Understanding the Role of Charge Storage Mechanisms in the Electrochromic Switching Kinetics of Metal Oxide Nanocrystals

Abstract

The development of electrochromic metal oxide nanocrystals holds promise for improving the sluggish switching kinetics of conventional electrochromic smart windows. Nevertheless, the microscopic processes controlling switching kinetics in nanocrystals may differ from those in traditional bulk materials where ion diffusion following intercalation is often rate limiting. Herein, by systematically investigating the electrochromic response of Sn-doped In 2 O 3 nanoparticles, orthorhombic Nb 2 O 5 nanorods, and monoclinic Nb 12 O 29 nanoplatelets, we elucidate how different charge storage mechanisms, including capacitive charging, surface redox, and intercalation, affect the switching kinetics of electrochromic nanocrystals. The nanocrystals were reduced in both lithium-and tetrabutylammonium-based electrolytes at various potentials to determine which charge storage mechanism governs their electrochromic response, and the optical switching kinetics at a reducing potential were quantified by fitting with an exponential-growth model based on the charging behavior of capacitors. For the surface-dominated capacitive charging and surface redox mechanisms, dual-stage switching kinetics were observed regardless of the materials, switching rapidly at the early stage of reduction and becoming slower over time as charge accumulates in the electric double layer. As for the intercalation mechanism, single-stage switching kinetics controlled by the reaction rate of ion intercalation were observed. By using spectroelectrochemical methods, we demonstrated approaches to define the charge storage mechanisms in electrochromic metal oxide nanocrystals and investigated how these mechanisms affect the switching kinetics of the electrochromic response.

Selective Electrochromic Regulation for Near-Infrared and Visible Light via Porous Tungsten Oxide Films with Core/Shell Architecture

“…To understand the electrochemical mechanisms underlying the dual-band electrochromism, we further performed the electrochemical and electrochromic measurement of the WO 3 NWs/NPs film in a TBA + -based electrolyte. , As we know, different from the small Li + ions, TBA + ions are too large to allow the occurring of an ion intercalation behavior, and the spectral modulation is ascribed to the capacitive process. The cyclic voltammogram in the TBA + -based electrolyte (Figure a) presents unconspicuous redox peaks and lower current densities, indicating that the electrochemical process is dominated by capacitive behavior.…”

Transparent dynamic infrared emissivity regulators

“…Understanding the underlying DIE regulatory mechanism of AZO NCs is a key issue. The electrochromic properties of transition-metal oxides are usually caused by surface redox reactions, ionic intercalation, and/or capacitive charging 14 . The electrochemical response of NCs can be used to distinguish between surface redox and capacitive charging 15 .…”

Alternative Energy Carriers: Unique Interfaces for Electrochemical Hydrogenic Transformations

“…[98][99][100][101] Since the excess charge is stored in SC bands, the band edge potentials and energy-level spacing dictate the SCNC's redox potentials. These band edge potentials can be synthetically controlled through NC size variation, [102,103] interfacial dipoles, [104][105][106][107] aliovalent or isovalent doping, [99,[107][108][109][110][111] electric double-layer engineering, [112] as well as other methods. [113] Moreover, the energy profile of stored charged at the SCNC surface is nearly flat with increasing electron density which enables multiple electron-proton chemistries with a single particle.…”

“…[120,121] In addition, the surface of SCNCs can be modified with a number of co-catalysts to further broaden the possible reaction scope. [122] Finally, piggy-backing off of research enabling SCNCbiocompatibility, [112,113] the tantalizing prospect of integrating these chemistries into more complex interconnected systems which involve biological transformations arises. These highly charged nanostructures are an exceptionally promising class of materials for both storing and transforming energy via electrochemical hydrogenation chemistry.…”