Ricerc@Sapienza

Here we discuss the incorporation of Cr(III) as dopant in the spinel lattice of the NiCo2O4cubic phase and its beneficial effect on the electro-catalytic activity of this material in aprotic Li-O2cells. To this aim, we synthesized highly porous carbon-free self-standing electrodes constituted by nanostructured undoped and Cr-doped NiCo2O4grown 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-O2cells of the undoped and Cr-doped NiCo2O4electrodes 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 NiCo2O4material is capable to give reversible limited capacity ORR/OER for 52 and 45 cycles at 0.2 mA cm−2/0.1 mAh cm−2and 0.1 mA cm−2/0.2 mAh cm−2, respectively, without oxygen flow in static Ar/O2overpressures (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.