Synthesis Of High-performance Electrocatalysts For Metal-air Battery Cathode

As the increase of fossil consumption, the caused environmental problems haveinvoked essential efforts to develop novel batteries technologiesas renewable energystorage and conversion devices. Among these batteries technologies, metal-air batterieshaveattracted extremelygreat attention due to their high energy density that can match the fossilenergy.However,the cathode is the central to developmetal-air battery because the airelectrode is generally kineticallysluggish due to the electrochemistry of the oxygenoxidation and oxygen evolution. Therefore, searching fora suitable, controllable andhigh-performance cathode electrocatalyst is the key challenge toboth increase output of themetal-air battery power and toimprove the charge-discharge reversibility.First, wesynthesized novel carbon nanotubes with richly embedded metals. A modifiedchemical vapor deposition method was developed to prepare the unique structured carbonnanotubes. The multi-walled nanotubes were well-maintained and the electrochemicalproperties of metal-embeddedcarbon nanotubes were characterized. It was found that theembedded metal inside the nanotubes can not only improve the conductive properties of thecarbon nanotubes,but also enhance the performance of electrocatalytic oxygen reduction.Second, we exploited novel electrocatalysts for oxygen reduction used in Mg-airbatteries. Mullite structure oxides were synthesized as a completely novel electrocatalystfor ORR.4electrontransferredoxygen reductionwas realized withthis newly developedcatalyst. Importantly, the oxygen reduction can be occurredunder neutral conditions.Due tothe fact that magnesium air battery cannot work under alkaline condition, this novel Mullitestructured electrocatalyst working in neutral solution enables us to assemble amagnesium-air batteryworking in neutral solution. With this newly fabricated Mg-airbattery,a working voltage of about1.4V can be achieved with a single battery.Consequently, two assembled Mg air batteries can deliver2.5V~2.8Vand0.05W power,therefore drive a LED bulb.Finally, we prepared the carbonaceous microspheres (CMSs) by a facile hydrothermaltreatment of glucose precursor and then the dopedCMSs with La2O3, resulting in a highperformance bi-functional electrocatalyst of La2O3@CMSs. In alkaline solution, the La2O3@CMSs catalyzes oxygen evolution reactions (OER) with an onset potential of0.80V vs. RHE and an overpotential only of600mV to achieve a current density of1.3mA/cm2. Meanwhile, oxygen reduction reaction (ORR) at La2O3@CMSs electrode occurs at anonset potential of1.60V vs. RHE and an overpotential only of0.40V. Also, the as-preparedLa2O3@CMSs exhibits high Faraday efficiency and long-term stability towards ORR andOER. Significantly, we demonstrate that La2O3@CMSs possesses surprisingly high massactivity, which is calculated to be28.4A/g for ORR and831.5A/g for OER, respectively.A potential window for ORR and OER at the modified electrode is estimated to be0.80V,implying a promising bi-functional electrocatalytical performance of La2O3@CMSs. Theimprovement of the bi-functional electrocatalytical activity may be due to the generation ofactive component of La-O and C-O at the surface and its synergistic interaction with theLa2O3@CMSs. This novel electrocatalyst was used as cathode material in reversible Li-airbatteries.