Elucidating the roles of oxygen defects-rich TiON shell in Ti-based electrocatalyst for enhanced oxygen reduction reaction.

Ti-based materials are among the most widely studied catalysts for the oxygen reduction reaction (ORR). However, the actual roles of the catalytically active sites in N-doped Ti-based electrocatalysts are still unclear. In this work, TiO and TiN were used as the precursors for the thermal nitridation and oxidation reactions at high temperatures, respectively. Titanium oxynitride (TiON) species with abundant oxygen defects, formed on the surface of the as-prepared catalysts, were found to play an essential role to achieve the uniform distribution of ultrafine Pt nanoparticles atomic layer deposition, thereby enhancing the ORR performance. The TiN-supported Pt catalyst showed excellent ORR performance and stability in acidic conditions, with an onset potential of 0.88 V and a half-wave potential of 0.76 V (. RHE). The catalyst also delivered a mass activity of 112 A g , which is 1.9 times higher than that of commercial Pt/C. A combination of experiments and characterizations confirmed that the synergistic effects between the outer TiON shell with abundant oxygen defects and the high-conductivity TiN core contribute to the enhanced ORR performance. The present work sheds light on the essential roles of oxygen defect-rich TiON species in Ti-based electrocatalysts.