The hydroxyl radical (●OH) is a crucial intermediate in electrocatalysis. It is proposed as intermediate in oxygen reduction and oxygen evolution electrocatalysis, and is one of the most attractive reactive oxygen species (ROS) due to its high oxidation power and its clean production. However,  detection  and  quantification  of this  species  hard  because  of  its  short  lifetime.  In solution, the golden  standard  for  its  detection  is  the  use  of  spin  traps  together  with  electron  spin resonance  (ESR).  Nonetheless,  these  measurements  are  far  from  ideal: the  detected  species  are transient, it suffers low sensitivity at electrodes, and using ESR severely limits the timescale of experiments. To address these shortcomings, recently, we reported on a radically different approach based on the detection of the redox-activity of a commonly used spin trap for ●OH, [DMPO-OH]●, formed by reaction with 5,5-dimethyl-1-pyrroline N-oxide (DMPO). This redox reactivity allows us to detect and quantify the formation  of ●OH with  unprecedented   versatility,  as  a  small  electrochemical  probe  positioned close to the electrode greatly amplifies the adduct signal by measuring it just over an active electrode. Scanning electrochemical microscopy (SECM) is used to position and raster the probe electrode over active interfaces to measure and image the production of [DMPO-OH]● in real time.<br/><br/>In this talk, we will present the potential and pH dependencies of ●OH formation using this method at several electrodes and photoelectrodes of interest towards reductive and oxidative processes involving O<sub>2. </sub>Such as the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). We will highlight the role that ●OH accomplishes in each of these systems, from acting as an intermediate and mechanistic indicator, to being involved actively in the degradation of the catalyst and supports. Importantly, we will show how the detection of [DMPO-OH]● correlates with experiments of adsorbed ROS performed using the Surface Interrogation SECM technique, thus demonstrating new ways to estimate the coverage of its adsorbed form during electrocatalysis. We will also highlight the combination of Raman spectroscopy and SECM to assess the impact of ●OH. By  simplifying ●OH detection  using  a  versatile electrochemical approach we enable the exploration of its role in crucial sustainable processes to power fuel cells, clean water, and discover electrosynthetic routes.

Redox-active spin trap approach for capturing •OH during reductive and oxidative processes at electrodes using scanning electrochemical microscopy

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