Air electrode parameters The values of air are

The coordination ionic liquids of C5H9NO·xMCln (M = Fe, Zn; x = 0.1–0.4; n = 2 or 3) were prepared by reacting NMP with FeCl3 or ZnCl2. Every 1 h, 0.005 mol of MCly was put into the 0.1 mol (9.6 mL) of NMP at 0 °C in GSK2636771 flask surrounded by a mixture of water and ice to avoid the intense heat release between the NMP and metal chlorides. The mixture was continuously mixed till the designed chloride was totally added and dissolved. Afterwards, limpid ionic liquids could be obtained. The dynamic viscosity of the ionic liquids was measured by NDJ-8S rotational viscometer. Conductivity was collected on a Mettler FE30 conductivity meter. Fourier transform infrared (FT-IR) spectra were collected on a Shimadzu IR-Prestige 21 spectrometer. To detect the generation of hydroxyl radical, electron paramagnetic resonance (EPR) signals of radicals spin-trapped by 5,5-dimethyl-l-pyrroline-N-oxide (DMPO) were obtained by a Bruker EMX-8/2.7 X-band EPR spectrometer.