RANEY-NI ELECTRODES FOR THE ALKALINE ...elyntegration.eu/wp-content/uploads/ICE20176_Christian...HER + OER Calculate cell voltage (only electrode overpotential) around 1.71 V @ 0.3

RANEY-NI ELECTRODES FOR THE ALKALINE ELECTROLYSIS OF WATER

C. I. Müller,Department of Hydrogen Technology

Fraunhofer IFAM Dresden

Dr. Christian Müller ([email protected])

-1.0 -0.8 -0.6 -0.4 -0.2 0.0

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

E / V

I / Acm-2

Motivation

Renewableenergy:

Wind,

Solar

eFuels

eChemicals

H2O CO2

Electrical power

Chemical energy carrier

1. Motivation 2. Electrodes @IFAM 3. Synthesis 4. Results 5. Summary

Low Voltage at a High Current Density

Energy H2-production rate

Demands

Stability

Degradation < 3 µV/h[A]

Life-Time Stack > 90 000 h (10 a)

Electrochemical Activ ity

Cell-voltage 1.8 – 2.2 V (< 0.6 A/cm²) [A]

Costs

Investment costs of the system < 1000 €/kWel[A]

Electrode Materials for AEL

[A] Smolinka et al., NOW Studie, 2011.

Hydrotechnik Wasserelektrolyse

NEL


Hydrogen: Electrodes with a large surface area

40 µm

20 µm

Structuring the surface of flat and porous materials

Structures in the range of 100 nm to 100 µm possible

Surface enlargement up to 10000-fold possible

300 µm

10 µm

[A][A] [C]

[C] [B]

[B]

[A] AMORPHEL (0327899A), funded by the BWMi of the Federal Republic of Germany .[B] Green-H2 (03ET6058), funded by the BWMi of the Federal Republic of Germany.[C] ELYntegration, funded by FCH-JU under grant agreement No 671458, FCH-JU receives support from the European Union’s Horizon 2020 program.


20 µm

Hydrogen: Electrode production techniques

Powder metallurgical route

Sintering of a powdery precursor

Electroplating

Electrodeposition of dissolved species

Laser ablation process

Femto-second pulse process

Rapid quenching technique

Amorphous ribbons

2 µm

10 µm

2 µm

[A] AMORPHEL (0327899A), funded by the BWMi of the Federal Republic of Germany .[B] Green-H2 (03ET6058), funded by the BWMi of the Federal Republic of Germany.[C] ELYntegration, funded by FCH-JU under grant agreement No 671458, FCH-JU receives support from the European Union’s Horizon 2020 program.

[A]

[A]

[B]

[C]


@ Kellenberger et al. (2007), Int. J. Hydrogen Energy, 32, 3258 @ Rausch et al. (1996), J. Electrochem. Soc., 143, 2852.

@ Rausch et al. (1996), J.

Electrochem. Soc., 143, 2852.

@ Kellenberger et al.

(2007), Int. J. Hydrogen

Energy, 32, 3258

@ Schiller et al. (1996) J. Therm. Spray

Technology, 4,185

Synthesis of Raney-Ni electrodes

DT

sintering

DT, KOH

leaching

State of the art:

Electroplating (NiZn) batch process, doping difficult

VPS (NiAl) batch process

Approach: sintering scalable (continuously produced), different alloy compositions possible, stable connection of catalyst to substrate

costs < 300 €/m²


Substrate Ni-mesh (Dexmet)

Al-powder-mesh-ratio (PMR): 17.1 % (calculated after sintering)

Ni-mesh perfectly surrounded by NiAl-phases

Sintered Raney-Ni electrodes (Raney-3)

Raney-3, PFR 17,1%

NiAl3-Al eutectic

Ni2Al3 NiAl3Ni-bars


Ni-mesh: enlarging the surface area

Raney-Ni production via a powder metallurgical and a chemical process

Porous layer is formed strongly increased surface area

No delamination of the Ni2Al3-phase detectable, due to the sintering process good stability

KOH,NaK-tartrate

90°C, 6 h

Ni coreNiAl3-Al eutectic

NiAl3Ni2Al3

NiAl3-Al and NiAl3 phases leached out.


