Conspectus
Metal oxide semiconductors have many features
that make them attractive
for both fundamental and applied studies. For example, these compounds
contain elements (e.g., Fe, Cu, Ti, etc.) that are derived from minerals
rendering them earth-abundant and, most often, are also not toxic.
Therefore, they have been examined for possible applicability in a
very diverse range of technological applications including photovoltaic
solar cells, charge storage devices, displays, smart windows, touch
screens, etc. The fact that metal oxide semiconductors have both n- and p-type conductivity makes them amenable
for use as hetero- or homojunctions in microelectronic devices and
as photoelectrodes in solar water-splitting devices. This Account
presents a review of collaborative research on the electrosynthesis
of metal oxides from our respective groups against the backdrop of
key developments on this topic. The many variants that interfacial
chemical modification schemes offer are shown herein to lead to the
targeted synthesis of a wide array of not only simple binary metal
oxides but also more complex chemistries involving multinary compound
semiconductors and alloys.
This Account presents our perspective
on how parallel developments
in the understanding of and ability to manipulate electrode–electrolyte
interfaces have correspondingly enabled the innovation of a broad
array of electrosynthetic strategies. These coupled with the advent
of versatile tools to probe interfacial processes (undoubtedly, a
child of the nanotechnology “revolution”) afford an
operando examination of how effective the strategies are to secure
the targeted metal oxide product as well as the mechanistic nuances.
Flow electrosynthesis, for example, removes many of the complications
accruing from the accumulation of interfering side productsveritably,
this is an Achilles heel of the electrosynthesis approach. Coupling
flow electrosynthesis with downstream analysis tools based on spectroscopic
or electroanalytical probes opens up the possibility of immediate
process feedback and optimization. The combination of electrosynthesis,
stripping voltammetry, and electrochemical quartz crystal nanogravimetry
(EQCN), either in a static or in a dynamic (flow) platform, is shown
below to offer intriguing possibilities for metal oxide electrosynthesis.
While many of the examples below are based on our current and recent
research and in other laboratories, unlocking even more potential
will hinge on future refinements and innovations that surely are around
the corner.