2 research outputs found
Spatial Mapping of Methanol Oxidation Activity on a Monolithic Variable-Composition PtNi Alloy Using Synchrotron Infrared Microspectroscopy
The
use of synchrotron-sourced infrared radiation to map the electrochemical
activity of a binary metal (Pt and Ni) alloy is demonstrated. The
alloy is created in such a way that its metal concentration varies
along one of its dimensions thus creating a continuum of electrocatalyst
compositions on a single electrode. Localized methanol oxidation activity
is determined spectroscopically by measuring the rate of CO<sub>2</sub> production at variable positions along the alloy concentration gradient
using an infrared microscope. Numerical simulations of the kinetically
controlled reaction demonstrate that qualitative assessment of relative
reaction rates is possible as long as the reaction is followed on
time scales smaller than those that lead to diffusional broadening.
Characterization of the alloy before and after electrochemical experiments
reveals significant levels of base metal leaching. Highly dealloyed
regions of the sample show the highest rates of methanol activity
and have a final Ni atomic composition of approximately 5%. Surface
roughening from the dealloying process is shown to be at least partially
responsible for enhanced activity
Femtomole Infrared Spectroscopy at the Electrified Metal–Solution Interface
Characterization
of surface adsorbed species using infrared (IR)
spectroscopy provides valuable information concerning interfacial
chemical and physical processes. However, <i>in situ</i> infrared studies of surface areas approaching the IR diffraction
limit, such as micrometer scale electrodes, require a hitherto unrealized
means to obtain high signal-to-noise (S/N) spectra from femtomole
quantities of adsorbed molecules. A major methodological breakthrough
is described that couples the high brilliance of synchrotron-sourced
infrared microscopy with attenuated total reflection surface enhanced
infrared spectroscopy (ATR-SEIRAS). The method is shown to allow the
spectral measurement of a monolayer of 4-methoxypyridine (MOP) adsorbed
on a surface enhancing gold film electrode under fully operational
electrochemistry conditions. A factor of 15 noise improvement is achieved
with small apertures using synchrotron IR relative to a thermal IR
source. The very low noise levels allow the measurement of high quality
IR spectra of 2.5 fmol of molecules confined to a 125 μm<sup>2</sup> beam spot