Sintered Raney-Ni electrodes (Raney-1)

Substrate Ni-mesh (Dexmet)

Al-powder-mesh-ratio (PMR): 10.1 % (calculated after sintering)

Ni-mesh perfectly surrounded by NiAl-phases

Raney-1, PMR 10,1%

NiAl3-Al eutectic

Ni2Al3 NiAl3Ni-bars


HER activity of sintered Raney-Ni electrodes

Raney-1: 10.1 % PMR

Raney-2: 15.8 % PMR

Raney-3: 17.1 % PMR

Raney-Ni layer has a strongly increased HER activity

Higher PMR value causes a higher HER-activity

0 2 4 6 8 10 12

-1.55

-1.50

-1.45

-1.40

-1.35

-1.30

-1.25

-1.20

-1.15

-1.10

400

350

300

250

200

150

100

50

0

mesh

mesh

Raney-1

Raney-1

Raney-2

Raney-2

Raney-3

Raney-3

t / h

3

00 /

mV

GS: 29.9 wt.-% KOH, N2, 333 K, 0.3 A/cm²

E /

V v

s.

Ag

/Ag

Cl,

KC

l (s

at'

d)

mesh

mesh

Raney-1

Raney-1

Raney-2

Raney-2

Raney-3

Raney-3

10

11

12

13

14

15

16

17

18

19

20

PM

R /

wt-

%

PMR

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

Overpotential

300 / V


Electrochemical surface area

Determining the double layer capacity Cdl 𝑖𝑐 = Cdl x 𝑣

CV-pretreatment, in order to remove H-ad and M-H

Cdl determined at the OCP (-400 to -600 mV)

0.00 0.02 0.04 0.06 0.08 0.10

-0.005

-0.004

-0.003

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

scan rate, v / Vs-1

CV, N2, 29.9 wt-% KOH, 25°C, 2 cm²

I / A

cm

-2

anodic current denstiy

cathodic current denstiy

average current denstiy

linear fit

linear fit

linear fit

-0.55 -0.50 -0.45 -0.40 -0.35-8000

-6000

-4000

-2000

0

2000

4000

6000

8000

0.1 V/s

0.09 V/s

0.08 V/s

0.07 V/s

0.06 V/s

0.05 V/s

0.04 V/s

0.03 V/s

0.02 V/s

0.01 V/s

E / V vs. Ag/AgCl

j ge

o /

µA

cm

-2

29.9 wt.-% KOH, 60°C, N2, 0.92 cm²


Electrochemical surface area

Correlation between PMR and Cdl

Correlation between 300 and Cdl

Main effect: enlarged surface area

Minor effect: increased intrinsic activity

mesh

mesh

Raney-1

Raney-1

Raney-2

Raney-2

Raney-3

Raney-3

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

300 / V

Overpotential

0.00

0.01

0.02

0.03

0.04

Cd

l / F

/cm

²

Cdl cathodic - after HER

mesh

mesh

Raney-1

Raney-1

Raney-2

Raney-2

Raney-3

Raney-3

10

11

12

13

14

15

16

17

18

19

20

PM

R /

wt-

%

PMR

0.00

0.01

0.02

0.03

0.04

Cdl cathodic - after HER

Cd

l / F

/cm

²


Accelerated stress test using ultrasonic treatment

Accelerated Stress test (AST)

GS @0.3 A/cm²

Ultra sonic treatment for 30 s

GS @0.3 A/cm²

0 5 10 15 20 25 30

-1.55

-1.50

-1.45

-1.40

-1.35

-1.30

-1.25

-1.20

-1.15

-1.10

-1.05

400

350

300

250

200

150

100

50

0

-50

mesh

mesh

Raney-2

Raney-2

Raney-3

Raney-3

t / h

30s US

3

00 /

mV

GS: 29.9 wt.-% KOH, N2, 333 K, -0.3 A/cm²

E /

V v

s.

