active sites. In summary, Ni doping, by taking the representative Cu sites, shifting the d-band center upwards, and strengthening Cu-S covalent bonds, fundamentally enhances the adsorption and activation capacity of Cu3P surface active sites for H2S.

[0046] 2) Inject 2 mL of H2S gas into a 5 L sealed chamber to prepare a 20 ppm H2S gas environment, and use a Keithley 2600S digital source meter to monitor the transient changes in the open-circuit voltage of both CP and NCP sensors in real time. Figure 7 (a) Figure 7 As shown in (b), both the CP and NCP sensors exhibit typical response curves when exposed to a 20 ppm H₂S gas environment. In contrast, the response and recovery times (t) of the NCP sensor are significantly different. res = 61 s,t rec = 95 s) compared to CP sensor (t res = 7 s,t recThe response time (= 30 s) is slightly slower, but its amplitude is much greater than the latter. This difference can be attributed to the richer active sites on the surface of the NCP catalyst, which enhances the adsorption of H2S molecules, promotes the oxidation reaction at the cathode, and has a greater impact on the catalytic activity of Cu3P for ORR. The baseline stability of the sensor was then examined through long-term continuous operation. The baseline stability of the NCP sensor was continuously monitored over a long period in a clean air atmosphere at room temperature and 40% relative humidity. Figure 7 As can be seen in (c), when the NCP sensor is placed in an air environment and operates continuously for 12 hours, the open-circuit voltage of the device remains stable and the voltage fluctuation is only 0.18 mV. This indicates that the sensor has a stable voltage output, which can effectively avoid the performance degradation caused by baseline drift and is beneficial for the sensor to detect lower concentrations of H2S.

[0047] 3) Place the NCP sensor in a clean air environment. After its output voltage signal reaches a steady state, calculate the volume of H2S standard gas required to prepare H2S target concentrations of 200 ppb, 400 ppb, 600 ppb, 800 ppb and 1000 ppb in the test chamber according to formula (1). The volumes are 20 μL, 40 μL, 60 μL, 80 μL and 100 μL, respectively. Test the performance of the NCP sensor in a low-concentration H2S atmosphere. The experimental method is the same as in this experimental example (1). Next, independently introduce 100 ppm of high-concentration interfering gases such as NH3 (0.5 mL), NO2 (5 mL), CO2 (0.5 mL), CO (10 mL) and SO2 (10 mL) and 20 ppm of H2S (2 mL) respectively, and compare the sensor's response to the above gases to verify the high selectivity of the NCP sensor. In the temperature and humidity adaptability test, a humidification device and a low-temperature cooling device were used to precisely control the relative humidity (40%~90%RH) and ambient temperature (–20℃~20℃) inside the gas chamber. After the system reached thermodynamic equilibrium, the anti-interference capability of the NCP sensor under complex wide temperature and humidity conditions was examined. In the repeatability and stability test, the sensor was subjected to multiple cycles of constant-volume gas injection-exhaust desorption, and a 35-day performance test was conducted at room temperature to quantitatively evaluate the repeatability and long-term operational stability of the device under practical application conditions. Figure 7 Figure (d) shows the response performance of the NCP sensor exposed to low concentrations of H2S (200-1000 ppb). Within this trace concentration range, the change in the sensor's voltage response (ΔV) exhibits a high linear correlation with the H2S gas concentration (C). The fitted linear standard curve equation is ΔV = -0.01341 × C + 2.35 (R²). 2=0.99), this linear characteristic indicates that the sensor has excellent quantitative detection capability at the trace level, and the theoretical detection limit of the gas sensor can be estimated by a signal-to-noise ratio of not less than 3. The theoretical detection limit is calculated by formula (2) and formula (3): (2); (3); In the formula, Ri is the measured response of the sensor exposed to H2S. Here, N is the average response value, N is the number of data points, and slope is the absolute value of the slope of the linear standard curve fitting the response value to H2S concentration (i.e., sensitivity, slope = 0.01341 mV / ppb). Using the slope of the linear curve fitting the response to H2S concentration and the root mean square (RMS) deviation, its LOD is calculated to be 45.9 ppb (R0). 2 =0.99), this excellent performance is mainly due to the large number of active sites in NCP and the improved interfacial charge transfer efficiency. Selectivity is a decisive indicator for evaluating whether a gas sensor can be applied in practical scenarios, reflecting the sensor's detection accuracy and reliability in complex environments. In practical use, the target gas often coexists with multiple interfering gases. If the sensor lacks sufficient selectivity, it is easy to make misjudgments due to cross-sensitivity, leading to incorrect detection results. Figure 7 Figure (e) shows the selectivity radar plot of the NCP sensor. As can be seen, in an environment with multiple interfering gases (NH3, NO2, CO2, CO, SO2) at a concentration of 100 ppm and H2S at 20 ppm, the NCP sensor only shows a significant response to the target gas H2S, while the response to other interfering gases is very weak. This high selectivity is mainly due to the specific interaction between the NCP catalyst and H2S (i.e., the formation of Cu-S bonds), and secondly, to the differences in redox potentials of different gases on the electrode surface. The influence of relative humidity (RH) on the sensor is as follows... Figure 7 As shown in (f), the sensor's gas-sensing response to 20 ppm H2S remains relatively stable within a RH range of 40%-90%. This is because the Zn(OTf)2 / PAM hydrogel electrolyte itself has good hydrophobicity, ensuring that the sensor performance is not significantly affected by changes in RH. Furthermore, Figure 7 Figure (g) shows the response curve of the NCP sensor to 20 ppm H2S over a wide temperature range of -20℃ to 30℃. The results indicate that the sensor maintains good performance even at low temperatures, thanks to its thermally induced electrochemical reaction mechanism and the antifreeze properties of the hydrogel electrolyte. Repeatability and long-term stability are core indicators for evaluating the practical application value of gas sensors. Figure 7As shown in Figure (h), the NCP sensor exhibits excellent repeatability with almost no decay in response value after 10 consecutive cycles of testing in 20 ppm H2S gas. Figure 7 As shown in Figure (i), after 35 days of storage at room temperature and repeated testing, the NCP sensor's response to 20 ppm H2S remained above 85% of its initial value, verifying its excellent long-term stability. This superior long-term stability prevents sensitivity decay, thus ensuring the reliability of the monitoring data. High repeatability means the sensor has good temporal consistency, effectively reducing detection errors and meeting the high accuracy requirements of practical applications.

