A novel cathode catalyst for aluminum-air fuel cells: Activity and durability of polytetraphenylporphyrin iron (II) absorbed on carbon black

A polytetraphenylporphyrin iron (II) (PTPPFe) oxygen reduction reaction (ORR) catalyst for aluminum-air fuel cells (AAFCs) is prepared. Thermogravimetric analysis results show that PTPPFe is stable at temperatures below 600 °C. X-ray photoelectron spectroscopy reveals that the active site of PTPPFe/C is Fe–N4 in the porphyrin ring. Rotating disk electrode measurements in 1 mol L−1 NaOH solution demonstrate that the initial potential for ORR is 0.142 V vs. Hg/HgO/OH− (1 mol L−1 KOH, 0.098 V vs. NHE) at 20 °C, and that ORR mainly occurs through a four-electron process. The half-wave potentials for PTPPFe/C and the Pt/C catalyst are 0.071 and 0.079 V, respectively. Almost no performance degradation is observed over continuous cyclic voltammetry at 10 000 cycles, linear sweep voltammetry at 200 cycles, and 60 h of chronoamperometry test. After durability tests, the ultraviolet–visible spectrum of PTPPFe does not change from the initial characteristics. The discharge performance of AAFC has a power density of 47.5 mW cm−2 at 20 °C in 6 mol L−1 NaOH electrolyte solution. During continuous discharge for 10 h, the potential of AAFC decreases by less than 0.01 V at 40 mA cm−2.