In Situ Optical Monitoring of the Electrochemical Conversion of Dielectric Nanoparticles: From Multistep Charge Injection to Nanoparticle Motion

Abstract

By shortening solid-state diffusion times, the nanoscale size reduction of dielectric materials -such as ionic crystalshas fueled synthetic efforts towards their use as nanoparticles, NPs, in electrochemical storage and conversion cells. Meanwhile, there is a lack of strategies able to image the dynamics of such conversion, operando and at the single NP level. It is achieved here by optical microscopy for a model dielectric ionic nanocrystal, a silver halide NP. Rather than the classical core-shrinking mechanism often used to rationalize the complete electrochemical conversion and charge storage in NPs, an alternative mechanism is proposed here. Owing to its poor conductivity, the NP conversion proceeds to completion through the formation of multiple inclusions. The super-localization of NP during such heterogeneous multiple-step conversion suggests the local release of ions, which propels the NP towards reacting sites enabling its full conversion.

Revealing the sub-50 ms electrochemical conversion of silver halide nanocolloids by stochastic electrochemistry and optical microscopy

“…We focus here on the reverse reaction, and study the EC reduction of CTAB-capped AgX ionic colloidal NPs into metallic Ag NPs. If earlier single silver-based ionic NP (AgO or AgX) studies suggest that this conversion is reversible but may be incomplete 29 or proceed to completion, 33,34 the conversion rate seems to depend on whether Brownian colloids in solution (<0.1s) 29,33 or CTABcapped AgX NPs immobilized on an electrode (>1s) 34 are considered. The difference may be due to the NP size, composition or capping agent, 35 but also to its interaction with the electrode surface 29b and its mobility (Brownian vs surfacebound).…”

The promise of antireflective gold electrodes for optically monitoring the electro-deposition of single silver nanoparticles

“…A linear relationship between the NP volume and the backgroundsubtracted intensity was demonstrated in previous work. 41 Thanks to such empirical law, the size of the NP is accessible throughout the potential sweep. The relationship between the BALM intensity and the volume of electrodeposited Ag NPs determined by SEM (Figure 4a, same location for SEM and BALM) is also linear and comparable but actually less sensitive, than that observed previously (slope <I BALM >- 41 Indeed, the condition for light extinction from the AR absorbing layer strongly depends on the Au layer thickness which is ~ 5nm.…”

“…41 Thanks to such empirical law, the size of the NP is accessible throughout the potential sweep. The relationship between the BALM intensity and the volume of electrodeposited Ag NPs determined by SEM (Figure 4a, same location for SEM and BALM) is also linear and comparable but actually less sensitive, than that observed previously (slope <I BALM >- 41 Indeed, the condition for light extinction from the AR absorbing layer strongly depends on the Au layer thickness which is ~ 5nm. Slight variation, from batch to batch, of this thickness is thus expected inducing both changes in the signal-to-noise ratio and in the extent of constructive or destructive (extinction) interferences and therefore in .…”

“…By optimizing the gold layer thickness as well as the video acquisition parameters, NPs <10 nm were observed. 41 It is also important to point out that the optical setup (a classical inverted microscope, a white LED and a standard 8-bit color CCD camera) is quite common. Then, there are still rooms for improving the optoelectrochemical setup and thus having a better sensitivity, which could theoretically reach nanometer scale vertical resolution.…”

“…Electrochemical cells were machined in house from plastic, as reported previously. 41 The UME was lithographed directly from the gold layer deposited on the glass substrate.…”