Download Intermetallic Catalysts: An Efficient Approach for the Reduction in the

Intermetallic Catalysts: An Efficient Approach for the Reduction in the Amounts of the
Precious Metals
Enormous efforts have been spent to
prevent the exhaust gas emissions in various
sectors by creation of new generation of energy,
such as fuel cells. Production of efficient fuel
cells with environment-friendly emissions for
instance
H 2O
have
taken
paramount
importance for the automobile and/or portable
energy generator applications (Figure 1).
Currently, most of the fuel cell technologies
are largely depended on the platinum group
metals (PGM) (Pt, Pd, Rh). These PGM have
Figure. 1 Schematic illustrations of fuel cell
been utilized for both anode and cathode catalysts which are immobilized in the form of nanoparticles
on supporting materials for instance, carbon. Although PGM showed an outstanding catalytic behavior
towards fuel cell applications, however, there would be an essential need to investigate the catalysts
that are containing less PGM or non-PGM due to the concerns over the cost and availability of PGM.
The goal of this proposal is to develop the electrode materials containing less- and/or non PGM
for fuel cells.
The anode and/or cathode catalysts containing less PGM can be achieved by synthesizing
of intermetallic phase of PGM with d- and f- block elements. This is because, the ever synthesized
PGM-based intermetallic catalysts with lower amounts of precious metals showed higher catalytic
activity for fuel cell and/or exhaust purification applications than pure PGM. (Langmuir, 2010, 26,
11446-11451; Chem. Comm. 2012. DOI: 10.1039/C2CC31039B).
Current research activities have demonstrated that the catalytic centers other than PGM, such as
Au, Cu, Ni, etc. also show the catalytic activity towards the conversion of fuels for instance CH3OH.
However, the conversion efficiency of the fuel cell catalysts is much lower than PGM. Also, the major
concern over these catalytic centers is the poor stability due to the formation of H2O2 at the cathode
surface which also contributes high over potential (> 0.3 V) (sluggish kinetics). Therefore, stable, less
PGM and/or non PGM intermetallic catalyst with d- and f- block elements would be developed to
achieve superior activity of fuel cells. The developed catalytic centers would be tested on various
possible fuels including NaBH4, N2H4 to determine the conversion efficiency. The stability of these
catalytic centers would also be tested in the presence of H2O2. Finally, the stable, better-performed
catalytic centers would be assembled on the desired supporting materials to realize the practical
catalyst for fuel cell applications.
Proposed plan
(i) Synthesis of PGM and nonPGM-based
intermetallic
catalysts
PGM based intermetallic
catalytic
centers
would
be
prepared with the combination of
the other d- and f-block elements
on various supporting materials,
for
instance
vulcan
carbon,
carbon nanotubes, graphenes, etc.
The relevant PGM precursors
Figure 1. Schematic illustration for the synthesis of intermetallic
would be mixed at the appropriate
phase for both PGM and non- PGM and dispersion of intermetallic
compositions and reduced by very
catalytic centers on support under Ar environment.
strong reducing agent, such as sodium naphthalide as shown in the Figure 1. A sodium-naphthalide
solution can be prepared by dissolving of the appropriate amounts of sodium metal and naphthalene in
tetrahydrofuran under inert environment. Non-PGM based intermetallic catalytic centers would be
prepared as similar to PGM-based intermetallic catalytic centers by using non-PGM precursors.
(ii) Characterization
The formation and composition of intermetallic phase for both PGM and non-PGM catalytic
centers would be confirmed by X-ray diffraction, X-ray photoelectron spectroscopy and single particle
energy dispersive X-ray spectroscopy. The particle size, morphology, and dispersivity of assynthesized nanoparticles should be examined by using transmission electron microscope (TEM). The
catalytic activity of the intermetallic catalytic centers on various possible fuels would be tested using
cyclic voltammetry. Pure PGM catalysts would be used as a standard to compare the catalytic activity.
(iii) Merits
™
Catalytic activity towards fuel cell applications should be enhanced considerably than PGM
catalysts.
™
Intermetallic PGM catalyst is very stable against most of the H2O2
™
Intermetallic PGM catalyst should require only small amounts of precious metals and therefore
the cost of the production of fuel cell catalysts can be reduced considerably.
™
The catalytic centers can be prepared at less than 5 nm by this proposed method which is one of
the preliminary requirements to attain large surface area of catalytic centers.
™
According to proposed method, intermetallic phase of PGM can be prepared even at room
temperature in the presence of very strong reducing agent such as sodium naphthalide. (Note: Most of
the PGM and/or non PGM-based intermetallic phase can be formed solely at elevated temperature
above 1000 °C.)
(iv) Demerits
™
It is not necessary that all intermetallic phase of both PGM and/or non-PGM show higher
catalytic activity towards fuel cell application than pure PGM.
™
Inert atmosphere (< 5ppm of O2 and H2O) would be required for the preparation of sodium
naphthalide.
(v) How to overcome?
™
The current glove box technologies provide the moisture- and oxygen-free environment.
™
Alternative methods would be tried to produce an intermetallic phase of both PGM and/or non-
PGM.
™
It is also necessary to check the reducing capability of the metal ions with other reducing agents
than sodium naphthalide.
(vi) Impacts
™
The proposed catalytic centers can be used for viable fuel cells.
™
Both PGM and/or non-PGM intermetallic catalysts would be an alternative candidate to the
precious metal catalysts.
™
The proposed catalysts can be prepared at reasonable cost.
™
The amounts of precious metals can be greatly reduced for the future practical catalysts.
™
Toxic gases-free environment can be achieved.