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CN-121994561-A - Method for measuring adsorption quantity of ionic polymer on noble metal surface in catalytic layer and application

CN121994561ACN 121994561 ACN121994561 ACN 121994561ACN-121994561-A

Abstract

The invention provides a method for measuring the adsorption capacity of an ionic polymer on the surface of noble metal in a catalytic layer, which comprises the steps of quantitatively replacing protons in the ionic polymer with selected metal cations for marking, respectively preparing the catalytic layer containing a noble metal catalyst and a pseudo-catalytic layer containing no noble metal by using the marked ionic polymer, measuring initial loading capacity of the noble metal, the ionic polymer and the selected metal cations in the catalytic layer and the pseudo-catalytic layer, respectively carrying out soaking and eluting experiments on the catalytic layer and the pseudo-catalytic layer, monitoring residual loading capacity of the selected metal cations and carrying out normalization treatment, respectively drawing normalized elution dynamics curves of the catalytic layer and the pseudo-catalytic layer, and calculating the amount of the ionic polymer specifically adsorbed on the surface of the noble metal by using a linear extrapolation method through comparing and analyzing the two curves. The method realizes nondestructive and specific quantitative characterization of the adsorption capacity of the metal-ion polymer interface, and has the advantages of clear principle, low equipment threshold and accurate result.

Inventors

  • ZHANG JIANBO
  • ZHANG YIMING
  • XIAO YEGUI

Assignees

  • 清华大学

Dates

Publication Date
20260508
Application Date
20260130

Claims (10)

  1. 1. A method for measuring the amount of ionic polymer adsorbed on the surface of noble metal in a catalytic layer, comprising the steps of: Quantitatively replacing protons in the ionic polymer with selected metal cations to obtain a marked ionic polymer; Mixing and dispersing the marked ionic polymer with a noble metal catalyst and a corresponding carrier without noble metal respectively to obtain catalytic layer slurry and pseudo catalytic layer slurry, and obtaining a catalytic layer and a pseudo catalytic layer respectively by using the catalytic layer slurry and the pseudo catalytic layer slurry; Measuring the loading amounts of noble metal, ionic polymer and metal cations in the catalytic layer; Respectively soaking the catalytic layer and the pseudo catalytic layer as samples in deionized water; Taking out samples according to a set time interval in the soaking process, and measuring residual metal cation loading in the samples after drying, wherein the residual metal cation loading of the catalytic layer and the pseudo catalytic layer is normalized by taking the loading of noble metal loading and/or ionic polymer as a reference respectively; And comparing and analyzing the two curves, and calculating the mass of the ionic polymer specifically adsorbed on the noble metal surface in the catalytic layer by using a linear extrapolation method.
  2. 2. The method of measurement according to claim 1, wherein the selected metal cation is an alkali metal ion or an alkaline earth metal ion.
  3. 3. The method of measurement according to claim 1, wherein the selected metal cation is potassium ion or cesium ion.
  4. 4. The measurement method according to claim 1, wherein the noble metal catalyst comprises a platinum group metal or an alloy thereof.
  5. 5. The method according to claim 1, wherein the thickness of the catalytic layer is not more than 10 μm and the loading of noble metal is not more than 。
  6. 6. The method of claim 1, wherein the deionized water has a resistivity of 18M Ω -cm or more and the soaking process is performed under air-tight conditions.
  7. 7. The method according to claim 1 or 6, wherein the liquid used for immersion is at a level The method meets the following conditions: Wherein For the diffusion coefficient of the metal cations in water, The soaking time is the soaking time.
  8. 8. The method according to claim 1, wherein the mass of the ionic polymer specifically adsorbed to the noble metal surface is calculated by linear extrapolation by comparing two curves, comprising: Extrapolation of the slowly linearly decreasing segment of the normalized metal cation elution kinetics curve of the catalytic layer to zero soak time yields intercept The slope of the section which is slowly and linearly reduced in the elution dynamics curve of the catalytic layer is the same as the slope of the elution dynamics curve of the normalized metal cations of the pseudo catalytic layer, and the initial normalized metal cation loading of the catalytic layer is recorded as The mass ratio of the ionic polymer adsorbed on the noble metal surface is: and obtaining the mass of the ionic polymer adsorbed on the noble metal surface according to the mass ratio and the loading of the ionic polymer.
  9. 9. The method according to claim 1, wherein the loading of the noble metal and the metal cation is measured using X-ray fluorescence spectroscopy, inductively coupled plasma mass spectrometry, or atomic absorption spectrometry, and the loading of the ionomer is determined based on the mass ratio of the ionomer to the noble metal and the measured loading of the noble metal.
  10. 10. Use of a measurement method according to any one of claims 1 to 9 for characterizing the performance of a catalytic layer of a proton exchange membrane fuel cell or an electrolyzed water apparatus.

