CN112481635A - Noble metal iridium hydrogen evolution electrocatalyst and application - Google Patents
Noble metal iridium hydrogen evolution electrocatalyst and application Download PDFInfo
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- 229910052739 hydrogen Inorganic materials 0.000 title claims abstract description 51
- 239000001257 hydrogen Substances 0.000 title claims abstract description 50
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 title claims abstract description 46
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 title claims abstract description 26
- 229910052741 iridium Inorganic materials 0.000 title claims abstract description 20
- 239000010411 electrocatalyst Substances 0.000 title claims abstract description 16
- 229910000510 noble metal Inorganic materials 0.000 title claims abstract description 15
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 52
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 17
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims abstract description 17
- 229910001868 water Inorganic materials 0.000 claims abstract description 13
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 9
- IHTFTOGFXXXQBO-UHFFFAOYSA-B [C+4].[C+4].[C+4].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O Chemical compound [C+4].[C+4].[C+4].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O IHTFTOGFXXXQBO-UHFFFAOYSA-B 0.000 claims abstract description 8
- 238000011068 loading method Methods 0.000 claims abstract description 8
- 238000004519 manufacturing process Methods 0.000 claims abstract description 6
- JEPOTLHJJKWIQQ-UHFFFAOYSA-N [Co]O[Ir] Chemical compound [Co]O[Ir] JEPOTLHJJKWIQQ-UHFFFAOYSA-N 0.000 claims abstract description 4
- 238000005868 electrolysis reaction Methods 0.000 claims abstract description 3
- 239000002041 carbon nanotube Substances 0.000 claims description 129
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- 239000000243 solution Substances 0.000 claims description 22
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- 238000004070 electrodeposition Methods 0.000 claims description 12
- 238000000034 method Methods 0.000 claims description 12
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- 239000000758 substrate Substances 0.000 claims description 10
- 229910021642 ultra pure water Inorganic materials 0.000 claims description 10
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- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 9
- 238000002360 preparation method Methods 0.000 claims description 9
- 229910017052 cobalt Inorganic materials 0.000 claims description 6
- 239000010941 cobalt Substances 0.000 claims description 6
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 4
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- 239000007864 aqueous solution Substances 0.000 claims description 2
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- 150000001868 cobalt Chemical class 0.000 claims description 2
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- 229910052719 titanium Inorganic materials 0.000 claims description 2
- 239000010936 titanium Substances 0.000 claims description 2
- 239000003054 catalyst Substances 0.000 abstract description 34
- 239000002131 composite material Substances 0.000 description 75
- HTXDPTMKBJXEOW-UHFFFAOYSA-N iridium(IV) oxide Inorganic materials O=[Ir]=O HTXDPTMKBJXEOW-UHFFFAOYSA-N 0.000 description 56
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- ZGTMUACCHSMWAC-UHFFFAOYSA-L EDTA disodium salt (anhydrous) Chemical compound [Na+].[Na+].OC(=O)CN(CC([O-])=O)CCN(CC(O)=O)CC([O-])=O ZGTMUACCHSMWAC-UHFFFAOYSA-L 0.000 description 2
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
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- LOKCTEFSRHRXRJ-UHFFFAOYSA-I dipotassium trisodium dihydrogen phosphate hydrogen phosphate dichloride Chemical compound P(=O)(O)(O)[O-].[K+].P(=O)(O)([O-])[O-].[Na+].[Na+].[Cl-].[K+].[Cl-].[Na+] LOKCTEFSRHRXRJ-UHFFFAOYSA-I 0.000 description 1
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Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/02—Hydrogen or oxygen
- C25B1/04—Hydrogen or oxygen by electrolysis of water
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D9/00—Electrolytic coating other than with metals
- C25D9/04—Electrolytic coating other than with metals with inorganic materials
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
Abstract
The invention belongs to the field of hydrogen evolution by electrolysis of water, and particularly relates to a noble metal iridium hydrogen evolution electrocatalyst and application thereof. The iridium wire is used as a counter electrode to synthesize the iridium oxide-cobalt-based phosphate-carbon carrier loaded on the carbon carrier, the iridium wire has low iridium loading capacity, shows excellent HER electrochemical performance, can be comparable with the performance of a commercial Pt/C catalyst, and has certain possibility of being suitable for efficient, stable and low-cost electrolytic hydrogen production.
Description
Technical Field
The invention belongs to the field of hydrogen evolution by electrolysis of water, and particularly relates to a noble metal iridium hydrogen evolution electrocatalyst and application thereof.
Background
With the continuous innovation and progress of science and technology, the problems of environmental pollution and the like are increasingly worsened. There is an urgent need to develop clean renewable energy sources to reduce the dependence on fossil fuels. At present, hydrogen energy is considered to be an ideal clean energy source because the combustion heat value is high and the combustion product is water. The method for producing Hydrogen (HER) by electrolyzing water is a high-efficiency, environment-friendly and high-purity hydrogen production method. The development of hydrogen evolution electrocatalysts with lower overpotentials is one of the important means to optimize the process. Catalyst activity is generally related to the theoretical Gibbs free energy of hydrogen (Δ G)H). Platinum (Pt) and its alloys have excellent Δ G so farHAre considered to be a superior class of catalysts in HER. But the scarcity and high price of Pt greatly limit the application of large-scale commercialization. Therefore, reducing the amount of Pt used or developing a Pt-free catalyst is a more effective way to realize a low-cost catalyst.
