Ir/g-C3N4/Nitrogen-Doped Graphene Nanocomposites as Bifunctional Electrocatalysts for Overall Water Splitting in Acidic Electrolytes

Nitrogen-doped graphene (NG) chemically coupled with graphitic carbon nitride (g-C3N4) may facilitate the kinetics of overall electrochemical water splitting. Herein, a facile strategy is adopted to synthesize monodispersed Ir nanoparticles on g-C3N4/NG layers. Benefiting from the synergistic effect between different components of the catalyst, the optimal Ir/g-C3N4/NG catalyst with a low content of Ir (5.9 wt %) exhibits highly active for electrochemical water splitting in acidic electrolyte. Specifically, as a hydrogen evolution reaction catalyst, the optimal Ir/g-C3N4/NG exhibits a Tafel slope of 22 mV·dec-1. The optimal catalyst requires an overpotential of 22 mV to reach the current density of 10 mA·cm-2, the value of which is superior to Ir/NG (32 mV) and 20 wt % Pt/C (28 mV) catalysts; as an oxygen evolution reaction catalyst, it also achieve the Tafel slope of only 72.8 mV·dec-1. At the overpotential of 300 mV, the mass activity of the optimal Ir/g-C3N4/NG catalyst is 2.8 times as large as that of 5.7 wt % Ir/NG catalyst. More significantly, as a bifunctional catalyst, the optimal Ir/g-C3N4/NG achieves a current density of 10 mA·cm-2 with a potential of only 1.56 V and displays good stability for overall water splitting. This work provides a new strategy to design highly efficient acidic catalysts for electrochemical overall water splitting.