| Summary: | <p>This thesis describes investigations into the synthesis of ammonia using the ceramic proton conductor,
barium zirconate. Described are the results of the fabrication and testing of barium zirconate cells for the
electrochemical synthesis of ammonia, and investigations on the use of proton conducting ceramics as
supports in heterogeneous catalysis. While ammonia synthesis is perhaps the most studied and optimised
chemical reaction, new challenges are facing the century old Haber-Bosch process in the 21st century. As
part of the need to move towards a carbon-free economy, new catalysts, and processes for the synthesis of
ammonia are currently being developed.</p>
<p>Electrochemical ammonia synthesis is a promising avenue of research, attracting much interest in recent
years. However, the goal of selectively and efficiently reducing the highly stable dinitrogen bond is not easy
to realise. Previous literature investigations of this process in high temperature proton conducting cells have
focussed on optimisation of electrolytes, leaving electrode catalysts relatively unexplored. This thesis aims
to investigate how modification of electrode catalysts may alter rates of electrochemical ammonia synthesis.
It is found that modification of the anode and cathode materials can dramatically alter the rates of
electrochemical processes, but that the elucidation of electrochemical ammonia is more complex.</p>
<p>Barium zirconate was explored as support material for ruthenium catalysts. Due to the ability of the
barium zirconate lattice to trap and store protons, it was proposed this could influence the ammonia
synthesis reaction over ruthenium particles. A systematic study of how barium zirconate materials may
promote ammonia synthesis was undertaken.</p>
<p>It was found that use of doped barium zirconate supports can provide a significant promotion effect
for the synthesis of ammonia over ruthenium nanocatalysts. This promoting effect which, can be quantified
using kinetic parameters, is ascribed to differences in the proton conductivities of the ceramic materials.
The mechanism of this promotion is explored using neutron diffraction and in-situ x-ray photoelectron
spectroscopy techniques.</p>
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