In recent years, in the HER field, transition metal phosphides have shown great potential due to their advantages of low cost, special electronic structure, abundant natural environmental reserve elements, and the like, and are considered as one of the catalyst classes that are a strong substitute for Pt. DFT calculation shows that P site in transition metal phosphide can directly participate in HER process and has certain binding with intermediate, which is the key of speed-determining step in HER process. To further improve the electrochemical performance of transition metal phosphides, some groups have utilized amorphous transition metal phosphorus oxygen compounds (TMPi) to greatly increase the catalytic active sites. However, these materials are susceptible to corrosion in acidic media, have poor stability, and result in reduced activity. And the HER performance of TMPi is still not comparable to that of noble metal-based catalysts. Therefore, it is still a serious challenge to improve the catalytic performance of amorphous TMPi catalyst.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a noble metal iridium hydrogen evolution electrocatalyst and application thereof.
The technical scheme adopted by the invention is as follows: a preparation process of a noble metal iridium hydrogen evolution electrocatalyst comprises the following steps:
(1) loading a carbon carrier on the conductive substrate to obtain a conductive substrate loaded with the carbon carrier;
(2) forming the conductive matrix loaded with the cobalt-based phosphate-carbon carrier by an electrodeposition method by using the conductive matrix loaded with the carbon carrier obtained in the step (1) as a working electrode, a graphite rod as a counter electrode and an aqueous solution containing a cobalt salt precursor and a phosphorus precursor as a deposition solution;
(3) and (3) forming the conductive matrix loaded with the iridium oxide-cobalt base phosphate-carbon carrier by an electrodeposition method by using the conductive matrix loaded with the cobalt base phosphate-carbon carrier obtained in the step (2) as a working electrode, an iridium wire as a counter electrode and sulfuric acid as a deposition solution.
In the step (1), the conductive matrix is one or a combination of glass carbon, platinum, titanium, copper, iron and nickel.
The conductive substrate is glassy carbon, the glassy carbon is firstly wiped clean by cotton wetted by alcohol, polishing is carried out by adopting polishing powder, finally polishing is carried out by adopting polishing cloth, after polishing is finished, the conductive substrate is sequentially placed in ultrapure water and alcohol solution for ultrasonic treatment, and the surface is dried by blowing.
In the step (1), the carbon carrier is dispersed in a solvent to prepare a uniformly dispersed suspension, the suspension is dripped on the conductive matrix, and the conductive matrix loaded with the carbon carrier is obtained after natural drying.
The carbon carrier is carbon black, carbon nano tube or graphene.
The noble metal iridium hydrogen evolution electrocatalyst is applied to hydrogen production by electrolyzing water.
The invention has the following beneficial effects: the iridium wire is used as a counter electrode to synthesize the iridium oxide-cobalt-based phosphate-carbon carrier loaded on the carbon carrier, the iridium wire has low iridium loading capacity, shows excellent HER electrochemical performance, can be comparable with the performance of a commercial Pt/C catalyst, and has certain possibility of being suitable for efficient, stable and low-cost electrolytic hydrogen production.
In one embodiment of the invention, the iridium loading is 0.41 wt% up to 29 mV of excessPotential (Current Density 10 mA cm at this time)-2) Corresponding to a Tafel slope of 27 mV dec-1And good stability at high overpotentials.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is within the scope of the present invention for those skilled in the art to obtain other drawings based on the drawings without inventive exercise.
FIG. 1 is a scanning electron micrograph of different composite materials for different numbers of deposition cycles: (a-c) CoPi20cyc-CNTs、CoPi30cyc-CNTs and CoPi40cyc-SEM images of CNTs composites; (d-f) IrO2-CoPi-CNTs-10000cyc、IrO2-CoPi-CNTs-12000cyc and IrO2-SEM picture of CoPi-CNTs-10000cyc composite; (g-i) IrO2-CNTs-10000cyc、IrO2-CNTs-12000cyc and IrO2-SEM picture of CNTs-14000cyc composite;
FIG. 2 is a transmission electron micrograph of different composites. (a) TEM image of CoPi-CNTs composite; (b) IrO2-TEM images and HRTEM images of CNTs composites; (c) IrO2TEM image of CoPi-CNTs composite, inset EDS elemental profile and STEM image of composite; (c, d) IrO2TEM image of-CoPi-CNTs, (e, f) IrO2-high resolution TEM images of CoPi-CNTs composites;
fig. 3 is a structural representation of various composite materials: CoPi-CNTs, IrO2-CNTs and IrO2-high resolution XPS spectra of CoPi-CNTs composites, (a) is the spectrum of Co 2P, (b) is the spectrum of P2P, (c) is the spectrum of Ir 4 f;
FIG. 4 is a cathodic polarization curve (a) and corresponding Tafel slope (b) for various numbers of deposited CoPi-CNTs composites;
FIG. 5 shows deposition of IrO at different turns2-CoPi-CNTs composite cathodal polarization curve (a) and corresponding towersA Fiell slope (b);
