Electrochemistry and Optical Microscopy

Abstract

Electrochemistry exploits local current heterogeneities at various scales ranging from the micrometer to the nanometer. The last decade has witnessed unprecedented progress in the development of a wide range of electroanalytical techniques allowing to reveal and quantify such heterogeneity through multiscale and multifonctionnal operando probing of electrochemical processes. However most of these advanced electrochemical imaging techniques, employing scanning probes, suffer from either low imaging throughput or limited imaging size. In parallel, optical microscopies, which can image a wide field of view in a single snapshot, have made considerable progress in terms of sensitivity, resolution and implementation of detection modes. Optical microscopies are then mature enough to propose, with basic bench equipment, to probe in a non destructive way a wide range of optical (and therefore structural) properties of a material in situ, in real time: under operating conditions. They offer promising alternative strategies for quantitative high-resolution imaging of electrochemistry. The first sections recall the optical properties of materials and how they can be probed optically. They discuss fluorescence, Raman, surface plasmon resonance, scattering or refractive index. Then the different optical microscopes used to image electrochemical processes are examined along with some strategies to extract quantitative electrochemical information from optical images. Finally the last section reviews some examples of in situ imaging, at micro-to nanometer resolution, and quantification of electrochemical processes ranging from solution diffusion to the conversion of molecular interfaces or solids.]

Imaging and quantifying the chemical communication between single particles in metal alloy

“…This is a crucial limitation as in principle, the crosstalk can interconnect active sites 10s-100s of µm away, instantaneously and dynamically, manifesting itself through nanoscopic solid conversion [12,14]. Therefore, the development of wide field highly resolved methods are required, among which optical methods are proved to be the most prominent to probe operando wide range of chemical processes in electrochemical energy-related systems [28][29][30].…”

The New Era of High-Throughput Nanoelectrochemistry

“…For details of the progress and the operational principles and applications of optical microscopy for imaging electrochemical systems, we refer to a number of recent reviews. ,,, Here we focus on new methodologies able to unravel greater levels of complexity in terms of electrochemical processes/information, including visualizing simultaneous phenomena, as well as new experimental and image-processing methodologies.…”

“…; see below). Several strategies have also been proposed, to convert the optical signature variation quantitatively into an optically inferred electrochemical curve, such as an optical-voltammogram. ,,− Light absorbance, or the extinction wavelength (for plasmonic NPs), is usually proportional to a local concentration or amount of electrochemically transformed material, i.e., an electrochemical charge . The electrochemical current then often tracks the time derivative of local optical transients.…”

“… Advanced optical microscopy techniques that have increasingly been used for imaging electrochemical interfaces operando with nanoscale resolution, using superlocalization principles. They are now expanding to a wide range of electrochemical systems, as illustrated by several recent reviews. − Their easy hyphenation with complementary electrochemical or structural analyses make them particularly compelling tools for high-throughput characterization as we discuss herein. …”

3D Spectroscopic Tracking of Individual Brownian Nanoparticles during Galvanic Exchange

“…Among these strategies, several optical microscopy configurations able to probe in situ and in real time electrochemical or chemical processes with single nanoobject sensitivity have been recently reviewed. − However, the optically inspected NPs are mostly static objects immobilized on a surface or in a gel-like matrix, or fabricated using top-down approaches. Immobility is indeed essential to provide sufficient instrument integration time when imaging faint objects. − A wide range of chemical reactions at the single-NP level have been reported, ranging from conformational change of the NP capping agent, which can be used as a sensing platform, ,, to the electrochemical or chemical conversion of the NP composition. − ,, However, such measurements are often performed at surface-tethered NPs, removing the complexity of bulk vs interfacial chemical processes. While particularly useful to study interfacial chemistry, or electrochemistry, these techniques cannot be applied to the most important type of solution-phase nanochemistries, which involve Brownian NPs, freely diffusing in reactive solutions.…”