SDC electronic conductivity becomes significant at >650oC. This drops OCV. Other things can affect your measured OCV, such as poor sealing. If your electrodes have other reactions going on, it also affect the OCV.

"SDC electronic conductivity becomes significant at >650oC."

It is true only for the anode side and not true for the cathode side.

Theoretically, the OCV should be changed during electrode degradations.

The problem is that the changing in the OCV during electrode degradations has never been reported.

M.Liu published a paper 20 years ago about the effect of electrode on OCV measurement. You can google it up.

Using Scopus, I searched a paper written by Liu, Meilin.

He wrote too many reports.

I published the unchanged OCV during electrode degradations in 1996.

The OCV measurement is the easiest experiment, but they cannot explain the unchanged OCV during electrode degradations.

There will as pointed out by several responses to your question be leak currents. As temperature exceeds 600 C electronic conductivity in CGO (or CSO) becomes significant leading to a reduced OCV and parasitic consumption of fuel if the material is used as electrolyte in an SOFC. This is well described in literature  (See e.g.  Gödickemaier, Riess). What complicates a conclusion on the importance of this, and the consequences of the electronic conductivity, is that it, besides temperature, depends on the quality of both your electrodes. If you have a "fast anode" and a "slow cathode" you introduce more electronic conductivity than if the opposite is the case. You can find a discussion of this in the following paper:

Journal of Solid State Electrochemistry 08/2006; 10(8):547-561. (Bjarke Dalslet, Peter Blennow, Peter Vang Hendriksen, Nikolaos Bonanos, Dorthe Lybye, Mogens Mogensen)      

kind regards Peter V. H.

“This voltage reduction is due to the electrode polarization and the ohmic loss in the electrolyte caused by the leak current.”

From your Riso report

From Riso, many excellent reports were published about the electrode degradations.

They cannot calculate the OCV using doped Ceria electrolyte during electrode degradations.

Why?

It is easy to notice the unchanged OCV during electrode degradations.

When the anode polarization loss is over 0.35 V, the leak current calculated by their method should be very small.

So, OCV = Vth – 0.35 V.

At 1073 K, OCV is 0.80 V (= 1.15 V – 0.35 V).

At 873 K, OCV is 0.83V (= 1.18 V – 0.35 V).

Journal of Solid State Electrochemistry 08/2006; 10(8):547-561. (Bjarke Dalslet, Peter Blennow, Peter Vang Hendriksen, Nikolaos Bonanos, Dorthe Lybye, Mogens Mogensen)

Thank you for your answers.

I read this report already in 2008.

“Anode shielding effect” is written in this paper, which is the great discovery.

When the large voltage loss (over 0.35 V) occurs, leakage currents should be stopped by the anode shielding effect.

Then, the open circuit voltage (OCV) can be unchanged during electrode degradations.

The denial of leakage currents does not deny Wagner’s model, when the large“Anode shielding effect” occurs.

Peter Vang Hendriksen cannot answer for this topic.

 I want to talk about this topic still yet.

 I am waiting for a new challenger.

Prof. Peter Vang Hendriksen must make sure by himself.

I want to talk about this topic still yet.

Views are only 212.

Prof. Peter Vang Hendriksen knows the experimental results.

Using doped Ceria electrolytes, the open circuit voltage is only 0.80 V, which was never changed during electrode degradations.

He does not want to talk about these results.

If one assumes the SOFC under open circuit is at thermodynamic equilibrium (no ionic/electronic current across the cell), the OCV is governed by the atmospheres of electrodes, that can be estimated by the Nernst Equation. But this is usually not the case, for example the cell with SDC electrolyte. By considering the short circuit current (induced by the electronic conductivity of SDC), one can estimate the OCV using the refined Nernst equation (). But it is noted that, this equation assumes the electrode processes are at thermodynamic equilibrium. The electrode resistance (caused by surface exchange and charge transfer) has never been considered. The OCV seems to be affected by the electrode resistance. By my calculation, the OCV is very close to the one by the refined Nernst equation if the electrode resistance is smaller than the ionic resistance of the SDC electrolyte. However, when the electrode resistance is very high, the OCV becomes very low. For example, the OCV is very low if the NiO anode is not reduced to Ni anode.

So, if the electrolyte is thick and the electrodes are very active, the OCV may be not changed with the degradation of electrodes.

The refined Nernst equation:

Journal of Applied Electrochemistry 31: 93±98, 2001

Calculation of the e.m.f. of solid oxide fuel cells

S.W. ZHA, C.R. XIA and G.Y. MENG

Journal of Applied Electrochemistry 31: 93, 2001.

> 

p. 97

3.3. Anodic PO2” effect

The refined Nernst equation may be

E = RT/4F ln(pO2’/ PO2*) (27)

> 

In Equation 27, the average ionic transference number is 0.92 at 1073 K.

The average ionic transference number is 0.94 at 873 K.

So, the polarization voltage loss should not be ignorable, even using Equation 27.

> 

Please calculate the average ionic transference number.

Thank you very much for a good answer.

I want to talk about this topic again.

This topic can be solved by the "anode shielding effect", which was discovered by RISO scientists (Prof. Peter Vang Hendriksen et. al.).

Due to the anode shielding effect (about 0.35 V), polarization voltage losses can be very small.

The details are written in the following report.

A Current-Independent Constant Anode Voltage Loss Using Sm-Doped Ceria Electrolytes in SOFCs

T. Miyashita

ECS Transactions 59(1):53 · September 2014

https://www.researchgate.net/publication/269866706_A_Current-Independent_Constant_Anode_Voltage_Loss_Using_Sm-Doped_Ceria_Electrolytes_in_SOFCs

(I noticed that I was talking about the anode shielding effect recently.)

Article A Current-Independent Constant Anode Voltage Loss Using Sm-D...