Tuning the wettability of carbon nanotube arrays for efficient bifunctional catalysts and Zn–air batteries

Carbon nanotube arrays (CNTAs) embedded with transition metal oxides (TMOs) have been considered as effective bifunctional catalysts. However, the hydrophobic nature of CNTAs usually limits the wetting of aqueous solutions containing inorganic precursors of TMOs, which results in poor decoration of TMOs on it. Herein, we report a facile strategy to tune the wettability of 3D CNTAs by controlling the nitrogen-doping degree. Particularly, superhydrophilic nitrogen-doped CNTAs (N-CNTAs) were obtained by using pyridine as the reactant, which allows uniform anchoring of cobalt oxide nanoparticles (NPs) on their surface through a simple self-priming freeze-drying assisted immobilization method. The heteroatom-doping and uniformly distributed cobalt oxide NPs endow the obtained hybrid material (Co3O4/N-CNTAs) with excellent OER and ORR performances, which also demonstrated their high efficiency as bifunctional catalysts for Zn–air batteries.