Contenu connexe Similaire à Cy 241-assignment03 (20) 2. Introduction:
Hydrogen fuel cells can be an efficient and alternate source of power, as some of
the variants of hydrogen fuel cells doesn’t produce greenhouse gases. The energy efficiency of
a fuel cell is generally between 40–60%, or up to 85% efficient if waste heat is captured for use.
Hydrogen is a most common fuel for its source is abundant.
Though Hydrogen fuel cells are efficient and lucrative sources of energy, much of
the capability is untapped for cost reasons. 40% of the cost of the Hydrogen fuel cell(HFC) is
because of the Platinum(Pt) cathode catalysts and the other reason stems from the intolerance
of catalyst towards CarbonMonoxide(CO). It is observed that CO concentration so low as few
10’s or 100’s of ppm can poisson the catalyst by reducing the active sites and hence reducing
the catalytic capacity and efficiency. This intolerance of catalyst towards CO renders common
way of hydrogen production through steam reforming of light useless as it contains CO to 13%,
hence forcing one to produce hydrogen by electrolysis of water. Because of the high cost of
HFC’s they are not yet successful in replacing IC engines.
The U.S. Department of Energy estimates that platinumbased catalysts will need
to use roughly four times less platinum than is used in current PEM fuel cell designs in order to
represent a realistic alternative to internal combustion engines.[1] Research is being carried out
with the following goals:
1. To increase the efficacy of the catalyst, the catalysts efficiency should be increased at
least 4 times to be able to replace IC engines.
2. To make it more tolerant to impurities like CO, even CO in ppm amount can poisson the
catalyst and render the catalyst useless. Generally high temperature Fuel cells are used
to avoid the catalyst poisoning(one of the variants of Fuel cells).
3. To design a metal free catalyst model that can be easily synthesised, with alloys or
composites that are copiously available, tolerant to CO poisonous and less degrading
with usage.
While these are some of the factors that stood as impediments, the research area has seen
some game changers.
Some game changers being nano technology and other nano imaging techniques
these help in better and more control over synthesis of defect less and desired amalgamate of
the various elements.
Also better imaging techniques mean that one can observe the adsorption and surface
absorptions better and this can help in better synthesis of the heterogeneous
Hydrogen has a high energy density and is a great energy carrier, Schaak said, but it requires
energy to produce. To make its production practical, scientists have been searching for a way to
trigger the required chemical reactions with an inexpensive catalyst.
1. Since then there has been a lot of research for a non metallic alternate to Pt and also
ways to 1. increase active sites in the catalyst either by occluding the Pt atoms on a nano
material.
2. Pt occlusions on other metals/elements to make it more CO tolerant.
5. crossover/CO poisoning effects and long term cycle stability. It is also implied that the catalyst in
itself is much cheaper because of easy synthesis and also pervasive nature of primary
elements.
Hetro atom or covalently bonded atoms can better function in Oxygen Reduction
reaction(ORR). The difference in electronegativity (x) between the heteroatom dopants (B =
2.04, I = 2.66, N = 3.04, P = 2.19 and S = 2.58) and carbon atom (2.55) in covalently doped
graphitic carbon frameworks can polarize adjacent carbon atoms. Indeed, quantum mechanics
calculations revealed that the electron accepting/donating ability of the heteroatom dopants
created net positive/negative charges on adjacent carbon atoms in graphitic lattice to facilitate
the oxygen reduction process. Thus, both the verticallyaligned nitrogendoped carbon
nanotubes (VANCNTs) and nitrogendoped graphene (Ngraphene) catalyzed an efficient
fourelectron ORR process with a higher electrocatalytic activity and better operation stability
than the commercially available Pt/Cbased electrocatalyst (Pt: 20 wt%, Vulcan XC72R). Many
of these were untapped because of their intricate synthesis processes and here in this paper
authors propose a very simple and scalable synthesis that is ball milling of graphite with halogen.
Figure 2 shows and summarises the synthesis step. The order of Electrocatalysis observed
was IGnP>BrIGnP>ClGnP, where XGnP is X halogenated grapheme nano platelets.
In a test of durability, electrodes coated with XGnP's maintained 85.6 to 87.4 percent of
their initial current after 10,000 cycles while platinum electrodes maintained only 62.5 percent.
The performance of graphene based catalysts was unaffected with induction of CO impurity with
Hydrogen fuel. When methanol was added to replicate methanol crossover from the anode to
cathode in direct methanol fuel cells, the current density of the platinum catalyst dropped
sharply. Again, the graphenebased catalysts were unaffected. Also in comparison with the Pt/C
commercially available catalyst: a cathode coated with iodineedged nanoplatelets performed
best. A cathode coated with bromineedged nanoparticles generated 7 percent less current than
the commercial cathode coated with platinum, the chlorineedged nanoplatelets 40 percent less.
