New palladium phosphide catalysts
for fuel cells based on a simple
conversion process
K. Fahy, B. Kakati, V. N. Naranammalpuram-Sundaram and A. Kucernak
Metal phosphides have interesting electronic and structural properties
for applications in many fields, including catalysis
1 J. Am. Chem. Soc., 2007, 129 (7), 1896–1897
Chemistry of Materials 2007 19 (17), 4234-4242
Solution–mediated reactions of supported metal nanoparticles with
trioctyl-phosphine was used to form metal phosphide nanoparticles
Pd/C (19 mg) + TOP (2mL)
Under Ar 300° C, 1 hour
Saturate with ethanol
Centrifuge & wash with hexane and
ethanol
Dry under Ar
Pd5P2/C & PdP2/C
J. Mater. Chem., 2011, 39, 4388-4401
Palladium Palladium
Phosphide
Palladium
Phosphorus
Diffusion of P
into nanoparticles
XRD and TEM showed a good yield of phosphide with little or no
particle aggregation or ripening
3
PdP2/ C
Pd5P2/ C
Pd / C
3
20 30 40 50
20 30 40 50
Inte
nsity (
a.u
)
2() (Deg)
Pd/Carbon
Inte
nsity (
a.u
)
Pd5P
2 /Carbon
Inte
nsity (
a.u
)
PdP2 /Carbon
11
1
20
0
carb
on
-11
3
42
0 0
22
01
1
20
0
-21
1
-11
3
42
0
02
2
Cyclic voltammetry for Pd-phosphides shows similar profile to Pd/C
with a slight shift of Pd oxidation peak to higher E
4
Pd-phosphides do show an increased activity towards the HER than
Pd/C, possibly due to lower Pd2H formation
5
Pd2H
Pd5P2/C shows faster onset of the HOR and reaches limiting current
almost 0.1 V sooner than Pd/C
6
KL plot taken at 0.45
V(RHE)
Based on HOR data would expect
PdP2/C to outperform Pd/C
Chloride is a common contaminant for the ORR on palladium and this
is not improved in the case of the phosphides
8
200 mM Cl- in the cell is ~1.1 mg NaCl
Both Pd5P2/C and PdP2/C show increased activity towards formic acid
oxidation compared to Pd/C
9
Max. current density:
PdP2/C: 50.1 mA cm-2
Pd5P2/C: 44.4 mA cm-2
Pd/C: 28.9 mA cm-2
0.5 M H2SO4 + 0.5M HCOOH N2
Loading 20 µg cm-2
1000 RPM
Both Pd-phosphides show increased durability undergoing cycling and
higher temperature stability in TGA compared to Pd/C
10
Pd/C ~ 75% carbon
Pd5P2/C ~65% carbon
PdP2/C ~55% carbon
DoE Webinar series, 2013, https://www1.eere.energy.gov/hydrogenandfuelcells/webinars.html
Conclusions
11
• Pd-phosphides can be synthesised by a simple reaction of supported
Pd/C with TOP
• The phosphides are stable in acid and show increased durability
compared to Pd/C
• Pd5P2/C shows increased activity to the HOR in acid compared to Pd/C
• Both Pd5P2/C and PdP2/C show increased activity towards HER compared to Pd/C
• Formic acid oxidation is almost double on the PdP2/C compared to Pd/C
• Both phosphides show decreased ORR activity and are strongly
affected by chloride contamination