Design And Synthesis Of Modified Carbon Nanotube-based AB₂O₄ Electrodes For Electrocatalytic Applications

Metal-air batteries as a new type of energy storage and energy conversion equipments possess desired advantages including high theoretical power density,high energy density,simple structure and environmental protection.However,the oxygen electrode materials in metal-air batteries are mainly composed of precious metal materials which cost expensive price hindering the development of metal-air batteries.In addition,the precious metal materials are easily corroded resulting in the poor stability.Therefore,a new type of transition metal oxides which possess efficient oxygen evolution and oxygen reduction catalysis are proposed based on the low cost transition metal oxides.One step beyond,carbon nanotubes with high conductivity and high specific surface area are introduced as the substrate for transitional metal oxides to improve their physical defects including the low specific surface area and conductivity.Electrochemical performance tests show that these types of carbon nanotube based AB₂O₄ composites have excellent oxygen reversible catalytic properties.Moreover,applying them in the metal-air batteries,they show excellent charging and discharging performances and high cycle stability.Detailed works are displayed as follows:?1?In view of the disadvantages of Ni Co₂O₄ nano materials,such as poor conductivity and easy agglomeration,carbon nanotubes are introduced for Ni Co₂O₄ to serve as the growth substrate.Benefiting from the carbon nanotubes,the conductivity and specific surface area of Ni Co₂O₄ gain improvement,leading to the highly efficient oxygen evolution reaction catalysis and high stability.?2?Based on Ni Co₂O₄/CNTs,Zn Co₂O₄ quantum dots with the ultrafine size and promoted valence state of Co ions is decorated on the nitrogen doped CNTs.Benefiting from the introduction of the Zn ions,a large number of Co ions with high valence state occupy the octahedron sites,improving the oxygen evolution reaction catalysis performances;on the other hand,the nitrogen doping further creates large amount of catalytic active sites,accelerating the oxygen reduction catalytic performances.Finally,the composite material serving as the oxygen electrode for the zinc-air battery shows excellent charging and discharging performances and long-term stability.?3?Owning to the highly efficient oxygen evolution catalysis performances of Co ions with high valence states,introducing Au nanoparticles with the strong electronegativity to accelerate the valence state of Co ions is an efficient strategy.The as-synthesized Zn Co₂O₄/Au/CNTs with the high ratio of high valence state Co ions exhibits smaller onset potential and larger catalytic current density.Compared with noble metal Ir O₂,Zn Co₂O₄/Au/CNTs shows superior oxygen evolution reaction catalysis in the alkaline and neutral electrolyte.?4?Owning to the good oxygen catalytic performance of copper ion,the introducing of copper ion in Co₃O₄/N-CNTs efficiently increase the active sites of the catalytic materials,thereby improving the oxygen reversible catalytic properties of the catalyst.The Cu Co₂O₄/N-CNTs composite shows that the Cu ions are formed in the presence of Cu²⁺state,providing additional catalytic active sites for cobalt based materials.The electrochemical properties show that Cu Co₂O₄/N-CNTs revelas the superior catalytic properties to that of noble metal materials.In addition,serving as the zinc-air battery electrode,Cu Co₂O₄/N-CNTs showed excellent charge and discharge performance,high cycle stability and flexibility.?5?Spinel type manganese based materials show excellent cathodic oxygen reduction performance.However,the inappropriate valence state of Mn ions induce the poor catalytic properties of the materials.Therefore,Co Mn₂O₄/N-CNTs with Mn³⁺ possesses the highly efficient oxygen reduction catalysis while Co²⁺possessing a strong alkalinity stabilize the Mn-O bonds.Therefore,compared with the precious metal materials,the CoMn₂O₄/N-CNTs composite shows a superior oxygen reduction reaction catalytic ability with smaller onset potential and a larger current density.Applying CoMn₂O₄/N-CNTs in zinc-air battery,the battery shows excellent discharge performance and high stability.