Direct vacuum inlet system enabling highly sensitive in-situ analysis of chemical reaction products

Electrochemical reactions play an increasingly important role in sustainable energy conversion and chemical synthesis. Better understanding of catalytic mechanisms at electrode surfaces is thus important for the transition to a clean-energy economy, but is hindered by the difficulty of real-time detection of products and reaction intermediates during electrochemistry experiments. Electrochemical mass spectrometry (EC-MS), including techniques referred to as DEMS and OLEMS, can enable in-situ detection of electrochemical products, but often fails to provide quantitative or reproducible results.

Herein, we present a new type of EC-MS based on a versatile gas inlet to vacuum fabricated onto a silicon microchip, and compare it to established techniques with focus on sensitivity, time response, and mass transport. The chip consists of a perforated membrane stablizing a large liquid-gas interface, a capillary maintaining a controlled flow over a pressure drop to ultra-high vacuum, and inlet and outlet channels for an inert make up gas. The use of a direct inlet enables orders of magnitude higher sensitivity than differentially pumped systems without a loss in time response for volatile products, while clean-room techniques for chipfabrication and a precicely controlled working distance between the electrode and chip membrane provide for a highly reproducible experimental setup. The make up gas can also be used to saturate the electrolyte from through the chip membrane enabling quick and precise exchange of dissolved gases. The well-characterized mass transport of both reactants and products in this setup enables single-turnover resolution for analysis of electrochemical reactions, as will be demonstrated with examples.