Enabling Real-Time Detection of Electrochemical Desorptionphenomena with Sub-Monolayer Sensitivity

Abstract

Across many scientific and industrial fields, it is a challenge to analyze chemical reaction products with high sensitivity and fast time-response. This is especially true in systems related to electrochemical energy conversion and storage, such as batteries and fuel cells, where accurate monitoring of fast and transient reaction phenomena often reveals key insights.Here, we present a unique analysis instrument using a microchip-based inlet system to couple a mass spectrometer directly to any liquid test environment, aqueous or non-aqueous, and exhibits a sensitivity 3-4 orders of magnitude than conventional differential electrochemical mass spectrometry (DEMS).1–3 The instrument allows to measure the evolution of volatile products and consumption of reactants at electrode surfaces. Due to its extraordinary sensitivity, the system can measure all the individual volatile molecules desorbing from an electrode surface during a single electrochemical turnover. Product formation can be measured from total Faradaic currents of 1 mA all the way down to 1 nA, corresponding to approximately 10 ppm of a monolayer desorbing from the electrode surface in 1s. These features enable time-resolved, fully quantitative measurements of transient phenomena during electrochemistry, providing fundamental insight in the electrochemical reaction mechanisms. Furthermore, an accurately calibrated on-chip gas system allows rapid gas switching between different gases, both inert and reactive. Due to the near-instantaneous equilibration between gas and electrolyte, the transient response of electrodes to rapid gas exposure changes can be measured.The capabilities of this analysis system are showcased by various examples, including electrochemical water-splitting at low overpotential and low-surface area CO-stripping. In situ quantification of hydrogen and oxygen evolution is shown at Faradaic currents on the order of 1 nA. In comparison, conventional techniques can only detect down to about 10 μA of continuous product formation. Finally, the electrochemical stripping of < 1 % of a CO monolayer at standard potential scan-rates of 50 mV/s is shown (Fig. 1).Figure 1. H2 evolution and CO stripping experiments using a polycrystalline Pt electrode in 1M HClO4. Trimarco, D. B. et al. Enabling real-time detection of electrochemical desorption phenomena with sub-monolayer sensitivity. Electrochim. Acta 268, 520–530 (2018).Roy, C. et al. Impact of nanoparticle size and lattice oxygen on water oxidation on NiFeOxHy. Nat. Catal. 1, 820–829 (2018).Winiwarter, A. et al. Towards an atomistic understanding of electrocatalytic partial hydrocarbon oxidation: propene on palladium. Energy Environ. Sci. (2019) doi:10.1039/C8EE03426E. Figure 1