Ag

/Ag

Cl,

KC

l (s

at'

d)

Raney-3 after AST


Raney-1 (lowest PMR)

Degradation detectable

delamination of Raney-catalyst

Due to eruptive gas bubble evolution

Due to M-H formation

0 1 2 3 4 5

-1.55

-1.50

-1.45

-1.40

-1.35

-1.30

-1.25

-1.20

-1.15

-1.10

-1.05

400

350

300

250

200

150

100

50

0

-50

mesh

mesh

Raney-1

Raney-1

t / h

3

00 /

mV

GS: 29.9 wt.-% KOH, N2, 333 K

E /

V v

s.

Ag

/Ag

Cl,

KC

l (s

at'

d)

Raney-1 after HER


Cyclic voltammetry

Formation of Ni-Hads and Ni-H (Nickelhydride) before and after HER

self-ignition of leached Raney-Ni due to Ni-Hads and Ni-H formation!

Formation of Ni-H is accompanied by a volumetric expansion of the phase delamination

Potential shift of the cathode above

-0.8 V should be prevented during

down time of ELY!

No peak observable for the second scan

Deactivating of leached electrodes


-1.0 -0.8 -0.6 -0.4 -0.2 0.0

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

20 mV/s, N2, 29.9 wt-% KOH, 333 K, 2 cm²

E / V vs. Ag/AgCl, KCl(sat'd)

I / A

cm

-2

1. CV before HER

2. CV before HER

1. CV after HER

2. CV after HER

Oxidation of Ni-Hads.

Oxidation of NiH

Oxidation of Ni0

HER + OER

Calculate cell voltage (only electrode overpotential) around 1.71 V @ 0.3 A/cm²

@3000 A/m² 1.684 V (cell voltage)

45,8 kWh/kgH2 4.58 €/kgH2 (0.1 €/kWh electricity costs)

0 2 4 6

-1.5

-1.0

-0.5

0.0

0.5

Sintered Raney-Ni

Sintered Raney-Ni

reversible potential for OER

reversible potential for HER

t / h

1.71 V

GS: 29.9 wt.-% KOH, N2, 333 K, 300 mA/cm²

E /

V v

s.

Ag

/Ag

Cl,

KC

l (s

at'

d)

10 µm


Summary

Raney-Ni electrodes developed using sinter technology

Higher PMR beneficial for HER-activity

Main degradation due to delamination of Raney-Ni layer

Caused by formation of Nickel-hydride (volumetric expansions)

Potential shift of the cathode above -0.8 V should be prevented during down time of ELY

CV can be used to deactivate the leached electrode for safe handling

Calculate cell voltage (only electrode overpotential) around 1.71 V @ 0.3 A/cm²

nm² - µm² cm² dm² m²


Acknowledgement

This project has received funding from the Fuel Cells and

Hydrogen 2 Joint Undertaking under grant agreement No

671458. This Joint Undertaking receives support from the

European Union’s Horizon 2020 research and innovation

programme and Spain, Belgium, Germany, Switzerland.

-1.0 -0.8 -0.6 -0.4 -0.2 0.0

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

E / V

I / Acm-2

10 µm

Thank youfor your

kind attention!

-1.5 -1.4 -1.3 -1.2 -1.1 -1.0

10-4

10-3

10-2

10-1

DX3175x1650_01

DX3175x1650_RNi6_01

DX3175x1650_RNi3_01

DX3175x1650_RNi3_01_30US

DX3175x1650_RNi2_02

DX3175x1650_RNi2_30US_01

DX3175x1650_RNi2_04

j /

Ac

m-2

E / V vs. Ag/AgCl, KCl (sat'd)

400 300 200 100 0 -100

overpotential / mV

-1.0 -0.8 -0.6 -0.4 -0.2 0.0

0.0

0.2

0.4

0.6

Oxidation of Ni-Hads.

20 mV/s, N2, 29.9 wt-% KOH, 333 K, 2 cm²

E / V vs. Ag/AgCl, KCl(sat'd)

I /

Acm

-2

1. CV after leaching

2. CV after leaching

1. CV after HER

2. CV after HER

Oxidation of NiH

Oxidation of Ni0

Documents

RANEY-NI ELECTRODES FOR THE ALKALINE ...elyntegration.eu/wp-content/uploads/ICE20176_Christian...HER + OER Calculate cell voltage (only electrode overpotential) around 1.71 V @ 0.3