Abstract:
This thesis concerns investigations on novel multistage electrochemical deposition
of nanostructured systems composed of noble metals platinum, ruthenium, and
gold. Various electrochemical synthetic pathways were systematically explored
producing multilayered nanoscale electrode systems composed of Pt, Ru, or Au on
glassy carbon or crystalline gold used as substrates. Electrochemical pathways
involved sequential surface-limited redox-replacement (SLRR) reactions of
underpotentially-deposited or overpotentially-deposited copper, potentiostatic
dealloying, direct spontaneous deposition of noble metals (without intermediary
steps involving redox-replacement templating reactions) as well as sequential
codeposition of noble metals (with or without SLRR templating reactions).
Fundamental studies were conducted using thermodynamic and kinetic models, in
situ electrochemical techniques and ex situ microscopic, spectroscopic, or
spectrophotometric techniques employed for probing factors controlling electrode
dynamics, electrocatalysis, morphology, bulk and surface compositional properties
of the noble metal-based electrode systems.
Unique multilayered multimetallic nanoclusters synthesized (with binary active
sites of Pt with Ru or Au) exhibited superior electrocatalytic activity towards
methanol or formic acid oxidation reactions when benchmarked to equivalent monometallic multilayered Pt. Hydrodynamic electrokinetic studies of the oxygen
reduction reaction (ORR) on the multilayered monometallic Pt and bimetallic Rucontaining
nanoclusters revealed that the monometallic nanoclusters exhibited
direct four-electron ORR whereas electrocatalysis on the bimetallic ones could be
tuned to proceed via a two-electron reaction pathway. Electrocatalytic bifunctional
reaction mechanisms were especially enhanced by the nanostructured systems
investigated.
Characterisation of multilayered nanoclusters surface and near-surface metal
contents revealed interactions between metal centers, carbon and oxygen containing
surface functional groups on the glassy carbon, which appeared to have played a
significant role in the overall stabilization and catalytic activity of the
electrochemically immobilized nanoclusters.
Physico chemical models and characteristics of intermediary Cu adlayers in the
electrosynthetic pathways revealed role of Cu surface coverage (within the
framework of electrochemical isotherms with kinetic and thermodynamic
parameters) and heterogeneity effects, adatom substrate interactions as well as
adatom adatom lateral interactions within individual adlayers during multilayer Pt
growth on crystalline Au. New relationships for computing trends in the apparent
Gibbs free energy of the SLRR reaction provided insights on reaction energetics of
the interfacial Pt layered growth.
