N, P co-doped graphene-supported monometallic nanoparticles for highly efficient hydrogen evolution by acid electrolysis of water

Reduced graphene oxide is doped with nitrogen (N) and phosphorus (P) to synthesize the catalyst support (rGNP) via hydrothermal and pyrolysis strategies, and M/rGNP supported monometallic electrocatalysts (such as Pt/rGNP, Ir/rGNP, Ru/rGNP, Co/rGNP, and Ni/rGNP) are successfully constructed by using impregnation and reduction methods. In 0.5 M H2SO4, Pt/rGNP shows much better catalytic behaviors for the hydrogen evolution reaction (HER) than other as-prepared M/rGNP supported catalysts; its overpotential is only 10.6 mV at 100 mA cm-2, much smaller than that of commercial 20 wt% Pt/C (named Pt/C) (66.5 mV). Its Tafel slope is 14.53 mV dec-1, much lower than that of Pt/C (21.73 mV dec-1). The overpotential and Tafel slope of Pt/rGNP for the HER are lower than those of rGNP, Ir/rGNP, Ru/rGNP, Co/rGNP, and Ni/rGNP under the same conditions. Additionally, Pt/rGNP displays high stability for the HER. This shows that modification with heteroatoms (N and P) can greatly improve the performance of M/rGNP for the HER. A series of characterization techniques such as XRD, ICP-OES, TEM, STEM, XPS, STEM-EDX etc. reveal that the N and P in rGNP can regulate the electronic structure of Pt (improving the electron density), promoting hydrogen formation. This report gives a novel strategy for designing and synthesizing efficient and stable electrocatalysts for the hydrogen evolution reaction. Pt/rGNP exhibits much higher catalytic properties than other transition metal/rGNP catalysts for hydrogen evolution; its overpotential at 100 mA cm-2 in 0.5 M H2SO4 is only 10.6 mV, and its Tafel slope is 14.53 mV dec-1.