Response time (τ, defined as the time required for 90% change in the full transmittance modulation, including coloring time τ c and bleaching time τ b ) is an important evaluation index for the performance of electrochromic (EC) materials, and it can directly reflect the microscopic rate of EC process. However, the research on the internal relationship between the response time and the process of electrochemical dynamics is rare. Herein, by controlling the thickness of the WO 3-x EC film, a complete reversal of the response time (from τ c > τ b in the thinner film to τ b > τ c in the thicker film) is observed. Based on the detailed analysis of the characteristics presented in electrochemical impedance spectroscopy (EIS), especially focusing on the changing trend about the arc of different frequency ranges and the slope value of the linear part, it can be found that this reversal is due to the change of the main dynamics process from surface capacitive-controlled to bulk diffusion-controlled with the increase of WO 3-x film thickness. Meanwhile, this change with obvious film thickness dependence requires a "trigger", which is reflected by the bleaching threshold potential. Besides, this study reveals the three stages of the EC coloring process from the perspective of dynamics, including the lithium-ions (Li-ions) adsorption charge layer, surface Faraday process, and bulk Faraday process, which also show significant film thickness dependence. The result of this work is beneficial to modulate the balance of response time and to improve the performance of EC films.
Siqi Qu,Jing Guan,Dongqi Cai,Qianshuo Wang,Xiuyun Wang,Wei Song,Wei Ji
Electrochemical surface-enhanced Raman scattering (EC-SERS) spectroscopy is an ultrasensitive spectro-electrochemistry technique that provides mechanistic and dynamic information on electrochemical interfaces at the molecular level. However, the plasmon-mediated photocatalysis hinders the intrinsic electrochemical behavior of molecules at electrochemical interfaces. This work aimed to develop a facile method for constructing a reliable EC-SERS substrate that can be used to study the molecular dynamics at electrochemical interfaces. Herein, a novel Ag-WO3−xelectrochromic heterostructure was synthesized for EC-SERS. Especially, the use of electrochromic WO3−xfilm suppresses the influence of hot-electrons-induced catalysis while offering a reliable SERS effect. Based on this finding, the real electrochemical behavior of p-aminothiophenol (PATP) on Ag nanoparticles (NPs) surface was revealed for the first time. We are confident that metal-semiconductor electrochromic heterostructures could be developed into reliable substrates for EC-SERS analysis. Furthermore, the results obtained in this work provide new insights not only into the chemical mechanism of SERS, but also into the hot-electron transfer mechanism in metal-semiconductor heterostructures.Keywords:SERS;defect states;EC-SERS;Ag-WO3−xfilm
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