Influence of a passive layer on the kinetics of nitric acid reduction

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Tribollet, V. Vivier

To cite this version:

M. Benoit, C. Bataillon, B. Gwinner, F. Miserque, C. Sanchez-Sanchez, et al.. Influence of a passive layer on the kinetics of nitric acid reduction. EIS 2016 - 10th International Symposium on Electro-chemical Impedance Spectroscopy, Jun 2016, A Toxa, Spain. �cea-02442336�

Marie Benoit1*_{, Christian Bataillon}2_{, Benoît Gwinner}1 _{; Frédéric}

Miserque2_{, Carlos M. Sanchez-Sanchez}3_{, Bernard Tribollet}3_{, Vincent}

Vivier3**

1_{CEA, DEN, DANS, DPC, SCCME, Laboratoire d’Etude de la Corrosion Non Aqueuse, F-91191}

Gif-sur-Yvette, France. *marie.benoit@cea.fr

2_{CEA, DEN, DANS, DPC, SCCME, Laboratoire d’Etude de la Corrosion Aqueuse, F-91191 Gif-sur-Yvette,}

France.

3_{Sorbonne Universités, UPMC Univ Paris 06, CNRS, Laboratoire Interfaces et Systèmes}

Electrochimiques, 4 place Jussieu, F-75005, France. **vincent.vivier@upmc.fr

Concentrated nitric acid environment

Use of stainless steel as materials for containing concentrated nitric acid (passive materials with good corrosion/dissolution resistance in oxidizing media)

Nitric acid

Stainless Steel 304L

Spent nuclear fuel

Concentrated nitric acid environment

Use of stainless steel as materials for containing concentrated nitric acid (passive materials with good corrosion/dissolution resistance in oxidizing media)

Nitric acid

Stainless Steel 304L

Spent nuclear fuel

Areva La Hague PUREX process

However, for the prediction of

the lifetime of the equipment,

it is essential to know the

corrosion mechanisms and

e- Fe Cr Ni Nip+ Crm+ Fen+ HNO2 HNO3 Stainless Steel medium Anodic process: oxidation of material Cathodic process: medium reduction

e- Fe Cr Ni Nip+ Crm+ Fen+ HNO2 HNO3 medium Anodic process: oxidation of material Cathodic process: medium reduction

4 to 8 M HNO3  highly concentrated acidic solution

The kinetics of these two processes can be characterized by their current density

Stainless Steel

Anodic process: oxidation of material Cathodic process: medium reduction j E

Active domain Passive domain Transpassive domain Nanometric passive layer acier FeIII _CrIII e- Fe Cr Ni Nip+ Crm+ Fen+ HNO2 HNO3 Stainless Steel medium

Anodic process: oxidation of material Cathodic process: medium reduction j E

Active domain Passive domain Transpassive domain

Nanometric passive layer

acier

FeIII _CrIII

4 to 8 M HNO3  highly concentrated

e- Fe Cr Ni Nip+ Crm+ Fen+ HNO2 HNO3 Stainless Steel medium

Anodic process: oxidation of material Cathodic process: medium reduction j E

Active domain Passive domain Transpassive domain Nanometric passive layer acier FeIII _CrIII e- Fe Cr Ni Nip+ Crm+ Fen+ HNO2 HNO3 Stainless Steel medium

Anodic process: oxidation of material Cathodic process: medium reduction j E

Active domain Passive domain Transpassive domain

E_corr

4 to 8 M HNO3  highly concentrated acidic solution e- Fe Cr Ni Nip+ Crm+ Fen+ HNO2 HNO3 Stainless Steel medium

Anodic process: oxidation of material Cathodic process: medium reduction j E

Active domain Passive domain Transpassive domain

E_corr

corrosion products increase reaction rate

e- Fe Cr Ni Nip+ Crm+ Fen+ HNO2 HNO3 Stainless Steel medium

Mechanisms of nitric reduction:

Kinetics of nitric reduction:

gold stainless steel

[D. Sicsic et al., Eur. J. Inorg. Chem., 2014]

