Catalytic effect of metal oxides on the oxidation resistance in carbon nanotube-inorganic hybrids

Hybridising carbon nanotubes (CNTs) with metal oxide nanostructures creates a new class of multifunctional materials with greatly enhanced performances as photocatalysts, chemical sensors, and in fuel cells and batteries. The low resistance of CNT towards oxidation often limits their applicability. On the other hand, exactly this ability to degrade CNTs at low temperatures is beneficial when using them as sacrificial templates for the synthesis of inorganic nanotubes. In this work, we investigate the oxidation resistance of 20 new hybrids and reveal that the presence of metal oxides can both inhibit and catalyse the oxidation of CNTs. As a result, the oxidation temperatures range from nearly 800 degrees C with Al2O3 to values as low as 330 degrees C with PbO and Bi2O3. We further demonstrate that the catalytic activity of the metal oxides correlates directly with their reducibility, i.e. the ability to create oxygen vacancies, and propose a mechanistic model based on Mars and van Krevelen, which allows prediction of the chemical stability of a wide range of CNT-metal oxide hybrids.