In conclusion, a metalfree easy to synthesise and easily available catalyst was
developed and tested to be better than Pt/C and more robust than Pt/C. Though the authors
state that they have to further optimise the nanocatalyst, the scope of commercialisation is very
high.
Electrocatalyst based on carbon nanotubesgraphene complexes
This section summarises [4].
Although this paper doesn't aim at commercially replacing Pt/C, it obviates some
misconceptions and also proposes a new nano catalyst based on carbon nanotubes whose
catalytic activity is close to platinum and thus considered relevant.
For the study, the Stanford team used multiwalled carbon nanotubes consisting of two
or three concentric tubes nested together. The scientists showed that shredding the outer wall,
while leaving the inner walls intact, enhances catalytic activity in nanotubes, yet does not
interfere with their ability to conduct electricity. A typical carbon nanotube has few defects. "But
defects are actually important to promote the formation of catalytic sites and to render the
nanotube very active for catalytic reactions.
The multiwalled carbon nanotube is treated to unzip outer wall and is as depicted in
6. figure3. Authors claim that though the outer wall is unzipped the conductivity remains intact
because of the inner wall and hence can help in charge mobility. The research also concluded
that metal impurities play a major role in the catalysis and can't be ignored.
NanoPhosphide based nano catalysts
This section constitutes information from [5].
According to a team lead by Chemistry professor in Penn state University and patent
filed, NickelPhosphide nano particles in solution has produced current at a greater efficacy than
Pt/C counterpart. This was possible because of very high surface area in nanoparticles and
increased number of active sites.
Though it is implied that it will be lot cheaper than Pt/C, it is unknown the effect of
impurities in Hydrogen source on the catalyst. It is also unknown the durability of the catalyst.
The research group states their future goal as to further improve the performance of these
nanoparticles and to understand what makes them function the way they do.
Summary:
We are evidencing a revolution in the research of nano catalysts with the advent of
Nanoscience and nano imaging techniques like STEM. Nanocatalysts have a larger scope in
catalysis because of increased surface area, possibility of producing defect free and hence very
conductive. Also because of the enhanced imaging techniques, the pioneers are able to observe
the factors that influence the active sites and catalytic abilities and thus leading to better
catalysts like NickelPhosphide.
We have seen metalfree catalysts that can function just as well as Pt/C and also have
seen modification to Pt catalysts to nanocatalysts to improve the robustness and alleviate cost.
We feel that the results that were presented here suffices for large scale
commercialisation of Hydrogen Fuel cells. These fuel cells can be much cheaper because of the
reduced catalyst cost which constitutes 40% and also reduced cost of hydrogen fuel because of
the relaxed constraint of CO poisoning. The day when HFC's replace IC engines is near and can
be one stop solution for depriving sources of oils and greenhouse gases. We feel the only
possible piece of puzzle that needs to be solved is efficient(Volume/weight ratio) and safe
storage of Hydrogen.
References:
1. Hydrogen, Fuel Cells & Infrastructure Technologies Program MultiYear Research
Development and Demonstration Plan, U.S. Department of Energy, October 2007
2. YuChi Hsieh, Yu Zhang, Dong Su, Vyacheslav Volkov, Rui Si, Lijun Wu, Yimei Zhu,
Wei An, Ping Liu, Ping He, Siyu Ye, Radoslav R. Adzic & Jia X Wang (2013) Ordered
bilayer ruthenium–platinum coreshell nanoparticles as carbon monoxidetolerant fuel cell
catalysts. Nature Communications 4, Article number: 2466 doi: 10.1038/ncomms3466
3. Jeon, I., Choi, H., Choi, M., Seo, J., Jung, S., Kim, M., Zhang, S., Zhang, L., Xia, Z., Dai, L.
and Others. 2013. Facile, scalable synthesis of edgehalogenated graphene
nanoplatelets as efficient metalfree eletrocatalysts for oxygen reduction reaction.
7. Scientific reports, 3.
4. Li, Y., Zhou, W., Wang, H., Xie, L., Liang, Y., Wei, F., Idrobo, J., Pennycook, S. and Dai,
H. 2012. An oxygen reduction electrocatalyst based on carbon nanotubegraphene
complexes. Nature nanotechnology, 7 (6), pp. 394400.
5. Theengineer.co.uk. 2013. Nanocatalyst could aid hydrogen production | News | The
Engineer. [online] Available at:
http://www.theengineer.co.uk/energyandenvironment/news/nanocatalystcouldaidhyd
rogenproduction/1016531.article [Accessed: 9 Nov 2013].