figure 6 is HER performance of the composite: (a) CNTs, CoPi-CNTs, IrO2-CNTs, Pt/C and IrO2-CoPi-CNTs composite at 0.5M H2SO4Sweeping speed of 5 mV s−1The polarization curve of (a); (b) tafel slope from the polarization curve; (c) overpotential (current density of 10 mA cm) of HER-CATALYST in other literature−2) Comparing with the Tafel slope; (d) double layer capacitance of the composite material; (e) at 0.5M H2SO4In which IrO is measured by chronoamperometry2-i-t curve of CoPi-CNTs composites (ŋ = 100 mV vs. RHE); (f) IrO2LSV curves before and after 100h testing of the CoPi-CNTs composite material;
FIG. 7 is a graph of CV curves for different catalysts at different sweep rates and corresponding electrochemical double layer capacitance values;
FIG. 8 shows IrO2A morphology representation chart of the CoPi-CNTs composite material after 100h of stability test; (a) SEM picture; (b) a TEM image;
FIG. 9 shows CoPi-CNTs and IrO2-CNTs and IrO2-nyquist plot of CoPi-CNTs composites, inset is fitted circuit diagram;
FIG. 10 shows CNTs, CoPi-CNTs, and IrO2-CNTs and IrO2CV diagram in 1.0M PBS (pH 7.0) of CoPi-CNTs composite with a scan rate of 50 mV s-1；
Fig. 11 is the TOF values of the composite: (a) calculating to obtain CNTs, CoPi-CNTs and IrO2-CNTs and IrO2-TOF curves of CoPi-CNTs composites; (b) at the same TOF value (0.8 s)-1) Comparing overpotentials of different composite materials; (c) comparing TOF values of different composite materials under multiple overpotentials;
FIG. 12 is a diagram for IrO2DFT calculation of HER catalytic activity of the CoPi complex catalyst: (a) IrO2-front and top views of a CoPi composite; (b) IrO2-projected state density of the CoPi composite; (c) IrO2-a HER gibbs free energy (Δ G) diagram for each active site of the CoPi composite; (d-g) IrO2Each active site of the-CoPi composite material is bonded with hydrogenAnd (4) a composite structure. White, red, navy blue sphere H, O, Ir atoms, rod-like H-O bond, CoO6Denotes light blue octahedra, PO4Representing pink tetrahedra. (h) IrO in acid Medium2-a CoPi composite mimics a schematic representation of the HER catalytic pathway.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings.
1. Pretreatment of glassy carbon electrodes
Firstly, wiping the glassy carbon electrode with cotton wetted by alcohol, and then taking polishing powder (aluminum oxide, Al) with different particle sizes2O3) (particle size: d = 0.3 μm, d = 0.05 μm) was wetted on a polishing cloth and then polished. And after each polishing, the electrode is washed by ultrapure water, and then polishing is continued. The polishing of the last step is performed on a polishing cloth having only ultrapure water. Each polish was about 1.5 minutes for a total of 3 times. And after polishing, placing the glassy carbon electrode in ultrapure water and ethanol solution successively and ultrasonically treating for 30 s. Finally, the surface of the glassy carbon electrode is dried (high-purity N is used for drying)2Airflow) and standing for standby.
2. Preparation of CoPi-CNTs material
(1) Preparation of CNTs-loaded electrodes
A certain amount (2 mg) of Carbon Nanotubes (CNTs) were weighed into a centrifuge tube, and ultrapure water and an ethanol solution in a volume ratio of 1: 4 (100. mu.l: 400. mu.l) were added to obtain a mixed solution. And placing the centrifuge tube filled with the mixed solution in an ultrasonic cleaning instrument, and performing ultrasonic treatment for 2 hours (the temperature of ultrasonic water is not too high) to obtain uniformly dispersed suspension. On the surface of the pretreated clean glassy carbon electrode, a CNTs suspension (8. mu.l) obtained after ultrasonication was added dropwise using a pipette gun. Naturally dried at room temperature overnight. And obtaining the CNTs loaded glassy carbon electrode.
(2) Preparation of deposition solution
Separately weighing quantitative disodium ethylene diamine tetraacetate cobalt salt hydrate (C)10H20CoN2Na2O12) Boric acid (H)3BO3) Andsodium hypophosphite (NaH)2PO2) The reagent was put in a beaker, ultrapure water was added thereto, and a sedimentation solution (C) having a concentration of 0.03M was prepared in a volumetric flask10H20CoN2Na2O12、H3BO3And NaH2PO2Both concentrations were 0.03M).
(3) Synthesis of CoPi-CNTs material by electrodeposition method
A three-electrode system is utilized, a CNTs loaded glassy carbon electrode is used as a working electrode, a graphite rod is used as a counter electrode, and a Saturated Calomel Electrode (SCE) is used as a reference electrode, and the electrodes are placed in an electrolytic cell filled with deposition liquid (wherein the SCE is calibrated according to a reversible hydrogen electrode). The potential was set from-1.8 to 0.5V using Cyclic Voltammetry (CV) at a scan rate of 50 mV s-1. And after circulation, rinsing the residual electrolyte on the surface of the deposited glassy carbon electrode by using ultrapure water, and naturally drying at room temperature to obtain the glassy carbon electrode loaded with the CoPi-CNTs. Wherein, the number of cycles of cyclic scanning during deposition is compared, and 20 cycles (20 cyc), 30 cycles (30 cyc) and 40 cycles (40 cyc) are respectively set and recorded as CoPi20cyc-CNTs、CoPi30cyc-CNTs and CoPi40cyc-CNTs。
3. IrO2Preparation of-CoPi-CNTs material
(1) Preparation of deposition solution
Measuring a certain amount of concentrated sulfuric acid (H)2SO498%) was slowly added to a beaker containing a volume of ultrapure water, and the solution was prepared in a volumetric flask to give a sulfuric acid solution having a concentration of 0.5M.
