Non-precious cathode electrocatalyst for magnesium air fuel cells: Activity and durability of iron-polyphthalocyanine absorbed on carbon black

摘要

A planar iron-polyphthalocyanine (PPcFe) oxygen reduction reaction (ORR) catalyst for magnesium air fuel cells (MAFC) is prepared by dispersing PPcFe on carbon black (C) and heating under argon. Ther-mogravimetric analysis shows PPcFe is stable below 600 ℃. The X-ray diffraction and X-ray photo-electron spectroscopy results show the active site of PPcFe/C is the FeN_4 in the phthalocyanine ring. The rotating disk electrode measurements in 0.5 M L~(-1) H_2SO_4 solution show the initial potential for ORR is 0.82 V vs. RHE at 20 ℃ and that it mainly occurs via a four-electron process. Almost no performance degradation is observed over continuous cyclic voltammetry at 10,000 cycles, linear sweep voltammetry at 200 cycles, and 60 h of the chronoamperometry test. The infrared spectrum of PPcFe, after all the durability tests, shows no changes from the initial characteristics. The polarization curves of the air electrodes with PPcFe/C, iron-phthalocyanine/C and Pt/C catalysts exhibit excellent polarization performances. The discharge performance of a MAFC single cell with PPcFe/C cathode catalyst shows an open circuit potential of 1.74 V, with a peak power density of 50.5 mW cm~(-2) at 20 ℃. The cell voltage decreases less than 0.01 V during continuing discharge @ 20 mA cm~(-2) for more than 11 h.