Dynamic Interfacial Reaction Rates from Electrochemistry–Mass Spectrometry

Abstract

Electrochemistry−mass spectrometry is a versatile and reliable tool to study the interfacial reaction rates of Faradaic processes with high temporal resolutions. However, the measured mass spectrometric signals typically do not directly correspond to the partial current density toward the analyte due to mass transport effects. Here, we introduce a mathematical framework, grounded on a mass transport model, to obtain a quantitative and truly dynamic partial current density from a measured mass spectrometer signal by means of deconvolution. Furthermore, it is shown that the time resolution of electrochemistry−mass spectrometry is limited by entropy-driven processes during mass transport to the mass spectrometer. The methodology is validated by comparing the measured impulse responses of hydrogen and oxygen evolution to the model predictions and subsequently applied to uncover dynamic phenomena during hydrogen and oxygen evolution in an acidic electrolyte.

Quantitative Operando Detection of Electro Synthesized Ammonia Using Mass Spectrometry

“…The observed linear increase of the ammonia signal is expected for a steady-state production of ammonia at the electrode because of its slow evaporation into the mass spectrometer. Simulations of the mass spectrometer signal based on an earlier introduced mass transport model [13] for the thin-layer electrochemical cell yield an almost identical signal profile compared to what is observed experimentally (Figure S2). Moreover, when the same experiment is carried out in helium atmosphere, no ammonia production is observed (Figure S3), corroborating the successful reduction of nitrogen to ammonia by the electroplated lithium.…”

“…Since the liquid volume of the electrochemical cell can be different among experiments, where the cell is repeatedly mounted and dismounted from the mass spectrometer, the approach based on knowledge of the micro‐capillary, which remains the same as long as the same chip is used, is chosen for this study. Moreover, the well‐defined nature of micro‐fabricated capillaries as mass spectrometry inlet systems has been extensively verified in previous studies [13,16,17] . In order to calibrate the mass spectrometer signal, nitrogen gas with 315 ppm of ammonia was used as auxiliary gas and the system was left to equilibrate for at least 10 hours until the ammonia signal reached a steady state (Figure S4 This was performed prior to the non‐aqueous electrochemical measurement shown earlier in Figure 3.…”

“…been extensively verified in previous studies. [13,16,17] In order to calibrate the mass spectrometer signal, nitrogen gas with 315 ppm of ammonia was used as auxiliary gas and the system was left to equilibrate for at least 10 hours until the ammonia signal reached a steady state (Figure S4 This was performed prior to the non-aqueous electrochemical measurement shown earlier in Figure 3. With knowledge of the capillary flow, which can be calculated according to Henriksen et al, [18] the ammonia molar flow into the mass spectrometer can be derived and a calibration factor determined (details see SI).…”

Transients in Electrochemical CO Reduction Explained by Mass Transport of Buffers

“…The formed products need to diffuse from the electrode to the mass spectrometer to be detected. As a result, the transient signal is stretched over a longer time period through diffusional broadening …”

Surface Hydride Formation on Cu(111) and Its Decomposition to Form H2 in Acid Electrolytes

“…The H2 quantification for EC-MS was calibrated following a previously published method. 3,4 Briefly, a 5 mm Pt disk was used as the working electrode in the same EC-MS setup, described above. A series of constant current steps between 10 μA cm -2 and 150 μA cm -2 were applied to the electrode for 120 s followed by a 120 s of rest at 0 V vs RHE.…”