Synergy of oxygen reduction for HO production and electro-fenton induced by atomic hydrogen over a bifunctional cathode towards water purification.

In the Electro-Fenton (EF) process, hydrogen peroxide (HO) is produced in situ by a two-electron oxygen reduction reaction (2e ORR), which is further activated by electrocatalysts to generate reactive oxygen specieces (ROS). However, the selectivity of 2e transfer from catalysts to O is still unsatisfactory, resulting in the insufficient HO availability. Carbon based materials with abundant oxygen-containing functional groups have been used as excellent 2e ORR electrocatalysts, and atomic hydrogen (H*) can quickly transfer one electron to HO in a wide pH range and avoiding the restrict of traditional Fenton reaction. Herein, nickel nanoparticles growth on oxidized carbon deposited on modified carbon felt (Ni/C@CF) was prepared as a bifunctional catalytic electrode coupling 2e ORR to form HO with H* reducing HO to produce ROS for highly efficient degradation of antibiotics. Electrochemical oxidation and thermal treatment were used to modulate the structure of carbon substrates for increasing the electro-generation of HO, while H* was produced over Ni sites through HO/H reduction constructing an in-situ EF system. The experimental results indicated that 2e ORR and H* induced EF processes could promote each other mutually. The optimized Ni/C@CF with a Ni:C mass ratio of 1:9 exhibited a high 2e selectivity and HO yield of 49 mg L. As a result, the designed Ni/C@CF exhibited excellent electrocatalytic ability to degrade tetracycline (TC) under different aqueous environmental conditions, and achieved 98.5% TC removal efficiency within 60 min HO and H* were generated simultaneously at the bifunctional cathode and react to form strong oxidizing free radicals •OH. At the same time, O gained an electron to form •O, which could react with •OH and HO to form O, which had relatively long life (10∼10 s), further promoting the efficient removal of antibiotics in water.