Nitrogen- and Phosphorus-Doped Nanoporous Graphene/Graphitic Carbon Nitride Hybrids as Efficient Electrocatalysts for Hydrogen Evolution

Abstract

The hydrogen evolution reaction (HER) is one of the key steps in clean and efficient energy conversion techniques; however, the mass production of current HER devices is hampered by several shortcomings, which include kinetically sluggish processes, stability, and the use of expensive catalysts. In this work we report the facile synthesis of metal-free hybrids by integrating graphitic carbon nitride (g-C3N4) with nitrogen-and phosphorus-doped nanoporous graphene sheets. A phosphorusdoped metal-free hybrid electrocatalyst (g-C3N4@P-pGr) displayed excellent HER performance with an overpotential of -0.34 V, high exchange current density of 3.33 x 10(-6) A cm(-2), onset potential of 0.076 V, Tafel slope of 90 mV dec(-1), Gibbs free energy of 0.16 eV, and long-term durability comparable to that of well-developed metal catalysts. Tafel slope analysis suggests that the Volmer-Tafel mechanism is the most favorable HER kinetics for these metal-free hybrids. The extraordinary HER performance stems from a strong synergistic effect between the highly exposed active sites generated by the introduction of in-plane pores into graphene and the coupling of g-C3N4.