CN106338459A - Method for measuring oxygen effective diffusion coefficient in fuel cell catalyst layer - Google Patents

Abstract

The invention designs a method for measuring the oxygen effective diffusion coefficient in a fuel cell catalyst layer. The method includes the steps of S1, assembling double membrane electrodes into a fuel cell; S2, detecting the limited current of the fuel cell; S3, substituting the limited current into a Fick law shown in the formula I to obtain the diffusion coefficient of an electrode layer, wherein CO2 is experiment control amount of oxygen concentration, CPt and suf are oxygen concentrations of a Pt surface, delta is the thickness of a simulation catalyst layer, and all can be obtained through experiment measurement. The method has the advantages that DCL does not contain Pt and is free of electrochemical reaction, so the mass transfer characteristic can be presented through the Fick law; the manufacturing method, material composition and CL of the DCL are completely consistent, and the mass transfer characteristic of CL can be effectively copied; by measuring the limited current, the relation between the oxygen flux and the concentration is obtained, and the effective mass transfer coefficient is calculated through the Fick law.

Description

The method of oxygen effective diffusion cofficient in measurement fuel cell catalyst layer

Technical field

The present invention relates to a kind of method measuring oxygen effective diffusion cofficient in fuel cell catalyst layer, belong to fuel cell Technical field.

Background technology

Membrane electrode includes anode catalyst layer, PEM and cathode catalysis layer.In cell operation, oxygen diffuses to In cathode catalysis layer, it is electrochemically reacted on pt surface.Therefore effective diffusion cofficient in cathode catalysis layer for the oxygen becomes One important parameter of restriction fuel battery performance.Different Memberane Electrode and condition, can obtain diffusion different Catalytic Layer, in time diffusion coefficient can be measured, to the performance evaluation of membrane electrode, all there is higher reference value.Mesh Before, oxygen obtains or directly quotes experience number in many calculating by using non-laboratory facilities of effective diffusion cofficient of Catalytic Layer Value, is difficult to the actual influence of reaction different experimental conditions.Therefore, situ method measurement diffusion coefficient has much to fuel cell test Meaning.

Content of the invention

For defect of the prior art, it is an object of the invention to provide in a kind of measurement fuel cell catalyst layer there being oxygen The method of effect diffusion coefficient.

The present invention is achieved by the following technical solutions:

In a first aspect, the invention provides a kind of bilayer membrane electrode, it includes cathode catalysis layer and is attached to described negative electrode The simulation Catalytic Layer of catalysis layer surface, the catalyst carrier group by nafion with without pt nano-particle for the described simulation Catalytic Layer Become.

Preferably, the preparation method of described simulation Catalytic Layer is identical with the preparation method of cathode catalysis layer.

Second aspect, present invention also offers a kind of be based on oxygen in aforesaid duplicature electrode measurement fuel cell catalyst layer The method of gas effective diffusion cofficient, it comprises the steps:

S1: duplicature electrode group is dressed up fuel cell；

S2: detect the carrying current of described fuel cell；

S3: described carrying current is brought in the fick law shown in formula i, obtains the diffusion coefficient of electrode layer,

$\frac{i}{4f}=d_{o2}^{eff}\frac{c_{o2}-c_{pt,suf}}{\mathrm{\δ}}---\[i\];$

Wherein, c_o2Oxygen concentration for experiment control amount, c_pt,sufFor the oxygen concentration on pt surface, δ is simulation Catalytic Layer Thickness, can be obtained by experiment measurement.

Preferably, the parallel fluid channels of the 1cm*2cm of described fuel cell.

Preferably, in step s2, detection temperature is 80 DEG C, h₂Test tolerance be 800cc/min, o₂/n₂Survey Gas testing amount is 1500cc/min.

Preferably, in step s3, specific derivation process is as follows:

Under the conditions of carrying current, the oxygen concentration on pt surface is 0, then formula i can be reduced to formula ii,

$\frac{i_{\lim }}{4f}=d_{o2}^{eff}\frac{c_{o2}}{\mathrm{\δ}}---\[ii\];$

Therefore in the case that diffusion coefficient is certain, limiting current density size is proportional with thickness of electrode inverse, accordingly Can get diffusivity expression formula iii,

$d_{o2}^{eff}=\frac{1}{4f*c_{o2}}*\frac{{\mathrm{di}}_{\lim }}{d1/\mathrm{\δ}}---\[iii\];$

By preparing the dcl of different-thickness, available i_limTo 1/ δ derivation, thus drawing the diffusion coefficient d of electrode layer^eff _o2.

Compared with prior art, the present invention has a following beneficial effect:

1st, the present invention devises a kind of experimental technique of effective diffusion cofficient in direct measurement cathode catalysis layer, with respect to ginseng Examine empirical value or estimation numerical value, more can real embodiment Catalytic Layer mass transfer feature；

2nd, the present invention addition of one layer of " simulation catalysis being made up of catalyst carbon support on the surface of cathode catalysis layer (cl) Layer " (dcl), this layer and cl have identical mass transfer characteristic, therefore, it is possible to, in the case of exclusion electrochemical reaction, isolate cl's Gas transfer characteristic；

3rd, the present invention has been firstly introduced electrochemistry experiment method, achieves in-site measurement to effective diffusion cofficient.

