Single-iron, cobalt, nickel, and copper-atom catalysts for the selective reduction of oxygen to H2O2

Abstract

The pursuit of hydrogen peroxide (H₂O₂) production via two-electron electrochemical oxygen reduction reaction (ORR) is hampered by the lack of high-performance electrocatalysts. In this work, a series of single metal (i.e., Fe, Co, Ni, and Cu) atom catalysts anchored into N-doped carbon nanosheets (NCNSs) are evaluated for H₂O₂ production at pH-universal electrolytes. The catalytic performance of the samples, including current density, H₂O₂ selectivity, turnover of frequency (TOF), and faradaic efficiency, are characterized by electrochemical measurements. The generation of H₂O₂ is monitored by a UV-vis spectrophotometer. Among the samples, Cu/NCNSs exhibits the best catalytic performance with a ring current density of 2.15 mA cm⁻², TOF of 15.8 s⁻¹ at 0.1 V vs. reversible hydrogen electrode, Tafel slope of 88 mV dec⁻¹, and H₂O₂ selectivity of 100% at 0.57 V in alkaline media. Importantly, the Cu/NCNSs yields H₂O₂ selectivity of 81% at 0.05 V in acidic electrolytes. In contrast, Cu nanoparticles possess an inferior current density and much lower H₂O₂ selectivity via the 4e⁻ ORR pathway. Further quantitative analysis of H₂O₂ demonstrates that the Cu/NCNSs catalyst has an H₂O₂ production rate of 5.1 mol g_catalyst⁻¹ L⁻¹ h⁻¹ in alkaline media at 0.4 V, which is larger than those in acidic media (3.2 mol g_catalyst⁻¹ L⁻¹ h⁻¹) and neutral media (2.2 mol g_catalyst⁻¹ L⁻¹ h⁻¹) at −0.2 V. Such performance of Cu/NCNSs renders it as one of the best catalysts for H₂O₂ production.