Facile synthesis of Ni-incorporated and nitrogen-doped reduced graphene oxide as an effective electrode material for tri(ammonium) phosphate electro-oxidation

Abstract

Tri(ammonium) phosphate is a cheap and commercially available compound and is used as a fertilizer. This substance possesses a considerable amount of hydrogen. Recently, it has been found that the embedded hydrogen could be extracted from tri(ammonium) phosphate using a Ni/C heterocatalytic reaction. In this study, for the first time based on our knowledge, extraction of hydrogen from tri(ammonium) phosphate was performed electrolytically using Ni-incorporated and N-doped reduced graphene oxide. The proposed electrocatalyst was prepared by a simple one-pot synthesis procedure. Typically, a well-mixed nickel acetate tetrahydrate/polyvinylpyrrolidone mixture has been calcined under a nitrogen atmosphere at 700 °C. X-Ray diffraction (XRD) analyses confirmed the formation of zero-valent nickel and reduced graphene oxide because of the clear appearance of the corresponding peaks. Moreover, X-ray photoelectron spectroscopy (XPS) analyses concluded the formation of graphene sheets functionalized by oxygenated groups and doped by pyrrolic and pyridinic nitrogen; however only pyrrolic nitrogen has been detected in Ni-free samples. Transmission electron microscopy (TEM) images indicated the formation of multilayer reduced graphene oxide. Electrochemical measurements indicated that the prepared composite is an effective electrocatalyst for tri(ammonium) phosphate oxidation when the nickel content is optimized. The electrode containing 31.9 wt% Ni shows the maximum generated current density; however, clear oxidation peaks were observed with 40.2 wt% formulation. Overall, the study introduces tri(ammonium) phosphate as a model for a new class of hydrogen-rich, cheap and available substances for hydrogen generation using non-precious electrodes. Besides that, the novel functionalized and N-doped reduced graphene oxide synthesis methodology may attract attention due to its distinct simplicity compared to the reported procedures.