(2) Synthesis of IrO by electrodeposition2-CoPi-CNTs material
Using a three-electrode system, the prepared CoPi-CNTs electrode was used as a working electrode, an iridium wire (Ir wire) as a counter electrode and a Saturated Calomel Electrode (SCE) as a reference electrode were placed in an apparatus containing a 0.5M sulfuric acid deposition solution. Setting the potential from-0.6 to-1.2V using Cyclic Voltammetry (CV) testing at a scan rate of 100 mV s-1Under long-time circulation, iridium filaments are continuously dissolved, and dissolved particles are slowly deposited on the working electrode to synthesize IrO2-CoPi-CNTs material. Wherein CoPi is selected30cyc-CNTsPreparation of IrO as primer2-CoPi-CNTs material, and the number of cycles scanned during deposition were also compared, and 10000 cycles (10000 cyc), 12000 cycles (12000 cyc) and 14000 cycles (14000 cyc) were set, respectively. Is named IrO2-CoPi-CNTs-10000cyc、IrO2-CoPi-CNTs-12000cyc and IrO2-CoPi-CNTs-14000cyc。
4. IrO2Preparation of CNTs Material
(1) Preparation of deposition solution
Separately weighing quantitative disodium ethylene diamine tetraacetate cobalt salt hydrate (C)10H20CoN2Na2O12) Boric acid (H)3BO3) And sodium hypophosphite (NaH)2PO2) The reagent was put in a beaker, ultrapure water was added thereto, and a sedimentation solution (C) having a concentration of 0.03M was prepared in a volumetric flask10H20CoN2Na2O12、H3BO3And NaH2PO2Both concentrations were 0.03M).
(2) Synthesis of IrO by electrodeposition2-CNTs materials
Using a three-electrode system, a pre-formed CNTs electrode was used as the working electrode, an iridium wire (Ir wire) as the counter electrode and a Saturated Calomel Electrode (SCE) as the reference electrode were placed in a device containing 0.5M sulfuric acid deposition solution. Setting the potential from-0.6 to-1.2V using Cyclic Voltammetry (CV) testing at a scan rate of 100 mV s-1Under long-time circulation, iridium filaments can be continuously dissolved, so that dissolved particles are deposited on the working electrode to synthesize IrO2-CNTs material. Wherein, the number of cycles of cyclic scanning during deposition is compared with that of IrO2-CoPi-CNTs composites were prepared for the same number of turns: 10000 cycles (10000 cyc), 12000 cycles (12000 cyc) and 14000 cycles (14000 cyc) and are named IrO2-CNTs-10000cyc、IrO2-CNTs-12000cyc and IrO2-CNTs-14000cyc。
As shown in fig. 1, materials deposited at different cop turns exhibit different morphologies. As shown in the (a-c) diagram, CNTs become thicker and thicker as the number of synthetic deposition turns increases. IrO is shown in (d-f)2The particles on the surface of the-CoPi-CNTs composite material are represented by uniformly dispersed bright points, which are different from the morphology of the CoPi-CNTs composite material. And with the increase of the number of the deposition turns, the particles on the surface of the composite material are changed from small to large, and after the number of the deposition turns reaches a certain value, certain agglomeration and growth trend are generated. While it is apparent from FIG. 1 (g-i) that the deposition of material on CNTs without CoPi priming modification is not substantially different, it can be seen that the surface is loaded with non-particulate matter and there is a significant tendency for flake growth and agglomerate growth with increasing number of turns. Therefore, by comparing the SEM images of the composite materials, it can be seen that CNTs modified with CoPi primer have a certain function of regulating the morphology of the subsequent deposited materials.
FIG. 2(a) is a TEM image of CoPi-CNTs composite, and it can be seen that some substances are loaded on the surface of the carbon nanotubes, and it can be seen from the inserted high resolution image (HRTEM) that these substances are amorphous materials without clear lattice fringes. By FIG. 2(b) IrO2-CNTs and FIG. 2(c) IrO2Comparison of-CoPi-CNTs, it can be seen that: IrO2The CNTs (b picture) are attached with flaky substances on the surface, and particles with higher contrast are agglomerated on the surface of the carbon nano tube. And IrO of FIG. 2(c)2The CoPi-CNTs composite material shows that the particles are uniformly dispersed on the carbon nanotubes, and the scanning transmission image (STEM) and the corresponding element distribution diagram show that the high-brightness particles have high compatibility with C, O, Co, P and Ir. IrO2The TEM image of FIG. 2(d) and the HRTEM image of FIG. 2 (e-f) of the CoPi-CNTs composite show two phases: one of the phases is amorphous and the other phase is a crystalline phase with lattice fringes. The spacing of these lattice fringes is 0.258 nm, 0.223 nm and 0.318 nm, respectively, corresponding to IrO2(101), (200) and (110). By pairing IrO2Transmission electron microscopy analysis of-CoPi-CNTs material, Ir is indeed supported on CoPi-CNTs material in electrochemical deposition and enables uniform deposition on carbon nanotubes with CoPi loading. Also by the measurement of the content of ICP element, Ir was determined to be 0.41 wt%, which also indicates from another point of view that the composite material synthesized by electrodeposition of noble metal wire (Ir wire) had better properties than the composite materialLow Ir content.
