Robust bifunctional catalytic activities of N-doped carbon aerogel-nickel composites for electrocatalytic hydrogen evolution and hydrogenation of nitrocompounds

Nitrogen doped carbonaceous aerogel (NCA) was prepared by a simple hydrothermal treatment of cotton and ovalbumin as a carbon and nitrogen source. Magnetic Ni/NCA composite was prepared by simple chemical reduction method using hydrazine hydrate. The similar method was used in the preparation of various Ni/NCA composites with Ni percentage in the composites ranging from 45% to 75%. The magnetically active Ni/NCA catalysts so-fabricated were characterized by different analytical techniques, viz., X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive x-ray spectroscopy (EDS). The as-prepared pure Ni nanoparticles (Ni NPs) and Ni/NCA composites were employed as a prospective electrocatalysts for hydrogen evolution reaction (HER) and reduction of 4-nitrophenol. Various electrochemical parameters of Ni NPs and Ni/NCA electrocatalysts were determined and studied extensively through voltammetric and impedance methods. Electrochemical studies reveal that the prepared Ni/NCA composites show high catalytic performances and good recyclability. Particularly, Ni/NCA-60 exhibited best electrocatalytic activity among the investigated electrocatalysts in alkaline medium. Tafel slopes and constants determined for the investigated electrocatalysts revealed superior electrocatalytic performance of Ni/NCA composites over Ni NPs. From the mechanistic view point, HER likely operates through Volmer-Heyrovsky mechanism with electrochemical hydrogen adsorption as the rate determining step. Furthermore, accelerated durability test (ADT) experiments showed that Ni NPs retained about 75% of the initial activity while Ni/NCA consistently retained about 90% of the initial activity after ADT. The high catalytic activities and good durability of the Ni/NCA materials can be of potential use in the fields of electrocatalysis for hydrogen production and catalytic reduction of organic toxic pollutant.