Nano-spinel cobalt decorated sulphur doped graphene: an efficient and durable electrocatalyst for oxygen evolution reaction and non-enzymatic sensing of H2O2

Abstract

We report the synthesis of a nano-spinel cobalt decorated sulphur doped reduced graphene oxide (Co@S–rGO) composite exhibiting excellent electrocatalytic performance and electrochemical stability toward oxygen evolution reaction (OER) in an alkaline medium. Moreover, the so crafted noble metal free Co@S–rGO electrocatalyst, well characterized by UV-Vis spectroscopy, FTIR, XRD, SEM, and energy dispersive X-ray spectroscopy, exhibits promising activity toward electrochemical sensing of H₂O₂. For OER in an alkaline medium, the Co@S–rGO composite exhibits a Tafel slope of ca. 49 mV dec⁻¹, with an overpotential requirement of just 389 mV for a specific current density of 10 mA cm⁻². In the OER electrochemical stability tests, the Co@S–rGO electrocatalyst could maintain its peak OER performance for a time span of about 50 000 seconds during chronoamperometric measurements, while in the linear sweep voltammetry records almost negligible difference was observed between the final and the initial scan in a total of 1000 scans recorded over 25 hours for OER over Co@S–rGO. These chronoamperometric and voltammetric observations establish the excellent activity and long-term electrochemical stability of Co@S–rGO for OER in alkaline media. These current/potential and stability parameters observed for the OER performance of the Co@S–rGO composite are far better than that reported for various non-noble metal based state-of-the-art materials specifically crafted for OER. For the electrochemical sensing of H₂O₂, the Co@S–rGO composite exhibits a limit of detection as low as 23 nM with a sensitivity of 22743.85 μA M⁻¹ cm⁻². The excellent OER performance and H₂O₂ sensing activity of the Co@S–rGO composite can be attributed to the special synergism between the Co and S–rGO components and the extended electrochemically active surface area of Co nanodeposits in this noble metal free electrocatalyst.