[0048] (4) In the sensor bending angle flexibility test, the sensor is fixed to the required bending angle using a clamp and the angle is measured with a protractor, and then the sensor performance is tested; in the sensor bending number flexibility test, the sensor is continuously bent at a fixed angle according to the required number of bending, and then the relevant gas-sensitive performance test is performed at an angle of 0°; in the sensor different shape flexibility test, the sensor is prepared as a whole into a uniform multiple shapes, including a gas-sensitive positive electrode, a hydrogel electrolyte layer and a zinc sheet negative electrode, rather than simply cutting the gas-sensitive positive electrode into different shapes, and then the gas-sensitive performance test is performed at an angle of 0°.

[0049] Figure 8 The results of flexibility tests on the NCP sensor were summarized. Regardless of the bending angle, number of bending cycles, or geometries, the sensor's H2S gas sensing performance did not show a significant decrease. Specifically, as... Figure 8 (a) ~ Figure 8 As shown in (d), when the sensor is bent at 45° and 90°, its sensing response to 20 ppm H2S gas still retains more than 95% of its initial state (0°), which fully demonstrates the sensor's excellent mechanical flexibility. Furthermore, as... Figure 8 (e) Figure 8 As shown in Figure (h), the initial response was -102 mV. After undergoing 30, 60, and 90 repeated bending cycles, the response values ​​were -97 mV, -93.88 mV, and -91 mV, respectively, with performance retention rates as high as 95.10%, 92.04%, and 89.22%. The gas-sensing performance of the sensor remained stable without significant attenuation, verifying its reliability under dynamic mechanical deformation conditions. Meanwhile, as shown in Figure (h), Figure 8 in(i)~ Figure 8As shown in Figure (l), thanks to its excellent flexibility and plasticity, the sensor was cut into different geometric shapes (such as circles, triangles, and pentagrams) for testing. The standard rectangular device responded to -96mV, while the circular, triangular, and pentagram devices responded to -94mV, -89mV, and -88mV, respectively. The retention rates relative to the rectangular reference reached 97.92%, 92.71%, and 91.67%, respectively, indicating that it still maintains a stable response. This characteristic provides more possibilities for the application of the sensor in complex curved surfaces or irregular pattern scenarios.

[0050] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A nickel-doped copper phosphide catalyst for detecting hydrogen sulfide gas, characterized in that, The catalyst comprises Cu3P and Ni doped in the Cu3P lattice; the nickel-doped copper phosphide catalyst is prepared by the following method: Copper and nickel sources were dissolved in deionized water, and then phosphorus source was added and stirred to carry out a hydrothermal reaction. The product was collected, washed, and dried to obtain nickel-doped copper phosphide catalyst. The copper source is CuCl2·6H2O; the nickel source is NiCl2·6H2O; and the phosphorus source is red phosphorus.

2. The nickel-doped copper phosphide catalyst according to claim 1, characterized in that, The molar ratio of Cu, Ni, and P contained in CuCl2·6H2O, NiCl2·6H2O, and red phosphorus is 0.95:0.05:

5.

3. The nickel-doped copper phosphide catalyst according to claim 1, characterized in that, The hydrothermal reaction was carried out at a temperature of 200°C for 36 hours.

4. The nickel-doped copper phosphide catalyst according to claim 1, characterized in that, The washing process involves alternating centrifugal washing with water and anhydrous ethanol; the drying process involves vacuum drying at 60°C for 24 hours.

5. A self-powered gas sensor for detecting hydrogen sulfide gas, characterized in that, It includes a zinc negative electrode, a solid electrolyte, and an air positive electrode; the air positive electrode includes a conductive substrate and a nickel-doped copper phosphide catalyst according to any one of claims 1 to 4 supported on the conductive substrate.

6. The self-powered gas sensor according to claim 5, characterized in that, The solid electrolyte is a Zn(OTf)₂ / PAM hydrogel; the conductive substrate is carbon paper; the air cathode is prepared by the following method: CMC was dissolved in deionized water, nickel-doped copper phosphide catalyst was added and stirred, and then ultrasonic treatment was performed to obtain a slurry. The slurry was uniformly coated onto carbon paper and dried to obtain an air cathode.

7. The application of the nickel-doped copper phosphide catalyst according to any one of claims 1 to 4, or the self-powered gas sensor according to claim 5 or 6, in the detection of hydrogen sulfide gas.

8. The application according to claim 7, characterized in that, The applications include improving the sensitivity, flexibility, and environmental tolerance of hydrogen sulfide gas detection.

9. The application according to claim 7, characterized in that, The detection method involves exposing an air cathode containing a nickel-doped copper phosphide catalyst to the test environment, detecting the change in the output voltage of the zinc-air battery, and determining the H2S concentration based on the change in output voltage.

10. The application according to claim 7, characterized in that, The lowest detection limit of the self-powered gas sensor is 45.9 ppb.

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