Boosting the O₂-to-H₂O₂ Selectivity Using Sn-Doped Carbon Electrocatalysts: Towards Highly Efficient Cathodes for...

The high cost and often complex synthesis procedure of new highly selective electrocatalysts (particularly those based on noble metals) for H₂O₂ production are daunting obstacles to penetration of this technology into the wastewater treatment market. In this work, a simple direct thermal method has been employed to synthesize Sn-doped carbon electrocatalysts, which showed an electron transfer number of 2.04 and outstanding two-electron oxygen reduction reaction (ORR) selectivity of up to 98.0 %. Physicochemical characterization revealed that this material contains 1.53 % pyrrolic nitrogen, which is beneficial for the production of H₂O₂, and -C≡N functional group, which is advantageous for H⁺ transport. Moreover, the high volume ratio of mesopores to micropores is known to favor the quick escape of H₂O₂ from the electrode surface, thus minimizing its further oxidation. A purpose-made gas-diffusion electrode (GDE) was prepared, yielding 20.4 mM H₂O₂ under optimal electrolysis conditions. The drug diphenhydramine was selected for the first time as model organic pollutant to evaluate the performance of an electrochemical advanced oxidation process. In conventional electro-Fenton process (pH 3), complete degradation was achieved in only 15 min at 10 mA cm^-2, whereas at natural pH 5.9 and 33.3 mA cm^-2, almost overall drug removal was reached in 120 min.