La₂O₃ doped carbonaceous microspheres: A novel bifunctional electrocatalyst for oxygen reduction and evolution reactions with ultrahigh mass activity

An efficient and robust bifunctional electrocatalyst for both ORR and OER is highly desired for the applications in renewable energy technologies. Here, we prepare the carbonaceous microspheres (CMSs) by a facile hydrothermal treatment of glucose precursor and then dope the CMSs with La₂O₃, resulting in a high performance bifunctional electrocatalyst of La₂O₃@CMSs. In alkaline solution, the La₂O₃@CMSs catalyzes oxygen reduction reactions (ORR) with an onset potential of 0.80 V versus RHE and an overpotential only of 600 mV to achieve a current density of 1.3 mA cm^-2. Meanwhile, oxygen evolution reaction (OER) at La₂O₃@CMSs electrode occurs at an onset potential of 1.60 V versus RHE and the overpotential is only 370 mV. Also, the as-prepared La₂O₃@CMSs exhibits high Faraday efficiency and long-term stability toward ORR and OER. Significantly, we demonstrate that La₂O₃@CMSs possesses surprisingly high mass activity, which is calculated to be 78.4 A g^-1 for ORR and 831.5 A g^-1 for OER, respectively. A potential window for ORR and OER at the modified electrode is estimated to be 0.80 V, implying a promising bifunctional electrocatalytical performance of La₂O₃@CMSs. The improvement of the bifunctional electrocatalytical activity may be due to the generation of active component of La-O and C-O at the surface and its synergistic interact with the La₂O₃@CMSs. This work not only provides a facile strategy for preparing highly efficient bifunctional electrocatalyst, but also offers an insight into the design of metal-oxides doped carbon materials for energy storage and conversion applications.