Spectroelectrochemistry (SEC) enables in-operando UV-Vis study of electrochemical cells to explore the evolution of different cell components and understand cell mechanisms. Researchers have demonstrated various custom UV-Vis cell designs to accommodate SEC experiments. However, existing designs do not easily permit temperature ramp techniques to examine the effects of rapidly changing cell temperature or high temperature conditions on cell mechanisms. This communication presents two easy-to-replicate, low-cost cell designs that are incorporable with existing UV-Vis systems (transmittance, reflectance) and enable high temperature, rapid heating SEC experiments. Each cell design was tested to evaluate temperature ramp and sealing performance.

Ultraviolet-visible (UV-Vis) spectroelectrochemistry (SEC) is a technique that enables simultaneous probing of the electrochemical behavior of a system and detection of transmitted or reflected light indicative of system material and chemical properties. UV-Vis SEC has found application in the study of lithium-ion batteries, metal-air batteries, electrocatalysis, and electrochromic devices, to name a few examples. For lithium-ion batteries, UV-Vis SEC or electrochromic measurements using visible light can be used to determine the state-of-charge of electrode intercalation materials as a function of applied current or potential. With many electrochemical systems, including batteries, being highly sensitive to temperature, it proves important to perform SEC measurements under various thermal conditions. Currently, there are limited solutions available for UV-Vis SEC or electrochromic measurements of electrochemical cells with temperature control. Significant challenges to implementing such a system include: spectrometer size constraints; sealing requirements for air- and moisture-sensitive electrolytes; electrode and separator positioning within the cell; achieving adequate temperature uniformity and fine temperature control; and enabling sufficient light transmission or reflection for SEC measurements. This work presents two different designs for temperature-controlled spectroelectrochemical cells with a focus on battery research applications. The systems we are proposing exceed both the temperature ranges as well as the ramping rates of designs commonly employed in traditional temperature-controlled UV-Vis applications, such as life sciences studies. The designs feature two different heating mechanisms: a Peltier device on a disk cell (Figure 1a, b) and a barrel style heater in a cuvette design (Figure 1c, d). The disk cell has an acrylic window to enable reflectance mode UV-Vis spectroelectrochemistry. The window is sealed against a stainless-steel casing, which is adhered to the Peltier device. The disk cell is configured for use as a two-electrode cell with separator. The Peltier device can both heat and cool the system while the external surface temperature is monitored, allowing for specific temperature control in reference to the heater. The disk cell design also permits electrochromic studies outside the UV-Vis instrument, and achieves temperature ramp rates of up to 0.5 °C/s. The cuvette cell, made of quartz, allows for transmission of the UV-Vis signal, and can be used with both two- and three-electrode configurations. The barrel style heater employed in the cuvette cell can reach temperatures much higher than the Peltier device while submerged in the electrolyte solution, thus increasing heat transfer compared to both the disk cell and commercially-available temperature controlled UV-Vis systems. This style of heater allows for a maximum temperature ramp rate of 3.8 °C/s. The temperature control system for the cuvette is that of a submersible thermocouple that can monitor the temperature of the electrolyte and stabilize the cartridge heater accordingly. Both systems allow for in-situ spectroscopy studies of the separator, and provide full sealing for battery electrolytes. The designs presented here are expected to advance current capabilities for monitoring chemical changes in electrochemical cells via UV-Vis spectroscopy under varying thermal conditions, while being easy-to-use and highly accessible to battery researchers. This work is supported in-part by NSF Award #1936636. Figure 1