Insights into electrochemical reactions by differential electrochemical mass spectrometry A.A. Abd-El-Latif 1 , C.J. Bondue, S. Ernst, M. Hegemann, J.K. Kaul, M. Khodayari, E. Mostafa 2 , A. Stefanova, H. Baltruschat * Institute of Physical and Theoretical Chemistry, Bonn University, Bonn 53117, Germany ARTICLE INFO Keywords: Aqueous electrolyte DEMS cell DEMS system Differential electrochemical mass spectrometry Electrochemical reaction Electrochemistry Faradaic reaction Mass spectrometry Non-aqueous electrolyte Volatile product A B ST R AC T Differential electrochemical mass spectrometry (DEMS) has become an indispensable tool for not only qualitative and quantitative detection of volatile products or intermediates of continuous Faradaic re- actions, but also determination of the amount of adsorbates (sub-layer or monolayer) at different electrode surfaces by means of their desorption. In the present review, we give a short introduction about the history of the combination of electro- chemistry and MS (EC-MS), followed by a summary of the several types of DEMS cell that are applicable for different purposes. We present in detail the calibration of DEMS systems and their application in aqueous and non-aqueous electrolytes. © 2015 Elsevier B.V. All rights reserved. Contents 1. Introduction ............................................................................................................................................................................................................................................................. 4 2. Types of DEMS cell ................................................................................................................................................................................................................................................ 5 3. Calibration of DEMS .............................................................................................................................................................................................................................................. 5 4. Applicable aqueous and aprotic electrolytes for DEMS ............................................................................................................................................................................ 5 4.1. Aqueous electrolytes ............................................................................................................................................................................................................................... 5 4.1.1. Oxidation reactions at BDD .................................................................................................................................................................................................. 5 4.1.2. Bulk oxidation of methanol ................................................................................................................................................................................................. 7 4.1.3. Bulk oxidation of ethanol ..................................................................................................................................................................................................... 9 4.1.4. Detection of adsorbates and adsorption rate ................................................................................................................................................................. 9 4.2. Aprotic electrolytes ............................................................................................................................................................................................................................... 10 4.2.1. ORR and OER reactions ....................................................................................................................................................................................................... 10 4.2.2. Diffusion coefficient and solubility of oxygen in aqueous and aprotic electrolytes ...................................................................................... 11 5. Future trends ......................................................................................................................................................................................................................................................... 12 Acknowledgments ............................................................................................................................................................................................................................................... 12 References .............................................................................................................................................................................................................................................................. 12 1. Introduction The online coupling of an electrochemical cell to mass spectrom- etry (EC-MS) has proved useful in the identification of intermediates or products of the electrochemical reactions, leading to the ability to do qualitative and quantitative analysis and mechanistic studies of redox reactions. In 1971, Bruckenstein and Gadde [1] were the first to detect electrochemically generated gaseous products qualitatively by in-situ EC-MS using a hydrophobic porous electrode with a time constant of about 20 s. In 1984, Wolter and Heitbaum [2,3] improved the vacuum system of the EC-MS and reduced the delay time of detection, in order to use EC-MS for quantitative studies (current efficiency and kinetic in- formation). Thus, the MS signal of the volatile species became proportional to its rate of formation instead of the accumulated product; this explains the term differential EC-MS. * Corresponding author. Tel.: +49 0228 73 2404; Fax: +49 0228 73 4160. E-mail address: baltruschat@uni-bonn.de (H. Baltruschat). 1 Permanent address: National Research Centre, Physical Chemistry Dept., El- Bohouth St., Dokki, 12311 Cairo, Egypt. 2 Permanent address: Chemistry Department, Faculty of Science, Mansoura Uni- versity, 35516 Mansoura, Egypt. http://dx.doi.org/10.1016/j.trac.2015.01.015 0165-9936/© 2015 Elsevier B.V. All rights reserved. Trends in Analytical Chemistry 70 (2015) 4–13 Contents lists available at ScienceDirect Trends in Analytical Chemistry journal homepage: www.elsevier.com/locate/trac