Development of Graphitic-Carbon Nitride as Catalyst
Support for Polymer Electrolyte Fuel Cell (PEFC)
N. Mansora, A. B. Jorgea,b, F. Corab, C. Gibbsa, R. Jervisa, P. F. McMillanb, X. Wangb, D. J. L Bretta
aElectrochemical
Innovation Lab, University College London, Torrington Place, London WC1E 7JE, UK
bDepartment of Chemistry, University College London, Gordon Street, London WC1H 0AJ, UK
.
Introduction
Alternative Catalyst Support
• The catalyst layers present a major challenge to PEFC commercialisation due to high
cost and insufficient durability
• The presence of nitrogen on carbon support was shown to improve durability and
activity for the oxygen reduction reaction (ORR) and methanol oxidation reaction
(MOR)
• Support material affects catalyst particle size and dispersion, and consequently affects
catalyst activity and durability
H2O + other
products
• Disadvantages of conventional carbon supports:
 Mass transport limitations
 Carbon corrosion which is accelerated by normal operating conditions resulting in
kinetic and ohmic loss
Adsorbed
oxygenated
surface group
N
N
Strongly adsorbed poisoning
intermediates
ORR
OH
N
N-doped carbon
OH
OH
N
MOR
N
N
N
N
Strongly adsorbed poisoning
intermediates
N-doped carbon
• PtRu supported on graphitic carbon nitride exhibits up to 83% higher power density
than commercial PtRu/C in DMFC
OH
Ohmic Loss
N
Pt
OH + CO
Diagram adapted from R. O'Hayre et. al., Energy Env. Sci., 3, 1437 (2010)
OH
Kinetic Loss
Adsorbed
oxygenated
surface group
Pt
OH + H2O
N
MeOH
CO2 + other
products
O2
M. Kim, S. Hwang and J.-S. Yu, J. Mater. Chem, 17 (2007)
Graphitic Carbon Nitride Materials
Intensity / arbitrary units
(c)
(b)
Intensity / arbitrary units Intensity / arbitrary units
(a)
(a)
Fig 1. Structural motifs in graphitic carbon nitrides (a) Liebig’s melon based on heptazine units linked by -NH- groups
with N-H groups on their edges (b) fully condensed layer based on heptazine units (c) layer based on triazine units
• Contains abundant Lewis acid and base sites – terminal and bridging NH-groups and N
lone pairs, respectively – which are potential Pt anchoring sites and CO adsorption sites
(a)
(b)
(c)
(b)
gCNM
0.32 nm
0.70 nm
10
10
20
20
30
40
50+
2degrees
60
PTI-Li Cl-
x2 B-gCNM
degrees
30

40
50
60
Normalised double layer capacitance / %
• Polymeric solids with high nitrogen contents with structure related to graphite/graphene
175
Vulcan
gCNM
PTI-Li+ClB-gCNM
150
125
100
10
10
20
30
40
50
100
1000
Number of scans
60
2 / degrees
Fig 3. (a) X-ray diffraction patterns of graphitic carbon nitrides. (b) The change in double layer capacitance (calculated at
0.40 V) and normalised to 10th scan) of the support materials as a result of accelerated carbon corrosion cycling (2000
cycles) compared to a commercial carbon black (Vulcan)
• B-gCNM and PTI-Li+Cl- demonstrate the highest stability – both materials are more
crystalline than Vulcan and gCNM (Fig 3)
100 nm
Fig 2. SEM images of graphitic carbon nitrides synthesised in this study (a) polymeric g-CNM with structure similar to Liebig’s
melon (b) PTI-Li+Cl- prepared by solvothermal synthesis from melamine with Cl- occupying the voids within the layers
(c) boron doped gCNM
• The presence of dopants (B, Li+ and Cl-) may contribute to stability
Graphitic Carbon Nitride Supported Catalysts
(a)
(d)
0.75
(c)
Pt/Vulcan
0.50
• The durability was found to be dependent on initial
ECSA (Table 1), suggesting there is a correlation
between metal – support interaction and durability
0.25
0.00
0.75
2.82
Pt/gCNM
1.88
j / mA cm-2
ECSA
(b)
Normalised change in ECSA
1.00
• Pt/PTI-Li+Cl- demonstrates the highest durability
with only 19% ECSA loss (Fig 4)
0.50
Pt/Vulcan
Pt/gCNM
Pt/PTI-Li+ClPt/B-gCNM
0.25
• Initial ECSAs of graphitic carbon nitride supported
catalysts are lower than that of commercial
Pt/Vulcan (Alfa Aesar) due to larger particle size
and higher degree of agglomeration
0.94
0.00
168
Pt/PTI-Li+Cl-
112
56
0
240
• All carbon nitride materials in this study have one
order of magnitude less BET surface area
compared to Vulcan – the same wt% loading of Pt
nanoparticles would result in higher density
Pt/B-gCNM
160
0.00
80
1
10
100
1000
0
0.4
Number of scans
0.5
0.6
0.7
0.8
0.9
1.0
1.1
E / V vs RHE
Pt/PTI-Li+Cl-
Fig 4. TEM images of supported Pt catalysts (a) Pt/gCNM (b)
(c) B-gCNM and (d) The change in ECSA
(calculated from hydrogen adsorption/desorption region and normalised to respective initial ECSAs) of the supported
catalysts as a result of accelerated carbon corrosion cycling (2000 cycles) compared to a commercial Pt/Vulcan
Fig 5. MOR activity of supported Pt catalysts in
1M CH3OH + 0.1 M HClO4 at 25°C
Particle Sizea
[nm]
Initial ECSA
[m2 g-1]
Final ECSA
[m2 g-1]
ECSA loss
[%]
MOR Epeak
[V]
MOR jmax
[mA cm-2ECSA]
Pt/Vulcan
3.5
28.6
18.2
36.3
0.903
0.821
Pt/gCNM
8.0
5.7
1.1
81.0
0.850
3.21
Pt/PTI-Li+Cl-
6.4
15.9
12.8
19.3
0.842
174
Pt/B-gCNM
4.2
1.9
0
100
0.858
209
Table 1. Summary of the properties of the supported Pt catalysts in comparison to commercial Pt/Vulcan.
a Estimated from TEM images based on the average of 100 particles
Collaborators logos
www.ucl.ac.uk/electrochemical-innovation-lab
www.facebook.com/UCLEIL
1.2
noramalina.mansor.09@ucl.ac.uk
+44 207 6797 683
• All graphitic carbon nitride supported Pt catalysts
have lower overpotential and higher methanol
oxidation activity per ECSA, compared to
Pt/Vulcan (Fig 5)
• Further research is already being developed to
optimize catalyst particle dispersion and utilisation
Acknowledgements
The authors acknowledge the EPSRC and UCL Enterprise Impact
Acceleration Account (EP/K503745/1) and EPSRC Supergen Fuel
Cells (EP/G030995/1) for financial support.