Description

Method for measuring adsorption quantity of ionic polymer on noble metal surface in catalytic layer and application Technical Field The invention belongs to the technical field of quantitative characterization of porous electrode interfaces, and particularly relates to a quantitative measurement method and application of ionic polymer adsorption capacity on a metal surface in a catalytic layer. Background In the catalytic layer of proton exchange membrane fuel cell, water electrolysis, etc., the ionic polymer (such as perfluorinated sulfonic acid ionic polymer) adsorbed on the surface of catalyst metal (such as platinum) forms nanometer thin layer, and the interface structure directly dominates electrochemical reaction, proton conduction and gas transmission processes, so that the interface structure is a key mesostructure for determining the performance and durability of the device. It is particularly important that the adsorption state properties of the ionic polymer at the metal surface are significantly different from bulk material properties of the bulk, due to the strong specific interactions between the ionic polymer and the noble metal catalyst. Therefore, the ion polymer adsorption quantity on the noble metal surface is accurately quantized, and the ion polymer adsorption quantity becomes a core premise for analyzing the structure-activity relationship of the catalytic layer and optimizing the electrode structure. However, the non-destructive and quantitative characterization of this critical parameter has remained a significant challenge to date. The prior art can be mainly divided into two types, but important limitations exist in the prior art: 1. off-line, phase-average characterization techniques, represented by small angle neutron scattering. For example, harada et al, a Toyota Central research and development laboratory, used contrast-changing small angle neutron scattering to distinguish "adsorbed" from "deposited" ionomers on carbon particles and extrapolate the adsorbed layer thickness (51A) [1]. However, the method depends on national large neutron source equipment, is rare in machine time and has extremely high cost. More importantly, the signal reflects the statistical average of the bulk structure of the material, and is difficult to specifically decouple and accurately quantify the adsorption of the local area of the metal surface. 2. Tomographic imaging techniques, typically frozen transmission electron microscope tomography. Girod et al have recently adopted deep learning assisted cryoelectron tomography to achieve three-dimensional nanoimaging [2] of all components (carbon, platinum, ionomer) of the catalytic layer for the first time. The work reveals key information such as morphology, coverage rate and the like of the ionic polymer network, and is a major breakthrough in the field. However, the method has the defects that (a) electron beam irradiation damage is that even under the high vacuum freezing condition (98K), the thickness loss of the ionic polymer film still occurs by 10-40%, the observation result is not completely lossless, and (b) the sample preparation and imaging are extremely complex, namely the method relies on ultrathin section, complex image acquisition and time-consuming deep learning segmentation reconstruction flow, and does not have the universality of high-throughput analysis. In summary, no matter the scattering technology relying on statistical average or the imaging technology pursuing high resolution, the existing advanced method can not realize nondestructive and quantitative analysis of the adsorption amount of the ionic polymer on the noble metal surface. Therefore, developing a method capable of carrying out nondestructive, specific and quantitative characterization on the adsorption quantity of the ionic polymer on the surface of the noble metal has become a technical problem to be solved in the field. Reference is made to: [1] Harada M, Takata S, Iwase H, et al. Distinguishing adsorbed and deposited ionomers in the catalyst layer of polymer electrolyte fuel cells using contrast-variation small-angle neutron scattering[J]. ACS omega, 2021, 6(23): 15257-15263. [2] Girod R, Lazaridis T, Gasteiger H A, et al. Three-dimensional nanoimaging of fuel cell catalyst layers[J]. Nature catalysis, 2023, 6(5): 383-391. Disclosure of Invention The invention aims to at least solve one of the technical problems in the background art, and provides a method capable of carrying out nondestructive and quantitative measurement on the adsorption quantity of ionic polymer on the surface of noble metal in a catalytic layer. The method has the advantages of clear principle and simple and convenient operation through chemical displacement marking and elution kinetics differential analysis, and provides a brand new characterization tool for accurately analyzing the metal-ion polymer interface structure in the catalytic layer. In order to achieve the above purpose, the pres