IrO is shown in FIG. 3 (a)2Two spin orbitals are observed in the high-resolution XPS spectrum of Co 2p in the-CoPi-CNTs composite material and are respectively classified as Co 2p3/2And Co 2p1/2Their binding energy was slightly increased compared to CoPi-CNTs. Co can be separated by spectrum peak separation of Co 2p3+(780.0 and 795.6 eV), Co2+(781.6 and 797.5 eV) and satellite peaks (786.1 and 803.2 eV). Analysis from the figure, in combination with IrO2Then, IrO2the-CoPi-CNTs composite material shows higher Co2 +/Co3+The intensity ratio of (a). Importantly, the P2P spectrum of FIG. 3 (b) exhibits one P-O peak, and the CoPi-CNTs composite and IrO are compared2The P-O peak of the-CoPi-CNTs composite, found to move from the peak position 133.3eV to 134.6eV, to a higher energy level, suggesting the electron donating ability of phosphorus. In contrast, IrO is shown in FIG. 3 (c) Ir 4f2-CoPi-CNTs composite and IrO2Compared with CNTs composite materials, the CNTs composite materials have a remarkable tendency to move to a low level. The peak separation is carried out on the Ir 4f spectrogram, corresponding to Ir4+(63.2 and 66.1 eV) and Ir3+(62.3 and 65.2 eV). Analysis gave IrO grown on a substrate with CoPi bridges2Ir in-CoPi-CNTs composite material4+To Ir3+The change shows that the existence of CoPi can obtain more IrO of low-price Ir2. The binding ability of the lower-priced Ir to hydrogen is slightly enhanced. Thus, XPS results indicate that IrO2The Co or Pi group in-CoPi-CNTs will react towards IrO2Providing electrons. The regulation of such electronic structures may significantly improve IrO2HER electrocatalytic properties of CoPi-CNTs composites.
The following are electrochemical performance tests, all of which are at 0.5M H2SO4Completed in solution environment, the test equipment was Shanghai Chenghua electrochemical workstation (CHI 760). Under room temperature, a three-electrode system is utilized [ wherein a glassy carbon electrode modified by a catalyst is used as a working electrode, a graphite electrode is used as a counter electrode, and SCE is used as a reference electrode (SCE is calibrated according to a reversible hydrogen electrode calibration, 0.5M H)2SO4In ERHE=ESCE+0.267+0.059pH) ]. 0.5M H before testing2SO4Gas saturation was achieved with a stream of high purity nitrogen gas over a period of 30 minutes to eliminate interference from other gases. Linear voltammetry (LSV) test of the polarization curve (sweep rate of 5 mV s)-1). Test conditions of CV curve: the test voltage range is 0.1-0.3V vs. RHE, different sweep rates are cycled: 20. 40, 80, 160 and 200 mV s-1. And alternating current impedance (EIS) curve testing: under the open circuit voltage, the test frequency is 0.01 Hz-100 kHz, and the amplitude is 5 mV. And the stability of the material was assessed by chronoamperometry (i-t) overpotential η = 100 mV vs. RHE. Transition frequency (TOF) testing: according to TOF = I/(2 nF);
wherein, I represents 0.5M H2SO4Current density of the LSV curve measured in (a); f represents the Faraday constant (C mol)-1) (ii) a n is the number (mol) of active sites of the catalyst. To obtain n, the CV test was performed in 1M PBS solution at a test voltage ranging from-0.2 to 0.6V (vs. RHE) at a sweep rate of 50 mV s-1Dividing the integral area in the whole potential range by 2 and then dividing by a Faraday constant to obtain the number of active sites of the sample; 1/2 shows that the entire HER process requires two electrons to generate one hydrogen molecule.
The LSV test was performed on CoPi-CNTs composites deposited at different cycles in an acidic medium, and the corresponding polarization curves were obtained by plotting, as shown in FIG. 4 (a). The LSV curve can be used for evaluating the activity of the catalyst, and the smaller the overpotential is, the more excellent the hydrogen evolution catalytic activity of the catalyst is represented by comparing the corresponding overpotentials at the same current density. By comparing CNTs and CoPi20cyc-CNTs、CoPi30cyc-CNTs and CoPi40cycCNTs composite material, it being possible to find, CoPi30cycThe CNTs composite material shows excellent hydrogen evolution performance in a comparison material, and the current density is 10 mA cm-2The lowest overpotential (410 mV) is shown below. The Tafel slope (Tafel slope) obtained by the LSV curve treatment is shown in fig. 4 (b): CoPi20cyc-CNTs、CoPi30cyc-CNTs and CoPi40cycThe Tafel slope of the-CNTs composite material is 162 mV dec-1、151 mV dec-1And 159 mV dec-1. Can seeOut of CoPi synthesized by 30-turn electrodeposition30cycthe-CNTs composite material is a substrate material with excellent HER performance, so that the subsequent CoPi-CNTs composite material is a catalyst synthesized under the synthesis condition.
