Niobium-doped conductive TiO-TiO₂ heterostructure supported bifunctional catalyst for efficient and stable zinc-air...

The development of highly active and durable nonprecious metal-based bifunctional electrocatalysts for oxygen reduction/evolution reaction (ORR/OER) is important for rechargeable zinc-air batteries. Herein, a three-dimensional conductive niobium-doped TiO-TiO₂ heterostructure supported ZIF-67-derived Co-NC bifunctional catalyst was fabricated. In the Co-NC@Nb-TiO_x catalyst, the Nb doping promoted the formation of TiO-TiO₂ heterojunction support, enhanced its conductivity and stability and provided strong electron metal-support interaction between Co-NC and Nb-TiO_x. Also, the supported Co-NC nanoparticles provided abundant active sites with excellent ORR/OER activity. Experimental analysis reveals that the high OER activity of Co-NC@Nb-TiO_x can be attributed to the in-situ generated CoOOH species. It exhibits excellent ORR activity, as shown by its onset potential (0.95 V vs. RHE) and half-wave potential (0.86 V vs. RHE). Its OER overpotential at 10 mA cm^-2 is 480 mV. The zinc-air battery realizes outstanding cycling stability over 225 h cycles tested at 10 mA cm^-2. This work demonstrates the importance of designing highly stable metal oxide-supported catalysts in electrochemical energy conversion devices.