Oral: Mechanistic Study of Anodic H2O2 Production in Bicarbonate Medium for a Paired Electro-Fenton Process: Identification of a Reactive Intermediate and its Use for Pollutant Degradation

Electrochemical Advanced Oxidation Processes (EAOPs) are effective methods for the efficient degradation of persistent water pollutants. They rely on electricity to generate strong oxidants such as reactive oxygen species responsible for the destruction of organic pollutants. While a wealth of research worldwide has been dedicated to the electrode-driven reduction of O2 into H2O2, its counter reaction continues to be the energy-intensive four-electron oxidation of water to O2 which interferes with the desired high efficiency generation of H2O2. We posited that modifying the mechanism of the OER to promote a two-electron pathway that produces H2O2 instead of O2 would help solve these issues. To this point, the identity of the anode material and electrolyte composition plays a crucial role in improving the faradaic efficiency to form H2O2. It is reported that the presence of HCO3- in the electrolyte is a crucial requirement for the anodic production of H2O2, but the exact role of H2O2 in a HCO3- mediated pathway is unclear.
Here, we introduce Scanning Electrochemical Microscopy (SECM) to monitor the real-time formation of chemical intermediates during the production of H2O2 for use in a convergent paired electro-Fenton process. The latter employs anodic materials and electrolytes that favors the production of H2O2. SECM was used to test the hypothesis that the H2O2 produced anodically follows a bicarbonate mediated pathway forming possible intermediates that distinctly enables pollutant degradation. SECM analysis revealed the production of an intermediate species collected across a variety of tip electrode materials and with distinct reactive properties compared to ROS. This species was further studied using ex-situ methods such as electrospray mass spectrometry and infrared spectroscopy. This study further highlights the applicability of SECM in investigating the in-situ generation of reactive species for new device concepts based on paired electro-Fenton reactions.