Quantitative Electrochemistry-Mass Spectrometry: Real-Time Detection of Volatile Products for Electrocatalysis and Batteries

Abstract

A major challenge both within electrocatalysis and battery research concerns the real-time (i) identification and (ii) quantification of volatile reaction products as a function of the applied electrochemical parameters and the reaction conditions. Analysis of both steadily evolving gases and of fast- and transient reaction phenomena can reveal key insights into reaction mechanisms. To this end, methods like Differential Electrochemical Mass Spectrometry (DEMS)1 and On-line Electrochemical Mass Spectrometry (OLEMS)2 have been used successfully to study reaction mechanisms to an ever-increasing degree in recent years, primarily in aqueous electrolytes. Similarly, Online Electrochemical Mass Spectrometers (OEMS)3 have been essential for the study of gas evolution in batteries.However, to gain an in-depth understanding of these mechanisms, the ability to accurately relate the electrochemical charge transferred in the reaction to the amount of evolved product is essential. To this end, accurate calibration of MS signals is paramount. Calibration procedures available for DEMS systems are by themselves cumbersome and unreliable and full quantification is not possible for OLEMS.Herein, we show how a simple gas-based calibration procedure using chip-based Electrochemistry-Mass Spectrometry (EC-MS) can be used for reliable, fully quantitative real-time analysis of volatile electrochemical reaction products. We validate this calibration with electrochemistry-based calibration methods described previously.4,5 The new procedure allows to extend the quantitative analysis to systems with no a priori knowledge of faradaic efficiencies. We demonstrate calibration of important gases like H2, O2 and C2H4 in aqueous and non-aqueous electrolytes and exemplify the calibration methodology’s usefulness on standard electrochemical reactions. References H. Baltruschat, J Am Soc Mass Spectrom, 15, 1693–1706 (2004).A. H. Wonders, T. H. M. Housmans, V. Rosca, and M. T. M. Koper, J Appl Electrochem, 36, 1215–1221 (2006).N. Tsiouvaras, S. Meini, I. Buchberger, and H. A. Gasteiger, J Electrochem Soc, 160, A471–A477 (2013).D. B. Trimarco et al., Electrochim Acta, 268 (2018).S. B. Scott, PhD thesis, Technical University of Denmark (2019). Figure 1: a) Schematic of the MS inlet chip’s working principle. b) Uncalibrated M2 and M32 signals (dotted lines) and the same signals after calibration for H2 and O2 (full lines) in a cyclic voltammogram of PtPoly in 0.1 M HClO4 obtained at room temperature at 20 mV/s. Figure 1