LaMnO3 is an inexpensive alternative to precious metals (e.g. platinum)
as a catalyst for the oxygen reduction reaction (ORR) in
alkaline fuel cells (AFCs). In fact, recent studies have shown that
among a range of non-noble metal catalysts, LaMnO3 provides
the highest catalytic activity. However, further
development of this catalyst is limited by the fact that very
little is known about LaMnO3 in the AFC environment.
While it has been established that the bulk phase
possesses an orthorhombic structure, it
has not been possible to determine the structure of the surfaces
or the sites active towards the ORR.
In this work, therefore, periodic hybrid-exchange (B3LYP) density functional
calculations are performed in order to understand the
origins of the catalytic activity of LaMnO3. The long
term goal is to suggest strategies for optimising
the activity of LaMnO3 through control of
its crystallite morphology.

Initially, the phase stability of LaMnO3 with respect to
its competing (La, Mn) oxides is determined by accurate
calculation of the Gibbs formation energies of each
compound (1.6% mean error).
The accuracy achieved is higher than in previous literature,
validating the methodology adopted and the
reliability of the chemical potentials determined to
limit the stability of the bulk and surfaces of LaMnO3.
Having determined the ground state of each Mn oxide
it was possible to simulate electron energy-loss spectroscopy (EELS) for
Mn in different valence states and local environments.
The simulated EELS demonstrated that it is possible to identify its
oxidation state and local coordination (i.e. the surface structure)
on LaMnO3 surface terminations, based on the shift and shape
of predicted L3 edges, which correlate well with
measured EEL spectra.

Calculations of the low-index, stoichiometric and non-polar
surfaces of LaMnO3 were then performed in order to predict the
equilibrium crystal morphology. For each low energy surface
the adsorption sites were also identified. The energetics of the
surfaces are rationalised in terms of the
cleavage of Jahn-Teller distorted Mn-O bonds, the
compensation of undercoordination for ions in
the terminating layer and relaxation effects.

Finally the adsorption sites identified are investigated
by adsorption of molecular O2. The
binding energies, adsorbate structure and charge transfer
are analysed to predict the reactivity of each site.
Results indicate that Jahn-Teller distortion
and the coordination of Mn sites modulate
the binding strength of O2.

The main results presented are the crystallite morphology,
the identification of surface reaction sites and the chemical
characterisation of those sites. This is a theoretical
characterisation of the LaMnO3 catalyst providing detailed
atomistic information that has not been possible
to deduce from experiment.