Sn Bulk Phase Doping and Surface Modification on Ti₄ O₇ for Oxygen Reduction to Hydrogen Peroxide

Developing stable and highly selective two-electron oxygen reduction reaction (2e^- ORR) electrocatalysts for producing hydrogen peroxide (H₂ O₂ ) is considered a major challenge to replace the anthraquinone process and achieve a sustainable green economy. Here, we doped Sn into Ti₄ O₇ (D-Sn-Ti₄ O₇ ) by simple polymerization post-calcination method as a high-efficiency 2e^- ORR electrocatalyst. In addition, we also applied plain calcination after the grinding method to load Sn on Ti₄ O₇ (L-Sn-Ti₄ O₇ ) as a comparison. However, the performance of L-Sn-Ti₄ O₇ is far inferior to that of the D-Sn-Ti₄ O₇ . D-Sn-Ti₄ O₇ exhibits a starting potential of 0.769 V (versus the reversible hydrogen electrode, RHE) and a high H₂ O₂ selectivity of 95.7 %. Excitingly, the catalyst can maintain a stable current density of 2.43 mA ⋅ cm^-2 for 3600 s in our self-made H-type cell, and the cumulative H₂ O₂ production reaches 359.2 mg ⋅ L^-1 within 50,000 s at 0.3 V. The performance of D-Sn-Ti₄ O₇ is better than that of the non-noble metal 2e^- ORR catalysts reported so far. The doping of Sn not only improves the conductivity but also leads to the lattice distortion of Ti₄ O₇ , further forming more oxygen vacancies and Ti³⁺ , which greatly improves its 2e^- ORR performance compared with the original Ti₄ O₇ . In contrast, since the Sn on the surface of L-Sn-Ti₄ O₇ displays a synergistic effect with Tiⁿ⁺ (3≤n≤4) of Ti₄ O₇ , the active center Tiⁿ⁺ dissociates the O=O bond, making it more inclined to 4e^- ORR.