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Second Regional Symposium on Electrochemistry South-East Europe June 6 to 10, 2010, Belgrade, Serbia. PERFECTUATION OF NANO-SCALED NON-PLATINUM ELECTROCATALYSTS FOR HE/O. Orce Popovski * , Perica Paunović** and Svetomir Hadži Jordanov**

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slide1

Second Regional Symposium on Electrochemistry South-East Europe

June 6 to 10, 2010, Belgrade, Serbia

PERFECTUATION OF NANO-SCALED NON-PLATINUM ELECTROCATALYSTS FOR HE/O

Orce Popovski *, Perica Paunović** and Svetomir Hadži Jordanov**

*Military Academy “General Mihailo Apostolski” Skopje, R. of Macedonia

**Faculty of Technology and Metallurgy, University „Sts. Cyril and Methodius“, Skopje, R. of Macedonia

orcepopovski@yahoo.com

the hydrogen economy concept
The Hydrogen economy concept
  • Fossil fuels are the most convenient and available energy sources
  • Unclosed loop of their exploitation makes them environmentally unfriendly and unsustainable source of energy
  • The combustion products go into the atmosphere, accompanied with other gases and cause serious pollution
  • On the other side, the enormous consumption rate of fossil fuels contribute to their soon total exhaust.
  • Modern science is facing a challenge to find out alternative source of energy which can satisfy the global energy needs, but also to be environmentally friendly.
  • In this context, the hydrogen economy as system of hydrogen production, storage, transportation and conversion in electricity by fuel cellsis very perspective.
slide3

Environment

Solar Energy

Oxygen in

Oxygen out

Photovoltaic Conversion

Water in

Water out

Hydrogen Storage & Transport

Electric Power

Water electrolysis

Electric Power

Fuel Cell

The Solar Hydrogen Energy Conversion Cycle

The ultimate solution for energy production, saving and conversion is the use of renewable energy sources, and particularly

Solar Photo-Voltaic Hydrogen Energy Conversion Cycle

slide4

Reducing the use of noble metals

  • Increasing catalytic activity the less

noble metals

– our crucial task

Electrode materials for hydrogen evolution

  • Electrode materials for HE/O are of critical importance in hydrogen economy concept
  • Their selection is not at all an easy task
  • The conflict of technical and economical issues is evident:
    • the best electrocatalysts (Pt, Pd, Ru) –low abundance,
    • – high cost
    • the cheaper one (Ni, Co etc.) –chemical unstable
    • –low activity
slide5

How to solve this problem?

There are two approaches:

Physical approach

Increasing of the active surface

by lowering the grain size of the

catalytic phase and supporting

materials to nano-scale

• highly developed surface

• excellent electrical conductivity

• optimal micro porosity

• adequate water handling capability

• good corrosion resistance

Chemical approach

Development of multicomponent

catalysts with catalytic activity

comparable with that of Pt

• decrease the noble metal mass

• increase the activity as a result of

inter electronic and/or inter ionic

interactions

slide6

Co-TiO2

Ni-TiO2

CoPt-TiO2

CoRu-TiO2

CoRuPt-TiO2

Vulcan XC-72; MWCNTs; MWCNTs(a)

Bi- and multi-component catalysts

E-Tek – 20% Pt / 80%Vulcan XC-72 – the most used electrode material

The main goal was: production, characterization and modification of platinum and non-platinum hypo-hyper d-electrocatalyst for HE/O

Followed multicomponent systems were prepared by sol-gel method and studied:

10%Me + 18%TiO2 + Vulcan XC-72; MWCNTs; MWCNTs(a)

slide7

Hypo d-phase

Metallic phase

(hyper d-)

TiO2

(anatase)

Ni, Co

Electroconductive

support material

Vulcan XC-72

Non-platinum mixed electrocatalysts

Improvement – I step

10% Me + 18% TiO2 + Vulcan XC-72

slide8

Bi-functional role of TiO2

  • Catalyst’s support
  • SMSI effect

Polarization curves

Aqeuose solution:

3.5 M KOH

room temperature

slide9

XRD analysis

10% Ni + 18% TiO2 + Vulcan XC-72

A - anatase

10% Co + 18% TiO2 + Vulcan XC-72

A - anatase

Co amorphous

grain size < 2 nm

Ni crystalline

grain size 1520 nm

TiO2 anatase

grain size 78 nm

slide11

Hypo d-phase

Metallic phase

(hyper d-)

TiO2

(anatase)

Ni, Co

Electroconductive

support material

MWCNTs

Non-platinum mixed electrocatalysts

Improvement – II step

10% Me + 18% TiO2 + MWCNTs

slide12

Non-platinum hypo-hyper d-electrocatalysts

Polarization curves

Aqeuose solution:

3.5 M KOH

room temperature

slide13

Metallic phase

(hyper d-)

Hypo d-phase

TiO2

(anatase)

Co, Pt

Electroconductive

support material

MWCNTs(a)

Cobalt-platinum mixed electrocatalysts

Improvement – III step

ACTIVATION

  • Me = Co
  • Me = CoPt (4:1)
  • Me = CoPt (1:1)
  • Me = Pt

28% HNO3

 = 4 h

t = 25oC

600 rpm

10% Me + 18% TiO2 + MWCNTs (a)

slide14

To1= 180oC

Tp1= 278oC

Tp3= 893oC

Tp2= 645oC

To2= 585oC

Non-activated MWCNTs

To3= 847oC

Activated MWCNTs

To1= 173oC

Tp1= 272oC

Tp2= 757oC

Tp2= 575oC

To3= 617oC

To2= 523oC

TGA/DTA

Activated MWCNTs

higher thermal stability  smaller diameter of tubes, higher level of purity

slide15

RAMAN spectroscopy

Activated MWCNTs

higher crystallinity

lower amount of amorphous carbon

slide17

XRD analysis

Pt – 11 nm

Anatase – 3-4 nm

Pt – 4 nm

Anatase – 3-4 nm

slide18

Electrocatalytic activity for hydrogen evolution in the EasyTest Cell

ELAT – 0.5 mg.cm-2 Pt + Vulcan XC-72

1 – 10% Co + 18% TiO2 + MWCNTs

2 – 10% CoPt (4:1) + 18% TiO2 + MWCNTs

3 – 10% CoPt (1:1) + 18% TiO2 + MWCNTs

slide19

CONCLUSIONS

1. Involving TiO2

stable catalyst support

increase of intrinsic catalytic activity trough SMSI

2. Involving MWCNTs as catalyst support

increase of catalyst’s surface area

imrovement of trans- and inter- particle porosity 

better dispersion of metallic phase

increase of intrinsic activity

3. Activation MWCNTs as catalyst support

higher stability of MWCNTs

higher purity (lower amount of amorphous carbon)

shortening of the MWCNTs length (increase of surface area)

4. Involving Pt in metallic phase

high activity of CoPt (with only 20% Pt in metallic phase)

the presence of Co reduces Pt particles (23 times)

increase of catalytic activity as result of size effect