The preparation and screening of nanoparticle (NP) electrocatalysts
for improved electrocatalytic oxygen evolution reactions (OER) will
require a better understanding and optimization of the interactions
between NPs and their support. First-row transition metals are used
extensively as electrocatalysts in electrochemical energy storage
and conversion systems. These electrocatalysts undergo transformations
in their phase and surface morphology, which are induced by oxidizing
potentials in the alkaline medium. A template-assisted approach to
prepare electrodes with regular surface morphologies was used to monitor
interactions between the NPs and their support both before and after
prolonged electrochemical aging. A template-assisted method was used
to prepare uniform surface inclusions of nickel ferrite (NiFe2O4) NPs on conductive nickel (Ni) supports for
evaluation toward the OER. Electron microscopy-based methods were
used to assess the resulting transformations of the embedded NPs within
the Ni support matrix. Electrochemical aging of these textured electrodes
was conducted by cyclic voltammetry (CV) techniques, which resulted
in the growth of a 200 nm thick Ni oxy(hydroxide) film on the surfaces
of the Ni supports. The growth of the active surface layer led to
the encapsulation of the NiFe2O4 NPs as determined
by correlative energy dispersive X-ray spectroscopy (EDS) techniques.
The NP-modified electrodes exhibited reduced overpotentials and higher
sustained current densities for the OER when compared to pure Ni supports.
The well-defined morphologies and NP surface inclusions prepared by
the template-assisted approach could serve as a platform for investigating
additional NP–support interactions for electrocatalytic systems.
We provide the initial
demonstration of a general thin film deposition
technique that leverages the unique solubility properties of supercritical
fluids. The technique is the solution-phase analogue of physical vapor
deposition and allows thin films of a semiconducting polymer to be
grown without the need for in situ chemical reactions. Film growth
is approximately linear with time, indicating that film thickness
can be controlled in a straightforward manner by varying the time
of deposition. To further demonstrate the flexibility of the technique,
we demonstrate precise control over the location of material deposition
using a combination of photolithography and resistive heating. The
potential for scalable manufacturing is demonstrated by use of a master
to control deposition onto a flexible polymer film. Finally, we demonstrate
a unique deposition capability of this technique by depositing patterns
onto the curved interior of a hemisphere made from a silicone elastomer.
This capability is not possible with any printing or line-of-sight
deposition technique. More generally, the ability to control the deposition
of solution processed materials with high accuracy provides the long
sought after bridge between top-down and bottom-up self-assembly.
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