Recent Advances in Detection of Electrochemical Reaction Intermediates at the Solid-Liquid Interface by Mass Spectrometry

Electrochemical reaction is a continuous dynamic process, accompanied by electron transfer and generation of short-lived intermediates. The mechanism investigation of electrochemical interfaces is pivotal for the progression of energy storage, electro-organic synthesis, electrocatalysis, and electroanalysis. The valuable insights for optimizing performance, improving efficiency, and developing novel methodologies can be attained by elucidating the complicated pathways involved in the electrochemical processes. Thus, how to monitor transient intermediates formed at the solid-liquid interface becomes the critical point in unraveling these intricate processes. To this end, a series of in-situ analytical methods such as in-situ electron paramagnetic resonance spectroscopy (in-situ EPR), in-situ Raman spectroscopy, in-situ infrared spectroscopy (in-situ IR) and in-situ electrochemical mass spectrometry (in-situ EC-MS) have been exploited to probe the chemical transformations at the electrode/electrolyte interface. Among them, due to the superior specificity for interpreting molecular information, EC-MS has progressively gained extensive attention as a powerful and reliable tool for capturing intermediates and revealing the mechanisms in electrochemical reactions. In this review, the research progresses in the recent advancements in the detection of transient reaction intermediates through electrochemical mass spectrometry were presented. The discussion centered on elucidating the principle and configuration of the devices employed in EC-MS, with a specific focus on electrospray ionization mass spectrometry (ESI-MS), atmospheric pressure ionization mass spectrometry (AIMS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). In addition, the review delved into the wide-ranging applications of EC-MS in monitoring electrochemical processes in electro-organic synthesis, electrocatalysis, lithium-ion batteries, electrochemiluminescence, and bioelectrochemical reactions. Despite the remarkable progress has made, the challenges in the field of EC-MS are prospected. There is still an urgent need for further improvement of the experimental apparatus to enhance the sampling efficiency and time resolution to capture short-lived and low-concentration reaction intermediates. In the future, we anticipate that EC-MS will be combined with other in situ analytical techniques, such as in situ infrared or Raman spectroscopy, enabling multi-dimensional characterization and monitoring of electrochemical reaction intermediates.