[R. Lange et al., Electrochem. Com. 2013] [F. Balbaud et al., Eur. J. Inorg. Chem.,2000]

e

-HNO₂ HNO₃

Gold

e

-HNO₂ HNO₃

Gold

medium

e

-HNO₂ HNO₃

Gold

medium

4 to 8 M HNO3  highly concentrated acidic solution

e

-HNO₂ HNO₃

Gold

medium

4 to 8 M HNO3  highly concentrated acidic solution

 oxidizing media

j

E

Active domain Passive domain Transpassive domain

[Thèse E. Tcharkhtchi, 2014]

Nanometric passive layer

The study of the medium reduction was done on inert material EV/ENH 1,15 0,90 0,60 0,20 Vetter Schmid

e

-HNO₂ HNO₃

Gold

medium

4 to 8 M HNO3  highly concentrated acidic solution

 oxidizing media

j

E

Active domain Passive domain Transpassive domain

[Thèse E. Tcharkhtchi, 2014]

Nanometric passive layer

The study of the medium reduction was done on inert material EV/ENH 1,15 0,90 0,60 0,20 0,05 Vetter Schmid

4 to 8 M HNO3  highly concentrated acidic solution

e

-HNO₂ HNO₃

Gold

medium

4 to 8 M HNO3  highly concentrated acidic solution

 oxidizing media

j

E

Active domain Passive domain Transpassive domain

[Thèse E. Tcharkhtchi, 2014]

Nanometric passive layer

The study of the medium reduction was done on inert material EV/ENH 1,15 0,90 0,60 0,20 Vetter Schmid

4 to 8 M HNO3  highly concentrated

e- Fe Cr Ni Nip+ Crm+ Fen+ HNO2 HNO3 Stainless Steel medium V. Razygraev [1] + F. Balbaud [2]:

Mechanisms in competition on stainless steel R. Lange [3]: Schmid dominates on stainless steel

HNO_{2,sol → HNO2,ads}

HNO_2,ads + e- _{+ H}+ _{→ NO}

ads + H2O

NO_ads +1₂H+ + 1₂NO₃− + 1₂H₂O → 3₂HNO_{2,𝑠𝑠𝑠𝑠𝑠𝑠} Schmid’s mechanisms:

RDE results

EIS results

-0,5 -0,4 -0,3 -0,2 -0,1 0,0 -200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 J( mA /c m² ) E-E° (V) ω = 30 rpm - exp ω = 50 rpm - exp ω = 70 rpm - exp ω = 100 rpm - exp ω = 150 rpm - exp 0 5 10 15 20 25 30 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 - I m (Z ) (o h m ) Re(Z) (ohm) exp f = 50 kHz f = 100 Hz f = 1 Hz f = 10 mHz 50 rpm Autocatalytic processes Charge transfer Diffusion process Adsorption

HNO_2,sol → HNO2,ads

HNO_2,ads+ e-_{+ H}+ _{→ NO}

-0,5 -0,4 -0,3 -0,2 -0,1 0,0 -200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 J( mA /c m² ) E-E° (V) ω = 30 rpm - fit ω = 50 rpm - fit ω = 70 rpm - fit ω = 100 rpm - fit ω = 150 rpm - fit ω = 30 rpm - exp ω = 50 rpm - exp ω = 70 rpm - exp ω = 100 rpm - exp ω = 150 rpm - exp

Modelling of current and EIS

0 5 10 15 20 25 30 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 - I m (Z ) (o h m ) Re(Z) (ohm) exp f = 50 kHz f = 100 Hz f = 1 Hz f = 10 mHz 50 rpm Charge transfer Diffusion process Adsorption

HNO_2,sol → HNO2,ads

𝑖𝑖𝑆𝑆=_{2𝑘𝑘𝑘}1

2𝛿𝛿 𝐹𝐹𝐹𝐹 2𝐶𝐶 ∗_{𝐷𝐷𝑘𝑘𝑘}

-0,5 -0,4 -0,3 -0,2 -0,1 0,0 -200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 J( mA /c m² ) E-E° (V) ω = 30 rpm - fit ω = 50 rpm - fit ω = 70 rpm - fit ω = 100 rpm - fit ω = 150 rpm - fit ω = 30 rpm - exp ω = 50 rpm - exp ω = 70 rpm - exp ω = 100 rpm - exp ω = 150 rpm - exp

