Enhanced Electrocatalytic Performance of BiFeO3/g-C3N4 Composites for the Two-Electron Oxygen Reduction Reaction

An efficient electrocatalyst for the eco-friendly synthesis of hydrogen peroxide (H₂O₂) via a two-electron oxygen reduction reaction (2e^– ORR) method, which serves as a viable alternative to the conventional anthraquinone process, is crucial for numerous applications. However, it remains a significant challenge for the electrocatalysis community, requiring an urgent demand for developing highly selective electrocatalysts for H₂O₂ generation. Herein, a cost-effective and nonprecious perovskite oxide composite material, BiFeO₃/g-C₃N₄ (BFO_gCN), has been successfully synthesized as an electrocatalyst for the 2e^– ORR through a simple physical mixing, followed by calcination, demonstrating its exceptional selectivity for H₂O₂ generation. The synthesis technique allows for altering the electronic structure of BiFeO₃ (BFO) and g-C₃N₄ (gCN), ensuring a high oxygen vacancy, increased hydroxyl adsorption on the surface of the BFO_gCN composite, and conductive gCN sheets that facilitate the ORR. The composite catalyst (50_BFO_gCN) exhibits high H₂O₂ selectivity, exceeding 70% throughout a broad potential range of 0.3–0.6 V versus RHE, compared to other composites for the ORR in an alkaline medium. The H₂O₂ selectivity of the synthesized electrocatalyst is consistently sustained for 50 h at 0.5 V during a durability assessment. The yield rate of H₂O₂ reaches a maximum of 1528.8 mmol g^–1 h^–1 at 0.5 V, exhibiting a faradaic efficiency (FE) of 94.9% after 3 h of electrocatalysis. To assist the experimental observation, the Perdew–Burke–Ernzerhof (PBE) functional with the Grimme’s third-order (-D3) dispersion corrections (in short PBE-D method) has been employed to explore the ORR mechanism. These calculations reveal that the improved performance of the subject material is due to the oxygen vacancy at the Fe site, and it also stabilizes the critical intermediates, such as OOH*, thereby preventing O–O bond breaking and suppressing the 4e^– pathway. This study introduces a highly selective electrocatalyst for the 2e^– ORR and offers an approach to electrocatalyst design.