Electrochemical behavior of ammonia on Ni 98 Pd 2 nano-structured catalyst Anis Allagui 1 , Saad Sarfraz, Spyridon Ntais, Fares Al momani, Elena A. Baranova* Department of Chemical & Biological Engineering, University of Ottawa, 161 Louis-Pasteur, Ottawa, ON K1N 6N5, Canada article info Article history: Received 17 April 2013 Received in revised form 24 September 2013 Accepted 3 October 2013 Available online 8 November 2013 Keywords: Ammonia electrooxidation pH effect Electrolysis Ni hydroxides abstract Small amounts of Pd served as a reducing agent to produce sub-100 nm polygonally-shaped Ni 98 Pd 2 materials in ethylene glycol. As-synthesized particles were crystallized into fcc Ni with a fraction of b-Ni(OH) 2 , and exhibited very low to no activity towards ammonia electrooxidation. Their catalytic activity has been significantly improved by building up a layer of Ni(OH) 2 by cyclic voltammetry between 0.95 and 1.35 V vs. HgO/Hg in NaNO 3 at pH 9. XPS analysis before and after the electrochemical treatment confirmed the trans- formation of Ni 0 to higher state of oxidation. Ammonia electrooxidation on Ni(OH) 2 /NiPd occurred at around 1.28 V vs. HgO/Hg and was highly pH-dependent. At concentrations less than 100 mM, the direct electron transfer took place, whereas at higher ammonia con- centrations it was the indirect electron transfer mechanism. A 9-h galvanostatic electrol- ysis at 20 mA cm 2 showed that 64% of the initial ammonia was degraded at 38% average current efficiency. Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Ammonia is a major toxic pollutant in discharged waters that leads to the eutrophication of the ecosystem [1]; thus its removal is essential for ecological and environmental reasons. On the other hand, anhydrous liquid ammonia is a compact hydrogen carrier, as well as a distribution and storage me- dium: its specific volume of hydrogen content is higher by 70% than liquid hydrogen with 50% increase in the specific energy density [2e7]. Ammonia can also be directly used as a fuel in direct ammonia fuel cells, as the theoretical specific charge of complete ammonia oxidation to N 2 is 4.75 A h g 1 which is 95% of the charge of methanol oxidation to CO 2 [8]. The requirements of recent electrochemical studies to oxidize ammonia consist on finding high-performance electro- catalysts with low overpotential and low production of ni- trogen and carbon oxides. While platinum group metals (PGM) and their bi-metallic alloys (e.g. PtIr, PtRu, PtPd, PtSnO 2 ) exhibit the highest degradation strength and stability towards this process [7e14], their application at industrial scale is restricted due to economical constraints, and therefore, there is an urgent need to develop non-PGM catalysts. To date, very few works are reported on the ammonia electrooxidation reaction on non-PGM. Despic et al. [15] re- ported that Raney nickel showed insignificant activity for the anodic oxidation of ammonia in 5 M KOH because of the * Corresponding author. Tel.: þ1 (613) 562 5800x6302; fax: þ1 (613) 562 5172. E-mail addresses: [email protected], [email protected](E.A. Baranova). 1 Present address: Department of Sustainable & Renewable Energy Engineering, College of Engineering, University of Sharjah, P.O. Box 27272, Sharjah, United Arab Emirates. Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 39 (2014) 41 e48 0360-3199/$ e see front matter Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijhydene.2013.10.024
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ww.sciencedirect.com
i n t e r n a t i o n a l j o u rn a l o f h y d r o g e n en e r g y 3 9 ( 2 0 1 4 ) 4 1e4 8
Available online at w
ScienceDirect
journal homepage: www.elsevier .com/locate/he
Electrochemical behavior of ammonia on Ni98Pd2
nano-structured catalyst
Anis Allagui 1, Saad Sarfraz, Spyridon Ntais, Fares Al momani,Elena A. Baranova*
Department of Chemical & Biological Engineering, University of Ottawa, 161 Louis-Pasteur, Ottawa, ON K1N 6N5,
1 Present address: Department of Sustaina27272, Sharjah, United Arab Emirates.0360-3199/$ e see front matter Copyright ªhttp://dx.doi.org/10.1016/j.ijhydene.2013.10.0
a b s t r a c t
Small amounts of Pd served as a reducing agent to produce sub-100 nm polygonally-shaped
Ni98Pd2 materials in ethylene glycol. As-synthesized particles were crystallized into fcc Ni
with a fraction of b-Ni(OH)2, and exhibited very low to no activity towards ammonia
electrooxidation. Their catalytic activity has been significantly improved by building up a
layer of Ni(OH)2 by cyclic voltammetry between �0.95 and 1.35 V vs. HgO/Hg in NaNO3 at
pH 9. XPS analysis before and after the electrochemical treatment confirmed the trans-
formation of Ni0 to higher state of oxidation. Ammonia electrooxidation on Ni(OH)2/NiPd
occurred at around 1.28 V vs. HgO/Hg and was highly pH-dependent. At concentrations less
than 100 mM, the direct electron transfer took place, whereas at higher ammonia con-
centrations it was the indirect electron transfer mechanism. A 9-h galvanostatic electrol-
ysis at 20 mA cm�2 showed that 64% of the initial ammonia was degraded at 38% average
current efficiency.
Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights
reserved.
1. Introduction requirements of recent electrochemical studies to oxidize
Ammonia is a major toxic pollutant in discharged waters that
leads to the eutrophication of the ecosystem [1]; thus its
removal is essential for ecological and environmental reasons.
On the other hand, anhydrous liquid ammonia is a compact
hydrogen carrier, as well as a distribution and storage me-
dium: its specific volume of hydrogen content is higher by 70%
than liquid hydrogen with 50% increase in the specific energy
density [2e7]. Ammonia can also be directly used as a fuel in
direct ammonia fuel cells, as the theoretical specific charge of
complete ammonia oxidation to N2 is 4.75 A h g�1 which is 95%
of the charge of methanol oxidation to CO2 [8]. The
00x6302; fax: þ1 (613) 562a.ca, obaranov@uottawa
ble & Renewable Energy E
2013, Hydrogen Energy P24
ammonia consist on finding high-performance electro-
catalysts with low overpotential and low production of ni-
trogen and carbon oxides.While platinum groupmetals (PGM)
and their bi-metallic alloys (e.g. PtIr, PtRu, PtPd, PtSnO2)
exhibit the highest degradation strength and stability towards
this process [7e14], their application at industrial scale is
restricted due to economical constraints, and therefore, there
is an urgent need to develop non-PGM catalysts.
To date, very few works are reported on the ammonia
electrooxidation reaction on non-PGM. Despic et al. [15] re-
ported that Raney nickel showed insignificant activity for the
anodic oxidation of ammonia in 5 M KOH because of the
5172..ca (E.A. Baranova).ngineering, College of Engineering, University of Sharjah, P.O. Box
ublications, LLC. Published by Elsevier Ltd. All rights reserved.
i n t e r n a t i o n a l j o u rn a l o f h y d r o g e n en e r g y 3 9 ( 2 0 1 4 ) 4 1e4 8 47
current efficiency. We concluded that Ni-rich Ni(OH)2/NiPd is
an effective catalyst for ammonia electrooxidation in alkaline
media.
Acknowledgments
The authors would like to thank the Natural Science and En-
gineering Research Council (NSERC) for financial support. Anis
Allagui acknowledges the support from Fonds quebecois de la
recherche sur la nature et les technologies (FQRNT) for the
Postdoctoral Fellowship.
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