Quantitative Differential Electrochemical Mass Spectroscopy Analysis of Electrochemical Carbon Corrosion Reactions in Alkaline Electrolyte Solutions
Authors: Shimizu Shugo , Ikezawa Atsunori , Okajima Takeyoshi , Arai Hajime 
Published: December 2024

Introduction

Zinc-air secondary batteries are attracting attention as next-generation large-scale energy storage devices. However, one of the challenges for practical application is the prevention of air electrode degradation caused by the oxidative corrosion of carbon. In order to suppress the carbon corrosion reaction, clarification of the reaction mechanism is required. The differential electrochemical mass spectrometry (DEMS) is the in-situ mass spectrometry for the volatile species generated by electrochemical reactions, and it is possible to measure the partial current of the carbon corrosion reaction by analyzing CO2 evolution. Therefore, DEMS has intensively been applied to carbon corrosion reactions under acidic conditions. However, applying DEMS to alkaline electrolyte systems is challenging due to the relatively high solubility of CO2 as carbonate ions. On the other hand, we have constructed a new DEMS measurement system combining a microreactor and an ion-exchange membrane and quantitatively analyzed CO2 evolution in an alkaline aqueous solution [1]. However, the current measurement system had relatively low temporal resolution and large IR-drop. In this study, we constructed the DEMS measurement system with improved temporal resolution and reduced IR-drop.

Experimental

A schematicof the electrochemical three-electrode cell used for the DEMS measurement is shown in Fig.1.A platinum-supported carbon composite electrode, a Hg/HgO electrode, a Pt wire, and 1 mol dm–3 KOH solution were used as the working, reference, and counter electrodes and the electrolyte solution, respectively. The electrolyte solution was flown into the cell using a syringe pump and acidified with a 1 mol dm–3 sulfuric acid solution in a microreactor installed downstream of the working electrode. The volatile components were installed from the electrolyte solution to the vacuumed chamber through a PTFE membrane interface placed at the downstream of the microreactor. The electrolyte path from the working electrode to the membrane interface was shortened from 13.5 cm to 4.5 cm to improve the temporal resolution of the previous system. In addition, the position of the reference electrode was changed from the outside of the working electrode chamber to inside of that to reduce the IR-drop at the ion-exchange membrane. We also increase the working electrode area from 78.5 mm2 to 201 mm2 in order to enhance the detectivity. CO stripping voltammetry (Eq. (1)) was performed to evaluate the CO2 detection property of the constructed DEMS system.
Pt-COad + 2OH– → Pt* + CO2 + H2O + 2e– (1)

Results and discussion

Fig.1 shows the CO stripping voltammogram and the corresponding mass signal of CO2. CO oxidation current is observed from –0.5 to –0.2 V, while our previous setup showed CO oxidation current from –0.4 to 0.1 V [1]. This result shows that the IR-drop is effectively suppressed in the new DEMS setup. In addition, the mass signal of CO2 is observed in the almost same potential range (–0.5 to –0.1 V) as that of the CO oxidation current, suggesting that the new DEMS setup has improved temporal resolution. On the other hand, the calibration constant (Eq. 2) of new DEMS setup is to the same extent as the previous one [1], indicating that the new DEMS setup has the comparable detectivity. Analyses of catalyst-loading carbon corrosions will also be presented at the site.
References
[1] A. Ikezawa, J. Kida, K. Miyazaki, H. Arai, Electrochem. Commun., 159, 107647_1-6 (2024).
This work was partially supported by
JSPS KAKENHI (JP23K13819)
JRP-LEAD with DFG (JPJSJRP20221602)

Figure 1