Highly efficient electro-oxidation catalyst under ultra-low voltage for degradation of aspirin.

A novel cryptomelane-Ir (cry-Ir) electrode is prepared for Ir to enter into the cryptomelane (named as cry-Mn) structure and used for aspirin degradation. This catalyst can efficiently reduce the Ir usage from 85 to 34%. Also, the onset potential of cry-Ir is about 1.40 V and the over potential is about 0.34 V at 10 mA cm-2, indicating that cry-Ir has an excellent oxygen evolution reaction (OER) activity to produce oxidizing species and can decrease electrolytic voltage during the electro-oxidation process. So, the electrical efficiency per log order (EE/O) for cry-Ir electrode is only 5% of PbO2 electrode, which is the best electrode for organic degradation. Also, cry-Ir has large tunnel size which favors insertion of aspirin molecule into cry-Ir structure and enhances the contact between reactive intermediates and the contaminant. Using cry-Ir as anode, 100% aspirin removal and 55% chemical oxygen demand (COD) removal could be obtained at 4 V. We also compare cry-Ir electrode with IrO2 and find that IrO2 anode can only eliminate 20% aspirin under the same condition. As a result, cry-Ir is a promising anode material for organic pollutant degradation. Graphical abstract Aspirin removal after 4h under different voltages. Aspirin removal on IrO2/Ti-f and cry-Ir/Ti-f after 4h.