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

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, TiO₂ and TiN were used as the precursors for the thermal nitridation and oxidation reactions at high temperatures, respectively. Titanium oxynitride (TiO_xN_y) 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 via 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 (vs. RHE). The catalyst also delivered a mass activity of 112 A g_Pt ^-1, 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 TiO_xN_y 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 TiO_xN_y species in Ti-based electrocatalysts.