Enhancement of the performance in Li-O2 cells of a NiCo2O4 based porous positive electrode by Cr(III) doping

Here we discuss the incorporation of Cr(III) as dopant in the spinel lattice of the NiCo2O4 cubic phase and its beneficial effect on the electro-catalytic activity of this material in aprotic Li-O2 cells. To this aim, we synthesized highly porous carbon-free self-standing electrodes constituted by nanostructured undoped and Cr-doped NiCo2O4 grown on open nickel mesh. These materials were characterized by X-ray diffraction, field emission scanning electron microscopy coupled with energy dispersive spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The performance in aprotic Li-O2 cells of the undoped and Cr-doped NiCo2O4 electrodes were tested in galvanostatic cycling using a LiTFSI 1 m in tetraethylene glycol dimethyl ether electrolyte without the incorporation of any carbon conductive agent. Cr(III) doping discloses a remarkable enhancement of more than 300% of the discharge capacity at J = 0.1 mA cm−2. Moreover, the Cr-doped NiCo2O4 material is capable to give reversible limited capacity ORR/OER for 52 and 45 cycles at 0.2 mA cm−2/0.1 mAh cm−2 and 0.1 mA cm−2/0.2 mAh cm−2, respectively, without oxygen flow in static Ar/O2 overpressures (pO2 = 1bar). Pseudo-Tafel data derived by galvanostatic titrations highlight the beneficial effect of Cr(III) doping on the electrode kinetics both for ORR and OER.