Method for ascertaining overvoltages in fuel cells

Patent metadata

Field	Value
Publication number	US-10637083-B2
Application number	US-201615560638-A
Country	US
Kind code	B2
Filing date	Feb 18, 2016
Priority date	Apr 23, 2015
Publication date	Apr 28, 2020
Grant date	Apr 28, 2020

Abstract

The invention relates to a method for ascertaining the overvoltage of a working electrode in a fuel cell, in which the potential of a reference electrode compared to the grounded counter electrode is measured. For the measurement, a fuel cell comprising a polymer electrolyte membrane is used, in which the counter electrode comprises a lateral edge having at least one convexly curved region, and the electrolyte membrane surface, adjoining the counter electrode, comprises an electrode-free region in which the reference electrode is disposed on the electrolyte membrane surface. In contrast, the working electrode is continuous, which is to say has a large surface. The minimum distance Lgap between the reference electrode and the edge of the counter electrode Lgap=3×Ll,r with (a) and (b), where m=ionic conductivity of the electrolyte membrane (Ω−1 cm-1), box=Tafel slope of the half cell for the electrochemical reaction of the working electrode lm=membrane layer thickness (cm) and jox0=exchange current density of the catalyst of the working electrode per unit of electrode surface in (A cm−2). This arrangement can advantageously be used to ensure that the potential measured at the hydrogen-fed reference electrode corresponds to the overvoltage of the working electrode with sufficient accuracy. The method can be applied to polymer electrolyte membrane fuel cells (PEMFC), to direct methanol fuel cells (DMFC) or to high-temperature fuel cells (SOFC).

First claim

The invention claimed is:

1. A method for ascertaining the overvoltage of a working electrode in a fuel cell, comprising a polymer electrolyte membrane, the working electrode, a counter electrode, and a reference electrode, and in which the working electrode is a continuous electrode and is disposed on one side of the polymer electrolyte membrane and the counter electrode is grounded and is disposed on the other side of the polymer electrolyte membrane, the method comprising:
measuring and comparing a potential of the reference electrode and a potential of the counter electrode in the fuel cell configured in which
the counter electrode has an outer edge spanning an entire circumference of the counter electrode along a surface of the polymer electrolyte membrane, said outer edge comprising a first portion forming a lateral edge having a convex curvature with a local radius R a and said outer edge comprising a second portion with a local radius greater than R a , so that said lateral edge forms a convexly curved tip which is more convexly curved than said second portion,
the polymer electrolyte membrane surface comprises an electrode-free region adjoining the counter electrode and opposite the working electrode, and
the reference electrode is disposed on the polymer electrolyte membrane surface in the region of the electrode-free region and in the immediate vicinity of the convex edge region of the counter electrode at a distance L gap ,
wherein the minimum distance for L gap between the reference electrode and the convexly curved edge region of the counter electrode in the region is given by

L
gap

=

3
·

L

l
,
r

⁢

⁢
where

L

1
,
r

≅

πλ
D

2

⁡

[

ln
⁡

(

67

18
⁢

(

R
a

⁢

/

⁢

λ
D

)

7
/
45

)

]

-
1

⁢

⁢
and

⁢

λ
D

=

σ
m

⁢

b
ox

⁢

l
m

2
⁢

j
ox
0

where
σ m =ionic conductivity of the polymer electrolyte membrane (Ω −1 cm −1 ),
b ox =Tafel slope of the half cell for the electrochemical reaction of the working electrode (V),
l m =polymer electrolyte membrane layer thickness (cm),
j ox 0 =exchange current density of the catalyst of the working electrode per unit of electrode surface in (A cm −2 ), and
R a =radius of the convexly curved edge region of the counter electrode (cm).

2. The method according to claim 1 , wherein the distance between the reference electrode and the convexly curved edge region of the counter electrode is selected in the range between L gap and 3 L gap , from the convexly curved edge region of the counter electrode.

3. The method according to claim 1 , wherein the reference electrode is supplied with hydrogen during the method.

4. A method according to claim 1 , wherein an anode is used as the counter electrode, and a cathode is used as the working electrode.

5. A method according to claim 1 , wherein a value between 0.01 and 1 cm is selected for the local radius of curvature of the curved edge region of the counter electrode.

6. A method according to claim 1 , wherein the fuel cell is one of a polymer electrolyte membrane fuel cell (PEMFC), a direct methanol fuel cell (DMFC), a solid oxide fuel cell (SOFC), and a high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC).

7. The method according to claim 1 , wherein the counter electrode disposed on said other side of the polymer electrolyte membrane has an outer edge spanning an entire outer periphery along a surface of polymer electrolyte membrane, and
wherein a shortest distance from a lateral edge of the working electrode to a nearest edge along said outer edge of the counter electrode is prescribed so that said nearest edge of the counter electrode does not influence the overvoltage of the working electrode in the working area of the fuel cell.

8. The method according to claim 1 , wherein the distance between the reference electrode and the convexly curved edge region of the counter electrode is selected in the range of Lgap to 100 Lgap from the convexly curved edge region of the counter electrode.

9. The method according to claim 1 , wherein the distance between the reference electrode and

Assignees

• Forschungszentrum Juelich Gmbh

Inventors

• Kulikovsky Andrei

Classifications

• H01M8/1006 Primary

  Corrugated, curved or wave-shaped MEA · CPC title

• H01M8/04552

  of the individual fuel cell · CPC title

• C25B11/00

  Electrodes; Manufacture thereof not otherwise provided for · CPC title

• H01M8/1011

  Direct alcohol fuel cells [DAFC], e.g. direct methanol fuel cells [DMFC] · CPC title

• H01M8/12

  operating at high temperature, e.g. with stabilised ZrO2 electrolyte · CPC title