Heat-treated metal phthalocyanine complex as an oxygen reduction catalyst for non-aqueous electrolyte Li/air batteries

Highlights: → Studied the catalytic effect of heat-treated metal phthalocyanine complex (MPc) on oxygen reduction in Li/air cells. → Heat-treated FeCuPc complex with carbon not only promotes two-electron oxygen reduction but also catalyzes non-redox Li2O2 disproportionation. → In Li/air cells the FeCu/C catalyst reduces cell's polarization and increases open-circuit voltage recovery rate. → The catalytic effect of FeCu/C catalyst on the Li2O2 disproportionation is not as effective as on the two-electron oxygen reduction. - Abstract: In this work we study heat-treated FeCu-phthalocyanine (FeCuPc) complexes as the catalyst for oxygen reduction in non-aqueous electrolyte Li/air cells by supporting the catalyst on a high surface area Ketjenblack EC-600JD carbon black. It is shown that the resultant FeCu/C catalyst not only accelerates the two-electron reduction of oxygen as 'O2 + 2Li+ + 2e → Li2O2', but also catalyzes the chemical disproportionation of Li2O2 as '2Li2O2 → 2Li2O + O2'. In Li/air cells, the catalyst reduces polarization on discharge while simultaneously reducing the fraction of Li2O2 in the final discharged products. In a 0.2 mol kg-1 LiSO3CF3 7:3 (wt.) propylene carbonate (PC)/tris(2,2,2-trifluoroethyl) phosphate (TFP) electrolyte, the Li/air cells with FeCu/C show at least 0.2 V higher discharge voltage at 0.2 mA cm-2 than those with pristine carbon. By measuring the charge-transfer resistance (Rct) of Li/air cells at temperatures ranging between -30 oC and 30 oC, we determine the apparent activation energy of the discharge of Li/air cells and discuss the effect of FeCu/C catalyst on the oxygen reduction in Li/air cells.