As can be seen from FIG. 5 (a), with IrO2Increase in the number of electrodeposition cycles of CoPi-CNTs at a current density of 10 mA cm-2The lower overpotential increases first and then decreases, and the optimal overpotential (only 29 mV) is generated at 12000 circles. IrO can be obtained from FIG. 5 (b)2-CoPi-CNTs-10000cyc、IrO2-CoPi-CNTs-12000cyc and IrO2The Tafel slope of the-CoPi-CNTs-14000 cyc composite material is 105 mV dec-1、27 mV dec-1And 38 mV dec-1. Therefore, the catalyst synthesized under the deposition condition of 12000 circles has excellent catalytic performance, so that the subsequent IrO2the-CoPi-CNTs composite material is a catalyst synthesized under the synthesis condition.
As can be seen from FIG. 6 (a), IrO2the-CoPi-CNTs composite material has higher catalytic activity (10 mA cm)-2The overpotential at this time is only 29 mV) is comparable to commercial Pt/C. And through comparison, the IrO is simply deposited2Obtained IrO2the-CNTs composite material has better performance than CoPi-CNTs, and may suggest IrO2Is the active center catalyzed by the material. IrO is seen from FIG. 6 (b)2Tafel slope excellence (27 mV dec) of-CoPi-CNTs composite-1) With commercial Pt/C (30 mV dec)-1) And (4) the equivalent. IrO can be inferred from the mechanism of electrocatalytic hydrogen evolution under acidic conditions2the-CoPi-CNTs composite material is subjected to hydrogen evolution through a Volmer-Tafel step, namely two adjacent hydrogen active intermediates are combined to form a hydrogen desorption rate-limiting step. And CNTs, CoPi-CNTs and IrO2CNTs and other composite materials are subjected to hydrogen evolution through a Volmer-Heyrovsky step, namely a hydrogen active intermediate is combined with a free hydrogen ion to form a rate-limiting step. FIGS. 2-6 (c) are comparisons with other reported catalysts and can be seen at a current density of 10 mA cm-2Lower IrO2the-CoPi-CNTs composite material shows the characteristic of more excellent electro-catalytic performance at lower loading.
By usingCyclic Voltammetry (CV) test and the value of electrochemical double layer capacitance (C)dl) The calculation is performed. CV testing (20 mV s) at different sweep rates-1、40 mV s-1、80 mV s-1、160 mV s-1And 200 mV s-1) Obtaining a CV standard curve and calculating to obtain CdlAs in fig. 7. CdlThe larger the effective active area of the corresponding catalyst. IrO is shown in FIG. 6 (d)2-CoPi-CNTs composite material having maximum CdlValue (15.4 mF cm-2) Higher than CoPi-CNTs (2.4 mF cm)-2) And IrO2- CNTs (6.5 mF cm-2) A composite material. Thus, IrO will be explained2the-CoPi-CNTs composite material has a large active area. Consistent with the results in FIG. 1, the particles are uniformly dispersed on the surface of CNTs, and have a larger and more desirable active area.
Long-term cycle stability of a catalyst is also one of the important indicators for evaluating HER activity of a catalyst. There are generally two methods to assess the stability of a material: firstly, a timing current method is utilized to give a certain voltage and observe the change of current density along with time; and secondly, after the LSV is circulated for a certain time or a certain number of times, the LSV before and after the circulation is tested, and the performance attenuation condition is compared.
As can be seen from FIG. 6 (e), IrO was tested for 100h at a higher overpotential of 100 mV (vs. RHE) in acidic media2the-CoPi-CNTs composite material shows a relatively smooth current density with time, and no obvious change. In addition, the material after 100h stability test was subjected to LSV test, as shown in FIG. 6 (f), and found to be almost the same as before the cycle, indicating that the IrO synthesized in this experiment2the-CoPi-CNTs composite material has excellent long-term cycling stability in an acidic environment. The samples after this stabilization test were also topographically characterized. As shown in fig. 8, both SEM and TEM images can be seen to have similar particles and uniform dispersion as before the stability test. The material has excellent stability.
Electrochemical Impedance (EIS) tests were performed on the different composites and, as shown in fig. 9, the circuit diagram shown in the inset was used to simulate the solid-liquid interface with good fit of the experimental data. In the nyuquiIn the Stutt diagram, the x-intercept of the high frequency region is generally equal to the solution resistance (R)s) And correspondingly. Charge transfer resistance (R)ct) The linear part of the low frequency region is a diffusion resistance (R) in accordance with the semicircular diameter of the high frequency regiond) The impedance parameters are shown in table 1. Lower RctThe values indicate that it has a faster surface charge transfer rate and a higher reaction rate in electrocatalytic kinetics. Larger CdlValues correspond to higher active surface areas, which can strongly contribute to improved HER performance. This may be IrO2The main reason why CoPi-CNTs are most active in all catalysts. In summary, IrO2The composite material combined with the CoPi-CNTs can effectively improve and enhance the charge transfer capability in the electrochemical dynamics of the catalyst.
