Real‐Time Mass Change: An Intrinsic Indicator to Dynamically Probe the Electrochemical Degradation Evolution in WO₃

Abstract

Although tungsten trioxide (WO3) films are considered as the most popular inorganic electrochromic cathode, the irreversible accumulation of lithium ion in it leads to the degradation of cycling stability. In situ monitoring of mass change is critical to intrinsically probe the dynamical degradation evolution of the WO3 films. Based on electrochemical quartz crystal microbalance analysis, a transfer model based on the migration of three mass carriers (lithium ion, perchlorate ion and propylene carbonate) is proposed. Higher potential can boost the migration of mass carriers, benefiting from the intensive driving force. Due to moderate intercalation of mass carriers and smallest difference in molar mass, the excellent electrochemical reversibility at 40 mV s−1 is observed. As the migration of mass carriers progresses, continuous corrosion of the WO3 films results in electrochemical degradation. It is demonstrated that electrochemical quartz crystal microbalance‐based analyses provide a valuable insight for the intercalation and extraction of mass carriers, in favor of further revealing degradation evolution induced by the irreversible intercalation of conductive ions in electrochemical devices.

Constructing an Al3+/Zn2+-Based Solid Electrolyte Interphase to Enable Extraordinarily Stable Al3+-Based Electrochromic Devices

“…Tungsten oxide (WO 3 ) is considered one of the most promising ECMs as the EC layer of EC devices (ECDs) owing to its simple preparation process and high coloration efficiency. , Typical WO 3 –NiO ECDs consist of five layers: a WO 3 thin film (EC layer), an ion-conducting layer, a NiO thin film (ion-storage layer), and transparent electrodes on both sides. − Conventionally, the monovalent Li + is used as the mainstream conducting ions of the electrolytes for the ECDs because of its small ionic radii, which is beneficial to the insertion and extraction processes between the layers. However, Li + still has disadvantages that limit its practical use, including the environmental issues related to lithium usage and the limited lithium salt resources. − …”

Investigation on the Properties and Mechanism of W-Doped TiO2 Electrochromic Films Deposited by Cosputtering

“…5,6 However, it only exhibits a color change from colorless to deep blue and is susceptible to corrosion in acidic solutions. To achieve more widespread practical application of electrochromic products, 7,8 it is important to explore other electrochromic materials that can provide the same level of colorization ability while having better electrochemical stability than WO 3 . 9−12 TiO 2 has been one of the most widely studied photocatalytic and battery materials for decades due to its stable physical and chemical properties and good photocatalysis activity.…”

“…Electrochromic materials can reversibly change the optical properties by controlling the insertion and extraction of electrons under the action of an external electric field which makes them promising for applications in smart windows and automotive rearview mirrors. − WO 3 is the most widely used anodically electrochromic cathode material due to its stability and ease of preparation. , However, it only exhibits a color change from colorless to deep blue and is susceptible to corrosion in acidic solutions. To achieve more widespread practical application of electrochromic products, , it is important to explore other electrochromic materials that can provide the same level of colorization ability while having better electrochemical stability than WO 3 . − …”

The Counterbalancing Role of Oxygen Vacancy between the Electrochromic Properties and the Trapping Effect Passivation for Amorphous Tungsten Oxide Films

“…[27] Further evidence was presented for three kinds of traps that degraded EC tungsten oxide during ion intercalation: 1) shallow traps eroding the colored state; 2) deep traps lowering the bleached-state transmittance; and 3) irreversible traps. [28,29] Recently, to intrinsically probe the dynamic degradation evolution of WO 3 films, the mass change, [30] hysteretic ions transport kinetics, [31] and mechanical stress/strain induced by insertion/ extraction of ions [32] were monitored. Thus, the internal mechanism of the "trapping effect" has been thoroughly studied but no effective solutions were proposed.…”