(486b) Nanostructured Robust Cobalt Alloy Based Anode Electro-Catalysts with Superior Electrochemical Activity for Proton Exchange Membrane Fuel Cells

          The rapid depletion of fossil fuels and increased
environmental pollution due to colossal consumption of ubiquitous fossil-fuel
is a major impetus for efficient use of energy and exploration of renewable and
clean energy sources.^{1, 2} Generation of electricity
from renewable energy sources, such as solar, wind without producing carbon
dioxide-an undesirable green house pollutant, offers enormous potential for
meeting the future energy demands.³ Development
of novel and efficient technology to store electrical energy is thus extremely important
for meeting the global energy demand and environmental concerns. Fuel cell
technology has garnered increasing attention over the years as it provides
promising and sustainable approach for the production of continuous power with potential
for reduced greenhouse gas emissions and higher efficiencies compared to hitherto
combustion based technologies. In
particular, proton exchange membrane fuel cells (PEMFCs) are considered to be suitable
power sources for automobiles, consumer electronic devices and auxiliary power
units due to the advantages of using hydrogen as fuel which is light-weight, clean
and has a low operating temperature. Hydrogen also offers quick start-up, extended
durability of system components, high power density with low weight and volume
due to elimination of additional steps needed for fuel reformation. The simple system
design would be reflected as an ease in operation, reduced cost and high
reliability. However, capital cost of the system is a major constraint limiting
commercialization of PEMFCs due to use of expensive noble metal based Pt/C
catalyst. Hence, development of non-noble metal based catalysts with high
electrochemical activity and durability is of specific interest to replace Pt/C
and thus, lower the cost of PEMFC system.

         
The present study explores Co_1-x(Ir_x) (x=0.2, 0.3, 0.4) solid solution alloys as anode electro-catalyst for
hydrogen oxidation reaction (HOR) for PEMFC applications. Fig. 1 shows the
SEM micrograph of Co_0.7(Ir_0.3) with x-ray mapping of Co
and Ir. The x-ray mapping shows homogeneous distribution of Co and Ir without
segregation on any specific site. Electrochemical characterization has been
carried out in H₂ saturated 0.5 M sulfuric acid (H₂SO₄)
as an electrolyte, employing Pt wire as the counter electrode and Hg/Hg₂SO₄
as the reference electrode (+0.65 V with respect to normal hydrogen electrode,
NHE), using a scan rate of 10 mV/sec at a temperature of 40^oC. The solid
solution electro-catalyst Co_1-x(Ir_x) (x=0.3, 0.4) exhibit superior electrochemical activity than Pt/C with
electrochemical stability matching to that of Pt/C. In addition, to obtain a
better understanding of the fundamental electrochemical activity of Co_1-x(Ir_x)
electro-catalyst, first-principles calculations of the total energies and
electronic structures of the model systems with chemical compositions similar
to those of the experimentally synthesized materials have been carried out to
complement the present experimental study.

         
The electrochemical study conducted in
half-cell configuration and single PEMFC full cell results shows the potential
of Co_1-x(Ir_x) (x=0.3, 0.4) as
replacement of Pt/C, owing to the excellent
electrochemical performance and stability. These results portend significant
reduction in the overall capital cost of PEMFCs. The results of structural characterization and
electrochemical activity of these electro-catalysts will be presented and
discussed.

References

1.     C. Liu, F. Li, L.-P. Ma and
H.-M. Cheng, Advanced Materials, 2010, 22, E28-E62.

2.     J. R. Miller, Science,
2012, 335, 1312-1313.

3.     M. S. Whittingham, Mrs
Bull, 2008, 33, 411-419.

Acknowledgement

Research
supported by the CBET, National Science Foundation, Grant-NSF-0933141. PNK also
acknowledges the Edward R. Weidlein Chair Professorship funds and the Center
for Complex Engineered Multifunctional Materials (CCEMM) for partial support of
this research.