Modelling of current and EIS

0 5 10 15 20 25 30 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 - I m (Z ) (o h m ) Re(Z) (ohm) exp f = 50 kHz f = 100 Hz f = 1 Hz f = 10 mHz 50 rpm Charge transfer Diffusion process Adsorption 0 5 10 15 20 25 30 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 - I m (Z ) (o h m ) Re(Z) (ohm) fit exp f = 50 kHz f = 100 Hz f = 1 Hz f = 10 mHz

Good fit for low speed HNO2,sol → HNO2,ads

HNO_2,ads+ e-_{+ H}+ _{→ NO} ads+ H2O 1 𝑍𝑍𝑓𝑓 = −𝐹𝐹𝐹𝐹 𝑘𝑘2 ′_{. 𝐶𝐶} 𝑆𝑆0. 𝑏𝑏2(1 − 𝜃𝜃𝑆𝑆) − 𝑘𝑘2′. 𝐶𝐶𝑆𝑆0._{∆𝐸𝐸 + 𝑘𝑘𝑘}∆𝜃𝜃 2(1 − 𝜃𝜃𝑆𝑆)∆𝐶𝐶 0 ∆𝐸𝐸 𝑖𝑖𝑆𝑆=_{2𝑘𝑘𝑘}1 2𝛿𝛿 𝐹𝐹𝐹𝐹 2𝐶𝐶 ∗_{𝐷𝐷𝑘𝑘𝑘} 2+ 2𝛽𝛽𝐷𝐷𝑘𝑘𝑘3− 𝛽𝛽𝑘𝑘′2𝑘𝑘3′ − 8𝐹𝐹2𝐹𝐹2𝛽𝛽𝐶𝐶∗𝐷𝐷𝑘𝑘𝑘22𝑘𝑘𝑘3𝛿𝛿 + 𝐹𝐹𝐹𝐹 𝛽𝛽𝑘𝑘𝑘2𝑘𝑘𝑘3𝛿𝛿 − 2𝐶𝐶∗𝐷𝐷𝑘𝑘′3− 2𝛽𝛽𝐷𝐷𝑘𝑘𝑘2 ²

Which is the limiting step on stainless steel?

0 2 4 6 8 -260 -240 -220 -200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 700rpm 500rpm 200rpm 0rpm j (µ A /c m ²) time (min) 0,95 V/ENH 0,85 V/ENH 0,65 V/ENH 0,55 V/ENH 0,50 V/ENH 0,45 V/ENH 0,40 V/ENH 1000rpm

Which is the limiting step on stainless steel?

0 2 4 6 8 -260 -240 -220 -200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 700rpm 500rpm 200rpm 0rpm j (µ A /c m ²) time (min) 0,95 V/ENH 0,85 V/ENH 0,65 V/ENH 0,55 V/ENH 0,50 V/ENH 0,45 V/ENH 0,40 V/ENH 1000rpm

No influence of rotation speed on stainless steel (from 4M 40°C – to 8M

Which is the limiting step on stainless steel?

0 2 4 6 8 -260 -240 -220 -200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 700rpm 500rpm 200rpm 0rpm j (µ A /c m ²) time (min) 0,95 V/ENH 0,85 V/ENH 0,65 V/ENH 0,55 V/ENH 0,50 V/ENH 0,45 V/ENH 0,40 V/ENH 1000rpm

No influence of rotation speed on stainless steel (from 4M 40°C – to 8M

Which is the limiting step on stainless steel?

0 2 4 6 8 -260 -240 -220 -200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 700rpm 500rpm 200rpm 0rpm j (µ A /c m ²) time (min) 0,95 V/ENH 0,85 V/ENH 0,65 V/ENH 0,55 V/ENH 0,50 V/ENH 0,45 V/ENH 0,40 V/ENH 1000rpm

No influence of rotation speed on stainless steel (from 4M 40°C – to 8M

Which is the limiting step on stainless steel?

0 2 4 6 8 -260 -240 -220 -200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 700rpm 500rpm 200rpm 0rpm j (µ A /c m ²) time (min) 0,95 V/ENH 0,85 V/ENH 0,65 V/ENH 0,55 V/ENH 0,50 V/ENH 0,45 V/ENH 0,40 V/ENH 1000rpm

No influence of rotation speed on stainless steel (from 4M 40°C – to 8M

Which is the limiting step on stainless steel?