Brief description

The detailed description with reference to the following drawings, non-limiting example made by reading, the further feature of the present invention, Objects and advantages will become more apparent upon:

Fig. 1 carries the film electrode structure schematic diagram of dcl；

Fig. 2 electron microscope measuring electrode thickness；

Fig. 3 carrying current linear volt-ampere curve test case；

Fig. 4 is according to formula iii gained and relation curve.

Specific embodiment

With reference to specific embodiment, the present invention is described in detail.Following examples will be helpful to the technology of this area Personnel further understand the present invention, but the invention is not limited in any way.It should be pointed out that the ordinary skill to this area For personnel, without departing from the inventive concept of the premise, some deformation can also be made and improve.These broadly fall into the present invention Protection domain.

Embodiment 1

, by membrane electrode needed for electrostatic spray preparation experiment, structure is as shown in Figure 1 for the present invention.Prepare pt/c catalysis first Agent slurry, ion exchange resin adopts business nafion, and solvent is ethanol.In slurry the mass fraction of carbon be 0.39%, nafion with The mass ratio of carbon is 0.8.The slurry preparing ultrasonic vibration is used for spraying after 20 minutes.This example is existed using electrostatic spray The spray of nafion proton membrane two sides applies anode and cathode Catalytic Layer respectively, and spraying temperature is 90 DEG C, and the pt carrying capacity of anode and cathode is respectively 0.1mg/ cm².Secondly, in the dcl of the negative electrode pole Catalytic Layer trypsin method different-thickness having sprayed.In this example choose dcl thickness be 15um, 22um、30um.The thickness of dcl measures (as shown in Figure 2) by electron microscope.Material with carbon element used by dcl is the carbon of catalyst in cl Carrier, with guarantee, both have identical architectural characteristic.

In this example, battery testing temperature is 80 DEG C, and humidity is 67%.Choose and survey under 1%, 2% and 4% 3 kind of oxygen concentration Amount carrying current.Runner selected by battery is 1cm*2cm parallel fluid channels, and test tolerance is 800cc/min (h₂)、1500cc/min (o₂/n₂) to ensure that oxygen concentration is equal everywhere on membrane electrode surface.

From formula ii, limiting current density is directly proportional to oxygen concentration.Carrying current test is as shown in Figure 3.Pass through Polarization curve measurement obtains, and measures membrane electrode carbon layers having thicknesses by electron microscope, draws relation described by formula iii bent Line, result is as shown in figure 4, Catalytic Layer effective diffusion cofficient can be drawn by the slope of in figure matched curve according to formula iii.

The slope of curve and diffusion coefficient that table 1 draws according to Fig. 4

Above the specific embodiment of the present invention is described.It is to be appreciated that the invention is not limited in above-mentioned Particular implementation, those skilled in the art can make various modifications or modification within the scope of the claims, this not shadow Ring the flesh and blood of the present invention.

Claims (6)

1. a kind of bilayer membrane electrode is it is characterised in that include cathode catalysis layer and the mould being attached to described cathode catalysis layer surface Intend Catalytic Layer, the catalyst carrier by nafion with without pt nano-particle for the described simulation Catalytic Layer forms.

2. bilayer membrane electrode as claimed in claim 1 is it is characterised in that the preparation method of described simulation Catalytic Layer is urged with negative electrode The preparation method changing layer is identical.

3. a kind of based on oxygen effective diffusion cofficient in the duplicature electrode measurement fuel cell catalyst layer described in claim 1 Method is it is characterised in that comprise the steps:

S1: duplicature electrode group is dressed up fuel cell；

S2: detect the carrying current of described fuel cell；

S3: described carrying current is brought in the fick law shown in formula i, obtains the diffusion coefficient of electrode layer；

$\frac{i}{4f}=d_{o2}^{eff}\frac{c_{o2}-c_{pt,suf}}{\mathrm{\δ}}---\[i\],$

Wherein, c_o2Oxygen concentration for experiment control amount, c_pt,sufFor the oxygen concentration on pt surface, δ is the thickness of simulation Catalytic Layer Degree, can be obtained by experiment measurement.

4. bilayer film electrode structure as claimed in claim 3 measures the side of oxygen effective diffusion cofficient in fuel cell catalyst layer Method is it is characterised in that the parallel fluid channels of the 1cm*2cm of described fuel cell.

5. in duplicature electrode measurement fuel cell catalyst layer as claimed in claim 3 oxygen effective diffusion cofficient method, It is characterized in that, in step s2, detection temperature is 80 DEG C, h₂Test tolerance be 800cc/min, o₂/n₂Test tolerance be 1500cc/min.

6. in duplicature electrode measurement fuel cell catalyst layer as claimed in claim 3 oxygen effective diffusion cofficient method, It is characterized in that, in step s3, specific derivation process is as follows:

Under the conditions of carrying current, the oxygen concentration on pt surface is 0, then formula i can be reduced to formula ii:

$\frac{i_{\lim }}{4f}=d_{o2}^{eff}\frac{c_{o2}}{\mathrm{\δ}}---\[ii\];$

Therefore in the case that diffusion coefficient is certain, limiting current density size is proportional with thickness of electrode inverse, can obtain accordingly To diffusivity expression formula iii；

$d_{o2}^{eff}=\frac{1}{4f*c_{o2}}*\frac{{\mathrm{di}}_{\lim }}{d1/\mathrm{\δ}}---\[iii\];$

By preparing the dcl of different-thickness, available i_limTo 1/ δ derivation, thus drawing the diffusion coefficient d of electrode layer^eff _o2.