Differentiating the reaction mechanism of three-dimensionally electrocatalytic system packed with different particle...

Recently, there are still some controversial mechanisms of the 3D electrocatalytic oxidation system, which would probably confound its industrial application. From the conventional viewpoint, the Ti₄O₇ material may be the desired particle electrodes in the 3D system since its high oxygen evolution potential favors the production of ^•OH via H₂O splitting reaction at the anode side of Ti₄O₇ particle electrodes. In fact, the incorporation of Ti₄O₇ particles showed phenol degradation of 88% and COD removal of 51% within 120 min, under the optimum conditions at energy consumption of 0.668 kWh g^-1 COD, the performance of which was much lower than those in many previous literatures. In contrast, the prepared carbon black-polytetrafluoroethylene composite (CB-PTFE) particles with abundant oxygen-containing functional groups could yield considerable amounts of H₂O₂ (200 mg L^-1) in the 3D reactor and achieved a complete degradation of phenol and COD removal of 80% in the presence of Fe²⁺, accompanying a low energy consumption of only 0.080 kWh g^-1 COD. It was estimated that only 20% of Ti₄O₇ particles near the anode attained the potential over 2.73 V/SCE at 30 mA cm^-2 based on the potential test and simulation, responsible for the low yield of ^•OH via the H₂O splitting on Ti₄O₇ (1.74 × 10^-14 M), and the main role of Ti₄O₇ particle electrodes in phenol degradation was through direct oxidation. For the CB-PTFE-based 3D system, current density of 10 mA cm^-2 was sufficient for all the CB-PTFE particles to attain cathodic potential of -0.67 V/SCE, conducive to the high yield of H₂O₂ and ^•OH (9.11 × 10^-14 M) in the presence of Fe²⁺, and the ^•OH-mediated indirect oxidation was mainly responsible for the phenol degradation. Generally, this study can provide a deep insight into the 3D electrocatalytic oxidation technology and help to develop the high-efficiency and cost-efficient 3D technologies for industrial application.