0 2 4 6 8 -260 -240 -220 -200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 700rpm 500rpm 200rpm 0rpm j (µ A /c m ²) time (min) 0,95 V/ENH 0,85 V/ENH 0,65 V/ENH 0,55 V/ENH 0,50 V/ENH 0,45 V/ENH 0,40 V/ENH 1000rpm

No influence of rotation speed on stainless steel (from 4M 40°C – to 8M

Which is the limiting step on stainless steel?

No diffusion limitation

Charge transfer and adsorption are limited steps on stainless steel

No influence of rotation speed on stainless steel (from 4M 40°C – to 8M

100°C) 0 2 4 6 8 -260 -240 -220 -200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 700rpm 500rpm 200rpm 0rpm j (µ A /c m ²) time (min) 0,95 V/ENH 0,85 V/ENH 0,65 V/ENH 0,55 V/ENH 0,50 V/ENH 0,45 V/ENH 0,40 V/ENH 1000rpm

Which is the limiting step on stainless steel?

No diffusion limitation

No influence of rotation speed on stainless steel (from 4M 40°C – to 8M

100°C) 0 2 4 6 8 -260 -240 -220 -200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 700rpm 500rpm 200rpm 0rpm j (µ A /c m ²) time (min) 0,95 V/ENH 0,85 V/ENH 0,65 V/ENH 0,55 V/ENH 0,50 V/ENH 0,45 V/ENH 0,40 V/ENH 1000rpm

0 1x104 2x104 3x104 4x104 5x104 6x104 7x104 8x104 9x104 0,0 5,0x103 1,0x104 1,5x104 2,0x104 2,5x104 3,0x104 3,5x104 4,0x104 20 mHz 260mHz 260mHz -I m(Z )/ O h m Re(Z)/ Ohm 0,40 V/ENH 0,45 V/ENH 0,50 V/ENH 0,55 V/ENH 0,60 V/ENH 0,65 V/ENH 0,70 V/ENH 0,75 V/ENH 0,80 V/ENH 0,85 V/ENH 163mHz

Experimental results at 4M 40°C on passivated stainless steel 0.5 cm²

20 30 40 50 60 70 80 90 101 102 103 104 105 0,85V/ENH 0,80V/ENH 0,75V/ENH 0,70V/ENH 0,65V/ENH 0,60V/ENH 0,55V/ENH 0,50V/ENH 0,45V/ENH 0,40V/ENH IZ I ( O h m ) P has e ( °)

-0 1x104 2x104 3x104 4x104 5x104 6x104 7x104 8x104 9x104 0,0 5,0x103 1,0x104 1,5x104 2,0x104 2,5x104 3,0x104 3,5x104 4,0x104 20 mHz 260mHz 260mHz -I m(Z )/ O h m Re(Z)/ Ohm 0,40 V/ENH 0,45 V/ENH 0,50 V/ENH 0,55 V/ENH 0,60 V/ENH 0,65 V/ENH 0,70 V/ENH 0,75 V/ENH 0,80 V/ENH 0,85 V/ENH 163mHz 50 60 70 80 90 103 104 105 0,85V/ENH 0,80V/ENH 0,75V/ENH 0,70V/ENH 0,65V/ENH 0,60V/ENH 0,55V/ENH 0,50V/ENH 0,45V/ENH I ( O h m ) e ( °) HF domain:

Oxide layer thickness

20 30 40 50 60 70 80 90 101 102 103 104 105 0,85V/ENH 0,80V/ENH 0,75V/ENH 0,70V/ENH 0,65V/ENH 0,60V/ENH 0,55V/ENH 0,50V/ENH 0,45V/ENH 0,40V/ENH IZ I ( O h m ) P has e ( °)

Constant Phase Element: Dielectric properties of the oxide layer

HF domain:

Oxide layer thickness

0 1x104 2x104 3x104 4x104 5x104 6x104 7x104 8x104 9x104 0,0 5,0x103 1,0x104 1,5x104 2,0x104 2,5x104 3,0x104 3,5x104 4,0x104 20 mHz 260mHz 260mHz -I m(Z )/ O h m Re(Z)/ Ohm 0,40 V/ENH 0,45 V/ENH 0,50 V/ENH 0,55 V/ENH 0,60 V/ENH 0,65 V/ENH 0,70 V/ENH 0,75 V/ENH 0,80 V/ENH 0,85 V/ENH 163mHz

Experimental results at 4M 40°C on passivated stainless steel 0.5 cm²

-50 60 70 80 90 103 104 105 0,85V/ENH 0,80V/ENH 0,75V/ENH 0,70V/ENH 0,65V/ENH 0,60V/ENH 0,55V/ENH 0,50V/ENH 0,45V/ENH I ( O h m ) e ( °)

Constant Phase Element: Dielectric properties of the oxide layer

Faradaic processes HF domain:

Oxide layer thickness

0 1x104 2x104 3x104 4x104 5x104 6x104 7x104 8x104 9x104 0,0 5,0x103 1,0x104 1,5x104 2,0x104 2,5x104 3,0x104 3,5x104 4,0x104 20 mHz 260mHz 260mHz -I m(Z )/ O h m Re(Z)/ Ohm 0,40 V/ENH 0,45 V/ENH 0,50 V/ENH 0,55 V/ENH 0,60 V/ENH 0,65 V/ENH 0,70 V/ENH 0,75 V/ENH 0,80 V/ENH 0,85 V/ENH 163mHz

20 30 40 50 60 70 80 90 101 102 103 104 105 0,85V/ENH 0,80V/ENH 0,75V/ENH 0,70V/ENH 0,65V/ENH 0,60V/ENH 0,55V/ENH 0,50V/ENH 0,45V/ENH 0,40V/ENH IZ I ( O h m ) P has e ( °)

Constant Phase Element: Dielectric properties of the oxide layer

Faradaic processes

CPE

Z

Re

metal oxide medium

Equivalent circuit used: HF domain:

Oxide layer thickness

0 1x104 2x104 3x104 4x104 5x104 6x104 7x104 8x104 9x104 0,0 5,0x103 1,0x104 1,5x104 2,0x104 2,5x104 3,0x104 3,5x104 4,0x104 20 mHz 260mHz 260mHz -I m(Z )/ O h m Re(Z)/ Ohm 0,40 V/ENH 0,45 V/ENH 0,50 V/ENH 0,55 V/ENH 0,60 V/ENH 0,65 V/ENH 0,70 V/ENH 0,75 V/ENH 0,80 V/ENH 0,85 V/ENH 163mHz

Experimental results at 4M 40°C on passivated stainless steel 0.5 cm²

-10-2 10-1 100 101 102 103 104 0 10 20 30 40 50 60 70 80 90 100 101 102 103 104 105 0,85V/ENH 0,80V/ENH 0,75V/ENH 0,70V/ENH 0,65V/ENH 0,60V/ENH 0,55V/ENH 0,50V/ENH 0,45V/ENH 0,40V/ENH IZ I ( O h m ) P has e ( °) f (Hz) Bode representation: C_dl C_ox At infinite frequencies:

-Cole & -Cole representation: 4M 40°C 0.85 V/ENH 10-2 10-1 100 101 102 103 104 0 10 20 30 40 50 60 70 80 90 100 101 102 103 104 105 0,85V/ENH 0,80V/ENH 0,75V/ENH 0,70V/ENH 0,65V/ENH 0,60V/ENH 0,55V/ENH 0,50V/ENH 0,45V/ENH 0,40V/ENH IZ I ( O h m ) P has e ( °) f (Hz) Bode representation: 0,0 5,0x10-5 1,0x10-4 1,5x10-4 2,0x10-4 0,0 5,0x10-5 1,0x10-4 1,5x10-4 2,0x10-4 C i m a g ( F /c m ²) C real (F/cm²) 0 1x10-5 2x10-5 0,0 5,0x10-6 1,0x10-5 1,5x10-5 2,0x10-5 C_dl C_ox At infinite frequencies:

-By extrapolation: C_∞ = 4.1 10-6 _F.cm-2

If we consider this value as the capacitance of Cole & Cole representation:

4M 40°C 0.85 V/ENH 10-2 10-1 100 101 102 103 104 0 10 20 30 40 50 60 70 80 90 100 101 102 103 104 105 0,85V/ENH 0,80V/ENH 0,75V/ENH 0,70V/ENH 0,65V/ENH 0,60V/ENH 0,55V/ENH 0,50V/ENH 0,45V/ENH 0,40V/ENH IZ I ( O h m ) P has e ( °) f (Hz) Bode representation: 0,0 5,0x10-5 1,0x10-4 1,5x10-4 2,0x10-4 0,0 5,0x10-5 1,0x10-4 1,5x10-4 2,0x10-4 C i m a g ( F /c m ²) C real (F/cm²) 0 1x10-5 2x10-5 0,0 5,0x10-6 1,0x10-5 1,5x10-5 2,0x10-5 C_dl C_ox At infinite frequencies:

-10-2 ₁₀-1 ₁₀0 ₁₀1 ₁₀2 ₁₀3 ₁₀4 0 10 20 30 40 50 60 70 80 90 10-3 10-2 10-1 100 101 102 103 104 105 106 0,85V/ENH 0,40V/ENH fit fit IZ I ( O h m ) P has e ( °) f (Hz) 0 1x104 2x104 3x104 4x104 5x104 6x104 7x104 8x104 9x104 0,0 5,0x103 1,0x104 1,5x104 2,0x104 2,5x104 3,0x104 3,5x104 4,0x104 20 mHz 260mHz 260mHz -I m(Z )/ O h m Re(Z)/ Ohm 0,40 V/ENH 0,45 V/ENH 0,50 V/ENH 0,55 V/ENH 0,60 V/ENH 0,65 V/ENH 0,70 V/ENH 0,75 V/ENH 0,80 V/ENH 0,85 V/ENH 163mHz CPE Z_f Re

metal oxide medium

-20 30 40 50 60 70 80 90 10-1 100 101 102 103 104 105 106 0,85V/ENH IZ I ( O h m ) P has e ( °) 5,0x103 1,0x104 1,5x104 2,0x104 2,5x104 3,0x104 3,5x104 4,0x104 20 mHz 260mHz 260mHz -I m(Z )/ O h m 0,40 V/ENH 0,45 V/ENH 0,50 V/ENH 0,55 V/ENH 0,60 V/ENH 0,65 V/ENH 0,70 V/ENH 0,75 V/ENH 0,80 V/ENH 0,85 V/ENH 163mHz CPE Z_f Re

metal oxide medium

-For CPE parameters we used Brugg’s formula to obtain capacitance

For CPE parameters we used Brugg’s formula to obtain capacitance

values:

HNO_2,sol → HNO2,ads HNO_2,ads+ e-_{+ H}+ _{→ NO} ads+ H2O NO_ads+1₂H++1₂NO₃− +1₂H2O → 3₂HNO2 CPE Z_f Re 𝜃𝜃_1𝑆𝑆 = 𝑘𝑘1′ 𝑘𝑘₁′ + 𝑘𝑘2′_𝑘𝑘. 𝑘𝑘1′ 3′ + 𝑘𝑘2 ′_{. 𝛽𝛽} 𝜃𝜃2𝑆𝑆 = 𝑘𝑘₂′ 𝑘𝑘₃′ 𝜃𝜃1𝑆𝑆 ∆𝜃𝜃₂ ∆𝐸𝐸 = 𝑘𝑘₂′. 𝑏𝑏₂. 𝜃𝜃_1𝑆𝑆 + 𝑘𝑘₂′. ∆𝜃𝜃_∆𝐸𝐸1 𝑗𝑗𝜔𝜔 + 𝑘𝑘₃′ ∆𝜃𝜃₁ ∆𝐸𝐸 = −𝑘𝑘₂′. 𝑏𝑏₂. 𝛽𝛽. 𝜃𝜃_1𝑆𝑆 − 𝑘𝑘1′_{𝑗𝑗𝜔𝜔 + 𝑘𝑘}. 𝑘𝑘2′. 𝑏𝑏2. 𝜃𝜃1𝑆𝑆 3′ 𝑗𝑗𝜔𝜔𝛽𝛽 + 𝑘𝑘₁′ + 𝑘𝑘₂′. 𝛽𝛽 + 𝑘𝑘_{𝑗𝑗𝜔𝜔 + 𝑘𝑘}2′. 𝑘𝑘1′ 3′ 1 = −𝐹𝐹𝐹𝐹 𝑘𝑘′. 𝛽𝛽.∆𝜃𝜃1 ′. 𝑏𝑏 . 𝛽𝛽. 𝜃𝜃 k1 k°2 k3 Stationary solutions:

Non stationary solutions:

Impedance:

𝑘𝑘𝑘1= 𝑘𝑘1[𝐻𝐻𝐻𝐻𝐻𝐻2]

𝑘𝑘𝑘2 = 𝑘𝑘2°𝑎𝑎𝐻𝐻𝑒𝑒(𝑏𝑏2 𝐸𝐸−𝐸𝐸𝐸 )

10-2 10-1 100 101 102 103 104 0 10 20 30 40 50 60 70 80 90 10-3 10-2 10-1 100 101 102 103 104 105 106 0,85V/ENH 0,40V/ENH fit fit IZ I ( O h m ) P has e ( °) f (Hz)

Fitted kinetic constants: k₁ = 0.03 ± 0.02 cm.s-1 k°₂= 6.10-4 _{± 2 10}-4 _s-1 [k₃= 2 107 _s-1_] On Gold [3] _{: k} 1= 1.103cm.s-1 k°₂= 1.105_s-1 k3= 1.107s-1 1,5x104 2,0x104 2,5x104 3,0x104 3,5x104 4,0x104 260mHz -I m(Z )/ O h m 0,40 V/ENH 0,45 V/ENH 0,50 V/ENH 0,55 V/ENH 0,60 V/ENH 0,65 V/ENH 163mHz

-Kinetic constants validated by stationary current (4M 40°C): Constants used: k₁= 0,03 cm.s-1 k°₂= 6.10-4 _s-1 k₃= 2.106 _s-1 fit exp 𝑖𝑖_𝑆𝑆 = −FS𝑘𝑘𝑘₂𝜃𝜃_1𝑆𝑆 𝛽𝛽 𝜃𝜃_1𝑆𝑆 = 𝑘𝑘1′ 𝑘𝑘₁′ + 𝑘𝑘2′_𝑘𝑘. 𝑘𝑘1′ 3′ + 𝑘𝑘2 ′_{. 𝛽𝛽}

On stainless steel:

Same mechanism as on gold

Conversely to gold electrode, the autocatalytic processes play

a minor role

Oxide layer slows down kinetics reduction

Oxide layer properties can be obtained by EIS (thickness &

dielectrics properties)

Kinetic constants have been determined and verified by

modelling of stationary current

DEN

Commissariat à l’énergie atomique et aux énergies alternatives | PAGE 49

J. Agullo, C. Bataillon, M. Bigot, N. Brijou-Mokrani, N. Cavaliere, C-A, Deblonde, P. Fauvet, O. Geneve, N. Gruet, S. Heurtault, P. Laghoutaris, B. Laurent, F. Miserque, B. Puga Nieto, M. Rivollier, R. Robin, C.M.

Sanchez-Sanchez, P. Suegama, B. Tribollet.

for your

attention

HNO2,sol → HNO2,ads

HNO2,sol+ e-+ H+ → NOads+ H2O

NO_ads+1₂H+₊1 2NO3−+ 1 2H2O → 3 2HNO2 NO_ads+ e-_{→ NO} -sol 1 k°2 k°4 k3

Successive mechanisms (Vetter and Schmid) on gold Mechanisms in competition on stainless steel

R. Lange [3]: Schmid dominates on stainless steel

HNO NO NO+ _NO

2

Chronoamperometry µ-electrode Pt (∅ 25 µm) I_statafter 400 s ;

d_S-S= 2 µm, HNO₃8 mol/L à Tamb.

HNO2,sol → HNO2,ads

HNO2,sol+ e-+ H+ → NOads+ H2O

NO_ads+1₂H+₊1 2NO3−+ 1 2H2O → 3 2HNO2 NO_ads+ e-_{→ NO} -sol CPE Z_f Re powerlaw 1 k°2 k°4 k3

Influence de la géométrie

Diffusion 1D

2D – 3D