External Links:
1. Batteries, '. 2012. 'Unzipped' carbon nanotubes could help energize fuel cells and
batteries. [online] Available at: http://www.nanowerk.com/news/newsid=25388.php
[Accessed: 9 Nov 2013].
2. Diolazo, J. 2013. New nanocatalyst for hydrogen production developed at Brookhaven.
[online] Available at:
http://www.ecoseed.org/renewables/hydrogenfuelcells/17082newnanocatalystforhyd
rogenproductiondevelopedatbrookhaven [Accessed: 9 Nov 2013].
3. Hamilton, T. 2013. Nanocrystal Catalyst Transforms Impure Hydrogen into Electricity.
[online] Available at:
http://scicasts.com/greenbiology/1865greennanotechnology/6631nanocrystalcatalyst
transformsimpurehydrogenintoelectricity [Accessed: 9 Nov 2013].
4. Media, B. 2013. Green Car Congress: New coreshell bilayer nanocatalyst tolerant to
CO; potential for lowtemperature fuel cells with reformates. [online] Available at:
http://www.greencarcongress.com/2013/09/20130921bnl.html [Accessed: 9 Nov 2013].
5. MIT Technology Review. 2013. A Cheaper Hydrogen Catalyst | MIT Technology Review.
[online] Available at:
http://www.technologyreview.com/news/416520/acheaperhydrogencatalyst/
[Accessed: 9 Nov 2013].
6. Newscientist.com. 2013. Platinumfree fuel cell promises cheap, green power tech 15
December 2008 New Scientist. [online] Available at:
http://www.newscientist.com/article/dn16275platinumfreefuelcellpromisescheapgree
npower.html#.UnzXdpQY3mQ [Accessed: 9 Nov 2013].
7. ScienceDaily. 2013. Metalfree catalyst outperforms platinum in fuel cell. [online]
Available at: http://www.sciencedaily.com/releases/2013/06/130605111518.htm
![Introduction:
Hydrogen fuel cells can be an efficient and alternate source of power, as some of
the variants of hydrogen fuel cells doesn’t produce greenhouse gases. The energy efficiency of
a fuel cell is generally between 40–60%, or up to 85% efficient if waste heat is captured for use.
Hydrogen is a most common fuel for its source is abundant.
Though Hydrogen fuel cells are efficient and lucrative sources of energy, much of
the capability is untapped for cost reasons. 40% of the cost of the Hydrogen fuel cell(HFC) is
because of the Platinum(Pt) cathode catalysts and the other reason stems from the intolerance
of catalyst towards CarbonMonoxide(CO). It is observed that CO concentration so low as few
10’s or 100’s of ppm can poisson the catalyst by reducing the active sites and hence reducing
the catalytic capacity and efficiency. This intolerance of catalyst towards CO renders common
way of hydrogen production through steam reforming of light useless as it contains CO to 13%,
hence forcing one to produce hydrogen by electrolysis of water. Because of the high cost of
HFC’s they are not yet successful in replacing IC engines.
The U.S. Department of Energy estimates that platinumbased catalysts will need
to use roughly four times less platinum than is used in current PEM fuel cell designs in order to
represent a realistic alternative to internal combustion engines.[1] Research is being carried out
with the following goals:
1. To increase the efficacy of the catalyst, the catalysts efficiency should be increased at
least 4 times to be able to replace IC engines.
2. To make it more tolerant to impurities like CO, even CO in ppm amount can poisson the
catalyst and render the catalyst useless. Generally high temperature Fuel cells are used
to avoid the catalyst poisoning(one of the variants of Fuel cells).
3. To design a metal free catalyst model that can be easily synthesised, with alloys or
composites that are copiously available, tolerant to CO poisonous and less degrading
with usage.
While these are some of the factors that stood as impediments, the research area has seen
some game changers.
Some game changers being nano technology and other nano imaging techniques
these help in better and more control over synthesis of defect less and desired amalgamate of
the various elements.
Also better imaging techniques mean that one can observe the adsorption and surface
absorptions better and this can help in better synthesis of the heterogeneous
Hydrogen has a high energy density and is a great energy carrier, Schaak said, but it requires
energy to produce. To make its production practical, scientists have been searching for a way to
trigger the required chemical reactions with an inexpensive catalyst.
1. Since then there has been a lot of research for a non metallic alternate to Pt and also
ways to 1. increase active sites in the catalyst either by occluding the Pt atoms on a nano
material.
2. Pt occlusions on other metals/elements to make it more CO tolerant.](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)