Fig. 1: Spontaneous Raman imaging setup and agglomerate particles imaged.
From: Concurrent oxygen evolution reaction pathways revealed by high-speed compressive Raman imaging
a Classical adsorbate mechanism for water oxidation on the surface of iridium oxide catalysts (blue box) and proposed mechanism for water oxidation with α-Li2IrO3 (red box). b (Green box) Cartoon schematic of confocal Raman microscope. The 532 nm laser is scanned across a sample using galvanometric mirrors (GM) with the excitation and Raman light separated by a dichroic mirror (DM). Either a conventional spectrometer (equipped with an EMCCD (conventional detector; blue box)) or a programmable spectrometer (equipped with a DMD (digital micromirror device) and avalanche photodiode (SPAD; red box)) are used to measure the Raman signal. Light is focussed onto the sample through the back side of an ITO or Ti-coated coverslip, which acts as the working electrode (WE). (Black box) Brightfield image of α-Li2IrO3 agglomerate particles (dark features) dispersed with Nafion onto ITO slide (left). The scale bar is 10 μm. (Centre) Scanning electron microscopy image of a ~ 1 (left) and ~ 2.5 μm (right) size α-Li2IrO3 agglomerate particle (without Nafion). The scale bar is 1 μm. (Right) Cartoon schematic of agglomerate particle simplified to a cubic shape. The 900 ± 200 nm axial resolution of our setup means we probe a 3D section of the particle bulk. When viewed in 2D projection (far right), an isotropic 3D deintercalation process gives rise to distinct patterns. The white to orange colour bar depicts the degree of a given ion intercalation phase. c Cyclic voltammogram of α-Li2IrO3 showing the first two cycles. The scan rate is 10 mV/s. The current is normalised to the geometric surface area that the electrolyte covers (~ 75 mm2; see “Methods”). The voltage is not iR-corrected.
