Electrochemical production of H₂O₂ via a 2-electron oxygen reduction reaction (2e^– ORR) provides a clean alternative to the traditional industrial process. H₂O₂ electrosynthesis in noncaustic neutral electrolytes is desirable for broader applications; however, it requires larger overpotentials compared to those in alkaline electrolytes where a high 2e^– ORR activity can be achieved even with metal-free carbon electrocatalysts. Although ceria has been widely adopted as a catalytic promoter in thermo- and electrocatalytic reactions, its roles in enhancing the neutral 2e^– ORR have seldom been explored and remain unclear. In this work, we prepared ceria nanoparticles supported on carbon nanotube (CeO_x/CNT) composite catalysts and investigated ceria’s promotional effect on the neutral 2e^– ORR. The optimal CeO_x/CNT catalyst demonstrated a 1.5-fold increase in ORR activity compared to CNT alone, with high H₂O₂ selectivity over 87%. Electrochemical impedance spectroscopy indicated that the activity improvement correlated with an enhanced electron transfer (ET) rate. In situ X-ray absorption near-edge structure analysis revealed a counterintuitive decrease in the Ce³⁺/Ce⁴⁺ ratio as the applied potential was lowered. This finding suggested ET from Ce³⁺ to O₂, as supported by further electrochemical measurements. In addition, in situ Raman spectroscopy indicated the participation of the CNT in the electrocatalysis. The combination of electrochemical tests and in situ spectroscopies proposes a cascade reaction pathway, where O₂ is initially reduced by Ce³⁺ and subsequently adsorbed onto the active carbon sites.

中文翻译：

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Ce4+/Ce3+ 氧化还原促进电子转移，用于双电子氧还原高效中性 H2O2 电合成

通过 2 电子氧还原反应 (2e ^– ORR)电化学生产 H ₂ O ₂提供了传统工业过程的清洁替代方案。非苛性中性电解质中的H ₂ O ₂电合成具有更广泛的应用前景；然而，与碱性电解质相比，它需要更大的过电势，即使使用不含金属的碳电催化剂也可以实现高 2e ^– ORR 活性。尽管二氧化铈已被广泛用作热催化和电催化反应中的催化促进剂，但其在增强中性 2e ^– ORR 中的作用很少被探索且仍不清楚。在这项工作中，我们制备了负载在碳纳米管（CeO _x /CNT）复合催化剂上的二氧化铈纳米颗粒，并研究了二氧化铈对中性2e ^- ORR的促进作用。与单独的CNT相比，最佳的CeO _x /CNT催化剂的ORR活性提高了1.5倍，并且H ₂ O ₂选择性超过87%。电化学阻抗谱表明活性的改善与电子转移（ET）速率的增强相关。原位X射线吸收近边缘结构分析表明，随着施加电势的降低， Ce ³⁺ /Ce ⁴⁺比率出现违反直觉的下降。这一发现表明 ET 从 Ce ³⁺转变为 O ₂，​​并得到进一步电化学测量的支持。此外，原位拉曼光谱表明CNT参与了电催化。电化学测试和原位光谱学的结合提出了级联反应途径，其中O _2最初被Ce ³⁺还原，随后吸附到活性碳位点上。