Elettrolita

YSZ

Electrolyte - A substance that conducts electricity through the movement of ions.

Most electrolytes are solutions or molten salts, but some electrolytes are solids and some of those are crystalline solids. Different names are given to such materials:

–Solid Electrolyte–Fast Ion Conductor–Superionic Conductor

Over the next two lectures we will be looking at materials which behave as solid electrolytes, their properties and applications.

Conduttori Ionici

Conduttori ionici e catodo

Electronic conductor (catalyst) + ionic conductor

• Higher specific surface area: O (ads) ⇑

• Composite electrodes: 3PB ⇑, 2PB⇑

• Effect of interfacial reaction on the electrical properties: additional resistive element at the 2PB

Ceramic Processing

Tape casting

SINTERING

oxide,YS oxide,YS

Estrusione

Techniche di deposizione di strati ceramici

•Conventional Spray

•Spray pyrolysis

•Electrophoretic deposition (EPD)

•Casting

•Plasma assisted methods

•Laser ablation methods

•Sputtering

Etc.

Film Spessi

Film Sottili

Spray pyrolysis

Spray pyrolysis

EPD

Caratterizzazione elettrochimica

1. Misure potenziostatiche2. Spettroscopia d’impedenza

Potenziostatica

Misura elettrica a corrente diretta (dc):

potenziali costanti sono applicati all’intero sistema(anodo+elettrolita+catodo) per misurarne le correntirisultanti dai processi elettrochimici ed dalle caduteohmiche complessive.

Polarizzazione degli elettrodi (anodo+catodo)Resistenza ohmica totale (elettrolita+interfacce+elettrodi)

Performace complessiva della cella

Spettroscopia d’impedenza

Misura elettrica a corrente alternata (ac):

Applicando una tensione costante permette oscillantea diverse frequenza permette di separare il contributodegli elettrodi (elettrochimici) da quelli ohmici.

L’uso di un ampio spettro di frequenze 107-10-2 Hz, permettedi individuare i processi in base ai loro tempi caratteristici

Polarizzazione degli elettrodi (anodo+catodo)Resistenza ohmica (elettrolita da interfacce ed elettrodi)

Electrochemical impedance spettroscopy (EIS)

Alcuni esempi

Celle simmetriche

Area Specific Resistance (ASR)

Pb2Ru2O6.5 electrodesdeposited onto ESB

sintered:@ 875 °C 30

min

Symmetric cell at high T:650 °C - 780 °CAir

Electrodes polaritazion:• Diffusion limited

processes (low T)• Co-limited

adsorption/gas diffusion processes (High T)

10 15 20 250

2

4

6

8

10

10 kHz10 kHz 10 kHz

1 Hz

650 °C 600 °C 550 °C

1 Hz10 Hz10 Hz

0.1 Hz

0.1 Hz

10 Hz1 Hz 0.1 Hz

-ImZ,

Ω

ReZ, Ω

4 5 6 7 80

1

2

1 kHz1 kHz1 kHz

100 Hz

1 Hz

780 °C 750 °C 700 °C

1 Hz10 Hz10 Hz

0.1 Hz 0.1 Hz10 Hz 1 Hz 0.1 Hz

-ImZ,

Ω

ReZ, Ω

12 14 16 18 20 220

1

2

3

4

5

1 kHz

1 Hz

700 °C 750 °C

100 Hz10 Hz

10 Hz

0.1 Hz

0.1 Hz

100 Hz1 Hz

1 kHz

-Im

Z, Ω

ReZ, Ω

• Pb2Ru2O6.5 - ESB /ESB/ Pb2Ru2O6.5 - ESB polarization at 700 °C and 750 °C in air;

Electrodes sintering temperature 800 °C for 180 °C

• ASR = Rchem·Aelectrode

Rchem

ASR related to the symmetric cells polarization (Rchem) in air;

ASRPyro800(750 °C) = 0.41 Ω cm2 , ASRcompo800(750 °C) = 1.77 Ω cm2

Different activation energies in relation to the electrodes sintering temperatures

0,8 1,0 1,2 1,4 1,6

-1,0

-0,5

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

1.03+/-0.09 eV1.18+/-0.02 eV

0.55+/-0.06 eV0.56+/-0.09 eV

0.42+/-0.03 eV

Pyro 875 °C Pyro 800 °C Pyro 700 °C Compo 800 °C Compo 700° C

Log(

AS

R),

Ωcm

2

1000/T, K-1

0.9 1.2 1.5-2

0

2

4 LSCF3020 LSCF3015 LSCF3005 LSCF3000

log(

ASR

), Ω

cm

2

1000/T, K-1

Effect of Fe doping on the ASR

ASR increases slightlywith Fe doping

Effect of the sintering temperature

0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 1.40 1.45 1.50 1.55

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0Lo

g(A

SR) (

ohm

Cm

2 )

1000/T(K)

900°C 1000°C 850°C 1150°C 1250°C

900 °C is the best sintering temperature