Metal-free sulfur-doped reduced graphene oxide electrocatalysts for promising production of hydrogen peroxide: construction and identification of active sites

Identifying and tailoring active sulfur configurations in heteroatom-doped carbon electrocatalysts for the selective 2e^- oxygen reduction reaction (ORR) pathway remains a significant challenge. Here we designed and synthesized sulfur-doped reduced graphene oxide electrocatalysts containing C-S and C-SO _<i>x</i> moieties (denoted as S _<i>x</i> RGO, <i>x</i> = 1, 10, 20) for promising ORR into hydrogen peroxide (H₂O₂). The optimized S₁₀RGO catalyst exhibits unexpected H₂O₂ selectivity of <i>ca.</i> 90% across a wide voltage range of 0.10-0.65 V, accompanied with excellent long-term stability (40 h) in an alkaline flow cell with 90.5% H₂O₂ faradaic efficiency at an industrial current density of 300 mA cm^-2. Theoretical and experimental analyses integrally reveal and identify the C-S and C-SO _<i>x</i> groups as the main active sites in the carbon-based catalyst. Specifically, the C-S group is found to favor the formation of OOH*, while the C-SO _<i>x</i> group not only facilitates the desorption of OOH* but also modulates interfacial mass transport kinetics, thereby creating a favorable microenvironment for H₂O₂ generation.