Operando Reflectance Microscopy on Polycrystalline Surfaces in Thermal Catalysis, Electrocatalysis, and Corrosion

Abstract

We have developed a microscope with a spatial resolution of 5 μm, which can be used to image the two-dimensional surface optical reflectance (2D-SOR) of polycrystalline samples in operando conditions. Within the field of surface science, operando tools that give information about the surface structure or chemistry of a sample under realistic experimental conditions have proven to be very valuable to understand the intrinsic reaction mechanisms in thermal catalysis, electrocatalysis, and corrosion science. To study heterogeneous surfaces in situ , the experimental technique must both have spatial resolution and be able to probe through gas or electrolyte. Traditional electron-based surface science techniques are difficult to use under high gas pressure conditions or in an electrolyte due to the short mean free path of electrons. Since it uses visible light, SOR can easily be used under high gas pressure conditions and in the presence of an electrolyte. In this work, we use SOR in combination with a light microscope to gain information about the surface under realistic experimental conditions. We demonstrate this by studying the different grains of three polycrystalline samples: Pd during CO oxidation, Au in electrocatalysis, and duplex stainless steel in corrosion. Optical light-based techniques such as SOR could prove to be a good alternative or addition to more complicated techniques in improving our understanding of complex polycrystalline surfaces with operando measurements.

Visualizing the Gas Diffusion Induced Ignition of a Catalytic Reaction

“…2D-SOR data as shown in Figure confirms that the reflectivity decreases radially starting from the sample center. We have previously shown that such a small decrease of the reflectivity coincides with oxide formation. , The formation of an oxide in similar conditions has also been described in the literature. , It is thus likely that oxide formation is driven by the local gas conditions present at ignition. An argument as to why the reflectance difference is not due to a temperature dependency is provided in the SI.…”

“…We have previously shown that such a small decrease of the reflectivity coincides with oxide formation. 24,28 The formation of an oxide in similar conditions has also been described in the literature. 3,29 It is thus likely that oxide formation is driven by the local gas conditions present at ignition.…”

Electrocatalytic Reduction of Nitrogen to Ammonia: the Roles of Lattice O and N in Reduction at Vanadium Oxynitride Surfaces

“…In probing gas/surface interactions, surface-sensitive probes such as X-ray photoelectron spectroscopy (XPS) have been, for some time, a critical tool for understanding heterogeneous catalysis reaction mechanisms and for optimizing catalyst activity and selectivity. The corresponding studies at the electrolyte/solid interface are, however, a still-developing area of research. − With respect to vanadium oxynitrides, recent ex situ photoemission studies on vanadium nitride nanoparticles have shown that vanadium oxynitrides formed in situ are the active species and that an N surface state with an N 1s binding energy of 396.5 eV is associated with NRR activity. Moreover, the relative photoemission intensity of this feature correlated with the NRR activity of the nanoparticle .…”

Reflective microscopy for mechanistic insights in corrosion research

“…3). [18] Identical colocalization of reflectivity images with electron backscatter diffraction (EBSD) analysis provided a direct correlation of activity from RM with crystallographic orientation. The reflectance voltammograms showed that the step atoms on Au interface ((110) and (111) steps on (210), ( 111) and ( 221) surfaces) are less stable during electrooxidation and oxidize at lower potentials than (111) terrace atoms.…”

“…[12] Details on the operational principles of particular RM setups can be found elsewhere. [13,[16][17][18] Standalone, RM provides wide field (up to a few mm wide) highly resolved (down to ca. 200 nm) and sensitive (down to 30 nm particles) measurements while also being amenable to coupling with another methods.…”