The switching frequency (TOF) refers to the conversion of the number of reactive molecules per active site of the catalyst per unit time. The larger the value of TOF, the stronger the catalytic activity of the catalyst. To evaluate the intrinsic HER performance of the catalysts, CNTs, CoPi-CNTs, IrO2-CNTs and IrO2the-CoPi-CNTs composites were subjected to TOF tests in 1M phosphate buffered saline (PBS, pH = 7). As shown in FIG. 10, the CV curves measured in 1M PBS were obtained. By calculation, TOF results as shown in fig. 11 were obtained. FIG. 11 (a) shows CNTs, CoPi-CNTs and IrO obtained by calculation2-CNTs and IrO2TOF curve of-CoPi-CNTs composite, it can be seen that IrO2the-CoPi-CNTs composite material has a larger TOF value. By contrast, as shown in fig. 11 (b), when TOF = 0.8 s-1CNTs, CoPi-CNTs, IrO2-CNTs and IrO2the-CoPi-CNTs composite material has overpotential of 540 mV, 348 mV, 237 mV and 73 mV respectively. In FIG. 11 (c), TOF values were compared with the same potential to find IrO2the-CoPi-CNTs composite material has larger TOF value, and CoPi and IrO2The TOF of the material recombination is much larger than the TOF values of both. This also suggests that CoPi and IrO2Of bothCompounding has the potential to synergistically promote HER performance.
The key steps of the reaction under the acidic condition are further researched by utilizing a Density Functional Theory (DFT) calculation method. Considering the supporting role of carbon nanotube in the experiment, three atom models [ i.e., (1 × 2) -IrO ] were established in the experiment2(110) Polyhedral CoPi cluster and IrO2-CoPi interface]. Stoichiometry IrO2 (110) Surface [ s-IrO2 (110)]Is one of the main reaction interfaces. As shown in FIG. 12 (a), the flat plate model of the ball stick is (1X 2) -IrO2(110). DFT calculation results show that hydrogen ions can coordinate with 2 coordinate bridge oxygen, 3 times coordinate surface oxygen and 5 coordinate unsaturated iridium (O)br、OsurfAnd Ircus) Atoms interacting with each other and attaching to the surface, binding energy (Δ E)b) Respectively-0.78, +0.34 and-0.45 eV. Studies have also shown that hydrogen reacts with O on the surfacebr/IrcusThe binding between atoms dominates the kinetics of the pairing strength being negative, resulting in a H-terminal surface at pH 0. Wherein s-IrO2(110) Surface 5-coordinated unsaturated iridium (Ir)cus) Atom as the major active site (Δ G)H* = 0.29 eV), close to the most common Pt (111) (ag)H* = 0.08 eV). Unfortunately, the 2-coordinate coordinating bridge oxygen site has a very negative Δ GH* (as low as-0.61 eV). The more negative gibbs free energy of hydrogen adsorption can hinder the diffusion of H intermediates, leading to slow reaction kinetics. And hydrogen atom to 3 times coordinated surface oxygen (O)surf) Weak chemical interaction between sites (Δ E)b) At +0.34 eV) breaks the surface lattice and limits hydrogen adsorption. Thus, IrO2The performance of the catalyst on the hydrogen evolution performance of an acidic medium is not excellent.
For comparison, a hydrogen evolution model of CoPi was calculated. The upper bluish octahedron and pink tetrahedron in FIG. 12 (a) are structural models of CoPi. The proton can be respectively linked with 2-coordinate oxygen and 3-fold coordinate oxygen (O)2c、O3c) Adsorption to the surface (Δ E) by binding to hydroxyl sitesb0.57, -0.12 and-0.91 eV, respectively), most protons tend to adsorb at hydroxyl sites to generate H2And (3) O molecules. Due to Co-OH2Tend to oxidize and deprotonate to Co-OH, even Co = O, so these H' s2The O molecule is easy to decompose. And adjacent O2cAnd O3cThe site has moderate free energy (Δ G) due to itsH* = 0.26eV, +0.27eV) to H*Migration of the intermediate. Thus, the CoPi nanoparticles act as a water dissociation promoter and H*And (4) intermediate transferors.
IrO is to be mixed2The complex structure formed after the connection with the CoPi is shown in fig. 12 (a). The phosphate species may be related to IrO2 (110) Incorporating one or two O-Co bonds on the face and bridging the Co-oxide and IrO2. Interestingly, as shown in FIG. 12 (b), the bonded IrcusAnd their nearby Co and P atoms will differ in their projected state density (PDOS). This variation is associated with different PDOS of these atoms, which are a function of coordination. IrO2The 2P band of the P atom in the CoPi compound is much deeper than the 2P band of the isolated CoPi cluster, and about 0.30 e is transferred from the P atom to IrcusA site. This structure further prevents IrO2To (3) is performed. Since the bridged phosphate is an electron donor, IrO2The HER catalytic activity of the-CoPi compound is greater than that of the isolated CoPi or IrO2The catalyst is high because the active sites possess more thermally neutral hydrogen adsorption. In this regard, different hydrogen adsorption sites are compared as shown in FIG. 12 (c-g) at IrO2Unsaturated Ir of CoPicusΔ G of hydrogen adsorption of sitesH*More preferably, the optimum value is about-0.13 eV. We attribute this apparent change to charge transfer IrO by bonding to phosphate2The interface of the matrix changes the surface charge distribution of their neighboring molecules.
