Porous Co/NPC@TiO2/TiN composite: Facile preparation and excellent catalytic activity for the oxygen reduction reaction

It is very important to develop efficient noble-metal-free catalysts for oxygen reduction reaction (ORR) to promote the application of commercial fuel cells. Inspired by this idea, ZIF 67 was selected as template to synthesize hierarchical porous TiO 2 /TiN coated Co/N co-doped carbon (Co/NPC) composite after being coated with tetrabutyl titanate (TBOT). The catalytic activity, stability and corrosion resistance of the optimal porous Co/NPC@TiO 2 /TiN composite towards ORR were improved by TiO 2 /TiN shell layer and carbon nanotubes. The results showed that the limit diffusion current (5.32 mA cm −2 , at 0.1 V vs. RHE), onset potential (0.87 V) and half-wave potential (0.754 V) of Co/NPC@TiO 2 /TiN-2 were closed to the corresponding values of 20 wt% Pt/C (5.53 mA cm −2 , 0.93 V and 0.773 V), respectively. The electron transfer number was 3.90–3.95 at a potential of 0.1–1.05 V, indicating a 4e - pathway for ORR and the yield of by-product hydrogen peroxide was below 6%. Additionally, Co/NPC@TiO 2 /TiN-2 also possessed good methanol tolerance and high cycle stability in alkaline media. This work provides a practical method to design ORR catalysts with distinguished performances.