(599e) Highly Active Robust F Doped Transition Metal Oxide Based Solid Solution Electro-Catalyst for Acidic Medium Oxygen Evolution Reaction in PEM Based Water Electrolysis

           The vast consumption of fossil fuels for meeting the energy
demand has led to major unsustainable environmental concerns due to excessive
greenhouse gas emissions warranting the identification and development of clean
non-carbonaceous energy sources.^1-5 In this regard, hydrogen has been
identified as a clean, non-carbonaceous and potential energy source with
superior energy density than currently adopted carbonaceous energy sources for
meeting the global energy demand. However, efficient and economic production
along with cost-effective storage and distribution of hydrogen utilizing the
clean non-carbonaceous approach is of paramount importance before universal
adoption of hydrogen as a clean energy source in the impending non-carbonaceous
fuel economy. Along these lines, electricity driven water splitting (water
electrolysis) is a frontrunner among other clean pollution free approaches for
hydrogen production (having low carbon footprint). The commercial development
of water electrolysis is thwarted due to the need of expensive and precious
noble metals based electro-catalysts (Pt, IrO₂) which exhibit
excellent electro-catalytic activity and stability for oxygen evolution
reaction (OER) in acid assisted proton exchange membrane (PEM) based water
electrolysis. Hence, the identification and development of novel
reduced noble metal containing electro-catalysts exhibiting excellent electro-catalytic
activity and superior long term electrochemical stability similar/superior to state
of the art OER electro-catalyst IrO₂ in harsh and highly acidic
operating conditions of OER, will aid in the reduction of capital cost of water
electrolysis cells and thus, its progression towards commercialization.⁶

          With this aim in mind, exploiting theoretical first principles
calculations of the total energies and
electronic structures, fluorine doped transition metal (TM) oxide based solid
solution electro-catalyst containing significantly lower noble metal content
has been identified exhibiting surface electronic structure and electro-catalytic
activity similar to that IrO₂.The thin films of 10 wt. % F doped (TM_1-xZ_x)O₂
(x=0.2, 0.3, 0.4; Z is a noble metal) coated on Ti foil were synthesized and studied as electro-catalyst for OER in acidic
media. Fig. 1 shows the
SEM micrograph showing the nanoscale architecture of the representative
composition (TM_0.8Z_0.2)O₂:10F.
Elemental x-ray maps show homogeneous distribution of elements throughout the material
without any segregation at specific site.

          
Electrochemical characterization of the synthesized electro-catalysts has been
carried out in a three-electrode configuration using 0.5 M sulfuric acid (H₂SO₄)
solution as a proton source as well as the electrolyte, Pt wire as counter
electrode and Hg/Hg₂SO₄ as the reference electrode (+0.65
V with respect to normal hydrogen electrode, NHE), with a scan rate of 10
mV/sec and at temperature of 40⁰C. (TM_1-xZ_x)O₂:10F (for x =
0.2, 0.3, 0.4) electro-catalysts (total loading = 0.3 mg/cm²)
exhibit excellent electrochemical activity for OER with significantly reduced
onset potential (~1.35 vs RHE)
compared to that of IrO₂ (~1.43 vs RHE) (total loading=0.3 mg/cm²). In
addition, (TM_1-xZ_x)O₂:10F displayed
outstanding ~8, ~14 and ~15 fold improved
electro-catalytic activity at ~1.45 V (vs
RHE) compared to IrO₂. Following chronoamperometry test conducted in 0.5 M H₂SO₄
solution at ~1.55 V (vs RHE) for 24 h, minimal loss in
current density as well as excellent long term electrochemical stability was
observed for (TM_0.8Z_0.2)O₂:10F,
similar to that of IrO₂.

          
These results show the promise of (TM_1-xZ_x)O₂:10F electro-catalyst portending ~80%
reduction in noble metal content displaying significantly much higher
electro-catalytic activity than IrO₂ and superior long term
stability. In addition, these results show the promise of the formation F-doped
solid solution in improving the electronic, physical, chemical and
electro-catalytic properties of the doped TM oxide structures in acidic media. This
will aid in significant reduction in the
overall capital cost of PEM based water electrolysis for efficient and economic
production of hydrogen. The results of these studies will be presented and discussed.

References:

1              Patel,
P. P. et al. Nanostructured robust cobalt metal alloy based anode
electro-catalysts exhibiting remarkably high performance and durability for
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2              Patel,
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3              Patel,
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4              Patel,
P. P. et al. Vertically aligned nitrogen doped (Sn,Nb)O₂
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5              Patel,
P. P. et al. Nitrogen and cobalt co-doped zinc oxide nanowires – Viable
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6              Datta,
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Acknowledgements:

          
The authors gratefully acknowledge the financial support of NSF-CBET grant#
1511390. The authors also acknowledge the Edward R. Weidlein Chair
Professorship funds and the Center for Complex Engineered Multifunctional
Materials (CCEMM) for partial support of this research.