Carbon supported Pd-Ni and Pd-Ru-Ni
nanocatalysts for the alkaline direct ethanol fuel cell (DEFC)
ASSAF-DST-NRF 2011, Pretoria
Mmalewane Modibedi
Outline
• Background and Introduction
• Synthesis of nanocatalysts
• Characterization and Electrochemical Evaluation of the nanocatalysts
• DEFC Performance measurement in alkaline medium
• Concluding remarks
• Acknowledgements
© CSIR 2011 www.csir.co.za
What is a fuel cell (FC)?
e e
e e
e
Oxygen
Protons Electrons
Membrane DC Electricity
e
Water
Heat
H2 2H+ + 2e-
0 Volts
1/2O2 + 2e- 1/2O2 - -
~1.23 Volts
H2 + 1/2O2 --> H2O
Approx, 1 volt or less/cell, therefore add cells together
What is a FC? (cont’d)
Alkaline 60 - 120 35 - 50 Medium Medium High
PAFC 100 - 400 35 - 45 Medium Medium Medium
MCFC 100 - 200 45 - 55 Low Low Low
SOFC 100 - 300 45 - 50 Low Medium Low
PEMFC 400 - 900 32 - 40 High High High Fuel Cell Current Density System Fuel Proc. Stack Power Transient
Type (mA/cm2) Efficiency Complexity Density Capability
• Categorized based on the type of electrolyte used.
• Electrolyte is sandwiched between anode and cathode.
• Anode catalyst: fuel oxidation
• Cathode catalyst: oxygen reduction
Proton exchange membrane Fuel cell (PEMFC): Challenges
• Catalysts: slow electrode kinetics, CO poisoning of Pt at low temp.
• Membrane: high fuel permeability, high cost
Alkaline Anion exchange membrane Fuel cell (AEMFC): Alternative
• Catalysts: use non-noble metals, faster kinetics of oxygen reduction and alcohol oxidation
• Membrane: reduced or no alcohol crossover
© CSIR 2011 www.csir.co.za
DAFC vs alkaline DAFC
Synthesis of nanocatalysts
reducing agent: mixture NaBH4 and ethylene glycol
Low ethanol oxidation
performance vs Pd+Ru-Ni/C
© CSIR 2011 www.csir.co.za
Characterization of nanocatalysts
TEM micrographs Binary:
7+- 0.8 nm
Ternary 6+- 0.5nm
Modibedi et al, International J. Hydrogen Energy 36 (8) 2011 4664-4672
XRD micrographs of nanocatalysts
20 40 60 80 100
2 Theta (degree)
Intensity (a.u.)
C (002)
Ru (101)
Pd (200)
Pd (220)
PdRuNi/C (a)
RuNi/C
Pd (111)
20 40 60 80 100
2 Theta (degree)
Intensity (a.u.)
RuNi/C C (002)
Ru (101)
Ru/C
(insert XRD patterns of Ru/C and Ru-Ni/C)
Pd fcc
Electrochemical Evaluation
-50 -40 -30 -20 -10 0 10 20 30
-1.1 -0.6 -0.1 0.4
Potential (V vs Ag/AgCl) Current density (mA/cm2 )
RuNi/C PdRu/C PdRuNi/C
Pd oxides reduction region
-4 -3 -2 -1 0 1 2
-1.1 -0.6 -0.1 0.4
Potential (V vs Ag/AgCl) Current density (mA/cm2 )
Pd/C PdNi/C
Pd oxides reduction region
cyclic voltammograms in 0.5 M NaOH
Pd+ Ru-Ni/C
cyclic voltammograms in ethanol
-30 -20 -10 0 10 20 30 40 50 60
-1.2 -0.7 -0.2 0.3
Potential (V vs Ag/AgCl)
Current density (mA/cm2 ) Pd/C
PdNi/C PdRuNi/C
\
-15 -10 -5 0 5 10 15 20
-1.2 -0.7 -0.2 0.3
Potential (V vs Ag/AgCl) Current density (mA/cm2 )
RuNi/C PdRu/C
RuNi/C and PdRu/C:
no or low activity towards ethanol oxidation
Electrochemical evaluation
Concentration studies effect on current density
PdNi/CPdRuNi/C
-40 -20 0 20 40 60 80 100 120
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2
Potential (V vs Ag/AgCl) Current density (mA/cm2 )
0.25M 0.5M 1.0M 2.0M 3.0M 4.0M CEtOH =
-1.0 -0.8 -0.6
Potential (V vs Ag/AgCl) Current density (mA/cm2 )
0.25M 0.5M 1.0M 2.0M 3.0M 4.0M CEtOH =
-40 -20 0 20 40 60 80 100 120
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2
Potential (V vs Ag/AgCl) Current density (mA/cm2 )
0.25M 0.5M 1.0M 2.0M 3.0M 4.0M CEtOH =
-1.0 -0.8 -0.6
Potential (V vs Ag/AgCl) Current density (mA/cm2 )
0.25M 0.5M 1.0M 2.0M 3.0M 4.0M CEtOH =
[EtOH] up to 3 M coverage of the CH3COads species on the nanocatalyst surface
Resulting in increase in current density
Alkaline DEFC performance: passive state
Electro- catalyst
Open circuit voltage
(V)
Power/total loading (mW/mgPd)
PdCeO2/C (ACTA-SpA)
0.795 3.1736
PdNi/C 0.653 3.1916 PdRuNi/C 0.768 2.5798 PdRuSn/C 0.623 0.2386
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
0 5 10 15 20 25
Current density (mA/cm2)
Potential (V)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Power density (mW/cm2 ) PdRuNi/C
ACTA-Spa.
anode PdNi/C
Cathode: 0.1mg/cm2 FeCo (ACTA-SpA)
Polarization and power curves
© CSIR 2011 www.csir.co.za
