Graphene as an intermediary for enhancing the electron transfer rate: A free-standing Ni3S2@graphene@Co9S8 electrocatalytic electrode for oxygen evolution reaction

A highly active and stable oxygen evolution reaction (OER) electrocatalyst is critical for hydrogen production from water splitting. Herein, three-dimensional Ni3S2@graphene@Co92S8 (Ni3S2@G@Co9S8), a sandwich-structured OER electrocatalyst, was grown in situ on nickel foam; it afforded an enhanced catalytic performance when highly conductive graphene is introduced as an intermediary for enhancing the electron transfer rate and stability. Serving as a free-standing electrocatalytic electrode, Ni3S2@G@Co9S8 presents excellent electrocatalytic activities for OER: A low onset overpotential (2 mA·cm−2 at 174 mV), large anode current density (10 mA·cm−2 at an overpotential of 210 mV), low Tafel slope (66 mV·dec−1), and predominant durability of over 96 h (releasing a current density of ∼14 mA·cm−2 with a low and constant overpotential of 215 mV) in a 1 M KOH solution. This work provides a promising, cost-efficient electrocatalyst and sheds new light on improving the electrochemical performance of composites through enhancing the electron transfer rate and stability by introducing graphene as an intermediary.