Insight into electrocatalytic activity of lattice-confined phosphorus in activated carbon fiber for recalcitrant pollutant degradation.

Conventional carbon-based cathodes suffer from low-efficiency in two electron oxygen reduction reaction (2e- ORR) and recalcitrant pollutant degradation. Herein, phosphorus-doped activated carbon fiber (PACF) catalyst was exploited as a cathode to achieve high-efficiency of 2e- ORR for rapidly purifying wastewater containing recalcitrant pollutant (Reactive Red X-3B, RR X-3B) in the electro-Fenton (EF) system. It was found that the calcination at 700 °C after the hydrothermal treatment with 65 % phosphoric acid at 170 °C for 24 h achieved the best electrocatalytic activity compared to traditional impregnation (without calcination). The dimensional stable anode (DSA)-PACF-EF system showed high efficacy in decolorization, UV254 removal and COD removal over a wide pH range of 3∼11 for RR X-3B. The lattice-confined effect and covalent skeleton were confirmed to improve the stability of PACF, which exhibited high reusability in five consecutive reuse experiments. Quenching experiments and electron paramagnetic resonance (EPR) spectroscopy revealed that •O2- was the main reactive species and RR X-3B degradation was dominated by •O2- and •OH in the DSA-PACF-EF system. Moreover, Density Functional Theory (DFT) calculations further affirmed that PACF cathode possessed a stronger capability for O2 reduction and enhanced the generation of •O2- and H2O2 compared to raw activated carbon fiber (RACF) cathode. The doped P atoms active sites confined in carbon frameworks of PACF played a crucial role in the adsorption and reduction of O2 and utilization of H2O2 due to the lattice-confined effect. This work demonstrated a way to the development of high-efficient lattice-confined electrocatalysts.