1. RESEARCH POSTER PRESENTATION DESIGN © 2015
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The poor kinetics of the oxygen evolution reaction (OER) are a
considerable barrier to the development of a water-derived hydrogen fuel.
By doping with iron and scandium, x-ray diffraction confirms that we have
been able to synthesize a series of perovskite SrCoO3-δ (SCO) catalysts of
various crystal structures, culminating in cubic SCO. In doing so, we show
that there is a limited correlation between the crystal structure and OER
performance in alkaline media. Instead, the use of iron as a dopant is found
to decrease the OER overpotential of the SCO by 40 mV in 0.1 M KOH,
and yield catalysts capable of performing water oxidation at an
overpotential of 410 mV at 10 mA/cm2. The doped, cubic SCO catalysts
are found to be more stable than the undoped material when tested for
extended periods, showing only an approximately 3 mV increase in
overpotential over a two hour period at 10 mA/cm2. Our results show that
proper doping of the B-site cation in SCO allows for tuning the structure,
performance, and stability of the oxide as an OER electrocatalyst.
Abstract
In this research, we demonstrate the effects of iron and
scandium doping on the crystal structure and catalytic
performance of SCO electrocatalysts for the OER half-
reaction. As the amount of either dopant in the SCO
increases, the material experiences a shift from a
hexagonal polymorph to the classical cubic perovskite
structure. OER testing shows that despite similar changes
to the crystal structures of both doped catalysts, only the
iron-doped SCO shows improvement with increasing
dopant levels. Therefore, we conclude that the crystal
structure of cobalt-based perovskite polymorphs has little
impact on the OER performance of the catalyst. Rather, it
is the choice of an appropriate catalytically-active metal
such as iron that improves electrocatalytic water oxidation
in SCO. Crystal structure does, however, appear to impact
catalytic stability, as observed in the increased stability of
cubic versus hexagonal SCO under oxidative conditions.
In conclusion, the presence of iron into the SCO lattice
results in the formation of an active, stable cubic
perovskite OER catalyst with an η10 value of 410 mV and
moderate stability over extended periods of operation in
alkaline media.
Voltammetry Results
Acknowledgements
• Water-splitting reactions can yield clean hydrogen fuel
• OER is the rate limiting step and requires more energy than the HER, so
research focuses on performing the OER at minimal overpotentials
• Best-performing catalysts for the OER are expensive and rare metals
such as Ir
• Research groups have focused on developing catalysts from more
abundant first row transition metals (Mn, Fe, Co, etc.)
• Density functional theory (DFT) simulations have found that the
perovskite SrCoO3-δ (SCO) was predicted to be among the most active
catalysts in the perovskite family studied
• Experimental results have found that the predicted and experimental
perovskite structures did not match
• Doping can affect crystal structure
aDepartments of Chemical Engineering and Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
bTexas Materials Institute, University of Texas at Austin, Austin, Texas 78712, United States
Nicholas N. Possisa, Bryan R. Wyganta, William D. Chemelewskib, Oluwaniyi Mabayojea, and C. Buddie Mullinsa,b
Structural and Catalytic Effects of Iron- and Scandium-Doping on a Strontium Cobalt
Oxide Electrocatalyst for Water Oxidation
Background
Overpotential-vs.-time plots.
Material Characterization
HER: 2H+ + 2e-  H2
OER: 4OH-  O2 + 2H2O + 4e-
Overall: 2H2O  2H2 + O2
SEM
XRD
• X-ray diffraction (XRD) shows a clear change in the oxide crystal
structure with doping levels
LSVs of iron- and scandium-doped SCO samples.
XRD spectra for iron-doped and scandium-doped SCO samples.
• Scanning electron microscopy (SEM) reveals that the microparticles are
composed of a collection of sintered nanoparticles
• Qualitatively, all dispersions appear to be of similar topography, with
similar distributions of particles sizes, morphologies, and spacing
• Because morphologies are similar, differences in catalytic performance
should not be caused by differences in morphologies, but by differences in
composition or crystal structure of SCO samples
SEM images of a) 10%Fe-SCO and b) undoped SCO micro-
particle catalysts. Surface morphology for the c) 10%Fe-SCO
and d) undoped SCO microparticles.
Cyclic Voltammetry
Stability
Conclusion
• Crystal structure shifts from hexagonal to orthorhombic to cubic
polymorph with increased doping levels
- Hexagonal (undoped, 1%)  orthorhombic (5%)  cubic (10%)
• Similar trend for both iron- and scandium-doped SCO
• Electrodes perform the OER with 410-450 mV of overpotential
• Iron-doped samples vary with doping level, whereas scandium-doped
samples do not
• Doped samples show improved stability compared to undoped samples
• More cubic crystal structures appear to be more stable
References
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