According to the above results, binding to HER [ H ] in acidic media+Ion adsorption to form H*Intermediate (Volmer step), IrO2-CoPi at the interface H*Diffusion or transfer and hydrogen generation (Tafel step or Heyrovsky step)]By the reaction route of (1), we are IrO2The reactive pathway of CoPi-acidic HER designed the Volmer-Tafel mechanism (FIG. 12 (h)). First, hydrogen ions are anchored on the surface of the CoPi cluster at the hydroxyl sites to generate H2O molecule andsuitable adsorption energy for IrO2Unsaturated Ir of CoPicusA site. H generated by effective decomposition of HO-H immediately after CoPi nanocluster*Intermediate, H*Will pass through the adjacent O2cAnd O3cIrO with site migration to nearby2A catalyst site. Co under the action of hydrogen adsorption on adjacent O/OH ligands3+ Reduction of sites to Co2+Then, with transfer of hydrogen, Co2+ Reoxidation of sites to Co3+. Finally, two adjacent hydrogen atoms combine to form H2And is desorbed. Thus, this heterostructure supports H2Is generated. This heterogeneous system opens new lines of thought for covalently bridging different catalytically active species in HER electrocatalysts.
In summary, the present embodiment utilizes the electrodeposition method to reduce the content of IrO2 (Ir loading is 0.41 wt%) IrO obtained by combining with CoPi-CNTs and regulating and controlling electronic structure2the-CoPi-CNTs catalyst achieves HER performance comparable to Pt. The composite material exhibits excellent HER performance: lower overpotential (at 10 mA cm)-2Current density of 29 mV), lower Tafel slope (27 mV dec)-1) And the catalyst has good catalytic cycle stability in an acidic medium. In addition, DFT calculations indicate that the phosphate (P/O bridge) of CoPi-CNT binds Co-oxide to IrO2Particles are connected to prevent IrO2Further agglomeration effect of the particles, thereby obtaining better Delta GH*The value (-0.13 eV) promotes the release of hydrogen. XPS results show that Pi and IrO2The charge transfer between them can affect the intrinsic activity of the catalyst. The compound has excellent catalytic performance and benefits from IrO2(Excellent hydrogen adsorption energy) with CoPi-CNTs (strongly cleaving HO-H bonds and providing abundant H*Intermediates) are used. These findings increase the possibilities of Ir application in HER and provide a new strategy for different active species to synthesize low cost, high performance Pt-free electrocatalysts via covalent bridging to improve HER performance.
The above disclosure is only for the purpose of illustrating the preferred embodiments of the present invention, and it is therefore to be understood that the invention is not limited by the scope of the appended claims.
Claims (6)
1. A noble metal iridium hydrogen evolution electrocatalyst is characterized in that the preparation process comprises the following steps:
(1) loading a carbon carrier on the conductive substrate to obtain a conductive substrate loaded with the carbon carrier;
(2) forming the conductive matrix loaded with the cobalt-based phosphate-carbon carrier by an electrodeposition method by using the conductive matrix loaded with the carbon carrier obtained in the step (1) as a working electrode, a graphite rod as a counter electrode and an aqueous solution containing a cobalt salt precursor and a phosphorus precursor as a deposition solution;
(3) and (3) forming the conductive matrix loaded with the iridium oxide-cobalt base phosphate-carbon carrier by an electrodeposition method by using the conductive matrix loaded with the cobalt base phosphate-carbon carrier obtained in the step (2) as a working electrode, an iridium wire as a counter electrode and sulfuric acid as a deposition solution.
2. The noble metal iridium hydrogen evolution electrocatalyst according to claim 1, characterized in that: in the step (1), the conductive matrix is one or a combination of glass carbon, platinum, titanium, copper, iron and nickel.
3. The noble metal iridium hydrogen evolution electrocatalyst according to claim 2, characterized in that: the conductive substrate is glassy carbon, the glassy carbon is firstly wiped clean by cotton wetted by alcohol, polishing is carried out by adopting polishing powder, finally polishing is carried out by adopting polishing cloth, after polishing is finished, the conductive substrate is sequentially placed in ultrapure water and alcohol solution for ultrasonic treatment, and the surface is dried by blowing.
4. The noble metal iridium hydrogen evolution electrocatalyst according to claim 1, characterized in that: in the step (1), the carbon carrier is dispersed in a solvent to prepare a uniformly dispersed suspension, the suspension is dripped on the conductive matrix, and the conductive matrix loaded with the carbon carrier is obtained after natural drying.
5. The noble metal iridium hydrogen evolution electrocatalyst according to claim 1, characterized in that: the carbon carrier is carbon black, carbon nano tube or graphene.
6. Use of the noble metal iridium hydrogen evolution electrocatalyst according to any one of claims 1 to 5 in the production of hydrogen by electrolysis of water.
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