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

Tests of the ORR do not show improvement of ORR onset potential

over Pd/C or Pt/C

7

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

Q&A

12

Fuel cell testing of PdP2/C

13